sigrok - User contributions [en]

Circuits for barebone boards

2014-02-03T22:39:12Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower, the used test probes can also make an influence. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistor
! Zener Diode
! With test probes?12
! Measurement Result

|-
| 4.7 k Ohm
| 3.6V
| Cheap Test probe, longer wires
| Only "high"

|-
| 890 Ohm
| 3.6V (unknown speed)
| Cheap Test probe, longer wires
| Only "high"

|-
| 1.4 k Ohm
| None
| Short direct wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| 3.6V
| Cheap Test probe, longer wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Short direct wires
| Sometimes "high", about 90% correct

|-
| None
| 3.6V
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct
|}

Cheap Test probe made out of:

1 [http://dx.com/p/133097 "Plastic Flat Multimeter Test Hook Clip Probes"]

2 [http://www.reichelt.de/PS-25-10G-BR/3/index.html?&ARTICLE=32203&artnr=PS+25%2F10G+BR Flexible PCB Connector]

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T23:59:39Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower, the used test probes can also make an influence. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistor
! Zener Diode
! With test probes?12
! Measurement Result

|-
| 4.7 k Ohm
| 3.6V
| Cheap Test probe, longer wires
| Only "high"

|-
| 890 Ohm
| 3.6V (unknown speed)
| Cheap Test probe, longer wires
| Only "high"

|-
| 1.4 k Ohm
| None
| Short direct wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| 3.6V
| Cheap Test probe, longer wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Short direct wires
| Sometimes "high", about 90% correct

|-
| None
| 3.6V
| Cheap Test probe
| Sometimes "high", about 90% correct
|}

Cheap Test probe made out of:

1 [http://dx.com/p/133097 "Plastic Flat Multimeter Test Hook Clip Probes"]

2 [http://www.reichelt.de/PS-25-10G-BR/3/index.html?&ARTICLE=32203&artnr=PS+25%2F10G+BR Flexible PCB Connector]

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T23:58:08Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower, the used test probes can also make an influence. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistor
! Zener Diode
! With test probes?12
! Measurement Result

|-
| 4.7 k Ohm
| 3.6V
| Cheap Test probe, longer wires
| Only "high"

|-
| 890 Ohm
| 3.6V (unknown speed)
| Cheap Test probe, longer wires
| Only "high"

|-
| 1.4 k Ohm
| None
| Short direct wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| 3.6V
| Cheap Test probe, longer wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Short direct wires
| Sometimes "high", about 90% correct

|-
| None
| 3.6V
| Cheap Test probe
| Sometimes "high", about 90% correct
|}

1 [http://dx.com/p/133097 "Plastic Flat Multimeter Test Hook Clip Probes"]
2 [http://www.reichelt.de/PS-25-10G-BR/3/index.html?&ARTICLE=32203&artnr=PS+25%2F10G+BR Flexible PCB Connector]

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T23:57:32Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower, the used test probes can also make an influence. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistor
! Zener Diode
! With test probes?12
! Measurement Result

|-
| 4.7 k Ohm
| 3.6V
| Cheap Test probe, longer wires
| Only "high"

|-
| 890 Ohm
| 3.6V (unknown speed)
| Cheap Test probe, longer wires
| Only "high"

|-
| 1.4 k Ohm
| None
| Short direct wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| 3.6V
| Cheap Test probe, longer wires
| Sometimes "high", about 75% correct

|-
| 100 Ohm
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Cheap Test probe, longer wires
| Sometimes "high", about 90% correct

|-
| None
| None
| Short direct wires
| Sometimes "high", about 90% correct (probably the best you can get with 24MHz samplerate @ 12MHz signal)

|-
| None
| 3.6V
| Cheap Test probe
| Always correct (still not recommended)
|}

1 [http://dx.com/p/133097 "Plastic Flat Multimeter Test Hook Clip Probes"]
2 [http://www.reichelt.de/PS-25-10G-BR/3/index.html?&ARTICLE=32203&artnr=PS+25%2F10G+BR Flexible PCB Connector]

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T17:23:02Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower, the used test probes can also make an influence. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistor
! Zener Diode
! With test probes?1
! Measurement Result

|-
| None
| None
| Direct wired
| Always correct (if you use this, be careful)

|-
| None
| 3.6V
| Cheap Test probe
| Always correct (but still not advised to do!)

|-
| 100 Ohm
| 3.6V
| Cheap Test probe
| Occasionally "high", but most times correct

|-
| 1.4 k Ohm
| None
| Direct wired
| Occasionally "high", but most times correct

|-
| 890 Ohm
| 3.6V (unknown speed)
| Cheap Test probe
| Only "high"

|-
| 4.7 k Ohm
| 3.6V
| Cheap Test probe
| Only "high"
|}

1 [http://dx.com/p/133097 "Plastic Flat Multimeter Test Hook Clip Probes"]

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T17:21:50Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower, the used test probes can also make an influence. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistor
! Zener Diode
! With test probes?1
! Measurement Result

|-
| None
| None
| Direct wired
| Always correct (if you use this, be careful)

|-
| None
| 3.6V
| Cheap Test probe
| Always correct (but still not advised to do!)

| 150 Ohm
| 3.6V
| Cheap Test probe
| Occasionally "high", but most times correct

|-
| 1.4 k Ohm
| None
| Direct wired
| Occasionally "high", but most times correct

|-
| 890 Ohm
| 3.6V (unknown speed)
| Cheap Test probe
| Only "high"

|-
| 4.7 k Ohm
| 3.6V
| Cheap Test probe
| Only "high"
|}

1 [http://dx.com/p/133097 "Plastic Flat Multimeter Test Hook Clip Probes"]

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T16:47:50Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (sampling @ 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistance
! Zener Diode
! Measurement Result

|-
| None
| None
| Always correct

|-
| None
| 3.6V
| Always correct

|-
| 1.4 k Ohm
| None
| Occasionally "high", but most times correct

|-
| 890 Ohm
| 3.6V (unknown speed)
| Only "high"

|-
| 4.7 k Ohm
| 3.6V
| Only "high"
|}

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T16:47:34Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something e.g. a 12 MHz Frequency (in 24MHz, so also just barely satisfying [http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem Nyquist-Shannon]) that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too much load to overpower. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistance
! Zener Diode
! Measurement Result

|-
| None
| None
| Always correct

|-
| None
| 3.6V
| Always correct

|-
| 1.4 k Ohm
| None
| Occasionally "high", but most times correct

|-
| 890 Ohm
| 3.6V (unknown speed)
| Only "high"

|-
| 4.7 k Ohm
| 3.6V
| Only "high"
|}

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T16:41:25Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something like a 12 MHz Frequency that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too "strong" to overpower. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistance
! Zener Diode
! Measurement Result

|-
| None
| None
| Always correct

|-
| None
| 3.6V
| Always correct

|-
| 1.4 k Ohm
| None
| Occasionally "high", but most times correct

|-
| 890 Ohm
| 3.6V (unknown speed)
| Only "high"

|-
| 4.7 k Ohm
| 3.6V
| Only "high"
|}

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T16:40:10Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something like a 12 MHz Frequency that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too "strong" to overpower. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistance
! Zener Diode
! Measurement Result

|-
| None
| None
| Always correct

|-
| 1.4 k Ohm
| None
| Occasionally "high", but most times correct

|-
| 890 Ohm
| 3.6V (unknown speed)
| Only "high"

|-
| None
| 3.6V
| Always correct
|}

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T16:39:24Z

Bluesceada: /* Issues measuring higher frequencies */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something like a 12 MHz Frequency that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too "strong" to overpower. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistance
! Zener Diode
! Measurement Result

|-
! None
! None
! Always correct

|-
! 1.4 k Ohm
! None
! Occasionally "high", but most times correct

|-
! 890 Ohm
! 3.6V (unknown speed)
! Only "high"

|-
! None
! 3.6V
! Always correct
|}

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2014-01-30T16:38:42Z

Bluesceada: /* Clamp circuits with resistor / Z-Diodes */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

==== Issues measuring higher frequencies ====

When measuring something like a 12 MHz Frequency that can push up to 20 pF load, the resistors in the mentioned circuit (4.7 k Ohm) together with "unknown" 3.6V Zener Diodes might be too "strong" to overpower. Here is a comparison table which values were tried and how it turned out measuring a 12 MHz square wave:

{|
! Resistance
! Zener Diode
! Measurement Result

! None
! None
! Always correct

! 1.4 k Ohm
! None
! Occasionally "high", but most times correct

! 890 Ohm
! 3.6V (unknown speed)
! Only "high"

! None
! 3.6V
! Always correct
|}

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2012-12-27T22:15:38Z

Bluesceada: /* Analog frontends */

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used.

== Probing a circuit ==

Usually for a logic analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter. This can not directly be advised for logic analyzers, but rather for analog instruments (oscilloscopes) that will usually be used in a bigger variety of cases with possibly more noise in the signal.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, for example view below at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog]. When using Zener diodes instead of the normal diodes in Spiralbrain's blog we can get also a protection from negative voltages:

The circuit is shown here again with Zener diodes and numbering for [[fx2lafw]] pins: [[File:Clamp_circuit1.png|thumb||3.3V clamping circuit]]. It works in the following way: Case 1: When we get a voltage over 3.3V, the overvoltage will get "absorbed" over the Z-diodes like with normal diodes normal forward-mode. Case 2: At negative voltages, the Zener effect will happen for a reverse flow from the 3.3V supply to pull up the negative input.

For boards based on the Cypress CY7C68013A and some others it can be discussed if 4.7V or 5V Zener Diodes are also okay, as the CY7C68013A is 5V I/O tolerant -- 5V supply could then be used from USB.

When doing all this, one should be aware that not all diodes might be sufficient, as they will also introduce a minor capacitance.

The [http://sigrok.org/wiki/Saleae_Logic Saleae Logic Analyzer] uses a specific "ESD protection IC" ( ST DVIULC6-4SC6 ) which is essentially a pair of diodes for a slightly different type of clamping / input protection, one will then just have to connect each input line after the resistors to one of the input pins of this IC. However this might not be as cheap as simple diodes and not as easily available.

<gallery>
File:Lcsoft_mini_board_in_tin_box.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box
File:Lcsoft_mini_board_in_tin_box_with_LA.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box with added clamp circuit and connectors for probes on a breakout board
File:Lcsoft_penguin_la.jpg|[[Lcsoft_Mini_Board]] inside a penguin peppermint tin box as an 8 channel logic analyzer
</gallery>

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping.

The 74HC241 can be driven at the measuring voltage up to 6V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Designing a decent analog frontend to be used for example for [[fx2lafw]] capable devices will be a more complicated task. An appropriate ADC has to be found and an input stage with filter, protection and amplification elements needs to be designed. A possible ADC for up to 40MHz sampling frequency is the TDA 8703. An interesting project using that ADC with a parallel port can be found on [http://www.volny.cz/elecon/pcoscilloscope/pcoscilloscope.html volny.cz]

You can also look at the analog frontend of the FX2 based [[EE Electronics ESLA201A]] or the better documented but more complex [[Nexus-Computing OsciPrime]] schematic there: [http://www.osciprime.com/repo/osciprime-schematic-dagobert.pdf]

For probes, an interesting DIY very high frequency probe can be found here at [http://emcesd.com/1ghzprob.htm Douglas C. Smith Web Page]

Circuits for barebone boards

2012-12-27T22:07:00Z

Bluesceada: /* Analog frontends */

Circuits for barebone boards

2012-12-27T22:05:01Z

Bluesceada: /* Clamp circuits with resistor / Z-Diodes */

File:Lcsoft penguin la.jpg

2012-12-27T22:04:01Z

Bluesceada: 8 channel logic analyzer made from Cypress FX2 LcSoft Miniboard inside a Penguin Peppermint Tin Box

8 channel logic analyzer made from Cypress FX2 LcSoft Miniboard inside a Penguin Peppermint Tin Box

File:Lcsoft mini board in tin box with LA.jpg

2012-12-27T22:02:16Z

Bluesceada: fx2 lc soft mini board inside a penguin peppermint tin box with an attached PCB for a 8 channel logic analyzer frontend

fx2 lc soft mini board inside a penguin peppermint tin box with an attached PCB for a 8 channel logic analyzer frontend

File:Lcsoft mini board in tin box.jpg

2012-12-27T21:55:22Z

Bluesceada: fx2 lc soft mini board inside a penguin peppermint tin box

== Summary ==
fx2 lc soft mini board inside a penguin peppermint tin box
== Licensing ==
{{PD}}

Circuits for barebone boards

2012-12-22T00:05:49Z

Bluesceada: Explanation of circuit with z-diodes, saleae chip explanation

Circuits for barebone boards

2012-06-27T22:32:48Z

Bluesceada: /* Analog frontends */

Circuits for barebone boards

2012-06-27T22:32:36Z

Bluesceada: /* Analog frontends */

Lcsoft Mini Board

2012-06-27T22:26:31Z

Bluesceada: /* Required Testing Hardware Extensions */

[[File:lcsoft-miniboard-front.png|thumb|right|Lcsoft CY7C68013A Mini Board]]
[[File:lcsoft-miniboard-back.png|thumb|right|Back of PCB]]

This is a barebones development board for the Cypress FX2 chip, as used in the [[Saleae Logic]] and other boards. It is available on Ebay for less than €15, or Taobao for even less.

== Hardware ==

All the pins on the FX2 are broken out to 40 header pins. There's an on/off toggle switch, a reset button, and a jumper that lets you select whether the FX2 gets its configuration from a small EEPROM, or boots into the default mode. The EEPROM's default settings make it come up with the same VID:PID as a Saleae board.

== Driver ==

The board is fully supported by sigrok, using the [[fx2lafw]] driver.

== Possible Issues ==

* With some kernel versions, and if the onboard eeprom is disconnected (the jumper not connected) the kernel will automatically claim the device with a "usbtest" kernel module, seen in dmesg like "usbtest 2-2:1.0: FX2 device" --- if this happens, sigrok will be unable to claim the device, remove the "usbtest" kernel module as root to be able to use it:

$ '''sudo rmmod usbtest'''

You can add the usbtest permanently to a module blacklist, at least in debian-based distributions found in /etc/modprobe.d/blacklist.conf :

$ '''sudo sh -c "echo 'blacklist usbtest' >> /etc/modprobe.d/blacklist.conf"'''

== Required Testing Hardware Extensions ==

'''Do not directly hook the board pins to another circuit, if you don't know what you are doing! This could damage the board!'''

The simplest circuit would be adding at least resistors in between your circuit-in-test and the LCSoft board, but be aware here that this cypress chip can only tolerate a maximum of 5V I/O. Better would be to use a clamp circuit like shown at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog] (but you do not need to add another eeprom for sigrok with [[fx2lafw]]!). A buffer circuit using a 74HC241 IC for protection is also possible. Check on the [[fx2lafw]] page to see which protection circuits are used on other logic analyzer boards.

More information can be found in [[Circuits for barebone boards]].

Circuits for barebone boards

2012-06-27T22:24:19Z

Bluesceada: /* Clamp circuits with resistor / Z-Diodes */

Circuits for barebone boards

2012-06-27T22:24:08Z

Bluesceada: /* Analog frontends */

Circuits for barebone boards

2012-06-27T22:23:27Z

Bluesceada:

Circuits for barebone boards

2012-06-27T22:13:13Z

Bluesceada: /* Clamp circuits with resistor / Z-Diodes */

File:Clamp circuit1.png

2012-06-27T22:12:02Z

Bluesceada: Clamping circuit to be used for devices to be protected from more than 3.3V, using a semi-high input resistance for probing.

== Summary ==
Clamping circuit to be used for devices to be protected from more than 3.3V, using a semi-high input resistance for probing.
== Licensing ==
{{PD}}

Circuits for barebone boards

2012-06-27T22:11:41Z

Bluesceada:

Circuits for barebone boards

2012-06-27T22:04:35Z

Bluesceada: /* With buffer IC */

Circuits for barebone boards

2012-06-27T21:59:52Z

Bluesceada: /* Clamp circuits with resistor / Z-Diodes */

Circuits for barebone boards

2012-06-27T21:59:18Z

Bluesceada:

Circuits for barebone boards

2012-06-27T21:56:43Z

Bluesceada: initial - edit again in a few minutes

This page describes which input protection / measuring circuits for barebone or other more minimal boards can be used. Usually for a Logic Analyzer high input impedance (and low capacitance) is wanted, to influence the measured circuit as least as possible (don't put an additional capacitive load on it). On the other hand, one might want to use an R-C low-pass filter for the signal to block possible higher frequency spikes. If that is wanted or required, it is best to introduce an additional buffering IC that will then drive the load of the introduced capacity of the filter.

== Input protection ==

=== Clamp circuits with resistor / Z-Diodes ===

A clamp circuit can be used, view below there: http://sunbizhosting.co.uk/~spiral/blog/?p=117

Shown here again with numbering for fx2lafw pins:

=== With buffer IC ===

Different buffer ICs can be used in combination with resistors (+ Z-Diodes to also protect the buffer IC). Depending on the IC, they can also be used for voltage-level conversion or clamping. For example the 74HC241 can be driven at the measuring voltage up to 7V and will output to 3.3V. Buffering can also be done by latch ICs like 74HC573 (3.3V) or 74HCT573 (5V).

== Analog frontends ==

Lcsoft Mini Board

2012-06-27T20:39:44Z

Bluesceada: /* Possible Issues */

Lcsoft Mini Board

2012-06-27T20:39:02Z

Bluesceada: added possible issues

[[File:lcsoft-miniboard-front.png|thumb|right|Lcsoft CY7C68013A Mini Board]]
[[File:lcsoft-miniboard-back.png|thumb|right|Back of PCB]]

This is a barebones development board for the Cypress FX2 chip, as used in the [[Saleae Logic]] and other boards. It is available on Ebay for less than €15, or Taobao for even less.

== Hardware ==

All the pins on the FX2 are broken out to 40 header pins. There's an on/off toggle switch, a reset button, and a jumper that lets you select whether the FX2 gets its configuration from a small EEPROM, or boots into the default mode. The EEPROM's default settings make it come up with the same VID:PID as a Saleae board.

== Driver ==

The board is fully supported by sigrok, using the [[fx2lafw]] driver.

== Possible Issues ==

* With some kernel versions, and if the onboard eeprom is disconnected (the jumper not connected) the kernel will automatically claim the device with a "usbtest" kernel module, seen in dmesg like "usbtest 2-2:1.0: FX2 device" --- if this happens, sigrok will be unable to claim the device, remove the "usbtest" kernel module as root to be able to use it:

$ '''sudo rmmod usbtest'''

You can add the usbtest permanently to a module blacklist, at least in debian-based distributions found in /etc/modprobe.d/blacklist.conf :
$ '''sudo sh -c "echo 'blacklist usbtest' >> /etc/modprobe.d/blacklist.conf"'''

== Required Testing Hardware Extensions ==

'''Do not directly hook the board pins to another circuit, if you don't know what you are doing! This could damage the board!'''

The simplest circuit would be adding at least resistors in between your circuit-in-test and the LCSoft board, but be aware here that this cypress chip can only tolerate a maximum of 5V I/O. Better would be to use a clamp circuit like shown at [http://sunbizhosting.co.uk/~spiral/blog/?p=117 Spiralbrain's Blog] (but you do not need to add another eeprom for sigrok with [[fx2lafw]]!). A buffer circuit using a 74HC241 IC for protection is also possible. Check on the [[fx2lafw]] page to see which protection circuits are used on other logic analyzer boards.

Lcsoft Mini Board

2012-06-26T13:07:52Z

Bluesceada: /* Required Testing Hardware Extensions */

Lcsoft Mini Board

2012-06-26T13:05:23Z

Bluesceada: added hardware extension info