Difference between revisions of "SainSmart DDS120"

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==== 1kHz calibration square wave ====
==== 1kHz calibration square wave ====


Pin PE2 controls the level of the calibration output on the PCB. This is most likely driven by an ISR timer from the 8051 core of the FX2 chip.
Pin PE2 controls the frequency of the calibration output on the PCB. It is driven by an ISR timer from the 8051 core of the FX2 chip.


== Resources ==
== Resources ==

Revision as of 17:40, 3 April 2016

SainSmart DDS120

The SainSmart DDS120 is a USB-based, 2-channel oscilloscope with an analog bandwidth of 20MS/s and 48MS/s sampling rate.

See SainSmart DDS120/Info for more details (such as lsusb -v output) about the device.

Hardware

Or in newer hardware:

Photos

Protocol

The vendor firmware uses the following protocol:

Oscilloscope command bRequest value Notes
Set CH0 coupling 0x24 Possible values: 0x00, 0x08 (AC-coupling, DC-coupling).
Set CH1 coupling 0x25 Possible values: 0x20, 0x10 (AC-coupling, DC-coupling).
Set CH0 voltage range 0x22 Possible values: 0x08, 0x04, 0x00, 0x06, 0x02 (50mV, 100mV, 200mV, 500mV, 1-5V).
Set CH1 voltage range 0x23 Possible values: 0x20, 0x10, 0x00, 0x12, 0x02 (50mV, 100mV, 200mV, 500mV, 1-5V).
Set sampling rate 0x94 Possible values: 0x11, 0x01, 0x10 (240kHz, 2.4MHz, 48MHz).
Trigger oscilloscope 0x33 Possible values: 0x00 == start sampling.

Firmware

Vendor firmware

The SainSmart vendor firmware is contained on the I²C EEPROM. The FX2 boots directly into that firmware.

Open-source firmware

There is an open-source firmware that can be used by sigrok. The open source firmware is missing the following planned features:

  • AC/DC coupling support
  • <1MHz, 2, 3, 5, 6, 7.5, 9.6, 10, 15, 24, 30 MHz sampling rate support
  • Turn on/off the calibration pulse
  • Change frequency of the calibration pulse (add 10kHz, 100kHz and 1MHz)

Gain stage

The gain stage is 2 stage approach. -6dB and -20dB on the first stage (attentuator). The second stage is then doing the gain by 3 different resistor values switched into the feedback loop. The following does not correlate with measure on real hardware, there is a 6th gain position that is working though. It is very similar to another gain and was most likely omitted because of that.

# Channel 0:
PC1=1; PC2=0; PC3= 0 -> Gain x0.1 = -20dB -> 0x02 (1V)
PC1=1; PC2=0; PC3= 1 -> Gain x0.2 = -14dB -> 0x0A (0.5V)
PC1=1; PC2=1; PC3= 0 -> Gain x0.4 =  -8dB -> 0x06 (0.250V)
PC1=0; PC2=0; PC3= 0 -> Gain x0.5 =  -6dB -> 0x00 (0.200V)
PC1=0; PC2=0; PC3= 1 -> Gain x1   =   0dB -> 0x08 (0.100V)
PC1=0; PC2=1; PC3= 0 -> Gain x2   =  +6dB -> 0x04 (0.050V)

# Channel 1:
PE1=1; PC4=0; PC5= 0 -> Gain x0.1 = -20dB -> 0x02 (1V)
PE1=1; PC4=0; PC5= 1 -> Gain x0.2 = -14dB -> 0x22 (0.5V)
PE1=1; PC4=1; PC5= 0 -> Gain x0.4 =  -8dB -> 0x12 (0.250V)
PE1=0; PC4=0; PC5= 0 -> Gain x0.5 =  -6dB -> 0x00 (0.200V)
PE1=0; PC4=0; PC5= 1 -> Gain x1   =   0dB -> 0x20 (0.100V)
PE1=0; PC4=1; PC5= 0 -> Gain x2   =  +6dB -> 0x10 (0.050V)

AC/DC coupling

The coupling is controlled via 2 PhotoMOS chips.

# Channel 0:
PE3=0 Disable AC-coupling capacitor (DC-Coupling)
PE3=1 Enable AC-coupling capacitor

# Channel 1:
PE0=0 Disable AC-coupling capacitor (DC-Coupling)
PE0=1 Enable AC-coupling capacitor

1kHz calibration square wave

Pin PE2 controls the frequency of the calibration output on the PCB. It is driven by an ISR timer from the 8051 core of the FX2 chip.

Resources