Latest revision as of 17:05, 17 December 2017

The fx2grok family consists of four devices (fx2grok-flat, fx2grok-tiny, fx2grok-bga, fx2grok-wide) of very small, Open Hardware FX2-based logic analyzers.

The schematics and layouts are done from scratch in KiCad, and are released under the CC-BY-SA 4.0 license.

Using the open-source fx2lafw firmware (and sigrok, of course) you can use these devices as 8-channel (or 16-channel, for the fx2grok-wide) logic analyzers.

Device comparison

Note: Most of this is work in progress and might change at any time!

Item	fx2grok-flat	fx2grok-tiny	fx2grok-bga	fxgrok-wide
Goals ²	Small Open Hardware Convenient and reliable to use in practice	Even smaller Open Hardware "Just for fun" project, doesn't have to be practical Sacrifices a lot of things for reduced size	Smallest-possible Open Hardware "Just for fun" project, doesn't have to be practical Sacrifices even more things for reduced size	Small, but 16 channels Open Hardware Reliable and convenient, with a few more channels
Author	Piotr Esden-Tempski	Uwe Hermann	Uwe Hermann	Ryan "Izzy" Bales, based off of Piotr Esden-Tempski's fx2grok-flat
Status	in progress	finished	WIP	WIP
Hardware license	CC-BY-SA 4.0	CC-BY-SA 4.0 ¹	CC-BY-SA 4.0	CC-BY-SA 4.0
Size	33 mm x 16 mm	11 mm x 11 mm	tbd	tbd
Logic channels	8 + CLK & TRIG	8	tbd	16
Layout specs	One sided load 4 layer PCB/layout 0.15 mm trace/space 0.3 mm drill & 0.1 mm annular ring	Double-sided 2-layer PCB/layout Components soldered on both sides 0.8 mm PCB thickness 5 mil traces, 6 mil trace clearance 8 mil via drill hole diameter, 5 mil annular ring	tbd	tbd
Cypress FX2	Cypress CY7C68013A-56LTXC, QFN, 8 mm x 8 mm	Cypress CY7C68013A-56LTXC, QFN, 8 mm x 8 mm	Cypress CY7C68013A-56BAXC, BGA, 5 mm x 5 mm	Cypress CY7C68013A-56LTXC, QFN, 8 mm x 8 mm
Input protection	3 x IP425x-4-TTL EMI/ESD filters on all probes + 100k pull-ups, 1x USBLC6-2 for USB	None whatsoever	None whatsoever	100Ω on each probe, 4x DSILC6-4 for all probes, 1x USBLC6-2 for USB
24 MHz crytal	ABM8	4-SMD, 300μW, 2 mm x 1.6 mm	tbd	tbd
USB connector	USB Micro-B SMD	USB Micro-B SMD	tbd	USB Micro-B SMD
Probe connector	2x6 1.27 mm PCB-edge connector	2x5 1.27 mm PCB-edge connector	tbd	2x 2x5 1.27 mm PCB-edge connectors
EEPROM	Yes, sigrok fx2lafw (8-channel) VID/PID 1d50:608c	None, default Cypress VID/PID 04b4:8613	None, default Cypress VID/PID 04b4:8613	Yes, sigrok fx2lafw (16-channel) VIP/PID 1d50:608d
Passives	Mostly 0402, some 0603 & 0.4 mm pitch DFN	Only 0402	tbd	Mostly 0402, some 0603
LED	1x 0603 LED on PA1	1x 0402 LED on PA1	tbd	1x 0603 LED on PA1

¹ The obsolete/nonworking fx2grok-tiny 0.1 was licensed CC-BY-SA 3.0, since version 0.2 the license is CC-BY-SA 4.0.
² Optional goal: Make a tiny 3D-printed enclosure, and/or an "enclosure" using resin (example) with the device (including probes) ideally looking similar to the sigrok logo in the end.

What is NOT the goal?

As you may know, there are tons of FX2-based logic analyzers (and tons of clones) already. There's not much use in creating yet another "standard" device.

The goal of these projects is thus NOT necessarily to make a better device, or to make a cheaper device, or anything like that. The main goals are to to make them Open Hardware and to have them be as tiny as possible (they're mostly "just for fun" projects, especially the fx2grok-tiny and fx2grok-bga variants).

Download

The schematics, PCB layout and Gerber files are available from the fx2grok Git repository:

$ git clone git://sigrok.org/fx2grok

fx2grok-tiny

Status

fx2grok-tiny 0.2 has been tested and is known to work. The first PCB version (fx2grok-tiny 0.1) is not working and thus obsolete.

Photos

Schematics, PCB layout, 3D preview

fx2grok-tiny 0.2:

Schematics
PCB layout
3D preview, top
3D preview, bottom
Connector pinout

Cable and connector variants

Samtec SFSD-05-28-H-10.00-SR + TFM-105-01-L-D:

Samtec SFSD-05-28-H-10.00-SR
Connector with notch
Crimp parts
Crimp
Crimp tool
Finished cable
Cable with probes
Heatshrink tube variant
Heatshrink tube variant
Heatshrink tube variant
Heatshrink tube cable
Samtec TFM-105-01-L-D
Samtec TFM-105-01-L-D
Cable connected
Cable + pinheader

Hand-soldered ribbon cable:

Ribbon cable
Individual wires
Soldered connector
Kapton tape
Finished cable
Cable comparison

Housing

Heatshrink tube
Heatshrink tube, LED

Assembly

The current set of red PCBs was manufactured by firstpcb.com, solder stencils are manufactured by oshstencils.com. You can use other PCB manufacturers of course, but don't forget that the PCB thickness must be 0.8mm (otherwise the probe connector won't fit) and that your PCB manufacturer must support all other specs (see table above).

The device can be assembled without too much hassle even though all parts are 0402 or otherwise very tiny.

Apply solderpaste with the stencil to one PCB side.
Place the parts with a pair of tweezers on the solderpaste (steady hands help, but no microscope is required).
Solder the parts (a Puhui T-962A oven was used in this case; it should also be doable with a hot air gun/station or a modified pizza oven, though).
Put some kapton tape on the soldered parts to prevent them from falling off while soldering the other PCB side in the oven.
Apply solderpaste with the stencil to the other PCB side, place the parts, solder in the oven again.
As a last step, manually solder (soldering iron) the 5x2 pins edge connector.

PCB panel
PCBs
PCB, top
PCB, bottom
Stencil, top
Stencil, bottom
Solderpaste
PCB, top, populated
PCB, bottom, populated
Example solderprofile
Device, top
Device, bottom
Device and cable
Size comparison

Bill of materials

Note: All prices are for single quantities, most parts get a lot cheaper if you buy higher quantities.

Qty	Device	Footprint	Size	Value	Refdes	Digikey	Mouser	Comments
Required parts
1	Cypress CY7C68013A-56LTXC	QFN-56	8 mm x 8 mm	—	IC1	10.05€	10.30€	Main chip. Alternatives: Future Electronics: 6.55€ eBay: 4.07€ Aliexpress: 1.52€ (10 pcs lot, 15.16€ total)
1	Amphenol FCI 10118192-0001LF	custom	9.8 mm x 5.6 mm	—	U1	0.38€	0.35€	USB Micro-B SMD connector
1	Murata XRCGB24M000FAN00R0	custom	2 mm x 1.6 mm	24 MHz	Y1	0.29€	0.46€	24MHz crystal, ±25ppm, 6pF, 150 Ohms, max. 300μW drive level, 4-SMD, no lead
1	Micrel MIC5504-3.3YM5-TR	SOT-23-5	2.9 mm x 1.6 mm	3.3 V	U2	0.10€	0.10€	3.3 V LDO, max. 300mA
4	Yageo RC0402JR-072R7L	0402	0.25 mm x 0.125 mm	2.7 kΩ	R2, R3, R4, R5	0.08€	0.08€	Resistor
1	Samsung RC1005J104CS	0402	0.25 mm x 0.125 mm	100 kΩ	R1	0.08€	—	Resistor
8	Samsung CL05A104KP5NNNC	0402	0.25 mm x 0.125 mm	100 nF	C2, C5, C7, C8, C10-C13	0.08€	—	Ceramic capacitor
3	Taiyo Yuden JMK105BJ105KV-F	0402	0.25 mm x 0.125 mm	1 µF	C1, C14, C16	0.08€	0.10€	Ceramic capacitor
2	Murata GRM155R61A225KE95D	0402	0.25 mm x 0.125 mm	2.2 µF	C3, C6	0.08€	0.08€	Ceramic capacitor
2	Samsung CL05C120JB5NNNC	0402	0.25 mm x 0.125 mm	12 pF	C4, C9	0.08	—	Ceramic capacitor
1	Vishay VLMB1500-GS08	0402	0.25 mm x 0.125 mm	—	D1	0.34€	0.51€	LED. When using other LED colors, you might also want a lower value for R5.
Optional parts / variants
1	Amphenol FCI 20021111-00010T4LF	custom	—	—	P1/P2	0.53€	0.55€	5x2 through-hole pin header (1.27 mm pitch), could soldered to the PCB (5 pins per side)
1	Amphenol FCI 20021311-00010T4LF	custom	—	—	—	0.68€	0.69€	5x2 connector/receptacle (1.27 mm pitch), could be used for soldering the probe cable/wires
1	Samtec TFM-105-01-L-D	custom	—	—	P1/P2	0.53€	—	5x2 through-hole pin header (1.27 mm pitch) with a notch, soldered to the PCB (5 pins per side), match for the Samtec SFSD-05-28-H-10.00-SR cable below
1	Samtec SFSD-05-28-H-10.00-SR	custom	—	—	—	4.77€	—	Potential probe cable, needs some crimping

Note: C15 is missing and there is a C16, which is correct. C15 was removed and the numbering wasn't reset.

Random notes

No, you cannot order assembled fx2grok-tiny devices or the bare PCBs anywhere, this is a pure hobby project. You can, however, make your own devices. Everything is Open Hardware, Open Source, and documented.
The fx2grok-tiny device sacrifices a lot of things in order to make it as tiny as possible:
- There's no input protection whatsoever on the probes, not even a simple resistor. This means (among other things) you'll see random garbage on unconnected probes (which can be avoided by explicitly attaching them to a GND, though).
- There's no protection circuitry whatsoever on the USB side either.
- The device has no EEPROM, so it'll enumerate with the default Cypress USB VID/PID of 04b4:8613. libsigrok/fx2fwla currently assume all such devices are plain FX2 eval boards with all 16 channels accessible. However, fx2grok-tiny only has 8 channels on the connector, so until we have a nicer permanent fix for this, you have to either limit your samplerate to 12MHz (you cannot use 16MHz or 24MHz), or you can patch the libsigrok fx2lafw driver to treat devices with a VID/PID of 04b4:8613 as 8-channel devices (instead of 16-channel devices):

diff --git a/src/hardware/fx2lafw/api.c b/src/hardware/fx2lafw/api.c
index 34c5bc41..1634635a 100644
--- a/src/hardware/fx2lafw/api.c
+++ b/src/hardware/fx2lafw/api.c
@@ -70,7 +70,7 @@ static const struct fx2lafw_profile supported_fx2[] = {
         */
        { 0x04B4, 0x8613, "Cypress", "FX2", NULL,
                "fx2lafw-cypress-fx2.fw",
-               DEV_CAPS_16BIT, NULL, NULL },
+               0, NULL, NULL },

Many of the recommendations from the Cypress FX2 datasheets and guides are ignored on the fx2grok-tiny (mostly in order to be able to make it smaller, sometimes also a bit simpler). While this seems to work fine regardless (for now), you shouldn't be too surprised if there are issues eventually.
- Unused pins should be tied to GND as per vendor (this is not done, though).
- The recommended crystal should have 12 pF (5 percent tolerance) load capacitors, we're using a crystal that wants 6 pF as per datasheet.
- The recommended crystal should have 500 µW drive level, we're using one with 300 µW.
- Cypress recommends a 4 layer PCB (we use a 2 layer PCB) and various other PCB layout / solderability related things that we're ignoring.
- The solderpaste is a big solid area under the FX2 device, it would be a bit nicer to have that part be a checkerboard pattern (but it seems to work well enough like this, too).
- etc. etc.
The Gerber files intentionally don't include silkscreen (not really needed, might be too tiny anyway, sometimes might increase PCB manufacturing costs). However, the silkscreen is "abused" in the KiCad files to generate nice 3D previews (see above) that can be helpful when assembling the device.
The fx2grok-tiny device currently has a blue LED with a 2k7 resistor (R5), which is sufficiently bright. If you want to use other LED colors you might also want to use a lower resistor value to increase brightness.

fx2grok-flat

Status

fx2grok-flat 0.2 has been tested and is known to work, but is not yet the final version. Additional improvements will be implemented in version 0.3.