Ugly FPGA Breakout

Ugly prototyping with diminutive FPGAs...why not?

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I'm standing on the shoulders of giants here. Luke Valenty is blazing a trail for low-cost hacker-friendly FPGA boards (TinyFPGA), but I wanted one for ugly-style prototyping over a ground plane. So, I decided to leverage his convenient TinyFPGA Programmer (available on Tindie) for blasting synthesized verilog into my own board.

I picked up a few TinyFPGA boards to play with on Tindie, and was impressed at how easy it all worked.  @Luke Valenty has done a great job of lowering the barrier to entry on this technology, and opening it up to a wider audience.  I've had some fun with the A2 boards, and their MachXO2-1200 FPGAs.  The only thing missing was a clean way to do ugly prototyping with them.  Those that have seen #Ugly SMD Adapters know that I prefer to prototype over a ground plane, and through-hole headers make that difficult.  So, I rolled up my sleeves and cranked out a very "tiny" board.  It's still a work-in-progress, so check the logs for updates.

The first version is in GitHub for anyone interested, but be warned that it hasn't been tested yet.  Once the PCBs arrive and I have a chance to test them, I'll remove this warning.

  • Tested. Works.

    Ted Yapo03/10/2018 at 23:31 0 comments

    The PCBs arrived last night, but I had to wait for this morning for the box of parts from DigiKey - I almost got the timing right this time.  Here's the assembled board with a Roman denarius for scale.  It's pretty small.  The #TinyFPGA Programmer is plugged in on top.  It programs the FPGA just fine.

    I was careful to apply just a little paste with a 25 Ga needle since I've been having issues with QFN packages. I still got 3 solder bridges I had to clean up with an iron, but otherwise it worked OK.  I think my paste is getting old - it's probably two years old now and never been in the fridge (I can hear you cringing, people :-)

    I wrote some quick test verilog just to make sure all the pins work, and they do.

    Now, I can build a few more of these things and put them to use.

    I think I'm going to make a composite video frame grabber as a test.

  • PCB: First Cut

    Ted Yapo03/01/2018 at 03:09 0 comments

    So, I threw together a quick breakout PCB for the MachXO2-1200 FPGA. The idea is that you mount it to a solid ground plane (un-etched copper clad) by soldering down the castellations on the edges, then connect it up with wire wrap (twisted pairs when needed).

    The bottom has no soldermask, so it can make good contact with the ground plane.  You could theoretically reflow it to the plane, but if you just tack-solder the 6 castellations, you could remove the PCB if desired.

    The circuit is pretty simple: FPGA, bypass caps, and a 4k7 pulldown on the JTAG clock line I shamelessly stole from the TinyFPGA design.  It presumably keeps the clock from toggling spontaneously and screwing things up. It's mostly solder pads, really.  I added s 5-pin surface-mount header that's compatible with the TinyFPGA programmer.

    I've sent design to OSH Park, and now just have to wait.

    In case anyone is wondering what this is all about, here's another project I made with similar boards:

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Jarrett wrote 07/25/2018 at 21:19 point

Which components are which?

I'm assuming the resistor is at the top right of your OSHPark render there.

  Are you sure? yes | no

Ted Yapo wrote 07/26/2018 at 01:40 point

Yes, the resistor is at the top right.  The caps could really go anywhere.  I put the 10uF cap right at the power input (top left), then the 1uF cap under that - the rest are all 100nF.  They're just bypass caps.  You could probably use all 100nF (or 1uF or 10uF, since they're all MLCCs in the same package with similar parasitics) or leave a few of them out or whatever.

The big one in the middle with lots of pads is the FPGA :-)

  Are you sure? yes | no

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