'Flea Ohm' FPGA Project

My own raspi-zero style board, based on the new ECP5 series FPGA from Lattice Semiconductor! ;-)

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FleaFPGA Ohm/Ohm+ are my own attempts at making a powerful FPGA-based development board in a raspi zero form-factor. This time however, I use the new ECP5 FPGA from Lattice Semiconductor! ;-)

Hello everyone!

So I got back into doing some hardware design again recently.. and decided on doing a new FPGA development board. I was somewhat inspired by a product that had appeared in the marketplace around the same time as my previous Uno board. That board was the raspberry pi zero!

From there on, I decided I wanted to do an all-FPGA variant that was compatible to the pi in terms of GPIO but with 'a few extras here and there'. I then saw Lattice Semiconductor's newest ECP5 series FPGA (and far more capable than the MachXO2) became available recently, so I thought what the hey and had a crack at it! :)

Long story short: I created two new FPGA prototype boards using the capable ECP5 FPGA, which I've called the "Ohm" and "Ohm+". Kindly check out the following video of my ohm board in action:

Final prototype pics have been released and will include the following specs:


- 32MB 16-bit wide SDRAM (or 128MB LPDDR for Ohm+).

- micro SD card slot

- Two Type-A USB + PS/2 host ports (since Ohm revision AB).

- High speed digital video and LVDS output port

- 35 User GPIO pins, including:

  • Four ADC channels
  • Eight differential/LVDS input pairs, or four LVDS input and four output pairs.

- Raspberry Pi compatible 40-pin GPIO header

- ESP-01 wifi module compatible 'Auxiliary' header

- On-board JTAG interface via USB slave serial AND provision for an external JTAG debugging pod are included.

Current Project Status 23/2/2017): Project hardware redesigned and currently under review.

Cheers, Valentin.

EDIT 7/12/2016: - Ohm specifications and status summary updated.

  • New year, new direction - Part II

    Valentin Angelovski02/23/2017 at 10:55 2 comments

    Hello again!

    Sorry about the delay in my last reply. Non-hobby matters, along with the added frustration over long part lead-times etc. did slow things down here quite a bit..

    Rather than wait an unknown lead-time on an FPGA part that I need, thought I'd try for a redesign of my Ohm board using larger (but more readily available) parts. While this might result in a larger (and more expensive) board, thought I'd also take this opportunity to make it a bit more useful..

    So, whilst I was in the process of exploring FPGA alternatives, (where nothing is really jumping out at me right now - apart from maybe Max-10) I gave Lattice and another variant of their ECP5 series one more spin..

    Anyway, here's my result (did I mention it's a bit bigger than before? :-) :

    I've retained all the existing Ohm board functions, but added a flexible lvds header (for display or camera modules, potentially) and also 10/100 Ethernet.

    Regarding the external DRAM: I have completed several versions of the above-mentioned design with different external RAM chips loaded, from SDRAM through to DDR3..

    I realize this is a major deviation from the original (pi zero form factor) design. However cool that was (and still is, I've not forgotten), I've decided that I always wanted to do something in-between a zero and a full-blown pi. Through this renewed effort, it will be as close as I'm ever going to get. :-)

    Next step: To decide upon the external RAM, review and then try fabricating one (or more) of these guys..

    Thanks for reading! :-)



  • New year. New direction.

    Valentin Angelovski01/08/2017 at 13:20 6 comments

    Hello again (and Happy New year to all! :-)

    Over the holiday break, I've been pondering what I could do to possibly revive this stalled project of mine..

    So, given I cannot obtain the parts I need for my current design I have therefore decided to look at redesigning my Ohm board using an FPGA from another manufacturer..

    Okay, we'll see what I can come up with now. Suggestions are also welcome! ;-)

    Cheers, Valentin

  • Ohm/Ohm+ project retirement

    Valentin Angelovski12/17/2016 at 14:26 0 comments

    EDIT: *** 09/01/2017: This project is being considered for possible revival ;-) See Blog post titled "New year. New direction" Thanks!

  • Ohm project update.

    Valentin Angelovski12/07/2016 at 14:05 8 comments

    Hello again!

    **** EDIT 12/12/2016: Due to the fact I still have no ETA on availability of certain key parts (like the FPGA) for this project, I have decided to put my Ohm and Ohm+ projects on-hold indefinitely and do other things with my spare time. This includes my newly-completed Ohm+ board with DDR3 RAM. Apologies to those of you who were waiting for positive news, but I am afraid without parts I cannot do much - Valentin ****

    Just a thought I'd post a quick update on my Ohm project. Last weekend, I managed to successfully assemble and test my 'pre-production ready' revision Ohm board (yay!). My initial function tests show the board is behaving largely as expected but my tests are ongoing. Following is a 'happy snap' of the final assembled board:

    So far, I've successfully configured the above with Next186 (x86) and Sweet32 SoC softcores. With luck, I should be able to set aside some time to complete the functional testing on the board in the coming days. More to follow..

  • Project delays and picking up where I left off..

    Valentin Angelovski11/15/2016 at 09:07 2 comments

    Hello everyone!

    It's been a long while since our last project news update. Progress had unfortunately stalled due to issues ranging from component availability to non-hobby matters.. :-(

    While I waited for matters beyond my control to resolve, I thought I'd have a decent crack at adding a 2nd USB host port to my Flea Ohm board. Didn't think it was possible.. but somehow I made it fit (yay! See below):

    Now, I had always intended my Ohm board to be a worthy successor for my earlier FleaFPGA Classic boards. This meant some means to add a PS/2 Keyboard and mouse as desired (thus making it backwards compatible with nearly all of the existing HDL projects implemented on the older board). Not having a 2nd USB host port with PS/2 secondary capability was something of a lament for me, hence my (successful) attempt..

    Now that my above-mentioned issues have now been resolved, I can now pick up where I left off two months ago.. :-)

    So here's my announcement: As soon as I have confirmed the above PCB to be functional (approximately 2 weeks from now), I will begin small-scale production of my Ohm board immediately thereafter. Pre-production Ohm boards may be ordered directly from me. Price will be set at USD$33 per board. Sales of pre-production Ohm boards will be limited to a maximum of two boards per customer.

    As for my Ohm+ board: I have yet to bring my Ohm+ board up to the same standard as my latest Ohm design. This is mainly due to the extensive modifications needed to include the second USB host port. Therefore I will make a separate announcement about Ohm+ at a later date.

    More to follow (and soon.. :-)

    Cheers, Valentin

  • Flea 'Ohm' ready for small-scale production!

    Valentin Angelovski09/12/2016 at 08:36 1 comment

    Hello again!

    Well folks, it's been a few weeks since my last post. So I am posting an overall update on my hobby project(s) now..

    'Ohm' board development status: Ready for a small-scale production run!

    After adding numerous fixes to the PCB artwork, I believe the resultant new revision is good enough for a pilot production run!

    There are sufficient (as well as cool) HDL examples for potential users to 'kick the tires' on the 'Ohm' board, so to speak. More cool examples would be nice, but those can be added later.

    Only thing left to do now is wait for a reply from component suppliers and then work out the final board pricing. Good times! :-D

    'Ohm+' board development status: Board tested OK but needs a 'killer' HDL application example..

    Successfully tested the 128MB LPDDR RAM on the Ohm+ prototype @ 100MHz max. using CAS=2 (yay!). However, it does not meet timing at that rate nor does the test code support burst mode transfers (yet). Tweaked ram controller HDL needs more work before it will be viable for use in system application. Another (probably better and faster) alternative would be to use Lattice's own LPDDR controller IP, but apparently that is not free..

    After adding numerous fixes to the PCB artwork, this board revision is also good enough IMHO for a pilot production run! Apart from RAM, it is 100% backwards compatible with the standard 'Ohm' board (which uses 32MB low-power SDRAM instead of 128MB LPDDR).

    Summary: My 'Ohm' board is now ready for a small-scale production run. My 'Ohm+' PCB artwork is also ready but needs worthy working HDL examples to make it a viable platform. Therefore I will focus on taking the 'Ohm' board on to the next level, but also see what examples could be brought to Ohm+ as well as the Ohm...

    Well, that's all for now. As soon as I know how much these boards will cost to make, I will post another update (hopefully soon). Watch this space! ;-)

  • Testing flea Ohm's ADC and PWM

    Valentin Angelovski08/26/2016 at 02:21 3 comments

    Hello Again!

    Before I continue on with RAM testing on the Ohm+, thought I'd do some more testing of the Ohm board's ADC and PWM capabilities.

    For this test, I knocked up a 'quick and dirty' Video overlay, with the FleaFPGA Ohm providing a 256x64 bitmap overlay for a video signal from a reverse parking camera. Here is a picture of the test setup:

    As you can see, there isn't really much to it! :-)

    In the above pic, RCA plug into the mini 'hat' is feeding into one of Flea Ohm's ADC inputs from the reversing camera (shown left). While the other RCA connection (bottom right) is connected to a PWM output pin with overlaid video driving a TV monitor (shown in the next picture.. :-).

    Anyway, here's our test result... and the result was better than expected:

    Admittedly, there is some noticeable loss in image quality as I am running the ADC and PWM @ approximately 6-7 bits resolution. However, I did not believe it would work as well as it did. While I am running the ADC and PWM sample clocks at 20% above normal (effectively over-clocking the ADC), I suspect there may be room for improved performance via tweaks to the hdl - tweaks that may allow the ADC to meet the FPGA's timing requirements at the faster sample clock. Still, it is good to see what Flea Ohm's humble ADC and PWM pins could be capable of..

    Well, that's it for now - back to more testing! :-)

  • My 'FleaFPGA Ohm+' is alive! :)

    Valentin Angelovski08/19/2016 at 05:02 0 comments

    Hello again!

    First pics of my most advanced flea yet - my 'FleaFPGA Ohm+' board prototype with 128MB of ddr RAM (versus my original 'Ohm' board, which has 32MB sdram..) :-D

    Initial functional tests suggest my ECP5 is alive and kicking! My next step will be to exercise the onboard dram. Fun times ahead.. :-)

  • Revised Flea Ohm boards arrived (yay! :-)

    Valentin Angelovski08/18/2016 at 10:11 0 comments

    Hello again! :)

    You may recall I was waiting for revised Ohm boards to arrive? Well, those boards arrived yesterday and I managed to assemble and test one for good measure:

    Apart from an incorrectly loaded capacitor on the ADC#4 circuit, (causing really poor ADC operation - fixed) I did not have too many problems bringing up what essentially was an incremental improvement/fix over the original (Hey, at least I now have four working ADC channels.. on the initial prototype three of the channels did not even work *facepalm* :-)

    Next on my to-do list is to assemble/test an "Ohm+" prototype (with more complex/advanced ddr ram onboard) and give that a spin.. Stay tuned! :)

  • More details and an attempt at 1080p.. :-)

    Valentin Angelovski08/10/2016 at 11:06 0 comments

    ello again :-)

    Just a quick update on my Ohm project.

    1.) Thought I'd release a little more info about my FleaFPGA Ohm board! Following is an overview of the FleaFPGA Ohm board in it's final physical layout:

    2.) For fun, I made an attempt at getting 1080p (30Hz) video output from the FleaFPGA Ohm:

    Worked better than I had expected! Unfortunately, it seems that 1080p30 does not appear to be a common supported screenmode among modern TVs. However, 720p60 and 1024x768 appear to work fine..

    More to follow.. :)

View all 10 project logs

Enjoy this project?



jonathanscottjames wrote 02/24/2017 at 23:19 point

what's the max 8 bit input rate of the gpio on flea ohm? and where can i guy one?

  Are you sure? yes | no

Valentin Angelovski wrote 02/28/2017 at 03:28 point

Hello! Good question. I've not tested maximum *input* data rates via the GPIO header yet, but suspect it may be in the ballpark of 100MHz (or possibly more, need to test). This is assuming the following:

1.) Data transfer occuring via a direct board-to-board connection, not via a ribbon cable..

2.) Single-ended data only i.e. not using the available lvds differential signal pairs which are also available via the main header and should provide much faster data transfer rates (again, needs further testing).

As for buying an Ohm board: Unfortunately I've had to completely redesign my board, due to non-availability of the FPGA I had previously used in my initial prototypes :-/ Feel free to check out my latest blogs about it. Cheers.

  Are you sure? yes | no

Lars R. wrote 11/15/2016 at 11:03 point

How much data can you squeeze out of the HDMI?




  Are you sure? yes | no

Valentin Angelovski wrote 11/15/2016 at 11:20 point

Hello Lars and thanks for your question.

Highest screen mode I've successfully attempted with the Ohm's video output was 1080p30 (i.e. 30Hz progressive). Of course, this means that anything below that i.e. 480p, 720p, 1024x768@60Hz etc. etc. should also work as well.

I did make an attempt to output test video at 1080p50 (50Hz). Unfortunately the image quality did not appear entirely stable, presumably due to FPGA timing limits being exceeded by a significant margin. 

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D H wrote 11/05/2016 at 11:46 point

A great project - two usage ideas

(a) use the board to recreate sound chips such as NES, SID or a OPL3 for distinctive sounds - attach a music keyboard to the usb or the io pins

(b) convert the cores from the MIST project ( for a wide variety of reimplemented consoles and computers

Two questions:

(i) can an audio jack be attached to the io pints?

(ii) Can it load HDL fpga cores from the sd card (for easy conversion to another project) or can it only be converted using a pc?

  Are you sure? yes | no

Valentin Angelovski wrote 11/09/2016 at 04:23 point

@D H

Thanks for your interest in my Flea Ohm project. 

Regarding your suggestions: (a) I would love to see OPL3 added to Nicolae's Next186 SoC (alas I have not yet done it myself as I only know VHDL well). Apart from Amiga and x86, I did successfully attempt a port of an old build of C64 softcore (with SID) to my Ohm board. (b) My own personal free time is rather limited however, so any outside help in this regard would be welcome.

My answers to your questions: (i) You would need to add an RC (or LC) filter circuit between the GPIO pin and your proposed audio jack. (ii) Currently, the FPGA's config ROM can only be altered via an external PC. By PC I also potentially mean a Raspberry Pi (zero?). I *think* the flea JTAG utility app. could be recompiled for ARM but I would need to confirm that.

While it may be theoretically possible (assuming the user's hardware design allows it) to transfer a new config ROM image to the FPGA in "background mode" from the SD card, it would be somewhat tricky and cumbersome to implement. You would also need to cycle power to the FPGA in order for it to accept the new ROM configuration. 

Cheers, Valentin

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dobredanielstelian wrote 10/04/2016 at 19:32 point


Your board looks nice.

I want to design one myself using Xilinx FPGA. I want to use Spartan 6 xc6slx25 or some equivalent Atrix 7.

If you have any suggestions on what i should add on it, something that maybe you forgot and you wanted to add.

Best Regards,


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Fredrik.c.johnsson wrote 09/18/2016 at 22:21 point


Love your work and need an FleaFPGA Ohm+ for a future Amiga projekt. Amiga in a joy (like the C64 in a joy butt WAY better).

Any ideas on what it will cost? I reeeeeealy whant one ;-) 

  Are you sure? yes | no

Valentin Angelovski wrote 09/20/2016 at 02:02 point

Hello Fredrik!

Thanks for your interest in my project and question. I also like the idea of an Amiga-in-joystick, but instead I built an "Amiga-cube" ;-) Picture of my "Amiga-cube" can be found in the gallery.

Currently focussing on Ohm (not Ohm+) board production due to the following things it has going for it:

   1.) List of working HDL projects already ported to it.

   2.) Possibility exists for a "sub-USD$40" FPGA development board (still working this one out currently. More soon).

Cheers Valentin

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Erik Piehl wrote 08/31/2016 at 06:36 point

Great project! A quick question on the assembly: if I understood properly you self assembled the boards, is that right? I am just wondering how you dealt with the BGA packages? I am planning to make an FPGA board, and it would be great to be able to use BGA packaged chips - but I suppose it means going to a 4 layer board... And I don't have a reflow oven...

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Lars R. wrote 08/31/2016 at 07:08 point

4 layer is not much more than 3 layer. And this is already tough for BGA: Vias consume the space below the package on the bottom layer. Assuming the 2nd layer being GND, your 3rd layer is for at least two VCC-voltages that connect to various balls, need to be routed to the package and require decoupling. So, it is hard to have a reference plane for signals on the 4th layer (bottom), which leaves you with one good layer for signals: top layer.

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Erik Piehl wrote 08/31/2016 at 08:41 point

Thank you for the comments! I guess I am wondering how many layers in practice would be required for a board like this - is it doable with 4 layers or you think one needs more?

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Lars R. wrote 08/31/2016 at 08:59 point

Erik, this highly depends on how 'intelligent' the pinout of the BGA is and what you need. I don't know the ECP5. In theory, with a very good BGA pinout, it is possible to connect LPDDR... with 4 layers. However, with the ICs I used so far, it was a pain even with 6 layers. If you are also satisfied with SDRAM with a reduced pincount interface or with Hyperram, you are probably fine with 4 layers or even less. However, for both options (reduced pincount SDRAM and Hyperram), there are no Hard IPs on current FPGAs.

  Are you sure? yes | no

Valentin Angelovski wrote 09/07/2016 at 08:26 point

Hello Erik! You are correct in that I assembled my flea Ohm prototypes by hand, but not without difficulties associated with various things.. including placement skill. I found that accurate hand-placement of a 0.5mm pitch BGA package or type 0201 SMD capacitors requires taking into account things like hand tremors as well as one's own heart beat! Tricky stuff...

My advice would be to go with something like 1mm ball-pitch BGA imho. In addition to the easier assembly, these are normally a much cheaper option when you factor in the PCB tooling cost as well.

Also, Lars was fairly accurate with his reply. Anyways, best of luck with your project. 

Cheers Valentin.

  Are you sure? yes | no

Erik Piehl wrote 09/08/2016 at 05:50 point

Hello Valentin, thank you for your comments! I think it is impressive that you we're able to put the boards together by hand. I guess difficulties are to be expected when dealing with those fine pitch parts. I was previously thinking that BGAs are pretty much out of the question for hand built hardware, but clearly that is not exactly the case. Anyway for my next step I will probably stick to TQFP parts, as the Xilinx part XC6SLX9 I'm planning to use is available in that package. Going to bigger parts would automatically mean going to BGA, hence the question.

Cheers, Erik

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KnivD wrote 08/11/2016 at 05:49 point

Excellent! Me want :)

When are you going to offer these on the market?

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Valentin Angelovski wrote 08/11/2016 at 10:48 point

Hello and thanks for your question.

I plan on testing my newly updated boards when they arrive next week (as shown in the diagram on my 2nd project log). Once the boards pass their functional testing I will look at what it might cost to do a production run of Flea Ohm boards.  Also note that I will ultimately be evaluating two board designs: FleaFPGA Ohm and Ohm+ :) Cheers.

  Are you sure? yes | no wrote 08/18/2016 at 11:24 point

Hello Valentin, you can count me in for a FleaFPGA Ohm+ :)

Didn't have  much done lately with the FleaFPGA Uno, but I have some ideas in which the extra LEs and LPDDR RAM would come very handy 

Oh and can you beef up the HDMI 5V output a bit? I had to add a wire from the USB connector 5V to the HDMI connector 5V out on the FleaFPGA Uno to get my HDMI2VGA adapter working with it

  Are you sure? yes | no

Valentin Angelovski wrote 08/18/2016 at 15:35 point

Hello Claude! It has been a while but good to hear from you! :) 
Thanks for your suggestion - For the sake of compatibility it is a good idea. I was previously made aware of the issue through some recent online research (that unfortunately did not make it into these prototypes, but that is OK since there will likely be another PCB re-spin for various reasons). I will see to it that my next board revision have an auxiliary 5V feed to the video connector, among other incremental improvements. Cheers.

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Qiang Zhang wrote 08/10/2016 at 16:15 point

Hi, Valentin, about the ADC, is it build into the FPGA or it requires extrac ADC chip?


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K.C. Lee wrote 08/10/2016 at 22:43 point

Sounds like it is a sigma-delta ADC - probably single bit comparator using a differential input on the FPGA.  The rest is DSP math to get more bit in return of lower conversion speed.

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Valentin Angelovski wrote 08/10/2016 at 23:59 point

Hello Qiang! As K.C. has suggested, the ADC is sigma-delta based with nearly all of the ADC's logic implemented in the FPGA using VHDL. As I did with my previous FleaFPGA Uno project, I included the external passive components on-board needed to complete each ADC circuit. Cheers.

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Qiang Zhang wrote 08/11/2016 at 02:46 point

Interesting! 250M samples/second scares me. After second reading, it is for 1 bit but still impressive.

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Valentin Angelovski wrote 08/11/2016 at 03:20 point

Just a reply to your comment about Flea Ohm's maximum ADC sample rate - my 250MSample/sec quote was purely theoretical (and not realistic in practice given the loop filter values used in the design - that's what I get for drawing my diagram late at night :-). I have since updated my diagram to provide more realistic possibilities with the ADC inputs.

Further, these ADC inputs admittedly won't be quite as accurate as a dedicated external ADC, but for a good number of applications they'll probably do just fine. Cheers.

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Tim Ansell wrote 08/09/2016 at 04:06 point

Do you have a schematic for the board? I'm interested in how the HDMI port is wired.

  Are you sure? yes | no

Valentin Angelovski wrote 08/09/2016 at 05:52 point

Hello Tim! I've not yet released schematics for flea Ohm (soon though), but you will find the video out interface to be virtually identical to that found on my FleaFPGA Uno board. More information on FleaFPGA Uno (including schematics) can be found here: Cheers.

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