Through-hole Braids PCBs/ICs/display bundles - LEARN FROM MY PAIN

DIY STUFF
1

Hey gang.

I’ve got five sets of Eurorack through-hole Braids PCBs. I’m not going to want all of them, so I was thinking about selling spares on. There’s a bunch of ICs and the LED displays that are just a little bit harder to source than the likes of TL074; I’ve got some of them as well (only three of each of the voltage reference ICs at the moment, sadly) and I’m going to order the ADC and DAC ICs in the next couple of days.

My question is, would anyone be interested in partial kits? You’d have to bring your own BluePill board and common components (resistors, pots, jacks etc) but I’d be looking at bundling together:

  • both Sound Force PCBs
  • the Eurorack front panel PCB that Sound Force linked to (I’m not keen on it but it’s serviceable and if you’re using Kosmo format you’ll be doing your own anyway)
  • two of the 2x14 segment LED displays in red
  • MCP4822 DAC
  • MCP3204 ADC
  • (hopefully) LM4040 2.5V and 10V reference regulators
  • (if needed) MCP6004 opamp
  • (if needed) rotary encoder

I’m assuming that the other ICs are part of everybody’s arsenal: TL074, TL072, 74HC595, 3.3V regulator for the BluePill. I have all these knocking around but I can’t vouch for the quality and authenticity of these particular components so don’t want to bundle them in. The ones listed are from one of RS, Farnell or Mouser.

PCBs are JLCPCB cheap-n-cheerful ones, so they’re 1.6mm (including the front panel) and probably have lead in the HASL finish (yes, including the front panel. We’re all going to die, anyway.)

No BluePill, no jacks, no pots, no caps, no diodes, no resistors, no headers, no warranties. It’s a bundle of useful bits, not a kit of parts :slight_smile: you’d be in the same situation as me, working your way through what documentation is available.

All that being said, is anyone interested? I’m not looking to make a fortune off this, just covering costs. I’ll work out exactly what those costs will be if there’s any takers. I’m in the UK so postage will vary based on where in the world you are (and you might be able to assemble the bits locally far cheaper than here on Brexit Island).

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I get the sense that while MCP4822s and LM4040s and MCP6004s are easy enough to come by, correct, properly spec’d BluePills are a pain to source. I haven’t tried and maybe my perception is wrong. But if it isn’t, I’d think if you know of a source, including the BluePill would make a significant difference in the degree of interest.

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I can confirm that getting blue pills that work with this build is a bit of a gamble. You don’t know that they will work until you actually try to get them programmed and tested. That is the most difficult part to source.

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Yeah, it can be tricky to find those boards. I happened to have a couple in my box of things from a project several years ago which was helpful. However the Sound Force BOM pointed in the direction of AITEXM ROBOT on AliExpress, so I made a test purchase of the C8T6 board listed here. This is what STM32CubeProgrammer responded with:

image
image1033×733 76.9 KB

Obviously without the hardware built I won’t know that it’s behaving the way it should, but it accepted the code and it verifies, and it ran the firmware for the through-hole Peaks perfectly, so it’s anecdotal but seems to be a good source.

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I will admit - I am pretty interested! Is there any way to tell if the single unspoken for arduino would be a good match?

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You already have the pcbs, right? Otherwise there might be value in integrating the improvements mentioned here: Braids THT in KOSMO format - #214 by Electro-resonance
It is only one additional resistor, I think and you get 16 bits in the dac instead of 12! I still want to try it, but I have not yet managed to build the modified firmware. This might improve the chord modes on braids, which I feel a little „thin“ on this 12 bit braids…

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I’m building out what I can with what I have on hand at the moment. I’m missing the DAC and ADC right now though - I can get small quantities of the SMD versions straight away from RS (the DIP versions either cost more or have large minimum quantities/shipping costs) but there’s not enough clearance to get an adaptor PCB squeezed in unless I flip the headers for them and add them to the underside. I’ll have a look later and see if there’s enough clearance with the BluePill for that option.

If I end up going that route I’d probably drop them from the list of components bundled - that’s getting into the territory of being a full-on supplier and life’s busy enough as it is without trying to maintain inventory to sell on :slight_smile:

1 Like
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I have the PCBs already, yes. But that’s a really interesting idea! I remember back in the days of the Amiga being able to get 14-bit audio out of the 8-bit audio system by doing a similar trick to that, blending the two voices on one of the audio channels with carefully selected gain. It worked really well so I imagine this modification would be similar.

The layout of the PCB is good and that hack is so simple that it could be switched out if it’s not satisfactory. I’ll keep that in mind as I build and see what can be achieved!

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Well, I investigated. My adaptor PCBs would fit perfectly for 8-pin ICs, but for 14-pin ones it’s a different matter altogether. They’re wider, because they’re not designed for replacing a DIP IC in the way I was hoping they would. I’d have to do a whole lot of creative wiring and it would become an absolute mess.

Boo. I’ll consider my options.

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A final update. I built one!

https://www.instagram.com/p/Crd-_jdoPFF/

I don’t recommend it. The bluepill boards are such a gamble, as @BenRufenacht said and @analogoutput had assumed. Obviously I’d considered whether or not the one I’d got could take the programming; what I hadn’t considered was the chance of horrific electrical noise spewing from it. The wild-west nature of their production means that quality control is roughly zero. The noise played havoc with the ICs - the 595s couldn’t drive all of their LEDs, half the pots didn’t work and the audio output made Metal Machine Music sound mellow.

Add to that the fact that I’d inadvertently soldered the 595s in the wrong way round (I was waiting for a socket order that never came so I thought “oh they’re cheap chips, no worries”, failing to consider all the components around them) and having to remove and resolder six capacitors that were about 0.8mm too tall to fit in the sandwich of boards (and destroying one of the traces in the process), and it was an experience I won’t forget.

Taking into account all my costs - not just financial either, my time and frustration - I don’t recommend doing this build, so I’m going to withdraw the offer of selling the parts on. The Behringer Brains is another MI clone and it won’t destroy your self confidence like this has. :unamused:

3 Likes
11

Sorry to hear that hard road you rode but i would like to try it on my own! :sweat_smile:
Do you still have any pcb you would like to sell?

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I wish I could help but I don’t know where the box with them is! My work area is small and cluttered so things get pushed around depending on active projects, and I’ve been working on non-synth things for quite a while, so where the box is… I have no idea. Sorry!

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