Suggestion: Add a Bill of Materials amd possibly a construction guide video.

[rcutcliffe]

Hi, this is a nice looking project, but there's a bit left to the imagination.

There's no list of components, so we'd need to look at the PCB description to find out the physical size of the passive components, let alone the values. Yes, there's reference circuits available on the net, but even so.

Also, the IC required is 3mm square, so one would assume that some sort of SMT experience is necessary. Any hints for the beginner would be appreciated.

[Harry4242]

First of all, i agree, this is a great project ! :)
Funny enought, i wanted to suggest the same thing when i came here :)
i was using JLCPBC to order the board, but i need the MPR121 mounted on the board..i kinda get stuck on the ording process since i obviously need a BOM for the component..and i am not really sure how to do that or what component i detail i need to add, same with orientation...Help would really be appreciated !
Keep up the good work !

[rcutcliffe]

I feel your pain. I ordered and received 5 boards from JLCPCB, and after wasting 3 mpr121s trying to mount them on one of the boards, I've come to the conclusion that the only way to get one of these keyboards going is to pay JLCPCB to do the component purchasing and placement.

It's a pity Hackster.io doesn't allow comments or I'd post there, asking if anyone was interested in doing a larger order of built boards.

I can only hope that Dominic eventually checks this issue and provides some guidance.

[2dom]

Hey there. I actually mounted all the components myself. The way I did it to buy a bunch of mpr121 boards on AliExpress (they contain all the necessary components already). The tricky bit is to unsolder and resolder them. For that purpose I bought a hotplate for 50 bucks that made the process bearable. Just make sure to only use enough heat to liquify the solder - the mpr121 is very easy to fry

[Harry4242]

Hi Dominic,

thanks for the information..i think i will go both ways...i'll order a the soldering station and try to place the controller myself, but i will also get into the BOM option on JLCPCB...
Could you give me some guidance on the orientation of the controller ? i suppose when you look at the back of the board, 1 is on the top left ?
also you have placeholders for resistors and capacitors, could you tell me the value for r1-r4 and c1-2 ? do i even need them all ?

thanks in advance for you help ! :)

Best regards,
Harry

[rcutcliffe]

Hi Harry,
Dominic can step in to suit himself, but there's a lot of reference circuits on the Net. https://www.nxp.com/docs/en/application-note/AN4600.pdf is one that has all the values available. The only important one appears to be the 75k resistor on 'Rext'.
As to building, I had a go with my rework station and decided that without a stencil, getting the IC properly located is almost impossible. If you do manage to get a set of boards successfully built by JLCPCB, please post the process that worked for you. I'd decided that if I can eventually get some done, I'd get enough for me and possibly offer extras to one of the Home Assistant groups on Facebook, at cost.
EDIT: I ran through the PCBA process, and 5 boards have come out at $46AUD. (plus postage I assume). Too much to risk without some assurance that what I get will work. I'll leave it in my cart and see if I feel braver later on.

[2dom]

To answer all that I added the schematic as pdf, the board as jpg and the BOM to the root folder. There you can find all the component values and orientation of the chip (black triable top left in footprint)