Struggling with BOM

Published on 2017-10-03 in PewPew FeatherWing.

The PewPew Lite was simple enough to solder by hand. The self- contained PewPew is not going to be so easy. Of course, I can solder a prototype or two — I even explicitly shied away from QFN parts — but just thinking about making a 20 pieces for a workshop makes me shudder. So I need a PCB assembly service.

I have been looking at the different services, and what they need as the input, and not very surprisingly, the main input they need is the bill of materials, also known ass the parts list. Unfortunately, it’s not enough to just say “a 10kΩ resistor” — you have to specify the size, tolerance, and most importantly, the product number. Actually, forget everything else, they just want the product number, and if the part is exotic, a link for where to buy it.

So I’ve spent the last couple of evenings trying to use the project-21525  service, and it has been a bumpy ride. I started with the pick-and- place file that Fritzing generated for me — it’s a CSV file that lists all the parts, together with their exact positions on the board. So I just removed the irrelevant position information, and got a list of parts in a format that could be imported into FindChips. Then FindChips started sugeesting parts. Oh boy.

It couldn’t find any tact switches at all. Apparently the best alternative to a USB micro socket is a HDMI socket. There is only one power switch with the pinout I need, and it’s a super-expensive ALPS. 0402 20kΩ resistors simply don’t exist. Forget about any LED matrices at all, not to mention bi-color ones. And so on and so forth.

With much struggling and some cheating, I finally put together a BOM list that only has 3 parts missing. I have simply added the URLs for those in the comments. The list is at  https://www.findchips.com/org/10-open- hardware/list/48895-pewpew-41-bomcsv

The good news is that the total cost of all parts seems to be around $15 at quantity 1. That means that together with the PCBs and the assembly service, there is a chance that the whole thing won’t be more expensive than a Feather board.