Large sparse keyboard PCB - Page 1
Forum section: electronics / general

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: June 29, 2021, 04:47:19 am
content: I am working on a keyboard project, and wondering how I will get the PCB made. This will be a rather large board, and since they are priced by area I am looking at around $300-$400 for 3-5 boards.Hmm. I'm trying to figure out how to game the system, but coming up empty. Most of the board is empty space with switch mounts and diodes. I swear that I've even considered point-to-point wiring like was done in the old old days.I can split the board up into smaller pieces (which increases the number of vendors capable of producing the boards). Chopping it into 2-3 pieces would be fine. Chopping the design into 3 parts would still cost about $300 ($100x3). Elecrow is asking about half of that, which makes me wonder what I would be getting.Are there any tricks I might use to lower costs?

author: tszaboo
author_rank: Super Contributor
timestamp: June 29, 2021, 04:56:14 am
content: When I made a project like this, I made the boards in China.A 300mm x 94mm board, which is a 65% keyboard was 28 EUR or 33 dollar plus shipping, five pieces.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: June 29, 2021, 05:06:08 am
content: This is considerably larger. I hesitate to mention the size... 600mmx140mm. It is a pretty ridiculous prototype.But I was just thinking to myself... perfboard! Only a small part needs to be SMD. I wonder if I could get away with perfboard for the switches...

author: ataradov
author_rank: Super Contributor
timestamp: June 29, 2021, 05:43:37 am
content: Your first issue would be to find anyone willing to make 600 mm board without special handling fees. You would need to split that in two at least. Then you will fit into "reasonable" size, and the price may drop a lot.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: June 29, 2021, 05:57:53 am
content: One would think the price would drop. But, as I mentioned in the original post, there was really no change.I found a couple of places (via pcbshopper) which would quote the full size. As I said, $300-$400 for 3 boards. Chopping the board up would still require about $300 ($100x3) for the full circuit.$30 or so of perfboard for the key matrix might be doable. The main circuit would be pretty cheap at that point.I had another crazy thought. I haven't wire wrapped in 30 years or so, but that might be a solution as well. The issue is that the boards need to be big for the switches, but the component density is very low. Throughhold parts would be easy. There would still be enough space between switches for a small battleship.

author: ataradov
author_rank: Super Contributor
timestamp: June 29, 2021, 06:10:02 am
content: 140 mm x 300 mm x 2 layers is $93 for 10 pcs on PcbWay.140 mm x 600 mm x 2 layers is $263 for 10 pcs.Either way does not seem to be excessively expensive. Shipping is somewhat expensive, especially in 600 mm case.pcbshopper is a pointless service for small quantities. AllPcb, JlcPcb and PcbWay would be the cheapest in absolute majority of cases. Just check all of them manually.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: June 29, 2021, 06:16:23 am
content: pcbshopper doesn't show that. I just put those dimensions in and did not see _anything_ from pcbway. But going to pcbway's site, the quote is as you described.Odd, because pcbshopper lists pcbway.Thanks for setting me straight. I need to check vendors directly.

author: tszaboo
author_rank: Super Contributor
timestamp: June 29, 2021, 07:18:13 am
content: Quote from: Jonathon_Doran on June 29, 2021, 05:06:08 amThat is a beast of a board, whats that 140%?In any case, going above 300mm maybe 400mm will increase shipping handling and manufacturing costs. That's usually the largest dimensions you can fit into most PnP machines, so they rarely make larger boards. So everything is an exception, increasing the price. Splitting it to two could make sense.Also, be careful with JLC, they might just charge your extra for "excessive milling" or some other reason they can think of. I had that for a plate.

author: NorthGuy
author_rank: Super Contributor
timestamp: June 29, 2021, 01:09:26 pm
content: If you split it in two and make both halves the same (which should be easy for a keyboard), it'll be considerably cheaper for small quantities.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: June 29, 2021, 11:08:55 pm
content: That is an interesting idea. And a design challenge.Both sides cannot be the same due to the non-matrix stuff like a microcontroller, USB, etc.But maybe the matrix could be made so that a few trace cuts could cut that off.

author: ataradov
author_rank: Super Contributor
timestamp: June 29, 2021, 11:17:29 pm
content: You can have placement for MCU on both sides, just don't populate it on the side that does not need it. Or have two MCUs and use a simple communication channel between them. This may simplify thr whole scanning procedure and make scan faster.

author: Ian.M
author_rank: Super Contributor
timestamp: June 29, 2021, 11:25:50 pm
content: If the switches have two pins per contact for at least one of their contacts, a single sided layout may be practical for the matrix. This opens up various DIY options for etching or milling the matrix PCB. Put the controller on a much smaller commercially manufactured daughterboard.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: June 29, 2021, 11:39:18 pm
content: We are discussing two sides as "left" and "right" -- Splitting a large PCB into two identical chunks to lower the board cost.