One of those useful things to have around on your bench is a decade resistance box, essentially a dial-a-resistance instrument. They used to be quite expensive in line with the cost of close-tolerance resistors, but the prices have come down and it’s within reach to build your own. Electronic design consultancy Dekimo have a nice design for one made from a series of PCBs which they normally give out at trade fairs, but now they’ve released the files for download.
It’s released as Gerbers and BOM with a pick-and-place file only, and there’s no licence so it’s free-as-in-beer, but that should be enough if you fancy a go. Our Gerber viewer is playing up so we’re not entirely sure how reliable using PCBs as wafer switches will be long-term, but since the pictures are all ENIG boards we’d guess the gold plating will be much better than the HASL on all those cheap multimeters.
We like this as a conference giveaway, being used to badges it’s refreshing to see a passive take on a PCB artwork. Meanwhile this isn’t the first resistance box we’ve seen with unconventional switches.
No license means no license.
The page does link to CC-BY-SA-4.0, but I agree it would be clearer if it was marked on silkscreen or in a text file in the zip.
there’s one in the zip file now
The ENIG coating is very thin and soft gold. It will not last long when used as switch contacts. Once it wears away, the copper will oxidize and the switches will make bad connections. The contacts must have a hard gold plating to be reliable.
I don’t know much about the finer details of PCB fabrication. Is there a coating that would work better for this?
As Cody said you’re better off with hard gold plating (sometimes the pcb manufacturer will refer to it as card edge connector plating or something similar). If unsure talk with your manufacturer to see what they suggest.
Ah, right. I didn’t realise that hard gold plating was the name of the coating. I’ll check for that if I ever do something like this, thanks.
Nice idea for a freeby, and probably got more publicity being fearured on HaD than they ever got giving them away physically!