As of late I’ve been making smaller and smaller circuit boards, fighting for every mm² of space. The typical 6pin ISP connector used for programming a lot of the AVR micro-controllers has been getting in the way more and more.
In one of my recent projects, Serial-Knob I was forced to use a smaller header (2.00mm raster), and was ‘punished’ by having had to make an adapter for every single board that had found a new home. That was a pretty unpleasant experience, as it involved too much improvisation and it was way too fiddly work.
One of the latest projects required an even smaller programming header, 1.27mm raster, and I just couldn’t see myself soldering wires to such tiny pins. So I went looking for pogo-pins and was lucky to find a pack of suitable ones (“P50 – E2″) on ebay.
As the images might show, it was quite a task to assemble this tiny tiny thing. Pin alignment is crucial and it is really hard to do it just by hand. I had to make a little jig to hold the pins in place while soldering.
I tried plastic first, but that failed miserably.
The one that worked was made from hard wood, I think oak. The 3×2 hole pattern, holes spaced 1.3mm, was drilled 10mm deep using a 1.0mm drill.
The pogo-pins have a weak spot. I couldn’t mount them to minimize stress or put a sleeve over it, so I added a small blob of solder to reenforce it.
A later revision comes with a little spacer/reinforcement board, which should be placed far enough down to keep stress away from the weak spot. I didn’t quite manage that in this photo, so I resorted to the solder-blob-method again.
Some time later…
I received another set of boards from OSHPARK, and there was something wrong with the drills sizes. Apparently the fab had done something, and some vital holes were 5mil under-sized. Not good.
After a couple more board revisions hammered into my git repository, I had a eureka moment: why not use the apparently useless sub-boards (meant to slide over the pogo-pin shafts) as an alignment tool. The pogo-pin heads fit very nicely. Totally obvious in hindsight – of course – but it makes assembly so much easier. All that is now needed for assembly is a spacer block (wood, plastic, metal…) of the right height and a bit of glue or tape. Gone is the need to drill straight 0.7mm holes! Before I forget, poke holes into the tape. Otherwise the pogo-pin heads won’t align properly.
This little project may be found tindie.