A little while ago, having decided to try my hand at making a PCB, I managed to etch a few MAX3232 serial-to-logic-level converter boards (Eagle files are available in a Github repository.) But I had never been entirely satisfied with the results and needed to brush up my toner transfer technique. Due to insatiable stockpiling, I found myself with a handful of Atmega-328P microcontrollers that I needed to do something with. So I set about making some homebrew Arduinos using a single sided layout — the so-called Severino. I chose a design with a serial connection, partly to make a dent in the bag of 30 DB9 connectors that I had bought for £0.10 each (don't ask me why).
A pair of severinos easily fit on a 100 x 160 mm board. The toner transfer and etching went well, and after drilling and hand-tinning the boards looked like this. (The other board was also perfectly usable, although I broke a couple of traces scraping off the toner.) You can probably see a few filled-in areas where the toner tended to flake away within the large blacked out areas. I have since started to protect these filled areas by overlaying them with cheap nail varnish.
Drilling the boards turned out to be a monstrous chore, even with a good drill and half-decent stand. The collet on the drill was too small for 1 mm bits. Wrapping the bits in heat shrink solved the problem for a while but tended to wander and eventually worked loose. And the number of drill holes was just huge. Even when I did eventually get in the groove, I kept on finding missed holes after I thought I had finished. (The trick is to hold the board up to the light.)
After tinning the drilled boards, I populated them with a few pulled components including the inductors, LEDs, contact switches, and the electrolytics. For the first of the boards I used some natty low profile electrolytics that would fit nicely under any shields. For the other board I decided to use male headers, so I wasn't worried about using much larger caps. I had to make a couple of minor substitutions, and the LEDs were mismatched. But that's not the sort of thing I worry too much about.
I had a little difficulty soldering in the gold plated male headers, which I probably should have pretinned. Here I discovered the limitations of my home made flux. It's a great wetting agent for soldering clean components and smells very nice — none of the usual choking fumes. But for removing oxides and tarnish it proved rather too mild, and I found myself reverting to an activated rosin flux.
After all that effort, the boards turned out quite acceptably in the end. Using a home made USBasp programmer, I wrote the fuse bits, burned the bootloaders, fired up the obligatory blinky lights sketch, and sat back for the show. Two severinos, good to go.
Now, instead of a stockpile of chips, I have Atmega development boards coming out of my ears. I got my Uno as a present, and use it all the time. But there's also an Atmega128 stamp I have used exactly once, a ChipKIT Uno I have yet to get to grips with, and a MegaMini on the way... I seriously need to get some microcontroller projects out the door. Keep tuned for the talking calculator build!
Etch Your Own
Try your hand at a Severino. Putting it together is a little bit Tricky and might take a couple of evenings. Toner transfer and etching takes an hour or two, but you might need several attempts if you haven't quite got the knack. Also, the etching chemicals are Dangerous and require safe handling and disposal. Add another couple of hours at least to drill and populate the board. For tips on making the PCB, take a look at our toner transfer tutorial. (Or just make a stripboard version.)