Friday, August 19, 2011

gMeter: Electronics

The electronics for this project are simple. So I asked myself, why spend money on a board from Advanced Circuits when I can make my own? After completing the etching process I have plenty of answers to this question, which I will address on a rolling basis.

First, the circuit itself. Laying a board out for single-sided etching adds some headache to the design process. Without vias you have to think a little harder about trace traffic, to minimize using jumper wires. It's a fun game until you realize that's probably something they play at EE parties. I scored a 7 (I think it's like golf). Other modifications for achieving etch-spec: minimum trace size of 24 mil and minimum clearance up to 16 mil. I really wouldn't etch a board that's any more complex than this unless the form factor is less constrained and bigger.

Export to png (monochrome) and...
...ready to be printed.

There are hundreds of DIY PCB etching tutorials out there so I'll spare you the step-by-step procedure. Besides, after etching one board I'm far from pro! I went the iron-on toner transfer route, messing up three blank boards before getting one that was "etchable." Partially that was not my fault because the laser printer I used was good but not great, leaving thin spots of toner here and there. Mainly I wasn't putting enough pressure on the iron. To get it to work, I literally put all of my weight on the iron for two minutes solid. Then 4-5 minutes moving the iron around giving the interior a lot of attention, and still maintaining absurd pressure.

I used a sharpie to touch up the spots the toner missed.

The etching part is where things got really sketchy though. The copper took at least 45 minutes of continuous agitation to etch...? That's at least 15 min longer than what I read online, so I'll need to hunt down the ferric chloride MSDS, perhaps it was diluted more than usual (around 60%). More likely rubbing it with a sponge probably would have cut the time, instead of waiting for the copper to dissolve on its own. As much work as this is, there is an unbeatable zero day lead time and low cost. Having the ability to wake up with an idea for a cool board and use it that day is plain awesome. With practice I'm confident it will take less time and it's far superior to leaving your project at breadboard status.

Soaking in ferric chloride...

Stipped of toner courtesy of spray carb cleaner

Finally got some use out of my Dremel drill press, I think this is what it was designed for.

Next, I soldered it all together and, who am I kidding it didn't work first shot. Again, I would advise against etching with 24 mil traces, especially in confined spaces. I made this mistake and spent a lot of time with a multimeter and an x-acto knife peeling up traces to resolve about ten different shorts. Finaly I got it to light up.

Ok, the board works. Now there are zero excuses left to procrastinate from coding. Well maybe that classes start next week, but I will do my best not to drag this project too far into the semester. Putting on my software hat...