The next stage was getting the PCB done in KiCAD. To be honest, I messed it up the first time, so here’s the improved version.
Firstly I checked the pinout of the transistors, which was a good job, because they weren’t as they should have been. For some reason KiCAD sometimes gets the footprints wrong, even when the numbered pins match the pinout labelled. I have also learnt that for DPDT switches you have to select an SPDT for unit A, and the same for unit B, and line the two up. I think there might be a glitch in my version of KiCAD (or my computer might just be on its way out), it deleted all the footprints I was using and replaced them with very similar ones with different names. Anyway, better to check everything.
I found that calipers are pretty much your best friend when you’re designing PCB layouts. I did my own switch footprint from two SPDT footprints by measuring the dimensions of actual switches with calipers and did oval holes for a tighter fit. I measured them several times over, and when the PCBs came back the switches fitted perfectly, which was very nice.
This time I sent the PCBs for this project to dirtyPCBS.com. I missed the cut off for Chinese New year by two days, so I didn’t get the PCBs back til late February. Then when I got them back there were a couple of other mistakes, so I had to redo them.
Here’s a rundown of what to do, and what to avoid
- Track width should be .3mm minimum, .6mm is better. Mine were set to default (.25mm).
- Tracks for power should be a bit chunkier. The maths is based on current draw, which is usually quite small in pedals, so isn’t a huge issue. 1mm is good, but anything down to .6mm should be fine according to various discussions on the usual forums.
- You don’t need a +9V pour. In fact that’s not a good thing. That’s what I did. It makes routing easier, but anyway…(in the picture above the green is the ground pour).
I was happy enough with the quality of dirty PCBs, so I went back for round two.
Anyway, in the next and final part we’ll have a look at the finished product hopefully. Fingers crossed.