The (wee) Fettle Boost (3) – finishing up

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.

pcb

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

  1. Track width should be .3mm minimum, .6mm is better. Mine were set to default (.25mm).
  2. 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.
  3. 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.

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