Thursday, May 4, 2017

Well THAT's not quite right!

The USPS delivered my PCBs from Osh Park today. They look fantastic! Except for one thing...

Click on the image and look closely at the holes where the VFD leads fit. Notice that the hole on the far left end is lined up with the wire in it, while the hole on the right end doesn't line up properly. Oops.

I pulled up the layout in KiCad and it says the two ends are 103.25mm apart. I measured the spacing on the PCB, and it's dead on 103.25mm. So the PCB was fabricated exactly as I laid it out it. Yet the hole spacing is wrong. Remeasuring the spacing between pins 1 and 60 on the original calculator PCB I get 105mm. Oops.

I think I figured out what I did wrong. I think I measured the spacing between pins 1 and  60 correctly. I then divided by the number of pins, 60, giving me 1.75mm. The problem is I needed to divide by the number of spaces between those 60 pins, which is 59. That would have given me 1.78mm, or 0.070 inches. The last mistake was not printing out the board layout on a 1:1 scale and making sure everything lined up.

All is not lost. The VFD leads are quite long and will easily fit into the test board. And this is why you make test boards: to test things before you commit to a final design.

Perhaps more importantly, the holes where the pin headers fit to connect to my iCEblink40 FPGA board do appear to line up properly. Tomorrow evening I'll verify the pads for the 25 RN4604 transistors line up properly and some other checks, then I'll do some board assembly.

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