Quiz: What’s wrong with this picture?


Take a guess and click through to see if you’re right!

I had hoped that this new pcb would be the last, but I was rushing a little bit to get it done ahead of some vacation. Well, I should have checked everything. Let that be a lesson to you. Anyways, here’s what it should look like and what it’ll look like in the end.

Multiplexing for the LEDs

I completely messed up the multiplexing of the LEDs. In the first version, I used some I/O Expanders. I’m still using one for the switches but I changed the LEDs to a multiplexing scheme. As you can see in the first image, the LEDs are all connected to LED multiplex channel two. They should be divided between two and one. You can’t easily tell but I also neglected to connect the emitters of those PNP transistors to the 5V VCC net, so they’re neither connected correctly nor do they have power. The worst thing is that I use this scheme every day at work and have yet to screw it up there in years of doing it.

So, how do you avoid this? What I should’ve done and what you should do each and every time you make a new pcb is check each and every trace to make sure that it’s connected exactly the way that it should be.

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