Driving the 4 digit 7 segment display

Here is the documentation of my next step: driving the LED display. The design and the C code were not really difficult; the steps to put the results here were.

As I noted before I use a PIC 16F887, but CadSoft Eagle didn’t have this component in its library, so I drew a 877 which is pin compatible. Now I wanted to get it right and so I started my own library. Copying the 877 to it and then renaming it to 887 was simple enough. The next step was to get my 4 digit 7 segment display (datasheet in PDF)  in Eagle. I did find a 3 segment display that came close and it took me a bit of time to add the fourth digit. Now my custom library contains two components!

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Step two: add latches

Even though I use a big 40 pin PIC for my experiments I decided to try how sharing output pins for multiple purposes works. To do that I use two 74HCT573 (PDF) octal latches. The goal is to drive 16 outputs from 10 pins. If you add one more octal latch, it only costs one more pin to drive 8 more outputs. So, with 16 pins and 8 octal latches, you could come to 64 outputs.

I also added an output stage with a reed relay. My final goal is to make a variation on the looper project that can be found at jimkim.de.

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