Hein (fub) wrote,

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Display testing

This evening, I wrote a small program to test the display. OK, so I had it all wired up -- but would it work? Maybe I made a connection I shouldn't have, maybe my soldering was off -- lots of things can go wrong. So testing the display is important, so that you know you can continue with the next step.
I put in a microcontroller (the 16F628A) and three shift registers. I drew (part of) the schematic in Eagle, so I could easily see which pins drove which part of the circuit. Then I got to work with a small test program that turned everything on and off again, and then lit each segment in turn.
All the segments can be lit and turned off, and it all worked correctly. The transistors, used for the multiplexing, all worked correctly too.

I couldn't believe it. This is the most complicated circuit I ever designed and implemented, and it all worked at the first try. That never happened before: there's always a little bug somewhere...

So, I wrote the initialisation routine for the display. When the machine is turned on, the display should say "MACH F". And that worked too!

Of course, we're not out of the woods yet. I need to test the MAX232, and write software to display a text that is received via the USART on the display. I see lots of lookup-tables in my future...

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