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Topic: 7 segment display MAX7219 issue (Read 985 times) previous topic - next topic


I made up a timing and display circuit for the Cub Scout Pinewood Derby.  I took pieces of code from around the internet and modified it to fit my specific design.  First thank you to all of those authors.  The setup is for 6 lanes and uses 6 IR leds and 6IR transistors to detect when a cat passes the finish line and the internal clock on my Arduino Duemilanove to produce a time in miliseconds.  When the car finishes I send its place and time to some 7-segment displays.  I had everything working great yesterday afternoon.  Timeing worked, displays were beautiful I was very proud of myself.  Then I tried to load another code for a static display and everything got messed up.  I now have no control of the 7-segement displays.

4 MAX7219
6 large 7-seg displays (controled from 1 MAX7219)
6 4-digit 7-seg displays (2 4-digit displays controled from each MAX7219)

The displays are powered by a sepeate power source, 12V wall wart using a LM7805 to get to 5V with the two recomended capacitors to clean the supply voltage.  As a note the 7805 does not get too hot when the power is on, but I do plane to add a heatsink.
Troubleshooting steps:
I went back to my last known good software configuration and loaded that.  The Arduino still does the timing correctly, but the displays are doing their own thing.  They will fully light up, some will light in random patterns but none with the correct display.

I replaced the first MAX7219 with another known good chip and triend again, same issue.

Any suggestions as to what i did to destroy the circuit?  


"Then I tried to load another code for a static display and everything got messed up.  I now have no control of the 7-segement displays."

And we have no code/schematics to review, so will be hard to offer any suggestions.
Probably a wiring error when you added the static display, or you didn't back out all the code changes you did.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


With separate power supplies, you need to connect the grounds together.

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