Strange LED display behavior

upand_at_them · Apr 18, 2010

Sometimes my 4-digit display stops showing the upper two digits. If I swap out the display for an identical one it works fine. If I put the original back in it's back to normal.

Is it possible I'm damaging the PIC by drawing too much current? I have a 16F886 connected to a 4-digit CA display. PortB to the segments. PortC.0-3 to the digits. No resistors.

I've run this TONS of times, though, and never had a problem until today...I'm making a tachometer and I have PortA.5 as analog, reading the output from an IR transistor.

Any ideas what's happening?

ericgibbs · Apr 19, 2010

upand_at_them said:
Sometimes my 4-digit display stops showing the upper two digits. If I swap out the display for an identical one it works fine. If I put the original back in it's back to normal.

Is it possible I'm damaging the PIC by drawing too much current? I have a 16F886 connected to a 4-digit CA display. PortB to the segments. PortC.0-3 to the digits. No resistors.

I've run this TONS of times, though, and never had a problem until today...I'm making a tachometer and I have PortA.5 as analog, reading the output from an IR transistor.

Any ideas what's happening?

hi,
It sounds as though the PIC drivers are overheating, ideally you should have series resistors with LED's.
If you are short of board space you could insert a low value resistor in series with the common cathode of each digit.
You may get a slight reduction in LED brightness depending on how many segments are lit on the LED.

upand_at_them · Apr 19, 2010

Thanks, Eric, I'll try it, because now I find that one particular program can induce the problem.

ericgibbs · Apr 19, 2010

upand_at_them said:
Thanks, Eric, I'll try it, because now I find that one particular program can induce the problem.

hi,
Pattern sensitive problems are often found in electronics equipment.
For example: when you have more than a certain number of segments lit the drivers shut down.

upand_at_them · Apr 19, 2010

It seems to be instigated by my analog read on RA5. Without that I can run the display without problems, for any length of time.

Strange LED display behavior

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