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Thread: Conducted noise causing program to restart
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face BY : NDuckworthspam@spam_OUTsignam.co.uk email (remove spam text)



My project is a gas fire controller using a 16F873, during the ignition
sequence the program will regularly restart as if a hardware reset has been
performed, I do not have the watchdog enabled.
The source of the noise is the mains powered spark generator which my
customer insists must remain on the same PCB.

The thyristor gate drive for the ignition circuit is opto isolated and I'm
using a flame rectification technique for flame detection.
The PIC is bypassed by 100nF directly across the supply pins and also has
47uF
soldered to the same point.
All of the PIC ports have at least 330 Ohms in series and its supply is a
78L05
with 100nF and 100uF either side.
MCLR has 10uF to 0V and 10K to +5V but I have tried tying MCLR to +5V
without success.

Generous use of 10 uH chokes is helping but becoming expensive, I'm
experimentally trying to reduce the noise level at source but would be
grateful for any advice on making my PIC circuitry more immune.
Any path into the control circuitry seems to cause the problem.

Thanks in advance.

Nigel Duckworth

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