555 RFI problem: reprise

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Some weeks ago I asked for help with a car blinker circuit, that was
prone to being affected by the (magneto) ignition system.

I think I've found the cause - the 555 IC itself.

I've only checked it on a bench so far, using a spark generator to
simulate the unsuppressed high tension ignition spark.
After breadboarding the circuit for the umpteenth time, I used a
different brand of 555 - a National Semiconductor. I'd previously used
KIA brand, thinking they'd all behave the same. Not the case - the NS
555 doesn't behave erratically with the spark nearby, whereas the KIA
555 always does.
No filtering was used either, just a cap on pin 5.

Lesson learnt!
Here's hoping it'll work OK on the vehicle now.

Many thanks to all who suggested fixes.


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