PIC resets when MOSFET is driving inductive load

Adding the schottky diode between the horn terminals (and not parallel with the MOSFET body diode) and adding a ceramic 100nF capacitor to the PIC supply seems to have cured the problem. At least I can make the horn work with either polarity on the horn terminals without resetting the PIC.

If I remove the schottky, the problem persists even with the ceramic 100nF in place, but it's no problem adding both to my circuit. The 100nF should have been there in the first place anyway :-/

Excellent news - thanks for the feedback

And thank you all for helping me solve my issue

I know I'm late to this thread, but assuming the original poster is still around, I am curious as to why you chose a 1N5817 (1A) diode over a 1N5820 (3A)? With a car horn drawing 5A and higher, I would assume that a more robust flyback diode would be best.

Futterama said:

This circuit now works on breadboard with short wires...

Click to expand...

Hi JDW1,

I had a look trough the thread and also my layouts, and I can see I used a SMB package diode on the PCB but no mention of a specific device on the schematic, but there is a very good chance that I used a S320 3A 200V schottky rectifier as I have a lot of them in stock. The 1N5817 was probably just the best I had for the breadboarding.

I hope this clarifies things for you.

Best regards,
Futterama

You can also try a simple diode-capacitor filter for the power supply to the micro only. You can also try to place a large cap (observing proper polarity) across the horn of say 1000uF or 2200uF.