Hi,
What's the powersupply voltage and what's the current draw of the horn?
I still think it's a Vg-s problem, ie the Gate to Source voltage is too low to fully turn on the MOSFET, why the PIC gets warm I don't know though - perhaps you get a dip in th epower supply voltage and the whole thing starts to oscillate or something (?).
If the powersupply is 12V then I'd try something like in the attached schematic. It has the drawback of inverting the signal but that can be taken care of if it works. Also, if the PIC is powered from the same supply as the horn (thru a regulator of course) make sure you have ample decoupling right at the powersupply pins of PIC.
The intrinsic body diode of the MOSFET is most likely enough in protection in this case.
/Henrik.
Bookmarks