PIC16F819 locking

[penelopepug]

I would pay close attention to the transients generated by the relay coils when switching. I like to use hexfets because of their high gate isolation from the drain and source. You have to add a reverse biased flyback diode like a 1N4001 accross the relay coil and provide further isolation from your port pin to the fet's gate with a resistor, perhaps 4.7K. If you have pic port wires in close proximity to the relay source/sink wires, you can get induced noise in the pic causing havoc as well.

[Calco]

Hi,

Thanks for all the replies,

Yes I have flyback diodes on each relay, I also have diodes from the pic's port output to the resistor on each transistor.

My confusion is to why it works perfectly when seperately powered but not when its powered off its own transformer, Iam using the same regulator circuit etc.

It is driving me mad.

Yes I did have power up issues with the design initially also, I found adjusting the settings for the start up timer etc in the config sorted that out.

I had similar problems with the 18F452 with random resetting so I had knowledge of this trickiness.

I also had a batch of F819's that would only program once, cost me about 10 chips in the end.

Thanks anyway

Darryl

[penelopepug]

It still sounds like your getting a power glitch that is affectig the pic. You could also try a larger capacitor parallel to 0.1uF accross the pic and turning off the brownout detect.