>I am just starting to use pic devices. I have just designed a PCB using a
>PIC16c55 as a logic controller for a system controling three phase contacors.
>The PCB opperates correctly on the bench, but once connected in it's real
>situation, it starts to reset almost every time one of the coils for the
>contactors comes in.
>
>I am not sure, but I think my problem may lie in the way I have connected
>the periferal components to the PIC. For example I am not sure of values
>for a reliable power on reset circuit. It is hard for me to know exactly
>what is causing my PCB to reset, but an interesting point I noted was
>that a 'Power-On' LED connected directly to the 5v suppy flickers sometimes
>when the coils in the system power down, but if I remove the PIC from the
>board it no longer flickers with the coils. It's almost as if the PIC is
>somehow having an extream loading effect on the power supply (but only when
>there are voltage transients around).
>
>Could anyone give me any tips as to the configuration of a reliable set of
>components external to the PIC.
>
>Or, could anyone point me in the direction of information (diagrams) to
>let me know what a good setup is.
>
>Any assistance would be greatly appreciated,
>
>Thanks,
>
>Wayne G Boyd.

Sounds like inductive kickback from the coils. Have this problem at work
all the time. Common solutions are to put a diode across the coil, and add
an RC circuit. I've also had luck using an opto-isolator or
solid-state-relay between the offending device and digital controller. (Had
a lot of problems once with a solenoid resetting a 8255 everytime it turned
off. The software "engineer" wanted to "solve" the problem by just
re-configuring the 8255 each time the solenoid turned off)

Chris


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