At 02:36 PM 8/28/01 -0400, you wrote:
>Hello,
>
>        I've got a 16f870 that I'm using to turn a relay (Tyco V23105 150 mW
>Nominal Coil Power, 960 ohm, 12 volt Nominal Coil Voltage) on/off.  This
>relay is controlling a very small DC motor (~0.5amps).  About 10% of the
>time when this relay turns on/off, it resets the PIC.  I've verified this
>is what's happening.  Seems to work fine when the motor isn't connected to
>the relay.  Only resets when the motor is connected.
>        I'm using PORTA.0 through a resistor to turn on a 2N4401
transistor that
>then powers the relay coil.  I have a 1N4004 diode across the relay
>coil.  I have two 0.1uf caps on the +5v to the PIC.
>        The +5v for the PIC is from a powered protoboard.  The +12v for the
>transistor and relay are from a +12v battery.  The grounds of these two
>power supplies are tied together.
>        Can anyone help me figure out what's going on and fix this?
>

Try a diode right across the motor terminals (assuming it only has to go in
one
direction). Obviously you want it to be reverse-biased normally.

Make sure that your 12V ground is only tied to the 5V ground at a single
point,
and preferably away from the chip on the 5V side.

What is /MCLR conected to?  Preferably tie it to a low-impedance external
BOR circuit or to Vdd.

Connect a 10 nF capacitor from C to E on the 2N4401.

Best regards,
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Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
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