Daniel Rubin wrote:
>
> If I use a transistor I'll have to add a resistor.  Anyone know of any
> transistors (in a SMD package) that don't require a resistor between the
> PIC and it's base?
>
> >Remove the back-emf diode, and use a transistor in emitter follwer
> >configuration.


Hi Daniel, using two paralleled PIC outputs
should be fine for your coil (provided you keep
the back-emf diode).

The PIC outputs are MOSFET type and will share
the current fairly well.

This is a reliable setup from a hardware view as
the main problem with outputs is that the input
latch gets set/clr due to voltages on the pin
itself, or output latches get state-change due
to large PSU glitches, but as they are tied together
the ins/outs are also tied together and the two
pins *should* always be the same state.

BUT, software could be a problem, always write to
the port as a complete byte, and be very careful
with any AND/XOR etc on that port that you don't
change one bit by mistake.

My preference would be to use SOME value of resistor
even if your current needs mean the resistors are
a low value, this will probably save your PIC when/if
you get the PSU glitches etc. In conjunction with
this I would set the pins constantly, (every few mS
if possible) so that if the PSU glitches and a pin
state gets trashed it will get fixed in a very short
time. Paranoia can be good. :o)
-Roman

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