On Mon, 08 Nov 1999, you wrote:
> Hello List,
>
> I have realized an alarm for my bycicle using a 12C508. It is powered by two A
A
> size alkaline battery.
>
> I would like to know if there is a simple (and economic!!) solution which
> I can use to protect my circuit against polarity inversion during battery chan
ge.
> (I know it's a remote possibility, but it exists)
>
> I thought to use a serie diode, but the voltage drop bring the PIC power volta
ge
> near the power supply limit of the MCU.
>
I can't think of it right now, but there is an arrangement using a single
MOSFET which will provide this. Possibly the gate is connected to the drain,
possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz and
Hill. It's a very simple circuit, but as I said, I can't think of it now (such
is the effect of a few beers..). Play around with this, and see what you can
come up with. I'll try again in the morning.

Jason Langenauer
Mechanical and Space Enginnering, The University of Queensland
--
Lady Astor: If you were my husband, I'd poison you drink.
Winston Churchill : If I was your husband, I'd drink it.