If you are using the reed switch to take your PIC out of sleep mode, no
deboucing is necessary, except that you might want to run for a few
milliseconds until the reed settles down.

The resistor is sized so that  the PIC sees a reliable state change over
all temperature ranges. Remember that if the reed switch is too far away,
external effects (such as nearby lightning and/or motors, flourescent
lamps, etc) can cause the PIC to not act correctly unless the resistor
value is low enough. If a few inches away, 100K is fine; if 200 meters
away, I'd drop to 10K. But you can help by making the wires to the reed
switch a twisted pair, and even better if the pair is inside a shielded
jacket. In that case 22K might suffice.

--Bob

At 09:55 AM 7/29/2003 +0300, you wrote:
>There is a reed switch connected to a cable and it is connected to portb
>of the PIC.  PIC is on battery voltage of 3 or 3.6 (lithium).  I have been
>reading the pulses generated from the reed switch when magnet is brought
>near.  I have two questions:
>
>* There seems to be no need for debouncing, should I still debounce?
>* What is the ideal resistor value to be used (note that the system needs
>low power consumption)
>* If the cable between the pic and the reed is about 100meters, (makes 200
>meters of total distance from one pic pin to reed and from reed to ground)
>should the above resistor value be changed?  Would I need any other parts
>like schmitt triggers etc.)?
>
>Any help is appricated,
>
>Omer
>
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