AVR-Chat

At 09:42 AM 11/9/2004, Dave Mucha wrote:



>Hi all,
>
>I am looking an alarm type switch and am thinking of using a Tiny11
>to generate a pulse of something like 10khz and then send that thru
>the 6 to 10 switches (in series) and then use the same Tiny11 to
>detect that pulse.  Any switch opens and the pulse is lost.

This is just a series loop, right?
No need for pulses, just give a current of 10-20mA and detect open/closed 
with debounce of about 100mS. Protection of your inputs and outputs is more 
interesting.

For a moment, I thought you meant addressable switches, as in "which switch 
is open".

Years and years ago, I did something like this in discrete logic (yecch!)
It sent a wide sync pulse, then narrow polling pulses down a single conductor.
Another conductor carried back answering pulses from each switch.

Today, a single Tiny-11 at each switch point could work, but you'd have to 
program in their address ranges. A micro with more pins would allow a 
dipswitch to set that. Four pins for a 0-F dipswitch, and four switch 
inputs, plus two pins for data, would be nice.