AVR-Chat

Correct, it is a series loop.  

It is for a machine where the wires can be cut or vibrate open or be 
shorted.

The current or pulse would offer a more accurate way to verify that 
the switches are in the circuit.

Dave






--- In AVR-Chat@yahoogroups.com, Dave VanHorn <dvanhorn@d...> wrote:
> 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.