Re: triggering multiple devices

["Bill" <billnomailnospamx@xxxxxxxxx>]

"Christopher Glaeser"  wrote in message
> When the output of a sensor (e.g. motion PIR) is used to trigger more than
> one device (e.g. two video cameras and an alarm system) what is the
> recommended approach to triggering multiple devices?
>

Best to keep things separate.

Security systems might use an "end of line resistor" and the signal will be
looking for a specific current flow. Attaching that line to another
electronic device could interfere with this.

Or the different devices might use different voltage levels. One may operate
with 5 volts, another with 12 volts. You could cause some serious problems
to a 5 volt electronic device by connecting it to 12 volts!

And then there is a "ground loop" problem. That is when you connect grounds
or "-" connections together from various electronic devices.

As to the relay used, first determine the power you will be using. Like 12
volts DC. Then how many "switches" you want on the relay. Say 3 switches.
This would be called "triple pole" or TP. Then relays will come with just an
on switch or an off and on switch. This is called throw. So single throw
(ST) or double throw (DT).

So you might want a 12V DC TPDT relay.

I search google.com for that and find this one...
http://parts.digikey.com/1/parts/752131-relay-gp-10a-3pdt-12vdc-kup-14d15-12.html

Then best to install a "flyback diode" backwards on the relay coil. Relays
when they are turned off will send out a pulse of electricity (which can
damage electronics just like static from your hand touching the circuit
board). If you install a diode backwards (- to the + connection), this will
damper that pulse of electricity. This shows a diagram about half way down.
Or search the page for the word "flyback"...
http://www.siongboon.com/projects/2006-06-19_switch/