Join Date: May 2005
Location: Ottawa (Kanata), Canada
Question for electronics gurus
'm trying to hook up a visual indicator (blinking LED) to my alarm system that does not have such an option.
With a multimeter, all I've been able to find is a +12V that is on when the alarm is off, and vice versa. This is used by the perimeter sensor.
At first I thought I could use this line as ground, and connect the positive lead of my LED to an always-on source (the battery). Then, when the alarm was off, the alarm lead would drop to 0v and the current would flow. Yes, this works, but the blinking LED caused a fluctuation in the current which triggered the alarm, as if it was the perimeter sensor. The alarm wasn't triggered with a steady LED.
So what I did is build an inverter out of some NPN transistors and resistors. It works just fine - just ugly with all the leads. But with the LED/alarm off, the battery needed to be charged after a two week hiatus.
Can someone offer an alternate solution?