Reading digital input from an alarm

Hardware
1

Hi,

I know some basic electronics, and am a software engineer. I have the April breakout board.

I’m wanting to hook up to my alarm system to detect various states and do something (like send a notification to my phone). The alarm has some digital outputs, and you can control them to go high based on events happening.

I think the outputs are going to be 12V from the alarm.

How can I feed these inputs into the alarm. It looks like I need some kind of pull up or down resistor, and a voltage divider to change the 12V to 3.3V, but I’m not sure how these two things combine together. All the examples I’ve seen seem to have a switch in the circuit, rather than an output from something else.

Can anyone help me with the circuit here?

Thanks,

Gary.

2

In my project I also have a 12v source. I got a 3.3v source by using a voltage regulator REG1117 (http://www.ti.com/lit/ds/symlink/reg1117a.pdf). It’s really easy to set up but it does get hot, which didn’t matter my my application. Hope that helps!

3

If you have a 12v signal from the alarm, and you’re sure it’ll be no more than 12v, then a simple voltage divider will work.

alarm signal - 130k resistor - imp pin - 47k resistor - GND

The imp pin will see 47/ (47+130) * 12 = 3.186v when 12v is present on the alarm signal.

4

Thanks!

Am I right in thinking I can feed the 12V supply straight to the April board as it has its own voltage regulator?

5

Yes, you can feed the supply into the VIN/GND pins (or P+/P- which will give reverse voltage protection) on an April to power the imp.