# self monitored security

Hi all,

Firstly, I am a beginner with arduino. I have done some research and tutorials and want to know if this project is feasible.

I have an existing security system that usually contacts a switchboard through a landline when triggered, I want an arduino to notify me when the system is triggered.

Here's my theory, a closed circuit window magnet reads 24 VDC at the security panel, when the circuit is opened (the window is open) it reads an infinite voltage on my multimeter.

If I run a wire from the security panel to a pin on the arduino and use a rising interrupt when a voltage over 24 VDC is detected, I can have the arduino send an email/SMS.

Questions: Is this feasible? Do I need to reduce the 24 VDC coming from the panel?

Sorry if this is a completely ridiculous post, I'm learning :)

eastyork3: a closed circuit window magnet reads 24 VDC at the security panel, when the circuit is opened (the window is open) it reads an infinite voltage on my multimeter.

Infinite voltage!?! Are you sure? A source of infinite voltage would cause all kinds of sparking. Even a few million volts would be unsafe to be near.

eastyork3: Do I need to reduce the 24 VDC coming from the panel?

Unless you think your Arduino is getting stressed and needs a smoke break...

You should try again with your measurement. You may have mistaken resistance with voltage. Arduino should be able to sense the magnet but you need to know how it works first.

Hahaha, thank you all for not being too harsh.

Unfortunately my security panel isn't producing infinite power and the answer to the world's energy crisis, I was reading everything wrong.

Okay, so here's how the panel works: When the window is closed, the voltage is 5 VDC. When the window is open, the voltage is 10 VDC.

I want the arduino to trigger an action when it senses a voltage change. Maybe anything over 7 VDC. Would I use a rising interrupt?

You could use a voltage divider to get 10V into 4V (HIGH) and thus 5V into 1.25V (LOW). Use a 3K and 2K resistors in series.

Would it work kind of like a potentiometer? EG: A pot with a range of 5v to 10v, if the voltage passes 7v, it triggers an action?

eastyork3: Would it work kind of like a potentiometer? EG: A pot with a range of 5v to 10v, if the voltage passes 7v, it triggers an action?

I would do this:

Output---3K ohm --- 2K ohm --- GND Then have arduino sense the junction between 3K and 2K with a digital input.