Arduino as an alarm sensor

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm building an Arduino based alarm monitor. I have normally closed door sensors installed and wired to my Arduino.

5v -> door sensor -> digialPin

Normally the circuit is closed. Do I need a resistor between 5v and the digital pin? When a digitalPin is set to INPUT it seems to have a pretty high resistance?

2

put a pull up/down resistor between digital and ground 10k i beleve... its much like a button

3

I have a pulldown resistor on the digital pin already. I guess that makes my diagram

5v -> door sensor -> digitalPin & 10k grounded resistor

4

i think thats it then... then you digital read it, and make it do dome sort of alarm...

5

I was trying to be efficient. No sense in have a closed circuit that's pumping a bunch of electricity through it. Would a resistor in-live save me some electricity, and maybe a little heat?

Or is it unnecessary?

6

if i understand correctly, there is only power flow if the door is open?

7

Reversed... there is electricity flow when the doors are closed (which is most of the time).

Part of the reason I asked is because if I put an LED inline with the door sensor and input pin it lights up really dim. It's like there is some sort of internal resistance on the digital pins.

8

Does your door sensor use a magnet on the door jam and a reed switch on the actual door. If so its just like wiring up a pushbutton.