I'm working on a project to integrate an off the shelf garage door monitor with an Arduino. The base station has a pair of LED's that flash in different patterns to indicate the state of the remote sensor, and my thought is that I can read these by connecting them to the the input pins, however I have some hurdles to cross. I've made some progress, but I'm just getting started with electronics and I'm unsure if I'm going in the right direction or if I'm going to fry $70 worth of stuff.
Here's what I know:
- The base station has a 100mA 12V power supply.
- The Arduino can use a up to a 12V power supply, but it's happier with 9V.
- The voltage across the base station leads is about 1.9V when they're lit.
- Arduinos use 5V logic, and read anything higher than 3V as high.
My plan is get a 12V power supply that can power both easily, feed the base station directly off of it, and use this converter to give the Arduino 9V. I assume that they share the same ground level.
Since the voltage across the LED is only 2V, which is not enough for the Arduino to read, I'm currently thinking of using a variation of this circuit below, which shows the ON state as about 1V and the OFF state as 5V at the input. The difference will be that I'll just run a wire from the positive side of one of the base station LED's to the transistor base.
simulate this circuit – Schematic created using CircuitLab
So, am I on the right track? Is there a better way to read these LED's using an Arduino?