I have looked at the OpenEnergyProject site's info about measuring voltage and current (and it's all good stuff). But I want a very simple, boolean/digital input indicating whether there is line voltage present or not.
I'll have 240v, split-phase wiring (2 * 120v AC and a Ground) to measure. I am only interested in using one of the two 120v lines (I can safely assume if one line is dead, so is the other). My Arduino Uno's power-supply is coming from a different source.
Basically want I want is some kind of "reverse relay", where the 120v available on the line holds my I/O to one state and flips when the voltage is gone.
The OpenEnergyProject uses an AC/AC transformer and then uses voltage-dropping-resistors to drop the range into the 0-5v that an analog I/O port can measure. But really I only want to know if it's present or not. I'm not interested in whether it's 120v or 110v on the line.
Is there a cheaper/simpler alternative working with the line-voltage to a (probably) digital input on the Arduino?