How to use this 12V Relay with Optocoupler?

Is the relay signal active high, or active low. In other words does the really turn on when the Arduino Outputs 5V to it, or does it turn on when the Arduino Outputs 0V. Most relay boards are active low, in that case the diode will not work. Besides there are two diodes that are there already. One for the optocoupler, And one LED. If your signal is active high, or if it is bidirectional set it up for active high, and there will be no chance of 12V getting into it. otherwise, the diodes and current limit resistor will prevent high current from getting to the Arduino. The clamping diodes within the Arduino should reduce the voltage to a safe level.

promacjoe: Is the relay signal active high, or active low. In other words does the really turn on when the Arduino Outputs 5V to it, or does it turn on when the Arduino Outputs 0V. Most relay boards are active low, in that case the diode will not work. Besides there are two diodes that are there already. One for the optocoupler, And one LED. If your signal is active high, or if it is bidirectional set it up for active high, and there will be no chance of 12V getting into it. otherwise, the diodes and current limit resistor will prevent high current from getting to the Arduino. The clamping diodes within the Arduino should reduce the voltage to a safe level.

It is possible to choose between active high or low, but I'll be using active high.

So, you are saying that it is not necessary to put a diode?

Thanks

If he powered the Arduino with a 12v - 5v buck converter would that provide any isolation from the 12v system (that could be 10-15vdc with the alternator running)?