Reading a PWM value from a self powered system

Forum 2005-2010 (read only) Hardware Troubleshooting
1

Hi,

I would like to be able to read a PWM value (analogRead) from a system which has is own 12V DC power supply.

In fact, on my system I have 3 wires, 1 x +12 V, 1 x GND and 1 x PWM (out, 0-1.5 V).

How can I connect all those (knowing that I use the USB to power the arduino !!!) wires in order to read the PWM value.

Many thanks

2

It's probably more tricky than you think.
First connect the GNDs together.

Next you need to smooth the PWM signal so it is an analogue signal between 0 and 1.8v with an R & C (C start with 0.1uF from GND to an analogue input pin, and R (1K) from the analogue input pin to your PWM. As your maximum voltage is 1.8V then you will only get a maximum reading of 1.8 * (5/1024), if you want more then put the PWM through a transistor to make it a 5V signal before putting it to the RC circuit.