New mains power probe

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Long time ago I published a mains power probe: Rivelatore di 230v

DISCLAIMER: this is a dangerous circuit. Mains voltage electricity is extremely dangerous.

This new circuit is far simpler than the previous one and it waste less power.

It is based on a Vactrol: an opto coupler using a fotoresistor instead of a diode or a transistor.

It is a quite slow component: this characteristic could be a problem for other applications but it is a feature for this.

Here is the schematics:


The pullup resistor can be a 100Kohm. The internal pull-up of arduinos makes the job.

Both leds (the one inside our VTL5 coupler and the other) are flashing at 50hz, but the Vactrol is to slow to change its output.

The result is a circuit requiring about 500uA so consuming 123mW. The ripple is less than 10mV (on 5V).

Acknowledgements: this circuit is based on an idea by Luca Barion