Here’s a
design circuit for simple 220V power interface is
intended as an interface for monitoring electric equipments and devices using a
computer. The interface only senses whether the device being monitored is
turned on or off. The most important aspect of the circuit is the galvanic
isolation between the AC main line being monitored and the interface to the
computer. This is done with the use of the opto coupler IC TIL111 but a
suitable replacement can be used too. This is the figure of the circuit;
In this
circuit, to
avoid having to modify the circuit for each device being monitored, the circuit
monitors the device’s AC power line directly. The resistor R1 lets a current of
around 0.5 mA through the opto coupler LED. The other half of the current is
rectified through the diode D1. It is obvious that the current to the opto
coupler LED is half wave rectified. This means that the phototransistor part of
the opto coupler receives only light impulses of around 100uA. The capacitor C1
filters out the current pulsation and maintains a smooth output current. In
case the current pulsation is needed, just remove C1.
