Posted on Sep 17, 2012

When the phone rings, the ring signal from the telephone company lights a neon lamp within a CLM3120 optocoupler. That causes a drop in the resistance of the CdS cell output of the device, turning on transistor Ql.

Click here to download the full size of the above Circuit.

When Ql turns on, relay Kl is energized. The circuit should be connected in series with the lamp that is to be activated.

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