Ringer Relay

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 Q1. When Q1 turns on, relay K1 is energized. The circuit should be connected in series with the lamp that is to be activated.

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Ringer Relay - Circuitos de Electronica