Phone Message Flasher

Posted on Nov 25, 2012

This circuit flashes an LED to indicate that your phone rang during your absence. A differential amplifier with hyste

Phone Message Flasher
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resis (Ql, Q2, and Q3) detects high line voltage (ringing), which turns on Q4, multivibrator Q5/Q6, and flashes the LED via Q7. Ql and Q2 remain on until the phone-line voltage drops to less than 9 V, which indicates an off-hook condition.

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