Here’s a design circuit of phone message flasher, an alternative way to get alarmed when there is an incoming call. This is the figure of the circuit;
When the phone rings, high line voltage will be detected by A differential amplifier with hysteresis (Q2, Q3, and Q1). This action will turn on multi vibrator Q5/Q6, Q4. The LED will flashed via Q7. When the phone line voltage drops to less then 9V, the Q2 and Q1 will be turned off, which indicates an off hook condition.
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