Phone Incoming Call Flasher

This is a circuit of phone message flasher, an alternative way to get alarmed when there is an incoming call. 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 multivibrator Q5/Q6, Q4. The LED will flashed via Q7. When the phone line voltage drops […]

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Burglar Alarm Works for Both N.O and N.C Contacts

Unlike other alarm circuit that provide normally-open only or normally-closed only configuration, this alarm circuit work for both configurations. The mechanism of this alarm circuit is very simple, that the output will be active (Q1 transistor will be conducting) if IC1 or IC2 “high”. If R2 is open, then IC1 output will be high since the non-inverting input voltage will […]

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Electronic Gain Control in Quartz-Stabilized Oscillator

This is a quartz-stabilized oscillator circuit with electronic gain control. Replacing the common filament lamp  for amplitude stabilization, this circuit use an electronic gain control inside the stabilization loop. A 50-Ω variable resistor should be trimmed until the output level show 2-Vpp magnitude oscillations op-amp A1 output. Here is  the schematic diagram of the circuit: [Circuit’s schematic diagram source: Linear […]

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