Delayed Car Door Alarm

Opening car’s door is very simple activity, and off course it’s just a daily activity which require no special skill. Almost nothing can go wrong, but forgetting to close the door when we doing or thinking on many tasks is a common thing. This can lead to many consequences, from as simple as air conditioner inefficiency to as dangerous as […]

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First-Response Monitor with SCR (Quiz Alarm)

A pair of cross-coupled SCRs can be used to build a first-response monitor circuit, as shown in the schematic diagram below.  First-response circuit is popular in quiz application where the first contestant who press the button will prevent the other activate the button/alarm. The purpose of this circuit in quiz application is to ease the identification of the first one […]

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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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