Automatic Headlight Dimmer, Safe Yourself and Others

This schematic diagram shows an automatic headlight dimmer circuit for your car’s headlight, keep you safe in the dark with maximum bright for farthest visibility, but will automatically switch from high to low  beam when traffic approach to save others sight. With Q1 in moderate darkness the variable resistor must be adjusted to generate no base current through Q2. This […]

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Small Broadcast-Band AM Transmitter

This AM radio circuit is a low power transmitter working on broadcast band. The simplicity is implemented using a single-transistor amplifier stage, and for the stability a crystal is used to excite the 670Hz oscillation. The output power of this AM transmitter circuit is 400 micro watts for antenna. L1 and L3 is 40-300 uH ferrite core antenna. Here is […]

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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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