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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Car Headlights On Reminder

More important than environmental issue of energy saving, avoiding car battery failure when you leave the headlamp turned on overnight in the garage is possibly more important for your concern. This is a circuit of automobile lights-on reminder if you turn off the engine but forget to turn off the main lamp, this circuit will give warning when the headlights […]

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Water Level Sensor/Detector/Monitor With Alarm

This schematic diagram shows a water level sensor/detector/monitor circuit. An alarm is also featured in this circuit. Any fluid with a resistance under 900K between the maximum separation distance of the probes will trigger this circuit. A 4050B CMOS hex buffer is used on this circuit that is working at 5 volt supply.  The 10M resistors connected between buffer input […]

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