Category Archives: Alarm

This is the collection of alarm schematic diagrams at circuitdiagram.net. The alarm provides a warning tone when an event takes place, for example: thefts, fires, and other events that are not normal. Alarms have the capability of causing a fight-or-flight response in humans; a person under this mindset will panic and either flee the perceived danger or attempt to eliminate it, often ignoring rational thought in either case. A person in such a state can be characterised as “alarmed”.



Pyroelectric Fire Alarm System

This is definitely an ultra-sensitive fire sensor that exploits the direct piezoelectric property of an ordinary piezo component to recognize the fire. The lead zirconate titanate crystals within the piezo component have the property to deform and produce an electrical potential when heated, thus converting the piezo component into a heat sensor. The circuit mentioned… Read More »

Easy Build Motorcycle Alarm

The following circuit is a simple, cheap and easy build motorcycle alarm. The circuit just required 2 transistors to drive the relay the the relay act as a switch to activate the buzzer. Any number of normally-open switches may possibly be applied. Fit the mercury switches to ensure that they close when the steering is… Read More »

Simple Fire Alarm with Thermistor and NE555

The following circuit is a simple fire alarm circuit based NE555 timer and use thermistor as a temperature detector. This sensor will activate the transistor when the temperature is in high value. The thermistor will have a low resistance at high temperature, while at low temperature, the transistor resistance is high. This characteristic of thermitor… Read More »

Sound Effects Generator (8 different sound) based IC HT2884

This is the circuit diagram of sound effects generator. All sounds in this circuit are generated by HT2884. The HT2884 is a CMOS LSI chip equipped with tone circuit, noise circuit, and other control logic to generate various sounds to be used in sound effects production. This IC features: single power supply (2.4V ? 3.3V),… Read More »

Wireless Car Alarm

This circuit is a wireless car alarm system that is built using two circuit modules, namely modules of transmitter and receiver modules. This circuit works on FM radio waves. Car alarms can be used on vehicles that have a 6-12VDC power supply. You can use the voltage stabilizer if your car power supply is too… Read More »



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