Tag «Alarm»

Loud 10-W Car Alarm Siren

By generating square-wave output that sweeps down and up in frequency, this circuit can produce force field of high-intensity sound inside car. This circuit can make a car thieve panics and decide to run before anyone catch his action. D1, C1 and R1 produce triangle waveform by shaping a square wave output of IC1.  If …

Discrete Sliding Tone (Frequency Ramp) Doorbell

This doorbell circuit produces a low tone that will slide up to higher frequency. The equivalent total resistance connected between the base of Q1 and ground (Rbg) , and coupling capacitor  C1  determines the AF oscillator’s frequency. The resistance (Rbg) is equal to (R2+R1)R3.  Here is the schematic diagram of the circuit: The R2 is …

555-IC Timed Beeper/Alarm

This is a simple circuit of beeper using 555 timer. This circuit can be employed to energize lights, horn, or other signaling device at any desired interval when the mercury switch is triggered. Since the current handling capability of mercury switch is not so high, an SCR is used to handle current drawn by the …

General Purpose Alarm Circuit for Resistive Sensor

When the resistance value of a temperature, light, pressure,  or any other resistive sensors  Rs drops below a certain point  (adjusted by a preset potentiometer),  the SCR (silicon controlled switch) will be triggered. The sensor (Rs) and the potentiometer placement can be interchanged to get opposite action, where the SCR need to be triggered  at …

Simple LDR Light Alarm

This is a light alarm circuit. This circuit uses Light dependent resistor (LDR). When there is no light fall on the LDR, the transistor driving the speaker is not turned on, because its resistance is high. When the LDR receives light, its resistance decreases and the collector of the second transistor falls. The first transistor …

Siren Driver Circuit

This is a driver circuit for siren. This circuit usually used for car alarms. To build this circuit, we use VD-MOS FETs. This circuit receives 12 v supply from battery. A microprocessor sends complementary pulse waveforms to the driver circuit as inputs.  Here is the circuit : This circuit uses two PHC21025 which each of …

Provide Remote Alarm for Smoke Detector

Ionization-based smoke detectors are efficient and cheap, so they are often installed in the house, other outbuildings, and  the garage. The Locations of the device is far from house, so we need to transmit the alarm signals back into central home-security system or the house. This is a simple circuit that sense a supply current …