Ordinary fire alarm circuits uses diode sensors to detect fire presence. But a pyroelectric fire alarm circuit described here is an ultra-sensitive fire sensor that uses direct piezoelectric property of an ordinary piezo element to detect fire.
Sensing capability of the circuit.
The circuit of fire alarm given here is very sensitive as it uses Pyroelectric Fire Sensor . It gives a warning alarm if the room temperature increases more than 10°C which cannot be provided using a diode sensor.
The entire circuit has two sections power supply section and sensor section.
Power supply with battery backup: This section consists of a0-12V, 1A step-down transformer with a standard full-wave rectifier formed by D1 through D4 and filter capacitor C1. A battery back up is also provided in case a power failure. the diode D5 and D6 plays an important role of working the power supply as a mini ups.
Sensor side circuit: CA3130 IC based sensitive signal amplifier gives a high output when temperature near the piezo element increases. As the amplifier is a CMOS operational amplifier with gate protected p-channel MOSFETs in the inputs, it gives a quick change in the output if there is any change in the non inverting input (pin3) according to the referance voltage set by the preset VR1. When the output of the amplifier going high, it turn on the transistor T1- BC547. This makes the reset pin 12 of IC2 CD4060 to ground. From this time onwards the IC2 starts oscillating according to the oscillating components C3 and R6. Now the output Q3 of CD4060 connected to red LED2 starts flashing after a few moments. If heat near the piezo persists, Q7 (pin 14) output of IC2 becomes high after one minute, and the alarm starts beeping.
The additional advantage of this piezoelectric fire alarm circuit is that it can be connected to a solenoid pump using a relay and transistor. If a fire is detected, the solenoid pump connected to fire sensing system will spray the fire-ceasing foam or water to the possible sites of fire.
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| Circuit Diagram of : Right Click >> View Image to view full size |
Sensing capability of the circuit.
The circuit of fire alarm given here is very sensitive as it uses Pyroelectric Fire Sensor . It gives a warning alarm if the room temperature increases more than 10°C which cannot be provided using a diode sensor.
The entire circuit has two sections power supply section and sensor section.
Power supply with battery backup: This section consists of a0-12V, 1A step-down transformer with a standard full-wave rectifier formed by D1 through D4 and filter capacitor C1. A battery back up is also provided in case a power failure. the diode D5 and D6 plays an important role of working the power supply as a mini ups.
Sensor side circuit: CA3130 IC based sensitive signal amplifier gives a high output when temperature near the piezo element increases. As the amplifier is a CMOS operational amplifier with gate protected p-channel MOSFETs in the inputs, it gives a quick change in the output if there is any change in the non inverting input (pin3) according to the referance voltage set by the preset VR1. When the output of the amplifier going high, it turn on the transistor T1- BC547. This makes the reset pin 12 of IC2 CD4060 to ground. From this time onwards the IC2 starts oscillating according to the oscillating components C3 and R6. Now the output Q3 of CD4060 connected to red LED2 starts flashing after a few moments. If heat near the piezo persists, Q7 (pin 14) output of IC2 becomes high after one minute, and the alarm starts beeping.
The additional advantage of this piezoelectric fire alarm circuit is that it can be connected to a solenoid pump using a relay and transistor. If a fire is detected, the solenoid pump connected to fire sensing system will spray the fire-ceasing foam or water to the possible sites of fire.
Note:
- Assemble the circuit on a general purpose PCB and enclose it in a suitable case.
- Connect the piezoelectric sensor (peizo element) using a thin insulated wire.
- Glue the peizo element to a small piece of thin aluminum sheet to increase sensitivity.
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