RF based Fire Alarm (Overheat Alarm)

This project presents another application of RF (radio frequency) communication. The capability of fire alarm circuit can be improved by incorporating an RF module. This way the temperature sensor and buzzer for alarm can be placed away from each other. This provides flexibility in installing various sensors at different locations in a building and thus overheating at a place (due to fire) would signal the buzzer to go on.[[wysiwyg_imageupload:192:]]

This project about fire alarm circuit can be divided into four parts, namely, temperature sensor, comparator, transceiver part (RF module) and the output. In this circuit a temperature sensor (LM35) is placed at a certain place and its output is given to the negative end of a comparator. LM324 has been provided in the circuit for comparator. The positive end of comparator is connected to a preset, to set the reference temperature. As long as the output of temperature sensor is below the set reference, the output of comparator stays high.

The output from comparator is connected to pin 10 of encoder IC (HT12E). Transmission enable (TE) pin of encoder is set low while its data pin (pin 17) is connected to the data pin (pin 2) of RF transmitter.

When the surrounding temperature becomes higher than reference temperature, the comparator output goes low which then leads to the transmission of a signal. This signal is received by the RF receiver and is fed to pin 14 of decoder IC (HT12D). Since this signal is low, it is passed to an inverter of 74LS04 and its output is taken on a buzzer which then goes on.

For details of signal transmission through RF, refer RF based wireless remote. More than one temperature sensors can also be installed at different places and can be connected to the RF module as has been explained.