This project presents another application of RF (radio frequency) communication. The capability of fire alarm circuit can be improved by incorporating an RF [[wysiwyg_imageupload::]]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. 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.
At times we forget to switch off our heating devices and eventually they get damaged. Therefore there is always a need of a device which can alert by sounding [[wysiwyg_imageupload::]]an alarm if the device temperature goes beyond a particular value. Same concept can be used in this project about fire alarm. If a building catches fire then it will raise an alarm and people could evacuate the building. This circuit uses a LM35 temperature sensor along with a LM339 comparator. Interfaced to LM339 are the following components: Resistors, Capacitors, Transistors, 555 Timer, Buzzer (output). This project about fire alarm circuit is based around LM35 which is a temperature sensor and could be used to switch an alarm when temperature goes beyond a preset value. In this circuit the output of LM35 is fed to the negative pin of comparator of LM339. The positive input is connected to a preset VR1 of value 10K.