When there is a break of fire in the room temperature ultra-compact increases.This cheap fire alarm senses fire starter based on this fact.
Transistor BC177 (Q1) is used as here.When fire sensor temperature increases the leakage current of this transistor also increases.The circuit is designed so that when there is an increased leakage current of Q1, Q2 transistor will partially. As a result, when a fire break transistor Q2 is on.The emitter of Q2 (BC 108) is connected to the base of Q3 (AC 128). So when Q2 is ON Q3 will also be the transistor Q3 on.The relay units used to carry the load, ie, light, bell, horn etc as an indication of the diode D1 is used as a fire.The freewheeling diode to protect the counter electromotive force generated when the relay is activated.
Notes.
Transistor BC177 (Q1) is used as here.When fire sensor temperature increases the leakage current of this transistor also increases.The circuit is designed so that when there is an increased leakage current of Q1, Q2 transistor will partially. As a result, when a fire break transistor Q2 is on.The emitter of Q2 (BC 108) is connected to the base of Q3 (AC 128). So when Q2 is ON Q3 will also be the transistor Q3 on.The relay units used to carry the load, ie, light, bell, horn etc as an indication of the diode D1 is used as a fire.The freewheeling diode to protect the counter electromotive force generated when the relay is activated.
Notes.
- The Preset R1 can be used to desired temperature level for setting the alarm ON.
- This is not a latching alarm,ie;when the temperature in the vicinity of the sensor decreases below the set point the alarm stops.
- The circuit can be powered using a 9V battery or a 9V battery eliminator.
- All capacitors are electrolytic and must be rated at least 10V.
- The load can be connected through the C,NC,NO points of the relay according to your need.
- The calibration can be done using a soldering iron,and a thermo meter.Switch ON the power supply.Keep the tip of soldering iron near to the Q1.Same time also keep the thermometer close to it.When the temperature reaches your desired value adjust R1 so that relay gets ON.Done!
