Posted by Circuits Arena on Thursday, 25 December 2014
Fire Alarm Circuit Diagram is the artlcle explaining Alarm Circuit : This ultra compact and low cost fire alarm senses fire breakout based on this fact. W hen there is a fire breakout in the...
Alarm Circuit:
This ultra compact and low cost fire alarm senses fire breakout based on this fact.
When there is a fire breakout in the room the temperature increases.
Fig. Fire Alarm Circuit Diagram
- The working of fire alarm circuit is when the temperature increases the leakage current of this transistor also increases.
- Transistor (Q1) is used as the fire sensor here. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased.
- As a result when there is a fire breakout the transistor Q2 will be on.
The emitter of Q2 is connected to the base of Q3. So
when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay
which is used to drive the load ie,light,bell,horn etc as an indication
of the fire. The diode D1 is used as a free wheeling diode to protect it
from back EMF generated when relay is switched.
- The circuit can be powered using a 9V battery or a 9V battery eliminator. This is not a latching alarm,that is;when the temperature in the
vicinity of the sensor decreases below the set point the alarm stops.
- The Preset R1 can be used to desired temperature level for setting the alarm ON.
- 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.
