•  
  •  

Fire Alarm

This circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This causes the resistance of LDR to increase and the voltage at the base of the transistor is pulled high due to which the supply to the COB (chip-on-board) is completed. Different COBs are available in the market to generate different sounds.

The choice of the COB depends on the user. The signal generated by COB is amplified by an audio amplifier. In this circuit, the audio power amplifier is wired around IC TDA 2002. The sensitivity of the circuit depends on the distance between bulb and LDR as well as setting of preset VR1. Thus by placing the bulb and the LDR at appropriate distances, one may vary preset VR1 to get optimum sensitivity.

An ON/OFF switch is suggested to turn the circuit on and off as desirable.

If there are any problems please contact webmaster@electronic-circuits-diagrams.com

Please share & like

Desktop 10 Slot Organizer- Fuji Electric- Collmer Semiconductor
$1.95 Desktop 10 Slot Organizer- Fuji Electric- Collmer Semiconductor  picture
10Pcs BD139 Genuine ON Semiconductor NPN Transistor 1.5A/80V To-126 Pop.PL
$0.99 10Pcs BD139 Genuine ON Semiconductor NPN Transistor 1.5A/80V To-126 Pop.PL picture
LM395T National Semiconductor NPN Ultra-Reliable Transistor - NOS Qty 5
$9.99 LM395T National Semiconductor NPN Ultra-Reliable Transistor - NOS Qty 5  picture
LM628N National Semiconductor Motion Control IC LM628 - NOS Qty 1
$9.99 LM628N National Semiconductor Motion Control IC LM628 - NOS Qty 1 picture
QM310M1 National Semiconductor Metal Can IC LM310 - NOS Qty 1
$4.99 QM310M1 National Semiconductor Metal Can IC LM310 - NOS Qty 1 picture