•  
  •  

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

NEW Starter Switch for Case International Tractor SUPER MV CUB
$12.95 NEW Starter Switch for Case International Tractor SUPER MV CUB picture
Siemens HF361R Heavy Duty Safety Switch.
$25.0 Siemens HF361R Heavy Duty Safety Switch.  picture
New EC11 Rotary Encoder Audio Digital Potentiometer with Switch Handle 20mm
$4.6 New EC11 Rotary Encoder Audio Digital Potentiometer with Switch Handle 20mm picture
ALLEN BRADLEY 800T-J2KC1 SER. T SELECTOR SWITCH *USED*
$20.0 ALLEN BRADLEY 800T-J2KC1 SER. T SELECTOR SWITCH *USED* picture
MERLIN GERIN 25841 CIRCUIT BREAKER 4A *NEW NO BOX*
$114.0 MERLIN GERIN 25841 CIRCUIT BREAKER 4A *NEW NO BOX* picture