Low cost fire alarm circuit.

admin January 21, 2014 89 Comments
Description. When there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact. Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. 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...
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Liquid Level Switch

admin October 12, 2012 9 Comments
Liquid Level Switch Description Here is a simple level switch circuit that switches on one relay and switches off another relay when the fluid level exceeds the set limit.This circuit is a modification of the Simple Water Level Indicator previously posted.When the water level touches the probes positive supply is connected to the base of Q1 through fluid.This makes transistor Q1 ON.Base of Q2 is connected to collector of Q1 and base of Q3 is connected to collector of...
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Touch Switch Circuit

admin April 27, 2011 33 Comments
Touch Switch Circuit using NE 555 Description This is the circuit diagram of a small touch plate controller using IC NE 555 .This circuit is ideally useful for making touch operated doorbells, buzzers,toys etc which when touched on the touch plate operates the relay for a preset time and the turns off automatically. This circuit is realized by utilizing the high input impedance of trigger pin of the 555 IC.When  the IC is triggered by the induced voltage of...
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Photo Switch Circuit

admin April 27, 2011 16 Comments
Photo Switch Circuit using 555 IC Description This is a simple photo switch suitable for home and industrial purpose.The circuit switches on a relay when the light intensity falling on the sensor crosses the set limit. The circuit is based on a NE 555 and two transistors for driving the relay.The resistor R1  is adjusted such a way that under normal condition the voltage across the LDR is less than 1/3 the supply voltage.In this condition output of IC...
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InfraRed (IR) Sensor/Detector

jacky November 22, 2011 11 Comments
InfraRed (IR) Sensor/Detector Circuit Description. The circuit shows that the output of IC1 555 IC,which is designed for a duty cycle of 0.8mSec,with a frequency of 120Hz and 300 mA peak current, is used to drive the infra red LED,D1.From the connection it is clear that the diodes D1 and D2 are on the same line,just a few centimeters apart, on the breadboard.Thus diode D2 receives the infra-red output from the diode D1.The diode signal, which is given to...
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