Detector circuit

Posted on Feb 5, 2014

This is Overheat Detector Alarm Switch using Temperature Sensor IC LM35 Electronic Suite Diagram, at the heart of this overhead detector (fire alarm) circuit is a precision integrated temperature sensor type LM35 (IC1), which provides an accurately linear and directly proportional output in mV, over the zero to +155 degrees C temperature range. Th

Detector circuit
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is can be used as part of fire smoke detectors but do not use it as a home fire alarm system. Here the output of the LM35 is applied to the non-inverting input of a comparator wired around a CA3130 opamp (IC2). A voltage divider network R3-P1 sets the threshold voltage, at the inverting input of the opamp. The threshold voltage determines the adjustable temperature trip level at which the circuit is activated. When the measured temperature exceeds the user-defined level, the comparator pulls its output High to approx. 2. 2 V causing transistor T1 to be forward biased instantly. T2 is also switched on, supplying the oscillator circuit around IC3 with sufficient voltage to start working. The 555 set up in astable mode directly drives active piezoelectric buzzer Bz1 to raise a loud alert. Components R7, R8 and C4 determine the on/off rhythm of the sounder. A transistor based relay driver may be driven off the emitter of T1 (TP1). Similarly, replacing the piezo sounder with a suitable relay allows switching of high-power flashers, sirens or horns working on the AC mains supply. This is Water Level Sensor and Alarm Circuit using CD4066 Circuit Schematic, forcircuit not only indicates the amount of water in the tank head, but also gives an alarm when the tank is full. If the water is empty the wires in the tank are open circuit and the 180K resistors pulls the switch to open the little switches and LEDs are off. When the water...

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