Zero degree Celsius alarm

Posted on Feb 6, 2014

This simple circuit will produce an alarm whenever the temperature falls below zero degree. A thermistor is used here to sense temperature. The op-amp LM7215 is used to compare the reference voltage and voltage from the thermistor network. Reference voltage is given to the non inverting input (pin3) of the IC and voltage from thermistor network is

Zero degree Celsius alarm
Click here to download the full size of the above Circuit.

given to the inverting input (pin4). When temperature becomes less than zero degree the voltage at the non inverting input becomes larger than the voltage at the inverting input and the output of the op-amp becomes high. This makes the transistor Q1 ON and drives the piezo buzzer to make the alarm. In the power supply section, IC 7805 is used to derive 5V from the 9V battery.

Leave Comment

characters left:

New Circuits



Popular Circuits

Ultrasonic / Bat detector
Audio Oscillator schematic
Monostable to bistable relay with momentary switch
Microcomputer-To-Triac Interface Circuit
PIC16F84A based LC Meter circuit with explanation
µP-Controlled Oscillator Delivers Rock-Bottom Distortion
ultrasonic switch sensor
Symmetric Output for USB Audio DAC
IR to RF converter circuit
Two-Channel PC Based Oscilloscope USB
The Nic Nac Tic Tac Crystal Radio Set
DIY ECG Machine On The Cheap