Thermometer How a digital thermometer works: There are three components of a digital thermometer 1. TVT that is a temperature to voltage transducer, which includes a sensor and for that purpose we have used a LM35 2. The LM35 works in mV so a little processing is required that is done by ICL7107. 3. After that we convert this analogue into digital number for that we have used a Analog to digital converter that is also ICL7107 Now to understand how these things work together we have to understand each one of them individually. LM35: The LM35 series are precision integrated-circuit temperature sensors whose output is linearly proportional to the celcius temperature. They use the fact as temperature increases, the votage across a diode increases at a known rate. Since its caliberated with celcius it is better than the sensors caliberated in kelvin so that we dont have to convert the kelvin reading into centigrade. It is very accurate the error or nonlinearity is only 14C (0.25) . Which isnt much compared to other transducer. The range is from -55 to 150 degree celcius but the range for ICL7107 is 0 to 70 degree celcius. We have to use it for medical purpose so that won't be problem. The linear scale factor is actually 10mV/C. with a minimum error so is pretty much accurate It operates on 4 V to 30 V. so we have to use a transformer as well. That is all about the LM35 after it detects the temperature converts it into volts we need to convert this into celsius for that a little processing is required so we either use a microprocessor since it is 10mV/C degree the formula to convert the output into celcius would be Temp in C = (Voltage output in mV) / 10 What is ICL7107? An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a device which converts continuous signals to discrete digital numbers. It processes out input as well such as the digital output will be a binary number that is proportional to the input. And in our case it is working as the equation given above. It works in this way:

It can drive a 3 digit LED display and the temperature range is from 0 to 70C more than that or less than that could destroy the circuit. Its a microprocessor and is easily available. It works on 5V power supply.