Celcius to Frequency Converter Circuit Diagrams

Celcius to Frequency Converter Circuit Diagrams

Celcius to Frequency Converter

In some cases of temperature measurements, it is more advantageous to convert the measured value into a frequency than into a voltage.

A temperature to frequency converter can be directly connected to a frequency counter or it can be connected to a computer without using any A/D interface to display the measured value.

The conversion factor of the circuit featured here is 10 Hz per degree centigrade. The measurable range is from 5 to 100C with a maximum error of (plus/minus) 0.3C.

A single IC LM335 is used as the temperature sensor. When the temperature sensed by LM335 is zero, its output is exactly 2.73 volts. The output signal comes out in the form of a squarewave.

Calibration: Put crushed ice in a glass of water and place the temperature sensor in it. Let the sensor cool down for a few minutes.

Using a voltmeter, measure the voltage level between the positive (+) pin of the temperature sensor (LM335) and pin 2 of the LM331.

Afterwards, adjust P1 to output a voltage level of 2.73V. After this initial calibration, heat a glass of water to 50C (use a normal thermometer to measure the temperature).

Connect the display device (e.g. frequency counter) to the circuit's output. Place the sensor into the warm water, and adjust P2 to generate the desired frequency representing this temperature.

For example: Adjust P2 so that the frequency is 50 Hz representing the temperature of 50C.

You must choose the output frequency so that you can easily adapt it to your display instrument (like frequency counter or computer).