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Topic: Adding thermometer feature to a regular digital multimeter (Read 1142 times) previous topic - next topic

Adding thermometer feature to a regular digital multimeter

Hi guys,
I recently added the thermometer feature to my digital multimeter using an analog temperature sensor (TMP35) and a couple of resistors. The technique is very simple. The TMP35 provides a linear output voltage proportional to the Centigrade temperature. The scale factor is 10mV per degree C. The sensor output is divided by 10 using a resistor divider network and is fed to the input terminals of the multimeter which is set to measure voltage between 0-200 mV. The meter displays temperature in degree Celsius.
Although this sounds pretty straight forward, there are some issues that should be taken care of to make this technique work. For instance the reference voltage of the multimeter's A/D converter and the sensor's ground terminal are at different potential when you power both of these with the same battery. You will find details on this here.