Digital Electronic Thermometer Circuit Diagram

Build a Electronic Thermometer Circuit Diagram. A thermometer thermos, meaning "hot" and  metron, "measure") is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor in which some physical change occurs with temperature, plus some means of converting this physical change into a numerical value. 

An inexpensive electronic thermometer is capable of measuring temperatures over a range of from -30°F to +120°F. A diode-connected 2N3904 transistor used as the temperature sensor forms a voltage divider with Rl. As temperature increases, the voltage drop across the transistor changes by approximately -1.166 millivolts-per°F. As a result, the current at pin 3 of IC1, a 741 op amp with a gain of 5, decreases as the temperature measured by the sensor increases. A second 741 op amp, IC2 is configured as an inverting amplifier.

 Electronic Thermometer Circuit Diagram



Electronic Thermometer Circuit Diagram

 Resistors R5 and R6 calibrate the circuit. Calibration is also straightforward. When properly done, a temperature of - 30°F will result in a meter reading of 0 milliamps, while a temperature of 120°F will result in a meter reading of 1 milliamp. Divide the scale between those points into equal segments and mark the divisions with the appropriate corresponding temperatures. The calibration is completed by placing the sensor in an environment with a known temperature, such as an ice-point bath. Place the sensor in the bath and adjust R6 until you get the correct meter reading.

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