To complete the procedure you will need two accurately known temperature sources (hot and cold) and an accurate mercury-in-glass thermometer. The procedure is a bit critical and requires special attention. M1 = 0 – 1 V, FSD moving coil type voltmeter.The relevant readings are directly translated into degree Celsius through a 0-1V FSD moving coil type meter. The sensed temperature variation is instantly amplified into a corresponding voltage level by the IC and is received at its output pin #6. These voltage variations as explained, is directly proportional to the changes in the ambient temperature. The inverting input of the IC is connected to the sensor and monitors even the slightest change in the voltage variation across the sensor diode D1. Transistor T1 and T2 are used as a constant current source and helps in maintaining higher accuracy of the circuit. Its non inverting pin # 3 is held at a particular fixed reference voltage with the help of Z1, R4, P1 and R6. Referring to the proposed room temperature monitor with indicator circuit diagram given below, we see that, IC1 is wired as an inverting amplifier and forms the heart of the circuit. This particular feature of 1N4148 is extensively exploited in many low range temperature sensor circuits. This voltage drop is around 2mV for every degree rise in temperature. The diode 1N4148 is comfortably able to produce a linear and an exponential voltage drop across itself in response to a corresponding increase in the ambient temperature. Here as usual we use the very versatile “garden diode” 1N4148 as the sensor due to its typical drawback (or rather an advantage for the present case) of changing its conduction characteristic in the influence of a varying ambient temperature. Let’s briefly study its circuit functioning: The present circuit of an electronic air temperature sensor gauge circuit is outstandingly accurate and can be very effectively used to monitor the atmospheric temperature variations. The electronic air temperature sensor gauge circuit presented here is very accurate in its function, categorically due to its minimum level of hysteresis.Ĭomplete circuit description and construction clues included herein. The unique drawback of a semiconductor diode such as a 1N4148 which shows forward voltage characteristic change with the influence of ambient temperature change has been effectively exploited here, and this device is used as a efficient, cheap temperature sensor. Using the Garden Diode 1N4148 as the Temperature Sensorĭiode 1N4148 (D1) is used as an active ambient temperature sensor here. The use of the highly versatile and accurate IC LM 308 makes the circuit respond and react superbly to the smallest temperature changes happening over its surrounding atmosphere. The second electronic thermometer design below is another very simple yet highly precise air temperature sensor gauge circuit has been presented here. Once you remove the sensor from the ice, within seconds it will start displaying the present room temperature over the meter directly in Celsius. The setting up procedure of this electronic thermometer is done.Now carefully start adjusting the preset, such that the meter reads a zero volts.Take a bowl of melting ice and immerse the IC inside the ice.Setting up the unitĪfter you have assembled the circuit and finished doing the shown connections, you may proceed with the setting of the thermometer as explained below: The circuit diagram shown below explains it all, no need of any complicated circuitry, just connect a 0-1 V FSD moving coil meter across the relevant pins of the IC, set the pot appropriately, and you are ready with your room temperature sensor circuit. The IC LM35 will show you a 10mv rise in its output volts in response to every degree rise in the temperature of the atmosphere surrounding it. It just requires a single IC to be connected with a suitable moving coil type of meter, and you start getting the readings almost immediately. 1) Electronic Thermometer using a Single IC LM35 This feature in particular makes the construction of the proposed room temperature thermometer circuit very simple. In the previous post we learned some of the features of the outstanding temperature sensor chip LM35, which gives outputs in varying voltages that's directly equivalent to ambient temperature changes, in Celsius.
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