Digital thermometer with LED / LCD display

Posted on Feb 7, 2014

Now we bring you two versions of a homemade digital thermometer with ICL7106 that I recently built. One version uses a LED display, the second version LCD display. In both versions, is used silicon transistor as a temperature sensor. The temperature is determined by the voltage drop, temperature dependence is approximately -2. 2 mV / °C. Power can

Digital thermometer with LED / LCD display
Click here to download the full size of the above Circuit.

be either a 9V battery or a suitable power supply. Oscillator with R1 and C1 determines the sampling frequency - using 100k and 100p the frequency is 3 Hz. Theoretical temperature range is from -199. 9 to 199. 9 °C, the real temperature range is limited by the measuring transistor to approximately -65. 0 To 150. 0 °C. Resolution to 0. 1 °C. If you want to use it as a room thermometer, it is not necessary to use the hundreds digit, (left) or minus sign. Also digit right from the decimal point may be omitted if 1 °C resolution is sufficient. A simple room thermometer thus requires only two-digit display, as on photo below. LED version is usually constructed with the circuit ICL7107, which has a higher output current, but this circuit requires symmetrical stabilized power supply. Advantage of 7106 is a simple power supply without stabilization. The problem is solved by a low curren (1 mA) superbright display. 7106 is also easier to salvage from something (like digital multimetr) than 7107. I will not discuss the 7107 here. Info on both those integrated circuits can be found in their datasheet. Here, the circuit 7106 is connected in the usual way. LCD is driven by AC 60Hz signal. At all outputs for display and the common electrode terminal have a rectangle 60Hz waveform. Outputs for the segments that are not to be displayed, have a voltage in phase with a common electrode. Outputs for segments that are displayed, are out of...

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