lm35 for precision centigrade

Posted on Feb 6, 2014

The LM35 series that is used in this project is a precision centigrade temperature sensor, which has an analog output voltage. It has a range of -55 C to +150 C and an accuracy of ±0. 5 C. The output voltage is 10mV/ C. The output voltage is converted by the AD convertor of the AT Mega8. The temperature is displayed on an LCD module. In this e

lm35 for precision centigrade
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xample the thermometer has a range of 0 C to 40 C and a resolution of 0. 5 C. If you want to have a read out in Fahrenheit you can use the LM34. The BASCOM AVR compiler has build in commands for reading out the ADC port of an AVR microcontroller. The result is displayed on a LCD module in a discrete value of the temperature and in a bar-graph. The AT Mega8 has a A/D converter which can give an output of 210 = 1024 discrete values. When a 5V supply is used you have a resolution of 5000mV/1024 = 4. 8mV. Because the LM35 has an output of 10mV/C the resolution of the thermometer is 10mV/4. 8mV ~ 0. 5 C. The LCD module has 20 columns. In the scale of 0 C to 40 C every column represents 2 C. The LM35 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued or cemented to a surface and its temperature will be within about 0. 01 °C of the surface temperature. This presumes that the ambient air temperature is almost the same as the surface temperature; if the air temperature were much higher or lower than the surface temperature, the actual temperature of the LM35 die would be at an intermediate temperature between the surface temperature and the air temperature. This is especially true for the TO-92 plastic package, where the copper leads are the principal thermal path to carry heat into the device, so its temperature might be closer to the air temperature than to the surface...

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