Posted on Feb 6, 2014

With the easy availability of inexpensive digital multimeters, and integrated circuit temperature sensors, it is now very easy to build a sensitive and accurate digital thermometer that can be used for many experiments around the house or in the amateur laboratory. There are two tenperature sensors that make this particulary easy - the LM34 and t

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he LM35. These are callibrated in Fahrenheit and Celsius respectively, and when read by the meter, they produce ten millivolts per degree in their respective scales, so the meter can be directly read in temperatures, down to a tenth of a degree. Above, we have placed an LM35 sensor on top of an ice cube, and the pool of water melted from the ice is reading 8. 9 degrees Celsius. For this experiment we have simply connected alligator clips to two of the leads of the sensor, and wrapped the third lead with the red wire from the battery clip. No soldering, nothing fancy, and we have a digital thermometer in the time it takes to unwrap the meter and clip on the test leads. For a more permanent thermometer, we solder three long wires (about 5 feet is nice) to the three leads of an LM34 Fahrenheit sensor. Use three different colors, and note which ones are attached to which leads. We put a little electrical tape around the middle lead so it won`t touch the other two, and then wrap the whole thing in electrical tape, or in this case, put it into a short length of heat shrinkable tubing, and warm it up so the tubing shrinks tightly around the whole assembly. We made the wires long so that we can measure things inside boxes or behind doors. Five feet makes it easy to place the sensor end in the refrigerator or freezer, and have the meter stay outside where it is easy to measure. This arrangement is great for incubators for eggs, and...

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