LED THERMOMETER
This device is a novel LED electronic thermometer for use in a home as a means of monitoring room temperatures and the operation of your homes heating and/or air conditioning system, greenhouse, attic, or cellar temperatures, or almost any location where a temperature readout is needed. It is a good science or experimenter project demonstrating the operation of bar graph LED displays and the LM34 Temperature sensor. It has a range of 60 to 78 deg F and uses ten LEDs as a readout. The temperature is indicated in 2 deg F steps by the particular LED lit or by the number of LEDs that are lit. This project, while useful, is also a good one to learn about LEDs, bar graph displays and drivers, and temperature sensors and their applications. It also makes an interesting conversation piece if packaged appropriately. The circuit can be calibrated for other temperature ranges and spans as well (i.e. 60-70F, 50-70F, 70-90F, 60-100F, etc) by simply readjusting internal potentiometers
The project uses an LM34 temperature sensor, an LM3914 dot/bar graph driver, and ten LEDs, and a few small parts. This project is low frequency, low voltage DC operated and can run from 7 to 9 volts of battery supply, and only a voltmeter is needed to calibrate the circuit, so it is suitable for beginners. It is built on a small PC board 1.75 X 2.75 inches in size. Current drain is about 33 milliamperes, which is mostly LED current. The driver IC and the sensor circuit require about 10 milliamperes. It is also feasible to operate this project from a small "wall" transformer providing 7 to 10 volts DC. More voltage is unnecessary and is not recommended as it will result in increased dissipation and resultant heat generation. The circuit tolerates supply ripple well and a few volts of this is permissible. In addition, a 9V transistor radio battery or a pack consisting of six AA alkaline cells can be used for power.
 
Price $27.50 USD    Kit
Price does not include shipping and handling (See Order Form)
 
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