Digital Thermometer with Memory


This digital thermometer remembers the 12-hours high and low temperatures. This design uses a PIC microcontroller with a built in A/D converter. All the parts are tolerant to temperatures from -40 to 100 degrees Fahrenheit, so you can keep the device outside. The LM34 temperature sensor used outputs a voltage proportional to temperature by 10 mV per degree Fahrenheit. The device then uses the A/D converter with it's LSB set to 10mV to read the temperature. Temperatures are stored in memory every 15 minutes with 48 memory locations dedicated for this, hence the device remembers only the past 12 hours worth of temperatures.
PC Board, both sides.PC Board, both sides.

Operating at 72 degreesOperating at 72 degrees

Thermometer put together.Thermometer put together.

Putting it all Together:
Circuit SchematicCircuit Schematic

Parts List:

  • LM34 temperature sensor
  • PIC16F872 or another 28-pin PIC
  • PIC Proto3 board from Jameco made by MicroEngineering Labs

Everything is pretty much self explanatory, except perhaps the pre-fab display units. They are simply a 7 segment decoder with a 4 bit D flip flop register to hold the data so you only need to refresh the display when you want to change the number. The decoder is a 74LS47 and the flip flop is a 74LS75. If you wanna use a 10mV per degree Celsius sensor, see here for some ideas.

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