Digital Thermostat with LED Temperature Display

Temperature range

Display of temperature between -55 and +124 deg C (-67 to 255 deg F)with 0.1 degree resolution between -10 and 100 degrees.

Thermostat settings between 1 and 100 deg C (34 to 212 deg F.)

Features

  • Simple,cheap,compact design, few components, no surface-mount types.
  • Uses an accurate digital sensor to avoid the need for calibration.
  • Low power consumption
  • Uses a modern Microchip PIC 18F1320 microcontroller
  • Temperature sensor is accurate to +/- 0.5 degree Centigrade with 0.1 degree C or F display resolution over most of the range.
  • Thermostat is easily adjusted in +/- 1 degree Centigrade or Fahrenheit intervals (all settings saved in memory)
  • Adjustable thermostat cycle delay to help reduce wear on heater/cooler
  • Adjustable thermostat temperature hysteresis to reduce heater/cooler wear.
  • Facility to automatically turn-off the heater/cooler while a door is left open (For Energy saving)
  • Under/Over temperature alarm LED indication
  • Selectable Celsius or Fahrenheit temperature display
  • Minimum and Maximum temperatures are logged for display.

Firmware info

The firmware for this project is written in assembler language.
The microcontroller currently determines if a DS18S20 or DS18B20 sensor is being used.
(It should also work with the old original DS1820 sensors (but with only 0.5 deg display resolution), although I do not have one to test it with.
Each temperature reading is CRC validated. I have experienced no errors with the readings, but decided the CRC checking was worth implementing as a safeguard.

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Source: unusualelectronics

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