This small thermometer board uses the Microchip TCN75 device. It is a cheaper clone of the LM75, it costs about 2,50 Euro. The TCN75 comes in a SO8 packaging. The TCN75 is a serially programmable temperature sensor.

It has an output that is programmable as either a simple comparator for thermostat operation or as a temperature event interrupt. Hysteresis is also programmable. Communication with the TCN75 goes via the serial I2C two-wire bus. The serial bus permits reading the current temperature, programming the set point and hysteresis, and configuring the device. Address selection inputs allow up to eight TCN75's to share the same 2-wire bus. The output's polarity is user programmable.

Features of the TCN75 sensor

  • Solid State Temperature Sensing; 0.5C Accuracy (Typ.)
  • Operates from – 55C to +125C
  • Operating Range ................................. 2.7V - 5.5V
  • Programmable Trip Point and Hysteresis
  • Standard 2-Wire Serial Interface
  • Thermal Event Alarm Output Functions as Interrupt or Comparator / Thermostat Output
  • Up to 8 TCN75's May Share the Same Bus
  • Shutdown Mode for Low Standby Power Consumption
  • 5V Tolerant I/O at VDD = 3V
  • Low Power..... 250µA (Typ.) Operating 1µA (Typ.) Shutdown Mode

Circuit Schematic and PCB Layout

The hardware consists of the TCN75 and two resistors that are placed on a small PCB. The board is connected to the PORT B of the ATTiny2313 microcontroller. The registers of the TCN75 are read by the microcontroller and the temperature is shown on a LCD display which is connected to PORT D.

<p">You can connect the small board to the ATTiny2313 board.

The Attiny2313 board is available at