This small thermometer board can be connected directly to PORTD of the AVR 2313 Project board. It uses the Dallas DS1621 Digital Thermometer and Thermostat chip. The DS1621 measures temperatures from -55° to +125° in 0.5° steps and doesn't need calibration or external components. It has also a build-in thermostat with high and low set-points which can be programmed by the user.

Below you see the pin description of the DS1621.
LCD Thermometer DS1621_pinout.jpg.

The data from the DS1621 is read via the 2 wire serial interface. The DS1621 can be linked together in a daisy chain in which each DS1621 has its own adress. Up to eight DS1621 chips can be linked together. The build in thermostat has high and low temperature settings which can be read from and write to the DS1621. The temperature is displayed on an 16*2 LCD module which is connected to PORTB of the AVR 2313 Project board.

Circuit Schematic and PCB Layout

The circuit consists of the DS1621 chip, two pull-up resistors of 10k, a ML10 flat cable connector and three 3 pole jumpers. The pull-up resistors are needed to connect the open collectors of the SDA and SCL lines of the DS1621 chip to VCC. With the jumpers the adress of the DS1621 can be selected. The DS1621 works as a slave in the 2-wire serial bus. To read the data from the DS1621 the AVR 90S2313 or the AVR tiny2313 microcontrollers can be used.

The circuit can be build on a breadboard, or you can use the ATTiny2313 board.

You can buy the ATTiny2313 board at

LCD Thermometer DS1621_sch.jpgLCD Thermometer DS1621_brd.jpg