SPICE simulation of a DS1621 digital Thermometer and Thermostat interfaced with a microcontroller PIC16F877 measures the temperature from -55 C to +125C in 0.5°C increments and shows the result on a LCD display. Setting a TH, high temperature and a TL, low temperature, the output of thermostat becomes active when the temperature measured exceeds TH, and stay active until the measured temperature falls below TL.The power supply ranges from 2.7V to 5.5V.
This project uses the i2c bus, with a master and a slave device. The master is the device that drives the clock, in this case the microcontroller PIC16F877, the DS1621 is the slave device and respond to the master. the DS1621 has a 2-Wire Serial Data Input/Output called SDA and 2-Wire Serial Clock, SCL.When the master want communicate with the slave begins a start sequence on the i2c bus, sending on SDA the address of slave with write or read operation code, and a series of commands, and ends with the stop sequence.The temperature is written/read from DS1621 as two bytes, the second byte contain the value of the least significant bit of the temperature (0.5 C). TH and TL can be set with or without the 0.5 C.The output of thermostat is set active high, and the 1SHOT bit of configuration register is set low, so the DS1621 will continuosly perform temperature conversions.