DS1821 Programmable Digital Thermostat and Thermometer IC

The DS1821 designed as an 8-bit temperature sensor with a 1-Wire digital interface that can be used as a standalone thermostat with user-programmable trip-points. The thermostat trip-points are stored in nonvolatile memory, hence DS1821 devices must be programmed before being installed in a system. The DS1821 operates in the range of –55°C to +125°C and is accurate to 1°C throughout a temperature range of 0°C to +85°C. The DQ pin, which is open-drain, is used to communicate with the DS1821. The thermostat output is likewise connected to this pin. This temperature sensor is commonly used to monitor temperature in harsh environments such as chemical solutions, mines, and soil, among others. The sensor’s constrictions are robust, and it may also be ordered with a water-proof variant, making the installation process simple.

The open-drain DQ pin serves as an rmostat output for thermostat operation as well as a data I/O pin for 1-Wire connection. The nonvolatile (EEPROM) thermostat trip-point registers (TH and TL), the status/configuration register, and hence the temperature register are all accessible via the 1-Wire interface. The DS1821 has two modes of operation: 1-Wire and Thermostat. The user-programmable T/R bit within the status/configuration register determines the power-up operation mode. T/R = 0 starts the device in 1-Wire mode. If T/R = 1, the gadget will turn on in thermostat mode. The T/R bit is kept in nonvolatile memory (EEPROM), which means it keeps its value even after the device is turned off.

When used as a stand-alone thermostat, temperature conversions begin as soon as the device is turned on. When the temperature of the DS1821 exceeds the limit put into the TH register, the DQ pin becomes active. And it stays active till the temperature falls below the TL register’s temperature limit.