The HN18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points. The HN18B20 communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a central microprocessor. It has an operating temperature range of -55°C to +125°C and is accurate to ±0.5°C over the range of -10°C to +85°C. In addition, the HN18B20 can derive power directly from the data line (“parasite power”), eliminating the need for an external power supply.
Each HN18B20 has a unique 64-bit serial code, which allows multiple HN18B20s to function on the same 1-Wire bus. Thus, it is simple to use one microprocessor to control many HN18B20s distributed over a large area. Applications that can benefit from this feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment, or machinery, and process monitoring and control systems.