DS1821 Programmable Digital Thermometer and Thermostat TO-92 (DS1821 IC)
The DS1821 is a specialized 1-Wire digital thermometer and programmable thermostat housed in a compact 3-pin TO-92 package. While it shares the same physical form as the more common DS18B20, the DS1821 is distinct in its ability to function as a standalone thermostat. It features internal nonvolatile memory (EEPROM) that stores high (TH) and low (TL) temperature trip points. Once programmed via the 1-Wire interface, the IC can be deployed without a microcontroller; in this "thermostat mode," the data pin (DQ) automatically acts as an output that toggles based on the sensed temperature.
This IC is an ideal solution for cooling fan control, heating systems, and industrial temperature monitoring where a simple hardware-level response is required. In the Indian electronics market, it is frequently used in power supply thermal protection circuits and DIY home automation projects that need a reliable, set-and-forget thermal switch in a standard through-hole transistor-style package.
Key Features
- Dual Operating Modes: Functions as either a 1-Wire digital thermometer or a standalone thermostat.
- Standalone Operation: Does not require a microcontroller to maintain thermostat functions after initial programming.
- Nonvolatile Trip Points: Temperature thresholds are saved in EEPROM and retained during power-off.
- 8-Bit Digital Output: Provides temperature readings in 1 degree Celsius increments.
- 1-Wire Interface: Requires only one data pin and ground for communication.
- Selectable Polarities: Thermostat output can be configured as active-high or active-low.
- No External Parts: Self-contained sensor requires no additional components to measure temperature.
Specifications
- IC Type: Digital Thermometer and Thermostat
- Temperature Range: -55 to +125 degrees Celsius
- Accuracy: +/- 1.0 degree Celsius (from 0 to +85 degrees Celsius)
- Resolution: 8-bit (1 degree Celsius steps)
- Supply Voltage (VDD): 2.7V to 5.5V
- Active Current: 1mA (Max)
- Conversion Time: 1 second (Max)
- Package Type: TO-92
- Mounting Type: Through-Hole
- Operating Temperature: -55 to +125 degrees Celsius
Interfaces (Facing Flat Side, Leads Down)
- Pin 1 (GND): Ground
- Pin 2 (DQ): Data Input/Output (1-Wire mode) or Thermostat Output (Thermostat mode)
- Pin 3 (VDD): Positive Supply Voltage (+5V typical)
