DS1821

DS1821 is an older Dallas/Maxim 1-Wire digital temperature sensor.
- What it is: a temperature-sensor IC with a unique 64-bit ROM code, allowing multiple devices on one 1-Wire bus.
- Output: digital temperature reading over the 1-Wire bus (no external ADC needed).
- How it works: host sends reset, ROM command (SKIP/MATCH ROM), then CONVERT_T to start a measurement; after conversion, read the scratchpad for the temperature (two’s complement; resolution typically 9–12 bits depending on model).
- Power: can be powered from VDD or via parasite power on the DQ line, with a pull-up on the data line.
- Pinout: VDD, GND, DQ (data line).
- Applications: simple, low-pin-count temperature sensing for microcontrollers, data loggers, environmental monitoring.
- Note: part of the DS18x family; DS18B20 is more common for new designs.

DS1821 is a Dallas/Maxim Maxim 1‑Wire temperature sensor. Equivalents are other DS18x0 family devices: DS18S20, DS18B20, DS18B22; older DS1820 is in the same line. All use 1‑Wire and can serve as drop‑ins, with DS18B20 being the most common replacement (resolution varies by model).

DS1821 features (concise):
- Digital thermometer with integrated temperature sensor and alarm
- Temperature range: -55°C to +125°C
- Resolution: selectable 9–12 bits (0.5°C to 0.0625°C steps)
- Accuracy: typically ±1°C to ±2°C over range (varies by grade)
- Power: single-supply operation 2.7–5.5 V
- Interface: compact serial digital output (low-pin-count, easy MCU interface)
- Alarm: programmable high and low temperature thresholds with alarm/status output
- Power/performance: suitable for low-power applications; conversion time depends on resolution
- Packaging: small 8-pin options (DIP-8/SOIC-8) for easy board integration
Ideal for temperature monitoring and alerting in HVAC, automotive, consumer, and industrial apps.

DS1821 pin count: 3 pins (Vcc, GND, DQ/data).
Function: a digital temperature sensor (1‑Wire/1‑Wire-like interface) that measures temperature and outputs a digital temperature value on the data line. It can operate with parasite power and supports programmable resolution and optional alarm features.

- Manufacturer: Dallas Semiconductor (the DS prefix indicates Dallas Semiconductor products).
- What kind of company: A U.S. semiconductor company that designed and manufactured integrated circuits, sensors, and other ICs. Dallas Semiconductor was later acquired by Maxim Integrated (and Maxim is now part of Analog Devices).

DS1821 is a digital temperature sensor. Common application areas include:
- Environmental monitoring and data logging
- HVAC, refrigeration, and thermostat control
- Automotive applications (engine/battery temperature)
- Industrial automation and process control
- Consumer appliances and electronics cooling/temperature sensing
- Medical equipment temperature monitoring (where applicable)
- Over-temperature protection and safety interlocks
It provides accurate, low-power, digital temperature measurement suitable for embedded systems and monitoring tasks.

DS1821 comes in an 8-pin package, typically DIP-8 or SOIC-8 (some revisions also in MSOP-8). Always verify the exact package in the datasheet for your specific part.