Description
The DHT21/AM2301 is a capacitive digital temperature and humidity sensor designed for cost-sensitive environmental monitoring in greenhouses, HVAC systems, data loggers, and DIY electronics projects. It combines a capacitive humidity sensing element and an NTC thermistor with an integrated 8-bit microcontroller, providing a fully calibrated digital output over a single-wire interface .
The sensor is factory-calibrated in a precision humidity chamber, with calibration coefficients stored in OTP memory and applied internally during measurement . It requires no external components—just a pull-up resistor on the data line and a connection to any digital GPIO. The single-bus protocol uses a proprietary timing scheme: the host pulls the data line low for at least 500µs (800µs recommended by some sources), then releases it; the sensor responds with a handshake and transmits 40 bits of data (16-bit humidity, 16-bit temperature, 8-bit checksum) .
The DHT21 is pin-compatible with the DHT22/AM2302 in terms of wiring and protocol, but offers lower accuracy at a lower price point. It is often marketed as a replacement for the SHT10/SHT11, but this refers to application suitability—the DHT21 is cheaper and easier to use, with a simpler protocol and wider supply voltage range, though its accuracy and long-term stability are inferior to the Sensirion parts .
Features
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Capacitive Humidity Sensing: Polymer capacitive element with calibrated digital output; no external ADC required .
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Single-Bus Digital Interface: 40-bit data packet over one wire; compatible with standard DHT libraries for Arduino and other platforms .
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Wide Supply Voltage (3.3–5.5V): Works directly with both 3.3V and 5V microcontrollers .
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Factory Calibrated: Calibration coefficients stored in OTP memory; fully interchangeable between units .
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Low Power Consumption: 1–1.5mA measuring current, suitable for battery-powered applications .
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Long Signal Transmission: Reliable communication up to 20 meters with appropriate cable and pull-up resistor .
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Wide Measurement Range: -40°C to +80°C and 0–100% RH .
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4-Pin Single-Row Package: Standard 0.1″ pitch header for breadboard and PCB mounting .
Technical Specifications
| Parameter | Specification |
|---|---|
| Model | DHT21 / AM2301 |
| Humidity Range | 0–100% RH |
| Humidity Accuracy | ±3% RH (typical); ±5% RH (max) |
| Temperature Range | -40°C to +80°C |
| Temperature Accuracy | ±0.5°C (typical) |
| Resolution | 0.1°C / 0.1% RH (16-bit) |
| Supply Voltage | 3.3V – 5.5V DC |
| Measuring Current | 1–1.5mA |
| Sampling Period | ≥ 2 seconds |
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