DHT21/AM2301A Digital Capacitive Temperature & Humidity Sensor – SHT10/SHT11 Replacement

Description

The DHT21/AM2301A is a capacitive digital temperature and humidity sensor designed for cost-sensitive environmental monitoring in greenhouses, storage rooms, HVAC systems, and DIY electronics projects. It combines a polymer 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, with calibration coefficients stored in OTP memory and applied internally. It requires no external ADC or signal conditioning—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, releases it, and the sensor responds with a handshake followed by 40 bits of data (16-bit humidity, 16-bit temperature, 8-bit checksum) .

The AM2301A designation suggests an optimized variant with potentially better temperature accuracy (±0.3°C per some sources) compared to the standard AM2301 (±0.5°C) . However, supplier documentation is inconsistent on this point. The sensor is widely used as a cost-effective alternative to the SHT10/SHT11 for applications where ±3% RH and ±0.5°C accuracy are sufficient—such as greenhouse monitoring, storage cabinets, and simple weather stations .

Critical limitations: The AM2301A’s timing may differ from the standard AM2301 (388µs vs. 80µs response-low time per one measurement) . Standard DHT libraries may require adjustment or may work without modification—test before publishing. The sensor is not waterproof and is not a precision instrument; its long-term stability and factory calibration are below the Sensirion SHT1x series .

Features

• Capacitive Humidity Sensing: Polymer capacitive element with calibrated digital output; no external ADC required .

• Single-Bus Digital Interface: 40-bit data packet over one wire; compatible with standard DHT libraries (verify AM2301A timing) .

• Wide Supply Voltage (3.3–5.5V): Works directly with both 3.3V and 5V microcontrollers .

• Factory Calibrated: Calibration coefficients stored in OTP memory; fully interchangeable between units .

• Low Power Consumption: ~500µA measuring current, 15µA dormancy, suitable for battery-powered applications .

• Long Signal Transmission: Reliable communication up to 20 meters with appropriate cable and pull-up resistor .

• Wide Measurement Range: -40°C to +80°C and 0–100% RH .

• 4-Pin Single-Row Package: Standard 0.1″ pitch header for breadboard and PCB mounting .

Technical Specifications