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4-pin Module / TO-92 · DHT22
ActiveTemperature + Humidity Sensor
DHT22
Aosong · 4-pin Module / TO-92 · Temperature + Humidity Sensor
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Overview
The DHT22 is Aosong's calibrated digital-output humidity and temperature sensor, sold under the alternative part number AM2302. Inside the epoxy case a capacitive polymer humidity element and a precision NTC thermistor are bonded to the same substrate as an 8-bit microcontroller. That microcontroller applies the factory calibration coefficients burned into OTP memory during production, converts both channels, and drives a single-bus (1-Wire-style but not Maxim 1-Wire) digital output. Because the conditioning, linearisation and checksum are all done on-chip, the host needs one GPIO, a pull-up on the data line (4.7 kΩ to 10 kΩ in practice) and the 100 nF decoupling capacitor the datasheet recommends — nothing else.
Electrical performance is what separates the DHT22 from the cheaper DHT11. Humidity spans the full 0 to 100 percent RH range with ±2 percent RH accuracy (±5 percent RH worst case over the full temperature range), 0.1 percent RH resolution, ±1 percent RH repeatability, ±0.3 percent RH hysteresis and ±0.5 percent RH per year long-term stability. Temperature runs from -40 to +80 °C with ±0.5 °C accuracy, 0.1 °C resolution and ±0.2 °C repeatability. A complete transfer is 40 bits — humidity integer, humidity decimal, temperature integer, temperature decimal and a checksum equal to the low 8 bits of the sum of the first four bytes — and takes about 5 ms. Supply is 3.3 V to 6 V DC, measuring current is 1 mA to 1.5 mA and standby current is 40 µA to 50 µA.
The single most common design error with this family is polling too fast. The datasheet specifies an average sensing period of 2 s and states that the collecting period should be greater than 2 s; reading at 1 Hz yields stale data, checksum failures and eventually a sensor that stops responding until it is power-cycled. Signal quality also matters: the DHT22 datasheet rates transmission distance at 20 m and shows a pull-up resistor on the data line without stating a value, so 4.7 kΩ to 10 kΩ is the normal choice; on a 3.3 V supply keep the run short (around 1 m or less), because line drop starves the internal regulator and biases the reading. Self-heating from repeated conversions adds a few tenths of a degree, so a 2 s cadence is not only a protocol requirement but an accuracy requirement.
Sourcing note: the DHT22 is one of the most remark-friendly parts in the sensor market because the AM2302 die, the DHT11 die and several unbranded copies share the same 4-pin outline (VDD, DATA, NC, GND). A frequent fraud is a DHT11 or an uncalibrated clone inside a DHT22 body — the part answers on the bus, but reports 8-bit integer-only data with the decimal bytes stuck at zero. The quick bench test is to breathe on the sensor and confirm 0.1-unit humidity resolution plus a temperature response inside ±1 °C of a reference. Buy through the Aosong authorized channel, insist on laser-etched marking and a lot code, and screen a sample from every reel. Our Shenzhen stock covers both the bare 4-pin sensor and the module version with pull-up resistor on a small PCB; MOQ is 200 pcs for the bare part or 100 pcs for modules, with 1-3 day dispatch.
Key Features
- 0 to 100 percent RH at ±2 percent RH and -40 to 80 °C at ±0.5 °C
- Calibrated digital single-bus output — no ADC, no external components
- 0.1 °C and 0.1 percent RH resolution with a 40-bit checksummed frame
- 3.3 V to 6 V supply, 40 µA standby, 1 mA to 1.5 mA while measuring
- Interchangeable: calibration coefficients are stored per device in OTP memory
Typical Applications
- HVAC controllers, thermostats and indoor air-quality monitors
- Weather stations, greenhouse and agricultural dataloggers
- Dehumidifiers, humidifiers and home appliance control boards
- Server-room, cold-chain and warehouse environment logging
- Arduino, ESP32 and Raspberry Pi prototyping and teaching kits
Specifications
- Temperature Range
- -40 to 80 °C
- Temperature Accuracy
- ±0.5 °C
- Humidity Range
- 0 to 100 %RH
- Humidity Accuracy
- ±2 (max ±5) %RH
- Resolution
- 0.1 °C / 0.1 %RH (16-bit)
- Interface
- Single-Bus Digital Serial
- Supply Voltage
- 3.3 to 6 V
- Sampling Period (Min)
- 2 s
- Pins
- 4
- RoHS
- Compliant
Procurement Tips
Specify DHT22 (AM2302) with the Aosong part number and a lot code on the purchase order, and screen a sample per reel for 0.1-unit resolution — that single test catches almost every remarked DHT11 before it reaches the production line.
Frequently Asked Questions
Is the DHT22 the same part as the AM2302?
Yes. AM2302 is Aosong's factory part number and DHT22 is the trade name used in the hobby and module market; the datasheet itself states "DHT22 also named as AM2302". Electrically and mechanically they are identical. Note that AM2301, AM2303 and AM2320 are different devices with different interfaces and should not be substituted without a schematic change.
DHT22 versus DHT11 — when is the cheaper part good enough?
The DHT11 covers 0 to 50 °C at ±2 °C and 20 to 90 percent RH at ±5 percent RH with 1-unit (8-bit) resolution, while the DHT22 covers -40 to 80 °C at ±0.5 °C and 0 to 100 percent RH at ±2 percent RH with 0.1-unit resolution. Both use the same single-bus protocol and the same 4-pin outline, so the upgrade is usually a firmware constant change. Use DHT11 for comfort-band indicators and classroom kits; use DHT22 for anything logged, controlled or audited.
How does the DHT22 compare with an I2C sensor such as the SHT31 or BME280?
The DHT22 wins on price and simplicity: one GPIO, no bus address, no driver. It loses on accuracy and speed. A Bosch BME280 specifies ±3 percent RH and ±1 hPa with a 1 s humidity response and can be sampled at tens of hertz, and a Sensirion SHT30/SHT31 offers ±2 percent RH with better long-term drift and a true I2C interface at up to 1 MHz. For a multi-sensor bus, a condensing environment or anything above 0.5 Hz sampling, specify the I2C part instead.
Why do I get intermittent read failures and checksum errors?
Almost always timing or polling rate. The host must hold the bus low for at least 1 ms (18 ms on the DHT11) to start a transfer, then release and wait 20 µs to 40 µs for the 80 µs response. Bits are 50 µs low followed by a high phase of 26 µs to 28 µs for a zero and about 70 µs for a one, so use cycle-accurate code and disable interrupts during the read. Finally, keep at least 2 s between reads — the sensor is still converting internally during that window.
What pull-up, decoupling and cable rules should I follow?
The DHT22 datasheet calls for a 100 nF capacitor between VDD and GND at the sensor and rates the transmission distance at 20 m, but it does not name a pull-up value; 4.7 kΩ to 10 kΩ on DATA is standard practice, and Aosong's companion DHT11 manual recommends about 5 kΩ for runs under 20 m, scaling the value for longer cables. On a 3.3 V supply keep the cable around 1 m or shorter, otherwise the line drop biases the reading. On modules the pull-up is usually already fitted, so do not add a second one below 4.7 kΩ.
How do I detect a counterfeit or remarked DHT22?
Three checks. First, resolution: a genuine DHT22 returns non-zero decimal bytes for both humidity and temperature, while a remarked DHT11 returns integer-only data with the decimal bytes at zero. Second, accuracy: breathe on the sensor and verify a fast, monotonic humidity rise and a temperature shift consistent with a reference meter, and confirm the part still responds at 0 °C and above 50 °C where a DHT11 die saturates or fails. Third, physical: laser-etched marking that resists a fingernail, uniform matte-tin leads, correct mass and a legible lot code traceable to Aosong. We sample-test every reel against a calibrated reference chamber.
What is the MOQ and lead time from your Shenzhen warehouse?
MOQ is 200 pcs for the bare 4-pin DHT22/AM2302 sensor, 100 pcs for the PCB module version, or 1,000 pcs on bagged production lots for OEM pricing. Local stock ships in 1-3 business days; replenishment through the Aosong channel typically takes 2-4 weeks. Ask for the reel or bag photo, lot code and certificate of conformance before dispatch.
Can I use the DHT22 outdoors or in a condensing environment?
Only with protection. The polymer capacitor tolerates the full 0 to 100 percent RH range, but liquid water on the element causes drift and long recovery. Mount it behind a PTFE membrane or in a ventilated radiation shield, keep it away from direct sun and self-heating components, and allow 10 min to 30 min of recovery after condensation. For permanently wet or IP67 duty, use a probe-style capacitive transmitter instead.
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