AHT25 temperature and humidity sensor: specs and pinout
A calibrated digital temperature and humidity sensor from Aosong (ASAIR) with an I2C interface. The sensor ships on a small 4-pin carrier board.
Specs
| Spec | Value | Source |
|---|---|---|
| Supply voltage VDD | 2.2 V min, 3.3 V typ, 5.5 V max | source Table 2 Electrical specifications (p.2) |
| Supply current (VDD 3.3 V) | 250 nA typ in sleep; 980 uA typ while measuring | source Table 2 (p.2); footnote 5 gives VDD 3.3 V, T below 60 C |
| Interface and I2C address | I2C, 7-bit device address 0x38 | source Section 5.3 Sending a command (p.10) |
| Humidity resolution and accuracy | 0.024 %RH typical resolution; +/-2 %RH typical accuracy at 25 C (maximum: see Figure 2) | source Table 1 Humidity (p.2) |
| Humidity operating range | 0 to 80 %RH normal; 0 to 100 %RH extended | source Table 1 and footnote 3 (p.2) |
| Temperature resolution and accuracy | 0.01 C typical resolution; +/-0.3 C typical accuracy (maximum: see Figure 3) | source Table 3 Temperature (p.3) |
| Temperature operating range | -40 C to 80 C (extended) | source Table 3 (p.3) |
| Response time (63 percent) | Humidity under 8 s; temperature 5 to 30 s | source Table 1 (p.2); Table 3 (p.3) |
| Measurement sequence timing | Wait at least 100 ms after power-up; send 0xAC with parameters 0x33 0x00; wait 80 ms; read 6 data bytes plus CRC | source Section 5.4 Sensor reading process (p.10) |
Power
| Value | Source | |
|---|---|---|
| Supply | 2.2-5.5 V (3.3 V typical) | source Table 2 Electrical specifications (p.2) |
| Current | 250 nA sleep; 980 uA measuring (VDD 3.3 V) | source Table 2 Electrical specifications (p.2) |
Pinout
Pin order is from the Aosong AHT25 sheet (top view, 4-pin carrier). Confirm the pin order printed on the unit in hand before wiring.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 VDD | Power supply | 2.2-5.5 V | source Table 4 pin assignment (p.7) | |
| 2 SDA | Serial data, bidirectional | -0.3 V to VDD + 0.3 V (absolute maximum) | Needs a pull-up resistor. | source Table 4 (p.7); Table 5 absolute maximum (p.8) |
| 3 GND | Ground | 0 V | source Table 4 (p.7) | |
| 4 SCL | Serial clock, bidirectional | -0.3 V to VDD + 0.3 V (absolute maximum) | Needs a pull-up resistor. | source Table 4 (p.7); Table 5 (p.8) |
Build with it
Project ideas for the AHT25 temperature and humidity sensor. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Room temperature and humidity display: The AHT25 and the ESP32 both work at 3.3 V (sensor 2.2-5.5 V) and both use I2C, so the sensor and the OLED can share the two bus wires with pull-ups on SDA and SCL.
- Desk weather station on a Pico: The Pico runs at 3.3 V logic, inside the sensor's 2.2-5.5 V supply range; trigger a measurement with command 0xAC and show the values on the OLED.
- Compare two humidity sensors: A learning project: show both readings on one screen to see how two sensors differ. The AHT25 uses I2C and the DHT22 uses one data pin, so they do not share a bus.
Common mistakes
- Leaving out the pull-up resistors: SDA and SCL need an external pull-up to the supply (the sheet's example is 4.7 kohm) (source: link, Section 3.3 p.7)
- Reading too early: wait at least 100 ms after power-up and 80 ms after the 0xAC trigger before reading, and check status bit 7 (busy) is 0 (source: link, Section 5.4 p.10)
- Running the host at a different supply voltage than the sensor: the sheet says the MCU supply in the circuit must match the sensor supply (source: link, Section 3 notes p.7)
Not covered by the official source
- Sheet is the Chinese-language Aosong specification V1.0 (May 2021); values were read from the page images.
- Maximum (not typical) accuracy is given only as graphs (Figures 2 and 3); no table values were taken from them.
- Pull-up value 4.7 kohm is the sheet's example, not a requirement.
- The product page's 'I2C digital output' wording was not used as a source.
Sources
- link (Aosong AHT25 product specification V1.0, May 2021, Chinese-language; copy hosted by LCSC)