#817 DHT21 Sensor Library Test

Logging temperature and humidity with an Aosong AM2301 DHT21-compatible sensor. Uses the Adafruit Arduino DHT Sensor Library directly.

Build

Notes

This is a test of the DHT21 with the Adafruit DHT Sensor Library directly (without the unified sensor framework).

About the Aosong AM2301 DHT21 sensor

The AM2301 is a DHT21-compatible temperature and humidity sensor. Key specifications:

temperature: -40-80°C ±0.3°C, 0.1°C resolution
relative humidity: 0-99% ±3%, 0.1% resolution
supply voltage range 3.3V - 5.2V, recommended supply voltage is 5V

module

Circuit Design

Designed with Fritzing: see Tester.fzz.

schematic

bb_build

Demonstration Script

The DHT11 uses a single-wire two-way communications protocol.

The Tester.ino sketch simply outputs current readings to the console.

Requires the following Arduino libraries:

DHT Sensor Library

It is based on the DHTtester.ino example.

#include "DHT.h"

const int DHT_PIN = 2;
const int DHT_TYPE = AM2301;
const int DELAY = 2000;

DHT dht(DHT_PIN, DHT_TYPE);


/*
 * Command: one-time setup
 */
void setup() {
  Serial.begin(115200);
  Serial.println("AM2301 test!");

  dht.begin();
}


/*
 * Command: main loop
 */
void loop() {
  delay(DELAY);

  float humidity = dht.readHumidity();
  float temp_c = dht.readTemperature();
  float temp_f = dht.readTemperature(true);

  if (isnan(humidity) || isnan(temp_c) || isnan(temp_f)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  float heat_index_c = dht.computeHeatIndex(temp_c, humidity, false);
  float heat_index_f = dht.computeHeatIndex(temp_f, humidity);

  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.print("%\t");
  Serial.print("Temperature: ");
  Serial.print(temp_c);
  Serial.print("˚C ");
  Serial.print(temp_f);
  Serial.print("˚F\t");
  Serial.print("Heat index: ");
  Serial.print(heat_index_c);
  Serial.print("˚C ");
  Serial.print(heat_index_f);
  Serial.println("˚F");
}

Test Results

Sample console output:

console-output

NOTE: I seem to have an issue with the humidity sensor on my device. It is consistently returning a 5.0% reading no matter what the actual humidity is. My current conclusion is that I have a faulty device. I’ll re-run this test when I can get my hands on a replacement sensor.

Credits and References

“AM2301 DHT21 Capacitance Digital Temperature & Humidity Sensor Replace SHT11 SHT15 free shipping 68” (aliexpress seller listing)
- Originally purchased for US $2.89 (Mar-2016). Currently no longer available from this seller.
“DHT11 DHT22 AM2302B AM2301 AM2320 Digital Temperature and Humidity Sensor AM2302 Temperature and Humidity Sensor For Arduino” (aliexpress seller listing)
- Currently lists the AM2301 for SG$3.50 (Jan-2026)
AM2301 datasheet (haoyuelectronics)
ASAIR AM2301 Temperature and Humidity Sensor Modules (aosong)
https://www.aosong.com/

Project Notes