Temperature Sensor Investigation (Electronic work)
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Overview

When actually using ESP32, investigate which temperature sensor is good.
We investigated 11 temperature sensors with prices ranging from 40 yen to 480 yen.

Video

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English

Sensor List

TemperatureListDownload

Circuit

Program

//*************************************************************************
//  Temprature1 Ver2023.2.23
//  Arduino board : ESP32(Arduino core for the ESP32) by Espressif Systems ver 2.0.7
//  Written by IT-Taro
//***********************************************************************

#include   <Wire.h>
#include   <Adafruit_AHTX0.h>

#define ADC1_PIN 34
#define ADC2_PIN 15
#define S5851_ADDRESS 0x48  // S-5851A Address

Adafruit_AHTX0 aht;

unsigned long loopCount = 0;

void setup() {
  // Serial monitor
  Serial.begin(115200);
  // ADC Setting
  //analogSetAttenuation(ADC_0db);  // ATT 0dB[Default 11db]
  //analogSetAttenuation(ADC_6db);  // ATT -6dB[Default 11db],
  //analogSetWidth(10);             // Resolution Default:12bit(0-4095)[9-12]
  pinMode(ADC1_PIN, ANALOG);
  pinMode(ADC2_PIN, ANALOG);
  // I2C Setting
  Wire.begin();
  // AHT Setting
  if (! aht.begin()) {
    Serial.println("Could not find AHT? Check wiring");
    while (1) delay(1000);
  }
  // Display Serial monitor
  Serial.println("Setup completed!");
}

void loop() {
  // Sleep[30 sec]
  delay(30000);
  loopCount++;
  // ADC1[MCP9700]
  uint16_t analog1_adc = analogRead(ADC1_PIN);
  uint32_t analog1_mv = analogReadMilliVolts(ADC1_PIN);
  double temprature1 = double(analog1_mv - 500) / 10.0;
  Serial.printf("[%ld] MCP9700 ADC=%d, mV=%d[mV], temprature=%2.2f[°]\n", loopCount, analog1_adc, analog1_mv, temprature1);
  // ADC2[MCP9700A]
  uint16_t analog2_adc = analogRead(ADC2_PIN);
  uint32_t analog2_mv = analogReadMilliVolts(ADC2_PIN);
  double temprature2 = double(analog2_mv - 500) / 10.0;
  Serial.printf("[%ld] MCP9700A, ADC=%d, mV=%d[mV], temprature=%2.2f[°]\n", loopCount, analog2_adc, analog2_mv, temprature2);
  // I2C[S5851]
  double temprature3 = updateS5851() * 0.0625 ;
  Serial.printf("[%ld] S-5851A[I2C], temprature=%f[°]\n", loopCount, temprature3); 
  // I2C[AHT21]
  sensors_event_t humidity, temp;
  aht.getEvent(&humidity, &temp);// populate temp and humidity objects with fresh data
  Serial.printf("[%ld] AHT21[I2C], temprature=%f[°], humidity=%f[%]\n", loopCount, temp.temperature, humidity.relative_humidity); 
}

int updateS5851 () {
    Wire.beginTransmission(S5851_ADDRESS); 
    Wire.write(0x00);      // Read Tempreture Sensor
    Wire.endTransmission();
    Wire.requestFrom(S5851_ADDRESS, 2);
    //wait for response
    while(Wire.available() == 0);
    int T = Wire.read(); 
    T = ( T << 8 | Wire.read() ) >> 4  ; 
    return  ( -(T & 0b100000000000) | (T & 0b011111111111) );
}
//*************************************************************************
//  Temprature2 Ver2023.2.23
//  Arduino board : ESP32(Arduino core for the ESP32) by Espressif Systems ver 2.0.7
//  Written by IT-Taro
//***********************************************************************

#include   <Wire.h>
#include   <CRC8.h>

#define ADC1_PIN 34
#define ADC2_PIN 15
#define AHT25_ADDRESS 0x38    // AHT25 ADDRESS

unsigned long loopCount = 0;
CRC8 crc;

void setup() {
  // Serial monitor
  Serial.begin(115200);
  // ADC Setting
  //analogSetAttenuation(ADC_0db);  // ATT 0dB[Default 11db]
  //analogSetAttenuation(ADC_6db);  // ATT -6dB[Default 11db],
  //analogSetWidth(10);             // Resolution Default:12bit(0-4095)[9-12]
  pinMode(ADC1_PIN, ANALOG);
  pinMode(ADC2_PIN, ANALOG);
  // I2C Setting
  Wire.begin();
  // Init AHT25
  initAht25();
  // Display Serial monitor
  Serial.println("Setup completed!");
}

void loop() {
  // Sleep[30 sec]
  delay(30000);
  loopCount++;
  // ADC1[TMP36]
  uint16_t analog1_adc = analogRead(ADC1_PIN);
  uint32_t analog1_mv = analogReadMilliVolts(ADC1_PIN);
  double temprature1 = double(analog1_mv - 500) / 10.0;
  Serial.printf("[%ld] TMP36 ADC=%d, mV=%d[mV], temprature=%2.2f[°]\n", loopCount, analog1_adc, analog1_mv, temprature1);
  // ADC2[LM335Z]
  uint16_t analog2_adc = analogRead(ADC2_PIN);
  uint32_t analog2_mv = analogReadMilliVolts(ADC2_PIN);
  double temprature2 = double(analog2_mv / 10) - 273.15;;
  Serial.printf("[%ld] LM335Z, ADC=%d, mV=%d[mV], temprature=%2.2f[°]\n", loopCount, analog2_adc, analog2_mv, temprature2);
  // I2C[AHT25]
  updateAht25();
}

void initAht25() {
  delay(100);
  Wire.beginTransmission(AHT25_ADDRESS);
  Wire.write(0x71);
  Wire.endTransmission();
  delay(10);

  crc.setPolynome(0x31);
  crc.setStartXOR(0xFF);
}

void updateAht25() {
  byte buf[7];
  uint32_t humidity_raw;
  uint32_t temperature_raw;
  byte state;

  Wire.beginTransmission(AHT25_ADDRESS);
  Wire.write(0xAC);
  Wire.write(0x33);
  Wire.write(0x00);
  Wire.endTransmission();
  do {
    delay(80);
    Wire.requestFrom(AHT25_ADDRESS, 7);
    if (Wire.available() >= 7) {
      for(int i=0; i<7; i++) {
        buf[i] = Wire.read();
      }
    }
  } while((buf[0] & 0x80) != 0);

  crc.restart();
  crc.add(buf, 6);

  if (buf[6] == crc.getCRC()) {
    state = buf[0];
    humidity_raw = ((uint32_t)buf[1] << 12)|((uint32_t)buf[2] << 4)|(((uint32_t)buf[3] >> 4) & 0x0F);
    temperature_raw = (((uint32_t)buf[3] & 0x0F) << 16)|((uint32_t)buf[4] << 8)|((uint32_t)buf[5]);

    double humidity = humidity_raw / 1048576.0 * 100;
    double temperature = temperature_raw / 1048576.0 * 200 - 50;
    Serial.printf("[%ld] AHT25[I2C], temprature=%f[°], humidity=%f[%]\n", loopCount, temperature, humidity); 

  } else {
    // error
    Serial.printf("[%ld] AHT25[I2C] Read Error!\n");
  }
}
//*************************************************************************
//  Temprature3 Ver2023.2.23
//  Arduino board : ESP32(Arduino core for the ESP32) by Espressif Systems ver 2.0.7
//  Written by IT-Taro
//***********************************************************************

#include   <Wire.h>
#include   <DHT.h>

#define ADC1_PIN  34
//#define ADC2_PIN  15
#define DHT11_PIN 32
#define DHT20_ADDRESS 0x38  // DHT20 Address

DHT dht11(DHT11_PIN, DHT11);

unsigned long loopCount = 0;

void setup() {
  // Serial monitor
  Serial.begin(115200);
  // ADC Setting
  //analogSetAttenuation(ADC_0db);  // ATT 0dB[Default 11db]
  //analogSetAttenuation(ADC_6db);  // ATT -6dB[Default 11db],
  //analogSetWidth(10);             // Resolution Default:12bit(0-4095)[9-12]
  pinMode(ADC1_PIN, ANALOG);
//  pinMode(ADC2_PIN, ANALOG);
  // I2C Setting
  Wire.begin();
  // DHT11 Setting
  dht11.begin();
  // Display Serial monitor
  Serial.println("Setup completed!");
}

void loop() {
  // Sleep[30 sec]
  delay(30000);
  loopCount++;
  // ADC1[LM61]
  uint16_t analog1_adc = analogRead(ADC1_PIN);
  uint32_t analog1_mv = analogReadMilliVolts(ADC1_PIN);
  double temprature1 = double(analog1_mv - 600) / 10.0;
  Serial.printf("[%ld] LM61 ADC=%d, mV=%d[mV], temprature=%2.2f[°]\n", loopCount, analog1_adc, analog1_mv, temprature1);
  /*/ ADC2[LM60]
  uint16_t analog2_adc = analogRead(ADC2_PIN);
  uint32_t analog2_mv = analogReadMilliVolts(ADC2_PIN);
  double temprature2 = double(analog2_mv - 424) / 6.25;
  Serial.printf("[%ld] LM60, ADC=%d, mV=%d[mV], temprature=%2.2f[°]\n", loopCount, analog2_adc, analog2_mv, temprature2);*/
  // I2C[DHT20]
  updateDht20();
  // IO26[DHT11]
  float humidity4 = dht11.readHumidity();
  float temperature4 = dht11.readTemperature();
  Serial.printf("[%ld] DHT11[IO26], temprature=%f[°], humidity=%f[%]\n", loopCount, temperature4, humidity4);
}

void updateDht20 () {
  float hu, tp;
  uint8_t buf[8];
  long a;
  int flg;

  delay(500);
  flg = 1;
  while (flg) {
      Wire.beginTransmission(DHT20_ADDRESS);
      Wire.write(0xac);
      Wire.write(0x33);
      Wire.write(0x00);
      Wire.endTransmission();
      delay(100);

      Wire.requestFrom(DHT20_ADDRESS, 6);
      for (uint8_t i = 0; i < 6; i++)  buf[i] = Wire.read();

      if (buf[0] & 0x80) Serial.println("Measurement not Comp");
      else flg = 0;
  }
  a = buf[1];
  a <<= 8;
  a |= buf[2];
  a <<= 4;
  a |= ((buf[3] >> 4) & 0x0f);
  hu = a / 10485.76;

  a = (buf[3] & 0xf);
  a <<= 8;
  a |= buf[4];
  a <<= 8;
  a |= buf[5];
  tp = a / 5242.88 - 50;

  Serial.printf("[%ld] DHT20[I2C], temprature=%f[°], humidity=%f[%]\n", loopCount, tp, hu);
}

Measurement result

・The temperature measurement was within the tolerance of the specification. (Excluding LM335Z/LM60)
・The data output sensor (I2C/serial) tends to have a smaller error than the voltage output sensor
・ Least error 1st place: AHT21B 2nd place: AHT25 3rd place: DHT11

Document

Japanese【日本語】

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English

TemperatureSensorSurveyDownload

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