Can't read DHT22 with Electron - SOLVED

kquainta · June 18, 2019, 7:29pm

Trying to get a reading from a DHT22/AM2302 with my E-Series electron dev board with no luck. I’m using the PietteTech_DHT library and an 10k resistor between the +5v vcc (pin 1) and data (pin 2), and have pin 3 to GND. (I also tried 4.77 resistor and 3.3v as suggested somewhere). I have multiple DHT22 units that I’ve swapped in to rule out a faulty sensor. (These sensors worked well on RPi with no issues)

SERIAL CONSOLE:

Serial monitor opened successfully:

0: Retrieving information from sensor: Read sensor: Error
        Response time out error
Humidity (%): -5.00
Temperature (oC): -5.00

1: Retrieving information from sensor: Read sensor: Error
        Response time out error
Humidity (%): -5.00
Temperature (oC): -5.00

MY .INO FILE:

// Include library for the temp sensors
#include "../lib/PietteTech_DHT/src/PietteTech_DHT.h"

#define DHTPIN D1
#define DHTTYPE DHT22

// Lib instantiate
PietteTech_DHT DHT(DHTPIN, DHTTYPE);
int n;      // counter

// setup() runs once, when the device is first turned on.
void setup() {
  // Put initialization like pinMode and begin functions here.

 	Serial.begin(9600); 
	Serial.println("DHT Simple program using DHT.acquireAndWait");
  Serial.print("LIB version: ");
  Serial.println(DHTLIB_VERSION);

	DHT.begin();
 
}

// loop() runs over and over again, as quickly as it can execute.
void loop() {
  // The core of your code will likely live here.
  
  // Temp sensors require 2 sec delay
  delay(2500);
  
  Serial.print("\n");
  Serial.print(n);
  Serial.print(": Retrieving information from sensor: ");
  Serial.print("Read sensor: ");

  int result = DHT.acquireAndWait(2500); // wait up to 1 sec (default indefinitely)

  switch (result) {
  case DHTLIB_OK:
    Serial.println("OK");
    break;
  case DHTLIB_ERROR_CHECKSUM:
    Serial.println("Error\n\r\tChecksum error");
    break;
  case DHTLIB_ERROR_ISR_TIMEOUT:
    Serial.println("Error\n\r\tISR time out error");
    break;
  case DHTLIB_ERROR_RESPONSE_TIMEOUT:
    Serial.println("Error\n\r\tResponse time out error");
    break;
  case DHTLIB_ERROR_DATA_TIMEOUT:
    Serial.println("Error\n\r\tData time out error");
    break;
  case DHTLIB_ERROR_ACQUIRING:
    Serial.println("Error\n\r\tAcquiring");
    break;
  case DHTLIB_ERROR_DELTA:
    Serial.println("Error\n\r\tDelta time to small");
    break;
  case DHTLIB_ERROR_NOTSTARTED:
    Serial.println("Error\n\r\tNot started");
    break;
  default:
    Serial.println("Unknown error");
    break;
  }

  Serial.print("Humidity (%): ");
  Serial.println(DHT.getHumidity(), 2);

  Serial.print("Temperature (oC): ");
  Serial.println(DHT.getCelsius(), 2);

 // Serial.print("Temperature (oF): ");
 // Serial.println(DHT.getFahrenheit(), 2);

 // Serial.print("Temperature (K): ");
 // Serial.println(DHT.getKelvin(), 2);

 // Serial.print("Dew Point (oC): ");
 // Serial.println(DHT.getDewPoint());

 // Serial.print("Dew Point Slow (oC): ");
 // Serial.println(DHT.getDewPointSlow());

  n++;
}

I’ve read several threads on this issue but most are very old now. I did switch from the Adafruit_DHT lib which wasn’t working either and many suggested PietteTech_DHT works better. My leads to the sensor are about 15cm long. I was planning to run this sensor on 5vdc at about 20 meters which the device specs claim is supported.

I appreciate any feedback. I switched my project from RPi to Particle Electron and am considering switching back due to this issue unless I can solve it soon.

peekay123 · June 18, 2019, 7:40pm

@kquainta, give the Adafruit_DHT library a try since it has been updated recently. When did you try it? Also, do make sure the VIN pin (pin 1) is actually at 5V.

I am currently reading a Grove DHT11 on an E0 series dev board and it works fine. I can share the code if you wish.

kquainta · June 18, 2019, 7:50pm

@peekay123 . Thanks for the quick reply. Yes, I measure 5.05vdc on pin 1.

I’ll switch back to the Adafruit_DHT library now but would love to see your code as well. Maybe I’m just missing something here.

peekay123 · June 18, 2019, 7:55pm

@kquainta, here is the code I use:

// This #include statement was automatically added by the Particle IDE.
#include <Adafruit_DHT.h>


// This example assumes the sensor to be plugged into CONN2
#define DHTPIN D1     // what pin we're connected to

// Here we define the type of sensor used
#define DHTTYPE DHT11        // DHT 11 

DHT dht(DHTPIN, DHTTYPE);

char msg[80];

void setup() {

    // We open up a serial port to monitor the sensor values
    Serial.begin(9600); 
    Serial.println("DHT11 test!");

    dht.begin();
}

void loop() {
    // Wait a few seconds between measurements.
    delay(60000);

    // Reading temperature or humidity takes about 250 milliseconds!
    // Sensor readings may also be up to 2 seconds 
    float h = dht.getHumidity();
    // Read temperature as Celsius
    float t = dht.getTempCelcius();
    // Read temperature as Farenheit
    float f = dht.getTempFarenheit();

    // Check if any reads failed and exit early (to try again).
    if (isnan(h) || isnan(t) || isnan(f)) {
        Serial.println("Failed to read from DHT sensor!");
        return;
    }

/*
    // Print the data over serial
    Serial.print("Humid: "); 
    Serial.print(h);
    Serial.print("% - ");
    Serial.print("Temp: "); 
    Serial.print(t);
    Serial.print("*C ");
    Serial.println(Time.timeStr());
*/

    // Publish data to the Particle cloud. 
    // Remember that you'll consume data every time you publish to the cloud.
    snprintf(msg, sizeof(msg), "%4.2fC   %4.2f%%", t, h);
    Particle.publish("temp_humi", msg, 60, PRIVATE);
}

The E0 dev board is sitting on my bench publishing every 60 seconds. I’ll be doing some sleep tests at some point.

kquainta · June 18, 2019, 8:17pm

@peekay123 Thanks for this. I switched over to ADAfruit_DHT but still cannot read anything. I confirmed +5v and tried two different DHT22’s.

SERIAL CONSOLE:

Serial monitor opened successfully:
Failed to read from DHT sensor!
Failed to read from DHT sensor!

MY CODE:

// Include library for the temp sensors
#include "../lib/Adafruit_DHT/src/Adafruit_DHT.h"

#define DHTPIN D1
#define DHTTYPE DHT22

// Lib instantiate
DHT dht(DHTPIN, DHTTYPE);

// setup() runs once, when the device is first turned on.
void setup() {
  // Put initialization like pinMode and begin functions here.

 	Serial.begin(9600); 
	Serial.println("DHT ADAfruit test");
	dht.begin();
}

// loop() runs over and over again, as quickly as it can execute.
void loop() {
 // Wait a few seconds between measurements.
	delay(10000);

// Reading temperature or humidity takes about 250 milliseconds!
// Sensor readings may also be up to 2 seconds 'old' (its a 
// very slow sensor)
	float h = dht.getHumidity();
// Read temperature as Celsius
	float t = dht.getTempCelcius();
// Read temperature as Farenheit
//	float f = dht.getTempFarenheit();
  
// Check if any reads failed and exit early (to try again).
	if (isnan(h) || isnan(t)) {
		Serial.println("Failed to read from DHT sensor!");
		return;
	}

	Serial.print("Humid: "); 
	Serial.print(h);
	Serial.print("% - ");
	Serial.print("Temp: "); 
	Serial.print(t);
	Serial.println("*C");
	Serial.println(Time.timeStr());
}

Questions:

I noticed you are using the CLI. I am using vbCode/Workbench. Any known issues here?
Attempting to flash via Workbench in DFU Mode is very flaky. I need to power down/up the board, remove/replace my USB cable, re-enter DFU mode many times before DFU-Util can successfully flash. I replaced my USB cable with no luck. I am using a Macbook Pro with an USB-C to USB-A adapter. Just curious if there are known issues.

kquainta · June 18, 2019, 10:46pm

UPDATE: So switched over to the grove DHT11 but unfortunately had the same issues but I stumbled on another library named ADAfruit_DHT_Particle and when I changed to this library from ADAfruit_DHT, it now WORKS!

I’m now reverting to my preferred DHT22 sensor and will report if it is also successful.

kquainta · June 19, 2019, 12:42am

SOLVED!

After replacing my DHT22 sensor, I’m pleased to report that it works. Here’s a recap:

Library: ADAfruit_DHT_Particle driver (NOT ADAfruit_DHT driver)
Sensor: DHT22/AM2302 (Labeled “ASAIR AM2302”)
Sensor Pinouts (Read from left to right while looking at the front):
PIN 1: +5vdc
PIN 2: To GPIO
PIN 3: Not Used
PIN 4: GND
100uf capacitor between pins 1 & 2 (for wave smoothing)
(Note: No 10k pullup resistor is needed between pins 1 & 2)

Particle E0 series dev board (Electron module with breakouts, connectors, etc):
* We can use any GPIO pin (I am using D0 - D3 & C5 since i need to run 5 temp sensors)
* +9v via barrel connector
* LiPoly battery connected

** program.ino file**

// This #include statement was automatically added by the Particle IDE.
#include <Adafruit_DHT_Particle.h>


// This example assumes the sensor to be plugged into CONN2
#define DHTPIN D1     // what pin we're connected to

// Here we define the type of sensor used
#define DHTTYPE DHT22       // DHT11 or DHT22 

DHT dht(DHTPIN, DHTTYPE);

void setup() {

    // We open up a serial port to monitor the sensor values
    Serial.begin(9600); 
    Serial.println("DHT22 test!");

    dht.begin();
}

void loop() {
    // Wait a few seconds between measurements.
    delay(5000);

    // Reading temperature or humidity takes about 250 milliseconds!
    // Sensor readings may also be up to 2 seconds 
    float h = dht.getHumidity();
    // Read temperature as Celsius
    float t = dht.getTempCelcius();
    // Read temperature as Farenheit
    float f = dht.getTempFarenheit();

    // Check if any reads failed and exit early (to try again).
    if (isnan(h) || isnan(t) || isnan(f)) {
        Serial.println("Failed to read from Grove DHT sensor!");
        return;
    }

    // Print the data over serial
    Serial.print("Humid: "); 
    Serial.print(h);
    Serial.print("% - ");
    Serial.print("Temp: "); 
    Serial.print(f);
    Serial.print("*F ");
    Serial.println(Time.timeStr());

    // Publish data to the Particle cloud. 
    // Remember that you'll consume data every time you publish to the cloud.
    // Particle.publish("temp", String (f));
    // Particle.publish("humi", String (h));
}

CONSOLE OUTPUT

Humid: 45.40% - Temp: 77.00*F Wed Jun 19 00:41:48 2019
Humid: 45.30% - Temp: 77.00*F Wed Jun 19 00:41:53 2019
Humid: 45.20% - Temp: 77.00*F Wed Jun 19 00:41:58 2019
Humid: 45.20% - Temp: 77.00*F Wed Jun 19 00:42:04 2019
Humid: 45.20% - Temp: 77.00*F Wed Jun 19 00:42:09 2019
Humid: 45.20% - Temp: 77.00*F Wed Jun 19 00:42:14 2019
Humid: 45.20% - Temp: 77.00*F Wed Jun 19 00:42:19 2019
Humid: 45.20% - Temp: 77.00*F Wed Jun 19 00:42:25 2019

NOTE: I also switched from the vbCode/Workbench IDE to the WebIDE. Not sure if that also helped.

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