Basics with DHT11

Question

I just bought the sensor DHT11 and trying to test it with the library code provided by the IDE, but I always get the same error on .read() . Code -2

/*####################################################################
FILE: dht11_functions.pde - DHT11 Usage Demo.
VERSION: 2S0A
PURPOSE: Measure and return temperature & Humidity. Additionally provides conversions.
LICENSE: GPL v3 (http://www.gnu.org/licenses/gpl.html)
GET UPDATES: https://www.virtuabotix.com/
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 VDD(5V) Readout(I/O) Ground
HISTORY:
Joseph Dattilo (Virtuabotix LLC) - Version 2S0A (27 May 12)
-Rewritten to with more powerful Versalino functionality
Joseph Dattilo (Virtuabotix LLC) - Version 0.4.5 (11/11/11)
-Made Library Arduino 1.0 Compatible
Joseph Dattilo (Virtuabotix LLC) - Version 0.4.0 (06/11/11)
-Fixed bugs (squish)
Mod by Rob Tillaart - Version 0.3 (28/03/2011)
Mod by SimKard - Version 0.2 (24/11/2010)
George Hadjikyriacou - Original version (??)
#######################################################################*/
#include <dht11.h>
dht11 DHT11;
void setup()
{
 DHT11.attach(2);
 Serial.begin(9600);
 Serial.println("DHT11 TEST PROGRAM ");
 Serial.print("LIBRARY VERSION: ");
 Serial.println(DHT11LIB_VERSION);
}
void loop()
{
 Serial.println("\n");
 int chk = DHT11.read();
 Serial.print("Read sensor: ");
 switch (chk)
 {
 case 0: Serial.println("OK"); break;
 case -1: Serial.println("Checksum error"); break;
 case -2: Serial.println("Time out error"); break;
 default: Serial.println("Unknown error"); break;
 }
 Serial.print("Humidity (%): ");
 Serial.println((float)DHT11.humidity, DEC);
 Serial.print("Temperature (°C): ");
 Serial.println((float)DHT11.temperature, DEC);
 Serial.print("Temperature (°F): ");
 Serial.println(DHT11.fahrenheit(), DEC);
 Serial.print("Temperature (°K): ");
 Serial.println(DHT11.kelvin(), DEC);
 Serial.print("Dew Point (°C): ");
 Serial.println(DHT11.dewPoint(), DEC);
 Serial.print("Dew PointFast (°C): ");
 Serial.println(DHT11.dewPointFast(), DEC);
 delay(2000);
}

And this is my ouput:

DHT11 TEST PROGRAM 
LIBRARY VERSION: 2S0A
Read sensor: Time out error
Humidity (%): 0.0000000000
Temperature (°C): 0.0000000000
Temperature (°F): 32.0000000000
Temperature (°K): 273.1499938964
Dew Point (°C): nan
Dew PointFast (°C): nan
Read sensor: Time out error
Humidity (%): 0.0000000000
Temperature (°C): 0.0000000000
Temperature (°F): 32.0000000000
Temperature (°K): 273.1499938964
Dew Point (°C): nan
Dew PointFast (°C): nan

The wiring:

-left pin: 5v

-right pin: gnd

-middle pin: 5v - digital2 - through 10kO resistor

enter image description here enter image description here

UPDATED: I found a library that works. I also changed the wiring because I found out the sainsmart dht11 switches the pins:

-left: signal with 10kO and to 5v

-middle: 5v

-right: GND

Now just a question. What is the difference between these two dht11 sensors. Dht11 basic dht11 with board

The one from sainsmart has a piece of circuit I don't know what it is.(I have a lack on electronics I try to fix step by step...)

It is a resitor, capacitor? it says 103.

How does this affect to the wiring?

• Djensen: In the code you linked, it says that you are reading pin 2 for input, but on your image, your wire is in pin 3.
• blfuentes: Hi, thanks for the answer. You are right. It was a problem in the wiring. After fixing it I was still getting errors. The problem was the library version, that was giving some problems with read response for dht11 sensors

Answer 1

The DHT11 sensor is available as-is and integrated on a break-out board. The break-out board shows following differences:

• the order of PINs is changed, e.g. in one version: 1 -> signal, 2 -> +, 3 -> GND (left-to-right, pins down, looking at the front)
• the unused pin is not connected
• the board already has a 10 KOhm pull-up resistor connected

Thus, when you have a DHT11 on a break-out board you have to adjust schematics that use it as-is - e.g. in this example you have to remove the external pull-up resistor and connect the pins in the correct order.

Be aware that there may be different versions of DHT11 breakout boards available - i.e. ones where the order of pins is different. You can look out for PIN markings like S (-> signal) and - (-> GND). Also, you can look at both sides of the breakout board to trace the connections.

The resistor usually comes as SMD on such a board - and if it has a marking it uses a special code. For example, 103 means 10 * 10^3 Ohm, i.e. 10 KOhm.

The adafruit DHT library comes with an example sketch that prints the sensor values over serial.

Answer 2

It seems you wiring is ok, although I think you already have pull-up resistor on breakout board (look for a small 103 resistor).

Maybe you can try another library for DHT? I have used one made by adafruit (https://github.com/adafruit/DHT-sensor-library) and everything worked just fine.

Regards, Ian

• blfuentes: Thank you for the answer, but it didn't work. I tried with and without resistor(I saw the 103 in the dht11's board). Also tried with the adafruit library and then I get the "Failed to read from DHT sensor!" error. I debugged the example and readHumidity readTemperature get errors on reading. Maybe my sensor is broken. I ordered a new one to check...
• vlad b.: The DHT11 board + sensor already has the resistor. I use those with arduino directly, no extra components required.