DHT11 Sensor - reading either all zeros or all -999 (depending on library)

Question

So I've been trying to get a small project set up for the upcoming eclipse, just to read changes in the humidity and temp during the eclipse.

I have two DHT11 sensors, I'm only using one.

I have downloaded this library (it's at the bottom), and this is the code I'm using.

#include <dht.h>
#define pin 13
dht DHT;
void setup() {
 Serial.begin(9600);
 delay(2500);
 Serial.print("DHT11 Sensor: April 8 Solar eclipse data\n\n");
 delay(1500);
}
void loop() {
 DHT.read11(pin);
 Serial.print(" ");
 Serial.print(DHT.humidity);
 Serial.print(" ");
 Serial.print(DHT.temperature);
 Serial.print(",\n");
 delay(2500);
 
}

The goal here is to have csv's that I can copy/paste into a .csv and import to matlab to do what I need on there.

I keep getting the title and "0.00 0.00," for the two data sets. With other libraries and borrowed code sometimes I get -999 for the datasets.

My set up

schematic

^{simulate this circuit – Schematic created using CircuitLab}

My schematic isn't super accurate, the sensor's on the breadboard. LMK your thoughts.

• jsotola: @StarCat just delete the comment then
• Jayven Mason: I attempted the resistor, I put one end in the power row between the 5V into the breadboard and the power pin for the sensor, and the other end into a slot between the data wire out to the Mega, and the pin for the sensor. Still zeros.
• Delta_G: Try a pin other than 13. There is additional circuitry around pin 13 for the built in LED.
• tepalia: Can be a bad sensor or bad cable too.
• tepalia: You can cross-check your sensor with this tutorial. theengineeringprojects.com/2017/08/… If your sensor does not work after following this, maybe you have to replace your sensor.

Answer 1

If you are using a standalone DHT11 sensor (Without breakout board) you will need a 1KΩ pullup-resistor between 5v and Data.

The DHT's data pin is an open collector, meaning it can only pull a wire to ground to transmit data. If that wire wasn't pulled up to begin with, it won't have anything to pull down.

If your DHT11 is on a breakout board with the 1KΩ resistor already in place, I would suspect a bad sensor...

• starship15: I have used DHT11's successfully in at least two different projects. Take a look at fpaynter.com/2021/07/… and fpaynter.com/2017/01/3d-printer-filament-de-humidifier-bin. Both these posts have the entire code.