DHT11 stops working when power comes from a power supply board

Question

I had a mini project with a DHT11, a temperature and humidity sensor, working perfectly on my Arduino UNO clone. Then, I bought a power supply board, that can feed the sensor with the 5V it requires, but for some reason, it does not work. Powering the sensor with the Arduino makes it get the correct values, powering it with the board makes it to stop working at all.

I have used a multimeter for checking the volts and amps. The readings on the sensor are the same with the Arduino and the board, 5V, but the amps are not. It seems that the sensor only uses power for an instant, while "sensing". Using Arduino, a 1.62mA current flows to the sensor and then drops to 0, but using the board it never gets higher than 0.001mA.

I repeated the test with different wires, protoboards and even power supply boards. I have three of them, all working apparently ok and reading the same on the multimeter. The board have the jumpers in the correct position: 5V.

I am just an amateur learning how electronics works, and I do not understand what is happening here. Some ideas?

Working:

Not working:

I don't think the problem is in the code, but just in case...

#include "DHTStable.h"

DHTStable DHT;

#define DHT11_PIN 5

void setup() {
    Serial.begin(115200);
    Serial.println(__FILE__);
    Serial.print("LIBRARY VERSION: ");
    Serial.println(DHTSTABLE_LIB_VERSION);
    Serial.println();
    Serial.println("Type,\tstatus,\tHumidity (%),\tTemperature (C)");
}

void loop() {

    // READ DATA
    Serial.print("DHT11, \t");
    int chk = DHT.read11(DHT11_PIN);

    switch (chk)
    {
        case DHTLIB_OK:
            Serial.print("OK,\t");
            break;
        case DHTLIB_ERROR_CHECKSUM:
            Serial.print("Checksum error,\t");
            break;
        case DHTLIB_ERROR_TIMEOUT:
            Serial.print("Time out error,\t");
            break;
        default:
            Serial.print("Unknown error,\t");
            break;
    }

    // DISPLAY DATA
    Serial.print(DHT.getHumidity(), 1);
    Serial.print(",\t");
    Serial.println(DHT.getTemperature(), 1);

    delay(2000);
}

Answer 1

In your question in the image below your grounds are not connected. The solution to your problem is to connect the ground (and only the ground, not the +5V) of your external power supply to the ground of the Arduino and the DHT11 will probably work again.

A bit of background

Sensors needs to be connected to the same ground as the Arduino. This is true in general with all parts of an electronic circuit. Ground functions as a fixed, common, reference voltage by which other signals (such as the digital data that's exchanged between the DHT11 sensor and the Arduino) are measured.

By connecting grounds, you make sure that a "high" that is output by the DHT11 is read as a "high" by Arduino and vice versa. When grounds are not connected, voltages between two parts of the circuit would "float" relative to each other and they would not be able to communicate. This link explains a bit more.