Reading from DHT22 with Arduino, powered by external source

Question

I have the following situation. When I power my DHT22 with the 3.3V from the Arduino UNO (and Ground it there), then I can read the data perfectly fine using the DHT library from Adafruit.

However, when I connect the DHT22 to my own external power supply (and respective ground), it fails. The reason for using this external power supply is so I can hook it up to a ESP8266 later.

The power supply I build uses a 5V adapter, then an LD33V converter and (just for experimentation) an 100nF capacitor to reduce any noise on the line. I measured this external power supply and it indeed gives off 3.3V after the LD33V. I check the datasheet of the LD33V and it should be able to 'give' 5mA, whereas the DHT22 needs less than 1mA for operation.

I don't know where to look at this moment. Can someone point me in the right direction? Much appreciated :)

Cheers

Answer 1

Have you connected the external power supply ground to the Arduino's ground? If not, one is "floating" with respect to the other. But they need to have the same reference - the ground sides of their power supplies.

• zwep: Ah, I edited the question to make that a bit more clear. When I power with the arduino, I use the ground provided by the arduino. When I use my own power supply, I use the ground provided by that. So to my idea nothing is 'floating' if I understand you correctly
• zwep: When I now attach the signal pin of the DHT22 to my Arduino, and power the DHT22 with my own power supply (and ground it there) AND connect a ground to the arduino. THEN I can measure the temperature on the arduino. Thanks
• JRobert: Perfect. "Floating" just means the two grounds are not (necessarily) at the same level. "... AND connect a ground to the arduino" is exactly what had been missing.