DHT22 ack timeout - Arduino connected with LCD display and relay

Hi all

I have connected to an Arduino Duemilanove an LCD Keypad Shield for Arduino Duemilanove & LCD 1602. Then, to the shield:

  • a DHT22 connected to the 5V Vcc, Gnd and the signal to Digital IO 2
  • a 5V relay connected to the 3.3V Vcc, GND and the signal to Digital IO 3

It seems that when the relay is connected, the DHT22 will get a very unreliable reading (reading once every 100s). 4 out of 5 times, giving an "Ack timeout".

When I connect the relay to another 3.3V source, the DHT22 get 100% good readings.

I am wondering if anybody has experienced something similar and if there is something I'm missing here.

Thank you in advance!

The relay can draw too much current and the switching might disturb the signal between sensor and processor with noise.
The LCD should not disturb the DHT sensor.

Are you making DHT readings direct after switching the relay?