dht22 - 10 k resistor ?

I have seen examples of the DHT 22 humidity sensor used with and without a resistor between signal and vcc wires

do you need this resistor or not ?

You need the resistor.

But... if the sensor is directly next to the Arduino, the internal pullup resistors of the Arduino will make it work. However, it is better to use that 10k resistor.

ok so its just a pull up

i guess you really need to use it when are not using an arduino

Gadget999: ok so its just a pull up

i guess you really need to use it when are not using an arduino

you need it when the distance between mcu and sensor is long. If it is real long (>10meter?) the resistor should be smaller e.g 4k7 or even 2k2