@ mark15 - that is indeed a mystery. Wikipedia has a good explanation of what an open collector is [url]http://en.wikipedia.org/wiki/Open_collector[/url], but it did not help me figure out the answer to this question.
Nice work, it took only 5 min to get DHT22 sensor up and running with Panda II. I have 3 of those sensors and I need to plug all of them to the same board. So my only choise is to use digital pins to power the sensors one by one or use some kind of multiplexer?
On which pins din you connect your first sensor ?
If you are not amoung the people who have trouble maiking it work outside of di2 and di3, you can select several different (interupt) pins for each sensor.
If you are stuck with di2 and di3 (I still don’t know why, I never encountered this problem myself), you could use a different approach, which may work (did not try):
- use di2 and di3 for the data pins
- use another (any) digital pin to power each sensor. So before reading a value from a sensor, just power it with the right output pin… However you need to check if an unpowered dht22 keeps high impedance enough not to perturbate the others in parallel.
The first solution is the best if you can use it ! 
I connected those to di2 and di3. I tried first d38/d40 but it didn’t work.
I would actually need the I2C pins for my barometer board 
has anybody found a solution yet?
Yes, I2C… I would need this BUS too - but still no way to run the dht22 on other interrupt ports… as panda is discontinued, it not seems to be solved - or?
solution:
the key was the open collector output: a NPN (BC547) with a 2.2k pull-up on collector and wired to DHT22SIG/Inputport, base with a 1.6k resistor to the output port, emitter wired to ground and then reverse the states of the output.
PHU… now I2C free for BMP035…
thx@ all for the hints!!!