SIM900 shield directly connect to UNO dont work

Hi,

I have SIM900 shield. If I use a wire to connect to arduino shield works fine, but if I connect the SIM900 shield directly to UNO by pins, the shield can not register to mobile network.SIM 900 is powered by battery, UNO by PC USB.

Thank you for your advice.

Schematics, details of the shield and the code that you are using would be helpful, don't you think ?

At the wildest guess: when you use wires, you fortunately omitted the wire that would get you into strife. When the shield is properly mounted, something is connected that shouldn't be. It is probably something to do with power, and you haven't got enough. Another guess is that there is switch somewhere that puts the right power into the right place. Now read reply #1 - again.