I have been trying to make a simple program to test communication between two arduinos. I have connected the RX/TX-pins and also ground. I have programmed one of the arduinos to send 1 och 2 (DEC) with a 1 or 2 second delay in between. The second arduino is programmed to light the led on pin 13 if it receives a 1, and to turn it off if it receives a 2.
The TX-light is blinking on the "sender", butnothing happens on the "receiver. Since i have not yet been able to get my hands on any external power-supply for the arduinos, i have them both connected to my computer via the USB. (The arduinos are Arduino NG's btw). I have also noticed that i cannot upload the programs to the arduinos if they are connected together. I must disconnect them from eacother everytime.
I'm a total electronics newbie, so maybe I'm making some obvious mistake here? Does it matter wether i connect the ground at the power connections (bottom of the board) or the GND pin next to digital pin13?
Does anyone have any suggestions? I could upload my code here as well, but it's on my home computer, and i'm not there at the moment. If you wish i could upload it when i get home.
Edit: Added a picture: