2 arduinos, 6 relays and usb power supply

Hi list,

I'm working on a project using arduino sms library for communication with the pc. I have a big enough logic circuit, including 6 relays (5V), many IC's, many led's and 2 arduino Duemilanove. The one arduino is getting the inputs from the breadboards and the other is sending the outputs to the logic circuit.

The 2 arduino's are being connected using USB cables. My major problem is how I have to supply the circuit with DC current.

I have been trying many ways, such as, giving 5V from one arduino with common grounds, 5V from two arduino's (not in series) & common ground, and also external power supply 5V from a computer power supply with common grounds with arduino's.

Which is the proper way, in order not to harm my USB ports


I’m guessing that when you have only one USB cable plugged in you get a notice that your USB port has been shut down because you were drawing more than 500 mA. If it works OK with BOTH USB cables plugged in you are probably drawing less than 1A total. If that’s the case you can connect a 5V 1A regulated power supply to everything to take the load off your USB ports.