One 9V AC/DC adapter for two Arduino

[system]

Hi, I'm trying to supply power to two Arduino from one 9V-600mA AC/DC power supply from main power.

Arduinos are Deumilanove and Nano. Deumilanove is running 4 LED matrix plus 4 digit LED segments with wifly shield. I put Nano is just for auto-reseting Duemilanove as it often crushes.

Duemilanove gets power through 2.1mm power socket and nano gets though 5V pin via 9V->5V external regulator.

It's working separately but when I connect to two Arduinos same time, LED seems randomly flashing and not work correctly.

I'm using 9V - 600mA AC/DC power supply.

Is it because the current is not enough? What the best way to handle two Arduinos with one power supply in this case?

I will really appreciate if anyone give me suggestions.

thanks in advance.

[system]

Thanks for your replying Richard! I've been trying things but I haven't still found a perfect solution.

A. Please confirm that you are supplying DC to your Arduinos.

Sorry I meant I'm using AC/DC adapter, so it's DC.

B. Measure how much current your "4 LED matrix plus 4 digit LED segments" loads are drawing.

I measured current between Duemilanove's 5V and circuits of LED matrix plus 4 digits pin and it's around 150-200mA depending on how many LEDs turn on. And also I measured how much current Nano draws and then it was 20mA. I put tester between 5V regulator and Nano's 5V pin. Not sure why 600mA can't cope with these amount. Sorry I'm not familiar with electronics?

C. Power your "4 LED matrix plus 4 digit LED segments" independently, perhaps directly from the 9V DC power source. You may have to change the circuit to run on 9V vs. 5V. But you DO NOT want to source the power for these FROM anywhere on any Arduino board. Arduinos are made to control power, not to source power.

LEDs powered from Duemilanove's 5V pin now. I know ideally they have own power supplier but it seems no problem at the moment if I don't connect Nano and I wanted to keep the circuit minimum.

Now powers go like this.

Main -> 9V adapter -> Duemilanove(VIN) -> Duemilanove(5V) -> LEDs | -> 5V regulator -> Nano(5V)

D. Power the Nano directly from the 9V DC power source. Connect the 9V to the "VIN" pin, NOT to the 5V pin!

I changed the voltage from 9V to 5V with a regulator (with two capacitor). It goes to 5V pin. I heard it's not a good idea to connect 9V power to VIN when I take a power from main with AC/DC adapter, not from battery. So, I changed the voltage to 5V and connected to 5V pin regarding to the article

"6-20V unregulated external power supply (pin 30= VIN), or 5V regulated external power supply (pin 27= 5V)". http://www.arduino.cc/en/Main/ArduinoBoardNano

But is it no problem if I connect 9V to VIN directly? Actually it's less circuit and I prefer it.

E. Make sure all the grounds are connected together.

yes, no problem to this at the moment.

Then, now.. I changed power supply from 600mA to 1A. It lights up LEDs now... but LEDs sometime/often turn off suddenly and Duemilanove seems reset in random timing. Is it because too much power now? Backside of Arduino's regulator's quite hot.

[system]

Thanks Richard!

Yes, you were totally right. I just connect LEDs individually from the power, now it's working perfectly with 600mA DC.

I'm still using 5V because it was easier to modify my ready-built circuits. However, as you say, if I connect 9V directly it would be even simpler and reliable. I will do that.

Sorry for not providing LED details. I put them here for a future reference.

I used: four of HE Red 5x7LED dots matrix (IF Typ: 20mA, VF Typ: 2.0V) four of 35mm 7 segments LED (IF Typ: 20mA, VF Typ: 2.0V) And LEDs are with a Max7219 and two capacitors (10uF, 0.1uF) and a 10K resister (each for matrixes and one for 4 digits).

Anyway thank you very much for your help! It was probably very basic mistake but it was a big learning for me.