how many mA needs ArduinoMega

Forum 2005-2010 (read only) Hardware Troubleshooting
1

I want to use my arduino mega without computer, so i need to buy an AC-to-DC adapter. In the hardware page: http://arduino.cc/en/Main/ArduinoBoardMega appears the input voltage recommended (7-12V).

I will use a 12V one, how many mA has to be?

thanks a lot!

2

I would get one between 0.5A and 1A. The Mega doesn't need that much only about 50mA but ll the stuff you can drive with it soon adds up so that sort of current rating will keep you going in the medium term.

3

Thanks.

Now I have a problem. I mounted this circuit for MIDI-IN http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1187962258/.

I made a code receiving midi messages from a controller, and now I change the power from USB to 9V and it doesn't work..!

4

and now I change the power from USB to 9V and it doesn't work.

What board are you using, some boards have a link to swap to determine where the power is coming from. Have you changed this?

You have connected the power to Vin or the black power jack?

5

i have connected the 9V to the black power jack (2.1mm etc..) it makes some lights, i think that the arduino is running..

6

So fundamentally there should be no difference. If the code works when powered from the USB then there is nothing wrong with the code.

So there is a problem with providing power externally.

What hardware board are you running?

  1. Make sure it is working from the 9V by downloading and running the blinking LEDs.
  2. Make sure you have connected the ground from you 9V to the ground of the Arduino and also the ground of your MIDI input interface. That is pin 4 on the opto isolator and the other end of the 100K resistor.
  3. Check that there is 5V on your MIDI interface circuit with the 9V connected.
7
  1. Make sure it is working from the 9V by downloading and running the blinking LEDs.

yes, it works.

  1. Make sure you have connected the ground from you 9V to the ground of the Arduino and also the ground of your MIDI input interface. That is pin 4 on the opto isolator and the other end of the 100K resistor.

yes, checked.

I have not any voltimeter.. i can't check the third think..

8

What is the 9vdc power packs maximum current rating?, it should be marked on it.

Lefty

9

is a changeable slot AC/DC adaptor. with the 9V slot, the maximum current is 6A.

i think it's not the problem..

10

well, i have a arduino mega, in that arduino the power source is selected automatically.

it works fine with codes like "blink". but it doesn't recieve MIDI messages with the circuit with octocoupler. I have done a AC/DV 5Vdc with a usb connexion and the arduino works well. has it any sense?

can it be possible that the 5V pin works well with USB connexion power supplies and wrong with the jack connexion?

11

can it be possible that the 5V pin works well with USB connexion power supplies and wrong with the jack connexion?

To put it bluntly no.

You need to see if the serial signal is getting on to your serial input pin. The best thing is to use an oscilloscope. If you haven't got one then an LED and resistor could show you. However you would be looking for occasional offs with normally on. This is hard to spot. If you could wire it up to an inverter first (like a 74LS04) then the LED would be showing off with occasional ons, this is very easy to spot.

12

sorry for that, i had a problem in my circuit. thanks for the instructions to check it!