Powering 9 Sensors with Arduino Mega?

Hi, first of all,I'm new to Arduino and I'm not an EE person, I'm more of a programmer guy so do forgive me if I ask stupid questions.

All those black boxes on the diagram are Hall Effect Sensors which consume around 9mA max?(if i'm not wrong) Here is the datasheet. http://www.farnell.com/datasheets/1538021.pdf
9x9mA will be 81mA.

So I am connecting 9 Hall Effect Sensors to the Arduino Mega 2560 , I am taking the outputs from the sensors and feeding it into the analog inputs of the Arduino.

The Arduino will read the analog inputs and pass it to my PC via USB(Serial)

Now here is my problem:

  1. Is Arduino Mega alone enough to power up all the 9 Hall Effect Sensors?
  2. Will it cause any false readings?
  3. Will it overheat?
  4. Since I plugged in a wall adapter and USB together, which power source will arduino draw from?The wall or my PC?
  5. Will my Serial communication be affected if I plug in both the 9V and USB?

Thanks for reading my post.

Typical 6.9mA, times nine makes 62mA.
Is it a regulator 9V power supply ? ( 9 - 0.6 - 5 ) * 0.062 = 211 mW

That means that the voltage regulator is extra heated with 211 mW. I think that is no problem. Unless you have also many leds.

The power supply to the power jack takes over the USB power when that voltage is above 7.5V. You can plug in the power supply while the Arduino board is running and also usb power, and unplug and whatever. The Arduino Mega will keep running fine.

Hi, thanks for the reply.

Yes, I believe it is a regulator 9V power supply.
May I know what is the formula you just used to calculate the power? So I can use it to calculate if I were to add more sensors in the future?

Alright, about the power supply, with that said, so can I assume that the Serial Communication will work fine too?

The onboard 5volt regulator is rated at 800mA.
The board could use ~100mA, so there is 700mA left.

The onboard regulator has to drop the difference between input voltage and the 5volt rail.
If you try to draw 500mA from the 5volt line, with a 9volt supply on the DC jack...

9 - 0.7 (reverse protection diode) = 8.3volt.
Votage across regulator is 8.3 - 5 = 3.3volt.
Power (heat) in regulator = 3.3 x 0.5 (500mA) = 1.65 watt.

Educated guess of the thermal resistance of the very small heatsink area is 50-60 degrees C per watt.
Temperature rise = 1.65 x 55 = 90 degrees C. OVER AMBIENT.
Stinking hot....

I'm sorry, I'm kinda lost, are you trying to say that I shouldn't power my board with 9V wall adapter?

A 9volt regulator is fine.
I just tried to make you understand the limitations of the onboard regulator.

Your nine sensors only draw 62mA.
With a 9volt supply, and at that current, the regulator will stay almost cold.
About ten degrees more than normal to be exact. Barely noticeable.

Alright, really thanks you all for confirming!

Hi, just a quick question, after powering up 6 or 7 hall effect sensors, my arduino board gets quite hot, am I doing anything wrong or is it normal?(I will be putting the board in a 30x30x10cm casing with one side of the casing left open)

Should I use a fan to cool the board down?
If yes, should I power up the fan using arduino or should I just get a usb mini fan and plug it via a wall adapter?

What exactly is getting hot ?
A fan would be wrong, nothing should get that hot.

You can put your finger on components to find what is getting hot. I bought a contactless IR thermometer for 8 dollars from Ebay, very handy to search for hot components.

The black square thing in the middle which has the label "ATMEGA2560 16AU 1015"

The sensor itself is not hot

The CPU (big block) should get warm, not hot.
The regulator is the small black block next to the DC socket, with the silver heatsink pad.
That should also be warm.
How warm..?
You should be able to rest your finger on both parts for a looong time.
If your finger sizzles, and you can see the mirror image of the part number on your finger, then it was too hot.

The big black ATmega2560 should not get hot. In my opinion it should not even get warm. Something is wrong. Please disconnect everything and run the sketch for the blinking led. Does it still get warm ?
If that is okay, try to make one hall sensor work.

What else was connected to the Arduino board ? Can you show your sketch between code tags ?
It is possible that something is wrong with your board and there is a shortcut somewhere. However, it it more likely that something is connected in a wrong way.

AFAIK, a Mega CPU draws about 50mA when doing nothing.
That's 250mw.
Just tested one without any load for 20 minutes.
The chip gets luke warm. I would say 10-15C above ambient.

Wawa, you are right. It is getting warm.
Room temperature : 24 degrees Celsius.
Average board temperature (the blue pcb) : 30 degrees
Very busy ATmega2560 : 41 degrees.