How to power an array of Arduinos+AnalogShields

[Dovale]

Hello everyone, and thanks in advance for reading this!

 

On a current project, I’m working with a network of Arduino UNOs R3, each with an AnalogShield installed (to be precise, it’s 4 Arduinos+AnalogShields total, communicating over I2C). I immediately found a problem when I connected all their Vin ports together to a 12V power supply: they sourced too much current (my main power supply was reading more than 1 A!). So I quickly stopped that and tried connecting the 5V ports together to a 5V power supply. At first this was OK, but soon they started to source too much current again. I also tried powering one of them via USB and connecting all the 5V ports together… This works most of the time, but some times the 5V line’s voltage oscillates badly or they start sourcing too much current again... It's funny because sometimes things seem to work, and then stop working.

 

I checked the health of all Arduinos and they are perfect. And I checked powering all Arduinos by themselves (no shields) both through their Vin and 5V ports, and that works with no issues... So it must be an issue with the AnalogShields...

 

For the moment, as a temporary measure, I’m powering all of them independently through their USB ports, and connecting only their grounds together. But in my final configuration I’d like to be able to power all of them with a single power supply.

 

Can anybody point to where the issue could be?

[JColvin]

Hi Dovale,

I don't know if this is necessarily the issue, but I suspect that the combination of the Arduino and the Analog Shield draws too much current for the 5V regulator to handle the 12V power supply. Looking around online, the Arduino with no load draws somewhere between 42 and 45 mA. I'm uncertain as to how much the Analog Shield draws but it for sure draws some current and the Arduino would draw more now that it is running a program. Looking at the datasheet for the 5V regulator on the Arduino (an NCP1117 from On Semiconductor) we can see that when powered at 12 V and taking into account the ~0.8 W power dissipation before the part goes into thermal shutdown, it can only consume around 65 mA before it reaches this shutdown mode and turns itself off. I'm guessing the combination of the microcontroller and shield approaches this current limit. I don't know why your supply was reporting over 1A of current draw though...

As for the 5V power supply, the Arduino board will automatically route the 5V supply through the 5V regulator (presuming you are powering the board with the external power supply through the barrel jack or the VIN pin), so the 5V regulator will inherently output less than 5V (due to dropout voltage). This lower voltage is then applied to the 3.3V regulator, which may result in an unstable 3.3V supply, potentially causing your board to fail.

A single USB port (presuming it's a 2.0 port, and not one of those with the new power specs) can only supply up to 500 mA at the most. It doesn't sound like your system will draw quite that much current, but I imagine the USB port isn't necessarily designed to handle any sort of varying power draw.

What I would probably do if I wanted to get all of the boards powered off of a single supply would be to try out a 9V power supply so you could get a little more current draw out of the regulator before the part overheats. It might still overheat from my experience, but at the time I was drawing a lot more current than you are. It doesn't look like you can bypass the 5V regulator reliably (at least according to Arduino website).

Let me know if you have any more questions.

Thanks,
JColvin