Arduino Shield how to Power?

In this thread I am making a shield for Arduino and/or Pokeys:
[Better way of routing tracks? - #60 by paulvdh]

But I have started to question my thinking about Power Distribution.

I think I drew 5 Volt input on all 5 Volts. This must be wrong?

This is how I think:

  1. All ground must be connected.

  2. I should connect 7-12 Volts on the VIN pin

  3. What do I do with the rest of the Power Pins?

  4. If I use Pokeys, it wants 3.3V for Potentiometers, while Arduino wants 5 V. I think this should be solved by +Analog being connected in parallel on the shield to either 3.3V on pokeys or 5 volts on Arduino. Then the question is which 5 V should I use? External or internal from Arduino?

The Mega 2560 can be powered via the USB connection or with an external power supply. The power source is selected automatically.

External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board’s power jack. Leads from a battery can be inserted in the GND and Vin pin headers of the POWER connector.

The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may become unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.

The power pins are as follows:

  • Vin. The input voltage to the board when it’s using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.

  • 5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don’t advise it.

  • 3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.

  • GND. Ground pins.

  • IOREF. This pin on the board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V.

I don’t want to power any thing from Arduino if I can avoid, but if it is safer to power things from arduino I want that. I don’t know how to discribe better.

Apparently it has a 5V voltage regulator:

Which implies it needs an input voltage of at least 6V.

According to that picture, all 5V pins are also outputs.

But to be sure, a better way is to verify it with the schematic of that PCB itself, or the arduino forum if you can’t find a schematic or documentation (which seems unlikely).

There are also variants of this PCB with an ATSAM processor, which runs at 3V3.

Rather depends what you want to do. Most shields use power from the Arduino to supply low power, logic functions. In you want to drive higher power devices that exceed the rating of the arduino, then the shield will need its own power supply. You will need to profile the power requirements for your board. So, a motor shield will likely have a mosfet driver and external power supply but a shield just interfacing an I2C sensor will likely just use the arduino supply.

I never worked with this board but remember there are ‘things’ about this platform that would probably get better answers on the Arduino forum. I vaguely, sorta, kinda remember that if you have a 5V controlled source there maybe a pin you can use that bypasses the onboard regulator.

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I believe @hermit is correct. Looking here:

The VIN pin comes straight from the Power Plug through a protection diode. If you have a good supply, you could drive whatever current you require.

You can also use the 5VDC but are limited to ~800mA total including the Mega board, or ~150mA for the 3.3VDC pin.

The point is, I think the folks on the Arduino Forum will answer questions you didn’t even know to ask. The sheer concentration of knowledge in one place makes it a valuable resource for what you are doing.

I’ve made well over 200 projects with Arduino’s (Uno, Nano, Mega, Teensy and Atmel-Chips(328, Tiny 13, 84, 85)).

Re Power:

Yes, connect All Grounds

Yes, Power from External (7 - 12 volts to VIN or Barrel-Jack). Powering in from USB is ok for low-level draw but, can cause issues with other pins (especially if output pins) best to avoid.

The Rest of the Power Pins?
• Do NOT power into to them!
• 3.3V and 5v are Output voltages to supply your attached gizmo’s
• AREF is for Analog Ref (not for powering)
• IOREF is for I/O Ref (not for powering)

• Each output pin can supply not more than 40mA BUT, you can Gang them to provide multiples of 40mA)

If your attached gizmo’s (sensor’s, etc) can live with 3.3v and/or 5v at 40mA (per pin) then, best to use them on the Board for convenience and power the Arduino from a Wall-Wart/other supply to the Barrel jack or Vin.

There’s a Mega board (shield) in the stock Templates panel. Once plugged in, it’s difficult to unplug due to so many Pins…

Photo of the Template below…

ADDED: Example of Ganged Pins on UNO (for higher current output) Last Screenshot

Shield Stacked onto Mega


So I should do as on the picture?

Thanks for a very good ansawer!

But use external 5 volt source insted of from arduino like th picture below?

I don’t remember where I found this Sheeld I use but it have worked before.

This is the projekt.

Basicly a shield that make it possible to connect a pokeys57E or arduino mega card.

It will be used in a flight sim project as digital input or output, and to drive 3 steppermotor instruments, and analog in.

2022-05-29_Shield for Pokeys and (493.7 KB)

I will use 4 I/O cards in total. 54x2=108 inputs
54 as digital outputs to ULN chip that will power leds, or 28Volt real aircraft bulbs.

the last card will power the instruments with smal steppers. and som extra inputs and outputs.

When I read this: Potentiometers Current Draw - #2 by system - Project Guidance - Arduino Forum

It make me think I need to use internal 5V, as I did?

Acording to Pokeys manual the pots for pokeys need 3.3V.
That is why I put a jumper on the shield, that you will select pokeys or arduino. 5V or 3.3V

Is this corect do you think?


I hade an ide of a thired input device card on the same shield but I have sort of given up that Ide.

A couple of things to take note of:

• Best to start Simple to gain understanding…

EDIT: The Arduino IDE has several good Example Sketches that are very usable for testing your knowledge. Build simple BreadBoard circuit with them. By end-of-day, you’ll be an expert…

• Your image shows Voltage incorrectly hooked up! Jumpers/Switch… Rather than my posting what/how to do it, you will gain a firm/better understanding by reviewing Info Here
And, here’s a link to Pot Example

• Both Arduino and Poky have Vin and Vout so, be sure you don’t mix them (In/Out and Voltage levels) as you seem to currently be doing. Draw a hand sketch of what’s needed (before making the schematic, this will save time)…

Pots use a range of voltages (depends on device/Resistance…) and both Arduino and Pokey (pretty much all devices) can use typical Pots. Just need to set their Range (with respect to Digital Range (example: 5v/256 = 0.02v each increment… Or, as the Arduino example shows, 5/1023 = 0.005v/increment)

Some homework is needed - good support for this sort of stuff is found at many sites… This site is more about using Kicad to Build your design…

I have a fair understanding of how pokeys work and ardunio.

I have a fair understanding of how pokeys work.

For switches I will use ground and a digital input. Simple as pie.

If I select a pokey card on my shield I will need 2 cables for it to work. Eathernet and powersuply of 5 volts.

If I select Arduino on my shield I will need usb and 7-12 volt power on ground and VIN.

Bothe the 2 voltages will come from the 37 pin D sub.

5 and 12 volt will always be supplied on those pins.

Depending on what I /O card I select 5 or 12 will be used.

This is all clear to me now.

Buttons and switches are solved on both alternatives.

My idé was to use jumper or switch to either supply 3.3v and ground plus analog input from pokeys to the analog input, and if I decide to use arduino I will move the jumper to 5V, ground and analog input.

I have by mistake as you can see on the files I made, connected all 5 volt together. That is as I understand it wrong.


If I understand correctly account to pokeys manual and 10 years of use of pokeys in simulator I should use 3.3 volt from pokeys, and the rest as I explained.

Then the question is arduino.

What Voltege source should I use from arduino?

Otherwise I think I have connected everything corect in the schematics if I seperat the power pins as you described.

I’ll leave everything to you… but will answer the question above:

If needing power to Any Device (Pokey, Sensors…etc) you can grab either or both 3.3v and/or 5v from the Arduino. Just don’t Mix voltages and In/out…

Power the Pokey from Arduino’s 5v.

EDIT: You ShouldNOT have Vin and USB hooked up at the same time! (on Arduino’s)
EDIT: Be sure to use the Pokey with desired Input Voltage level… Last screenshot

USB powering is for convenience testing and Programming. Real power (to Arduino and attached devices should come from Vin. Unplug the USB cable when powering Vin

EDIT-ADDED: Simple screenshot to convey the Powering (you can have the Grounds connected or also have it switchable (I wouldn’t bother to do that…). And, before you ask, ‘Yes’ you can use the 3.3v out and 5v out at the same time (on different devices, of course)

That was interesting.

Did not know that I could have 12V input on pokeys 57E.

But I have to have usb to arduino to comunicate with flightsim software.

Dose that mean that I should not have power conected to arduino?or How would you power ardunio?

And should I select 5 Volt or 3.3 to 10k pot? What would you select?

It looks to me like I don’t need a jumper. I could have the same voltage on both arduino and pokeys for pot.

I will not have ardunio and pokeys connected on the same shield.

You can have them Connected at same time BUT, the Arduino senses it and will auto-select the External Power. Best to Google this kind of stuff and use Arduino site.
This will help…

Sorry but, below Quote cautions me re your knowledge… (no offense intended…)

You decide (based on a handful of considerations…). 3.3 and 5.0 yield different resolutions - thus, software changes/etc… So, answer depends on what your design needs…

And, notice the 57E has two Versions - only 1.2 accepts higher voltage.

You ShouldNOT have Vin and USB hooked up at the same time!

But why did you say this?

The only thing I see that is wrong is that I have connected internal 5V with external to the potentiometers.

I think it is better to have 5 volt to pokeys and 12 to arduino.

I barely have an idea what an Arduino is, and have no idea what is an Arduino shield. But I admire such unequivocal responses!

I also read about that:

But what use do I have of that.

I don’t want to over comlicate any thing.

The thing is, how to connect a pot on arduino. On pokeys it is quiet clear to me, and have worked for 10 years in my simulator.

I would need too much background study to understand most of this discussion. I do not know what are “pokeys” but the answer to that question would probably lead me to another question.

However, in simple terms you can theoretically power a load (such as 5V @ 2 Amps) from one of several input sources by using “ORing diodes”.to automatically select the highest voltage source. The issue with that is the diodes will waste 300 mV to 700 mV (sort of a typical range) depending on whether you use schottky or general purpose silicon diodes. This voltage drop can be virtually eliminated with any one of several “ideal diode” circuits. A discrete version of this uses op amps and MOSFETs. If a higher bias voltage (such as 12V) is available it can use Nch MOSFETs. If the bias voltage is not available, then the design can use “low threshold voltage” Pch MOSFETs.

I don’t really understand what this have to do with connecting a potentiometer to arduino?

The important thing as I understand it is to not mix input voltage with output voltage from Arduino?