r/arduino • u/d_test_2030 • 7d ago

Hardware Help How to attach multiple modules to external power supply via a single DC Barrel Jack?

Hi. I have an external wall power supply that is connected to a DC Barell Jack. The DC Jack can only directly take one red V and one black ground cable. Can I simply put these two cables into braidboard rails and then connect the components' jumper wires into the same rails to provide them with power? I don't need to power just a few components however, there are multiple.
Or is there a more professional way to do so?

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u/JamesNihiliate 7d ago

Yepp, the barrel jack should have a positive and negative lead coming out of whatever plug you're using. Use a multimeter to confirm polarity but generally red would go to your positive rail, and black to your negative rail.

On a breadboard, these rails run vertically and allow you to connect multiple items in parallel, just like you need for your modules.

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u/ripred3 My other dev board is a Porsche 6d ago edited 6d ago

I think some clarification is needed here.

The Arduino Uno (and some other boards) have a female "Barrel Jack" connector on the board that can be used to supply external power to the board instead of using the 5V (V+) from the USB connector.

A 2.1mm "Barrel Plug" can be inserted into the barrel jack to supply the external voltage. The V+ of the barrel jack is also connected to the Vin header pin on the board.

The voltage from the external adapter to the barrel plug (Vin) needs to be in the range of 7V - 12V according to the docs and I would stay within the range of 7V - 10V if the board is a clone.

This external voltage is used as the input to the 5V linear regulator that is on the board. At least 2V over the regulated 5V output is needed which is why the minimum external voltage is 7V.

The output from the 5V regulator is used as Vcc - the power used for all digital TTL chips and it also supplies the 5V output pin.

That 5V signal/power path (Vcc) is what users normally connect to their breadboard's power rail along with the GND path for the other rail. That 5V rail (Vcc) is then often used to also supply power to other digital TTL chips and to strap inputs to a HIGH state when needed. This is NOT the voltage normally supplied from an external barrel plug unless you know that the voltage on the plug matches the Vcc of the semiconductors (5V in this case).

It just needs to be pointed out and clarified that if the external V+ power on your barrel plug is above 5V then you do not want to use that to power any semiconductor chips that do not also include their own regulation specifically for that need. You also never want to connect any voltage above 5V to any digital TTL inputs.

Your post never specifies what voltage the external barrel plug supplies and depending on that critical piece of information and how you are planning on using it, the answers to your question are radically different and require different warnings/guidance.

I hope that helps

edit/update: if you already knew all of that and are just asking if you can use the rails on the breadboard to allow multiple connections to a single electrical point such as the external 12V the answer should be an obvious yes. As long as you understand what voltages you are working with and what components they can and cannot be connected to. The only limitations of breadboard connections are the amperage limits and possibly an understanding of how noisy they can be when using sensitive circuits such as RF or when op-amps are involved.

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u/d_test_2030 5d ago

Thanks for your in-depth explanation.
I plan on using 10 servos and 10 water atomization modules (each require 5V).
Would I connect the 20 modules to one rail which is then connected to the barrel plug/5V wall supply or should I create two rails? Is one wall power supply sufficient?
I assume instead of using rails I should better use WAGO components to connect the 10 components?
Further I would like to use two 12V components.

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u/ripred3 My other dev board is a Porsche 5d ago edited 5d ago

Would I connect the 20 modules to one rail which is then connected to the barrel plug/5V wall supply or should I create two rails?

Either way would work fine. Now that I know that your external power source is 5V that removes some of the warnings I had mentioned. Just be sure that you connect the GND of the external power with GND of the Arduino so that the control signal is interpreted correctly.

Is one wall power supply sufficient?

That all depends on the current sourcing capacity of the adapter. One adapter will probably not be enough. You will need to estimate and plan out a power budget. And you will have to make design choices that factor in how power is used. You will need to go read up and learn a bit about voltage and current. The "Learn Basic Electronics" link in our community's sidebar is an excellent resource for complete beginners and more experienced users who just need to refresh on one topic or component.

Conceptually voltage is pushed from a power source to the device/component being powered. Integrated circuits (IC's, chips) are digital TTL (transistor-transistor logic) and they have very strict voltage requirements. All devices powered at a certain voltage use the same 5V/3.3V rail and ideally it never changes and has very little noise/ripple on it.

Current is different. Conceptually current is pulled by the devices being powered and they will only pull the amount of current that they need. Unlike voltage, the worst-case (max) current needed by all devices is added together to know what the current needs are for the power supply. That can be quite high and probably higher than a single wall adapter. But the devil is in the details...

The amount of current needed by an electric motor is relative to the amount of force needed to make it spin. The higher the resistance to being turned (e.g. the workload) the more current a motor will take to get it to move. At a certain point the workload is too much and the motor will stop and the current being pulled will be at its maximum for the motor. This is known as the "stall current" for the motor.

So in theory the power source needs to be able to supply the stall current for all motors added together. For a servo this would happen if you told it to move from one side to the other but held it with your hand and stopped it from moving. The stall current can be quite high depending on the torque rating. 1 amp or much more is not uncommon. So that means that if your servos had a stall current of 1A then your external power supply would technically need to be rated at 5V 10A. Plus you want to add about 10% - 15% as a safety margin so it can easily reach 20A.

Now that is the technical answer. In practice your motors might have a very light workload and that might mean that on average they never need more than 200mA. If you can be sure of that then you really don't have to get the biggest worst case power source and might only need to get one rated at 5V, 2A. So you can see it depends on each specific project and what the workloads are.

And since the motors pull more current when working and less when they are not doing work, the question of whether all of the motors will be on at the same time is something to take into account. If for example your project needs allowed you to move each servo one at a time over 20 seconds instead of needing them to all move at the same time and be finished in 2 seconds, then you could get away needing even less from the power source at any one time and you might be able to get away with a 5V, 1A supply.

So you will have to do some experimenting and measuring of the current pulled while your servo(s) are running with a multimeter and see what you need. Then add it all up and then add 10% more for a safety margin.

You could use one big supply for all servos, or you could use multiple power adapters (all with their GND's connected together and to the Arduino's GND) and power only 3 or 5 servos with each adapter, which limits the worst case current needed by any one adapter.

You have a fair bit of flexibility in your choices on how to design it, you just have to stay within the worst case boundaries or bad things start to happen.. 😄

The voltage has to stay the same and not change. The current rating of the power source can always be much higher than what you need and your project will only pull the current that it needs. So if you need a 5V 1A supply you can always use a 5V 2A, or 5V 5A, or 5V 20A supply etc.

Hope that helps!

update:

I assume instead of using rails I should better use WAGO components to connect the 10 components?

yes that would work fine and make solid connections

Further I would like to use two 12V components.

You can do that no problem. What are the 12V components? Do you need to be able to turn them on and off or communicate with them in any way? If so then just like with the servos you would want to connect the GND of the 12V power to the GND of the Arduino. And you would likely need a controller for the higher voltage (like a common DC motor driver) since the Arduino pins cannot control 12V directly.

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u/d_test_2030 4d ago

Thanks so much. That post was very helpful.
Do you think I can simply use standard dupon jumper wires to connect all my components (Breadboard, microcontroller pins, DC barrel jack, WAGO, ....) for a simple protoype or do I need to buy my own cables (maybe around 22AWG?) and then crimp them? I was wondering if DC barrel jacks (the green ones for the wall plugs) or WAGO can handle these standard dupon wires with the black headings. (I wanted to experiment with 12V water pumps).

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u/ripred3 My other dev board is a Porsche 4d ago

The Dupont breadboard wires should work fine for the breadboard, servos, and Arduino connections. You will either need to find the correct mating connector (female barrel jack) for your wall adapter's barrel plug that you can then solder wires to or cut the barrel plug connector off and connect the two wires to two Dupont breadboard wires using more Wago connectors.

You should really consider getting a soldering iron. It's not like welding or anything scary or difficult and is really no different than learning to use a pocketknife safely. In under 10 minutes you know the basics, and just like using a pocketknife your 100th attempt will always be better than your first. But there are no secret hidden dangers. Just don't touch the hot end. Thats it, it's less complicated than the safety rules for cooking and honestly less dangerous too 😉

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u/WereCatf 7d ago

Can I simply put these two cables into braidboard rails

Breadboards are neither reliable or designed to carry a lot of current. Either solder the wires, as many as you need, or use something like e.g. Wago blocks to properly distribute power.

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u/Rayzwave 7d ago edited 6d ago

I wouldn’t rely on breadboard for large current, try to break down large projects into stages that can be powered separately and try to monitor the voltage and current of your project so you get used to what the typical current levels are, that will help you determine if something has gone wrong(high current, short circuit or low current, possible wire disconnect)

There are lots of ways to distribute power to project hardware and comes down to personal preference. You could use cheap screw terminal block or you could use a faster no tools quick release terminal block. You could even make your own fancy distribution board with coloured terminals and metered outputs or buy a bench power supply with full metering, current and voltage limiting etc.

I’ve gone a bit off piste here but I think power considerations are paramount in electronics development.

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u/Infamous-Amphibian-6 6d ago

Get multiple-channel Wago splitters o rail terminals (pricier and uglier). Add electrolytic and ceramic capacitors as needed.

Can also feed a breadboard-style perboard (Electrocookie) and pull all power lines from single rail. 1 electrolytic capacitor close to barrel, ceramic capacitors between MCUs power lines.

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u/JGhostThing 6d ago

Yes, you can connect multiple items to V+. There should only be one ground used by all components.

However, will it work depends on the power supply: how many volts and how many amps. Some power supplies get flaky near their limits.

For my robots, I usually use a single battery (currently 4s1p) and use buck converters to give me the voltages I need. Except the motors just get their supply directly from the battery.

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u/RepresentativeCry294 6d ago

Thats called a parallel circuit?