Verify my project schema by more experienced world

Hi guys,

I'm new in world of Arduino and low-voltage projects.
I'm working as a software developer (C# & (C++ occasionally)), so coding part is not problem for me! In fact, I already prepared code for IR control, motor control, RF communication...

I'm trying to make a small RC robot and I designed this schema, so I would like to verify if everything can work together, if I miss something, advices + suggestions.

What do you guys think about this schema above? Can it work? Do I have to add/remove something? Is it a good idea to use LiPo battery as power source? If yes, which voltage should I use (7.4V or 11.1V)? Do I need to put protection board? etc...

I will welcome and appreciate any suggestions, ideas and advices!

Thanks a lot!


Hi, @budonl
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".

Thanks for the diagram, but it may be better if you use pen(cil) and paper and hand draw your project, then post an image of your circuit.

As a couple of suggestions;
Try not to use diagonal wires, use a mix of horizontal and vertical.
You have labelled the components, which is great, but you also need to label the pins that your wires are connected to.
You can simplify you diagram even more by using the gnd symbol at the output negative of the DC-DC converters, the negative terminal on input and output are connected together, so that will help to remove some wires.

A good first try mate.
Just work at it.
From what I can see your configuration looks good and should work.

Thanks.. Tom... :smiley: :+1: :coffee: :australia:
PS, use this symbol for your motor.

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A good suggestion, rather than have you battery connected to Vin, there is nothing stopping you using the 5V from the IR DC-DC converter into the Vcc or 5V pin of the ProMini.
The Vin needs 7.5V or more, not 5V to operate as it is into a linear regulator and it needs more than really 7.5V to operate.
Using the DC-DC converter will be more efficient.

Tom... :smiley: :+1: :australia:

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Hi @TomGeorge,

Thanks a lot for your welcome message and for very useful tips, trick and notes!
Next time I will sketch schema on paper or by using Eagle, EasyEDA.

About connecting Arduino to IR DC-DC converter.
Simply I don't connect Arduino Raw pin to LiPo battery, but instead I connect from 5V DC-DC output to Vin pin?

If I connect to raw, in that case Arduino will use Linear regulator and there I have also some energy waste (for that reason I need >7.5V to get 5V operative). Since I already have DC-DC converter, I can use that output and connect directly to Arduino Vin.

What do you think, can I instead of using 3 DC-DC converters, use 2?

  • DC-DC Converter (5V): Using for IR LEDs, Arduino Vin, Motor L9110S H-bridge
  • DC-DC Converter (3.3V): Using for NRF24L01

About power supply:
Is it okay to use LiPo battery? Should I use 7.4V or 11.1V? Do I have to add some protection boards for LiPo?


The nominal 7.4 volt lipo will be good until the cells are around 3.5 volts (I am very conservative, you can take them down further).

I would try the 7.4 volt pack first, and see if it can power the step downs and give you good voltage to operate you peripherals at the point where you would be stopping the lipo discharge, 7 volts or 6.5, whatever.

If there is insufficient headroom with the 7.4 volt nominal then use the 11.1volt "3s" pack.

I agree the 5 volts for the Arduino should come from a step-down for greatest efficiency, more so at 11.1 than 7.4 volts.

Lipos are amazing. But they do need care. I use naked lipo cells and batteries of them, but I also

  • monitor cell voltage carefully when in use
  • charge them with a real lipo charger while disconnected from projects they power

You can learn more than you need to know at At the very least know that lipos can store a huge amount of energy and are quite capable of delivering it rapidly whether that was your intention or not. Sometimes this energy does undesirable things.

Lipos need a little more care and attention.

If you want to have a neat rechargeable device with a build in battery, then yes, I would recommend additional circuitry to manage charge and discharge, which circuitry or module should include all protections.


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Fritzing pictures and Fritzing "schematics" are barely useful. Many here will not even try to read them.

First- why so many "adjustable step down" modules. You only need one buck converter with enough power to run your 5V devices. You don't say which NRF24L01 board you are using, but all the boards I've seen have a 3.3V regulator on-board and run from 5V.

Your "schematic" as drawn won't work. All grounds should be connected together. As drawn, the data line at the base of the transistor (a MOSFET might be better) has no reference to the ground pin of the Pro Micro, so the Base-Emitter voltage will never turn on the transistor. It might see the ground through the "step-down" (whatever is in that box), but I wouldn't count on it.

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Hi @SteveMann,

I appreciate your feedback and advices.

I am aware that Fritzing drawings are not acceptable and I'm planning to use Eagle or EasyEDA to draw diagrams or by hand (might be better for practicing and to learn signs and symbols).

I was thinking the same, to reduce step down modules to avoid unnecessary waste.

I'm planning to use LM2596 DC-DC Buck module:

  • Input voltage :4V ~ 35V
  • The output voltage : 1.23V ~ 30V
  • Output Current :3A(Max)
  • Conversion efficiency:92%(MAX)
  • Output ripple: <30mV

I will try to power my: L9110S H-bridge module (2 motors will be connected), Arduino board and IR circuit with one LM2596 module.

About NRF24L01 module. All of them what I saw they require from 1.9V to 3.6V and there is a possibility to buy "Expansion board" which will do regulation from 5V to 3.3V and have already decoupling capacitor. I don't have that expansion board, so I guess that I have to use additional LM2596 step down module to power NRF24L01 with 3.3V. I was thinking to power it via Arduino 3.3V pin, but after some research I saw that it is better to power it "externally" to make NRF24L01 module more stable.

About IR diagram. If I replace 2N2222 with MOSFET, do I have to change something on that diagram?

Good point about my drawing skills. I have to improve it!
Beside my drawing skills, I'm aware of common grounding and that everything has to be connected to the same ground.

Thanks a lot!
I really appreciate your time and advices.


Hi @alto777,

Thank you so much for your time!

Do you have any reference link where I can get trustworthy 11.1V LiPo batteries, charger and module with all protection (if I wanna to make rechargeable device -> *I would love to make it rechargeable)?

I'm living in Europe, so sites like: Amazon, AliExpress, Bangood are accepted if they are trustworthy.

Thanks a lot!
Best Regards,

Here is an example of how I drive an LED with a 2N7000 MOSFET. I am certainly no expert using MOSFETS, and some will say that the 1K resistor is not needed.

And the 10k is connected wrongly. :roll_eyes:

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I have no experience other than using naked lipos and separate (from the project circuitry) charging solutions.

But I have seen, and a bit of casual googling finds

I just searched for

protection charge discharge lipo module

and there are others. I don't see a way to adjust the charging current with the one I linked above - part of making lipos last is two charge them gently if you have the patience...

As for the batteries themselves, again all my experience is with flight batteries which typically have nothing but the lipo cells. These are available at all sizes and voltages and power capacities.

Go to Amazon and search there, for example

2s 2000mah

turns up a nice variety.

HTH and be careful.


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