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Kimchii , 12-05-2023, 08:30 PM

There may be one or more videos on youtube that already answers the question I have. I haven't found one that does, so I hope no one mind me asking this question. I am not really sure how to ask it properly. But I hope someone will understand what I am trying to ask. My terminology **will probably** be off, so feel free to correct me.

If I were to make it into a one line question it would be:
*How do I know what components to pick, not just the "major" (IC, SoC, battery, etc) ones, but also the "minor" (resistors, capacitors, etc) ones.*
For example if I have a SoC, how do I know what "minor" components I need together with it?

I am a total beginner of PCB design, I can make a LED light light up without it exploding on my breadboard, but that is about it. So I wonder how do I know what components I need outside of the "main" components in a project.

In my first real project I want to try and make it a bit more complex. I want to use an SoC to control the speed of a small motor that is powered by a rechargeable LiPo battery.

So the "big" components would be:
**System-on-Chip**
I have no idea how to pick this for my project (I will watch "What to consider when selecting chips for your new board" though). So I picked nRF52840 that had some features I liked (like blue tooth) when I was looking around. I picked this chip because when I get it to work eventually I can also learn how to program it.
**Battery**
I haven't picked one yet, I think it will be a flat 3.7V battery.
**USB**
USB-C for charging, no data.
**Motor**
A 3.7V motor, and I still need to find one.

It is a bit ambitious for my skill level, but I believe it can be educational to make it a bit more challenging. These are "just" four components, but I am pretty sure I need far more components around these to make this a project that won't go up in smokes. So how do I know what components I need? I hope my "over ambitious for a beginner" question makes sense!

QDrives , 12-05-2023, 08:49 PM

"...a bit ambitious..." is an understatement. Motor control is:
- Power electronics
- Power supplies
- Analog
- Digital
- Thermal
- Control loops
- EMC
- Safety
Then you add LiPo battery -- another huge demand on safety.

Anyhow, to answer you question... in one short sentence: you read the datasheet and application notes. Robert would add reference designs (I do not).
In the datasheet they will tell you which components are **required** to get that component working (ie. decoupling capacitors, pull-up resistors, etc.).
When you check example circuits, they may state other components (ICs) that you then need to check. It may also provide you with terminology that you can use to find the knowledge you seek.

Then on the motor: DC brush, BLDC, stepper or ...??

Kimchii , 12-05-2023, 09:12 PM

I'll see if I can find some to read and/or watch about the topics you mentioned for motor control. I will also dig around in the datasheet for the nRF52840.

I've found LiPo charging circuits here and there, but they never included a load.

I have been looking at brush-less DC motors. The ones I have looked at are very small, but it is always at places like Amazon so I don't really now what I get my hands on.

I don't mind making this in steps, so building the entire thing in one iteration isn't the most important.

Robert Feranec , 12-06-2023, 07:11 AM

@QDrives knows me very well 😄 Yes, my recomendation is, use reference designs. For example if you pick a CPU, there will be a reference design which would include all the "small" components around it. And then your task would be to connect multiple reference designs together. That is the simplest way to start with and has a high chance that your circuit will work ok. PS: when starting with something you have never used before it can be useful to buy development kits - so in your case you could buy development kits for each block (CPU, battery circuit, Motor circuit, ...), connect them together and then draw your schematic based on the development kit schematics + your connections between the kits. This may not be the most optimum design, but as I said it has a high chance it will work. Once you have it and it works, then you can optimize it.

QDrives , 12-06-2023, 08:56 PM

You can start here: https://www.youtube.com/watch?v=VI7pdKrchM0&list=PLel9lxsexEZaVM6uOlAwi2aga1lcd1MzB

ATHONOR , 12-06-2023, 09:36 PM

I agree with both the comments above. Start in blocks (evaluation boards)..... if there is reference designs available try and understand them rather than just use them. Once you have proven the "blocks" you can then start thinking about putting together or in other words design a PCB.

If there is anything engineering has taught me, it's providing enough evidence that your judgement is correct at the time of design. If you have too many question marks, answer them 🙂