I want to learn designing IOT PCBs (with 2.4Ghz wireless)

Submitted ⁨⁨2⁩ ⁨weeks⁩ ago⁩ by ⁨ntn888@lemmy.ml⁩ to ⁨askelectronics@discuss.tchncs.de⁩

Hi all! I’m a firmware developer with little knowledge in analog electronics… I deal with firmware for IOT projects all the time.

I had to make a breakout board with an off the shelf RF module with self contained PCB antenna. Now I’m intrigued in the hardware side. I’m inclined to design them from scratch myself. (Obviously ignoring the EMI and FCC certifications for the time being).

What concepts should I be familiar with to achieve this? Starting on I figured to brush up on circuit theory and signals. Where do I go from here? What materials would you recommend? Hopefully I don’t need to get into hardcore RF theory to design these PCBs (I know kicad already has these premade antenna blocks).

Thank you.

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remotelove@lemmy.ca ⁨2⁩ ⁨weeks⁩ ago
Start looking for YouTube videos with Eric Bogatin. He is a professor at CSU Boulder and has re-written the book on proper PCB design. (He does have a book, but he debunked a ton of old theories on high frequency board design and signal integrity.)

Once your signal get past a certain speed, you need to learn how electricity actually flows while understanding that both AC and DC theory applies. If you didn’t know that energy flows in the field around a wire, you probably need to step back a little before you step forward. (Reference Veritasium on YouTube: The Big Misconception About Electricity )

You don’t really need to get into heavy RF theory, but it helps. If there is anything you must learn about, it’s impedance matching and why it matters. To summarize quickly, if there is an impedance mismatch between your transmitter and your antenna, you could easily blow out your transmitter due to excessive power draw and signal reflection. (That is somewhat rare for low power devices, but not uncommon once you start to transmit above 5-10 watts.) If a device needs an antenna, use it, even if were are talking about something as common as WiFi.

For your first designs, respect trace lengths and recommended components. Most of all, respect the keep out areas around an antenna diagram and ensure your ground plane is properly designed and away from the antenna. There are many shitty designs that do work, but you want to strive for precision for your first few iterations.

Also, decoupling becomes more than just a thing to do that might improve stability of your MCU or other components. It’s entirely possible to get the rest of your PCB resonating which will cause all kinds of noise. This is partially negated with proper decoupling.

High frequency design just takes a little more care. Just remember the basic saying: Everything is a resistor, capacitor and inductor.

Now, if you just work with modules (and ESP32 with an integrated antenna comes to mind), almost all of the hard work is done. Make sure you have proper clearances, slap the thing on a board and you are good to go.

For the absolute basics, impedance matching with proper antenna length is what you need to learn first. (Receivers are much more forgiving than transmitters, btw.)

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- ikidd@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
  
  There are many shitty designs that do work
  
  I feel personally attacked.
  
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  - remotelove@lemmy.ca ⁨2⁩ ⁨weeks⁩ ago
    Lol! I suppose the million dollar question is if you are generating interference. You are allowed to have a shitty design that works as long as you aren’t causing grandmas pacemaker any problems.
    
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- ntn888@lemmy.ml ⁨2⁩ ⁨weeks⁩ ago
  Wow, thank you for the very detailed post! I see that impedance matching is an important base subject. Is it covered in standard circuit theory textbooks. I’m looking to use this book. I tried to skim the contents but couldn’t find it… Maybe I need to separately learn it? Thanks.
  
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  - remotelove@lemmy.ca ⁨2⁩ ⁨weeks⁩ ago
    That book is a great start, actually. AC theory is critical in understanding RF circuits.
    
    I noticed there were dedicated sections in that book for LC/RLC circuits. In regards to RF, you might see those referenced as resonant tank circuits, so keep that in mind as you move forward.
    
    You aren’t going to see too much about impedance matching until you start working with transmission lines, as far as I know.
    
    I just looked this up and ready through it and it seems like a good intro. It’ll be confusing unless you have a basic understanding of AC: …cadence.com/…/msa2021-understanding-impedance-ma…
    
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litchralee@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
To start, it might be worth reviewing the recommended antenna traces for wireless ICs, since vendors often provide precomputed and validated reference designs in their data sheets. These are often what are made into breakout boards, and there’s a lot which can be learned by what these reference designs take into consideration.

I’ve not specifically done PCB designs with antennas, but I have done my own designs for high-speed differential signals, where the impedance of two traces have to be consistent along their length, whether side-by-side or on opposite sides of the PCB. As you observed, KiCAD can do a lot of this computation but good antenna design means even the pads that attach to the IC also need to be impedance-matched. And that requires both an understanding of where problems arise (eg when traces turn a corner), how to compute the effects (using KiCAD’s features), and whether the issue might not even make a big difference in overall performance.

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- ntn888@lemmy.ml ⁨2⁩ ⁨weeks⁩ ago
  I see, that reference design suggestion sounds good. And it sounds like there’s more practical consideration in tracing/routing on top of the theory… Thanks for the input!
  
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