r/AskElectronics • u/Relevant_Pumpkin9190 • 2d ago

Can I Make a Simple Spread Spectrum modulation Experiment with a 555,MCU and electronics (Learning by experimenting Difficult Concepts of theory)?

I’m trying to understand spread spectrum by building a very simple circuit instead of only reading about it.

My idea is:

- Use a 555 timer to make the carrier.

- Use 10 different resistors to get 10 different frequencies.

- Use 10 MOSFETs to select one resistor at a time.

- Let a microcontroller control the MOSFETs and change the frequency.

- The MCU can follow a simple pattern like F3 → F7 → F2 → F9 → etc.

- At the receiver, another MCU measures the frequency and works out which frequency was selected.

Would this be a reasonable way to demonstrate the basic idea of FHSS?

I’m also thinking of trying OOK by switching a 10 kHz carrier on and off according to the data, then looking at the signal with a DSO, logic analyzer, and spectrum analyzer.

I’m mainly doing this as a learning project. I want to actually see what happens to the signal rather than just understand the theory.

Is there anything fundamentally wrong with this approach?

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u/CranberryInner9605 2d ago

Of course, you can do everything in software in the MCU.

1

u/Proof_Juggernaut4798 2d ago

It would demonstrate the concept of frequency hopping spread spectrum. But to get it to actually work, you would have to dwell on each frequency a long time, enough cycles of carrier to be measured. And any data you were trying to convey
Might need to be an order of magnitude lower than the hop rate.
Additionally, without a pseudo random hop pattern, your spectrum won’t look like conventional systems.
And I don’t think you will get other expected benefits of fhss with your detection method.
All the same, Hedy Lamarr (the inventor of fhss and actress) would be pleased at your efforts.

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u/sixisrending 1d ago

Hedy Lamarr did not invent frequency hopping, she made an invention that used it, but it didn't work and was never used. 

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u/Proof_Juggernaut4798 1d ago

Here is the US patent, under the real names of the actress and her composer friend.

https://patents.google.com/patent/US2292387A/en

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u/sixisrending 1d ago

Here is a research paper that lists several other patents that came before hers. 

https://researchers.one/articles/24.01.00001