Electronics > Beginners
Demodulation
baksuz:
Hello,
I need to do demodulation of modulated signal where I have 2 wires sin+ and sin-(negative voltage) 3.3v peak voltage 10kHz, I need to do it with Arduino or STM32. Can someone give me any advice on how to do it or is it even possible?
janoc:
--- Quote from: baksuz on March 19, 2019, 01:09:22 pm ---Hello,
I need to do demodulation of modulated signal where I have 2 wires sin+ and sin-(negative voltage) 3.3v peak voltage 10kHz, I need to do it with Arduino or STM32. Can someone give me any advice on how to do it or is it even possible?
--- End quote ---
That's quite a confused mess. So all we know is that you have 2 power rails and a 10kHz signal. No idea what the 3.3V is about - are the two power rails +-3.3V? Or the input signal? (commas in sentences are kinda important, you know?).
What kind of modulation are we talking about? What kind of signal? Which Arduino? 8bit one? Or 32bit ARM-based ones? Which STM32? They exist from tiny Cortex M0 that are unlikely to be able to do much up to a Cortex M7 that could demodulate radio signals in real time while still having most of the resources free ...
Unless you tell us more, it is very unlikely that anyone will be able to help you.
rstofer:
Is the 10 kHz the modulating frequency or the carrier frequency? I would run the signal into a low pass filter to remove the carrier (envelope detector).
Then I would run the demodulated signal into an ADC and sample at least twice the modulating frequency. Shannon/Nyquist will lead the way on sampling. Now you have a digital representation but memory is filling up fast!
If you have to run the modulated carrier into the ADC, you are going to need a lot more bandwidth. You still need to sample at a rate at least twice the highest frequency and, depending on the carrier, this could be quite high.
https://en.wikipedia.org/wiki/Envelope_detector
I don't know which uCs can sample at 20 kHz and still have time for other tasks. I would buy the chip with the fastest ADC on the planet and work down.
Benta:
--- Quote from: rstofer on March 19, 2019, 04:42:18 pm ---I would run the signal into a low pass filter to remove the carrier (envelope detector).
--- End quote ---
Assuming it's AM, ASK or OOK, which we don't know.
janoc:
--- Quote from: rstofer on March 19, 2019, 04:42:18 pm ---I don't know which uCs can sample at 20 kHz and still have time for other tasks. I would buy the chip with the fastest ADC on the planet and work down.
--- End quote ---
Some STM32s can do it, possibly even faster, especially if you use DMA. 20kHz is not that fast.
Look up e.g. STM32-SDR project - here is one guy running a full HAM receiver on one of those Bluepill (STM32F103xxx) boards:
And that's an old and relatively slow/low end STM32. The bigger ones can handle a lot more - this guy has an STM32F4xx running an oscilloscope at 2.8Msps:
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