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Trying to understand NFC ASK Modulation

BigG

According to my Google search, NFC uses ASK modulation to transmit data:

https://www.rfwireless-world.com/Tutorials/NFC-Near-Field-Communication-tutorial.html

https://www.rfwireless-world.com/Tutorials/NFC-Modulation-and-NFC-Coding.html

Which I have interpreted as the following where the "Mixing Circuit" includes the NFC tuned antenna and two picoFarad capacitors... but what else is needed.

image

As a non electronics engineer I am trying to work out a minimum circuit required.

Then my lofty intentions is to use a Raspberry Pi Pico to generate my clock signal using PIO and as there is also a Manchester Encoding PIO example, I will attempt to use that too.

So could this work, I wonder?

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  • 0 in reply to BigG

    A slightly similar (but different) project was a heartbeat monitor strap, they transmit ASK-like pulses at a much lower frequency (5 kHz) which in theory sounds as if it should make the project easier, but with low frequencies come other issues, especially dealing with noise. I built the front end to it last year, but didn't get around to blogging it. For that, I used op-amp buffers basically, but because the signal is weak (compared to NFC, the heartbeat straps need to be monitorable from a slightly larger distance, and they run from a coin cell so not a lot of power), it needed heavy filtering to extract the signal from the noise. I didn't use SDR, but just used sharp filters. I did manage to get the signal (receivable to almost a couple of metres!, which was more than enough for its use-case) in a decent form, but other stuff got in the way and I never got to complete it. Also my pickup coil was massive : ) About the size of a coke-can.

    I don't have the schematic (I didn't create one, because I was just experimenting, and thought I was going to write the circuit down soon, but didn't) but could dig up the stripboard I created it on, would need some reverse-engineering by someone!

  • 0 in reply to shabaz

    I discovered this interesting project online... which uses lower frequencies etc. Schematics etc included.

    github.com/.../pico-dco