Trying to understand NFC ASK Modulation

It is possible for sure, but its not really a project I would recommend taking on without an oscilloscope.

So if your looking for an excuse to purchase an MXO4 scope, id say go for it ;) 

I am Rx/Tx USB-PD with the pio on a PI pico right now which is differential Manchester, so that could provide some inspiration  

Well this project doesn't require anything fancy, right now I am using a 555 timer as a level translator and $10 logic analyzer! 

I am transmitting the same source advertisement packet from a Pico

Pico sending a good crc packet,

A source request

Transmitting usb-pd with the pico is quite simple, for example here is my python code for sending a goodcrc message

def goodCRC():
    # If preamble can be 65 BMC bits then it could be done here
    # Right now, PIOSM takes care of 64 BMC bits preamble
    preamble = []#[0b1010101010]*7
    sop = [symtable['S1']]*3 + [symtable['S2']]
    header = b'\x01\x01'
    data = array.array('i',[])
    payload = header+bytes(data)
    
    crc = binascii.crc32(payload)
    payload += crc.to_bytes(4,'little')
    
    txsyms = preamble + sop
    txsyms += usbpd4b5bencode(payload)
    txsyms += [symtable['EOP'],0]

    pdtx(txsyms)

The receive side is a bit more complicated... 

I think it will be a helpful project for someone just wanting to experiment and learn about usb-pd signaling 

This looks great!

Thanks! Its been quite enjoyable experimenting with the pico, its like I'm building an my first power supply again many years later its fun try to new things!

To send the same message as my power supply, the code was also quite simple too

def usbpdbroadcast():
    # If preamble can be 65 BMC bits then it could be done here
    # Right now, PIOSM takes care of 64 BMC bits preamble
    preamble = []#[0b1010101010]*7
    sop = [symtable['S1']]*3 + [symtable['S2']]
    header = b'\xa1\x69'
    data = array.array('i',[0x0a01912c,0x0002d12c,0x0003c12c,0x0004b12c,0x0005a0fa,0x000640e1])
    payload = header+bytes(data)
    
    crc = binascii.crc32(payload)
    payload += crc.to_bytes(4,'little')
    
    txsyms = preamble + sop
    txsyms += usbpd4b5bencode(payload)
    txsyms += [symtable['EOP'],0]

    pdtx(txsyms)
    
    
symtable = {
    0: 0b11110,
    1: 0b01001,
    2: 0b10100,
    3: 0b10101,
    4: 0b01010,
    5: 0b01011,
    6: 0b01110,
    7: 0b01111,
    8: 0b10010,
    9: 0b10011,
    10: 0b10110,
    11: 0b10111,
    12: 0b11010,
    13: 0b11011,
    14: 0b11100,
    15: 0b11101,
    'S1': 0b11000,
    'S2': 0b10001,
    'S3': 0b00110,
    'RST1': 0b00111,
    'RST2': 0b11001,
    'EOP': 0b01101}

Hopefully soon I will have the 2 talking to each other, I think I have most of the pieces... 

Thanks! Its been quite enjoyable experimenting with the pico, its like I'm building an my first power supply again many years later its fun try to new things!

To send the same message as my power supply, the code was also quite simple too

def usbpdbroadcast():
    # If preamble can be 65 BMC bits then it could be done here
    # Right now, PIOSM takes care of 64 BMC bits preamble
    preamble = []#[0b1010101010]*7
    sop = [symtable['S1']]*3 + [symtable['S2']]
    header = b'\xa1\x69'
    data = array.array('i',[0x0a01912c,0x0002d12c,0x0003c12c,0x0004b12c,0x0005a0fa,0x000640e1])
    payload = header+bytes(data)
    
    crc = binascii.crc32(payload)
    payload += crc.to_bytes(4,'little')
    
    txsyms = preamble + sop
    txsyms += usbpd4b5bencode(payload)
    txsyms += [symtable['EOP'],0]

    pdtx(txsyms)
    
    
symtable = {
    0: 0b11110,
    1: 0b01001,
    2: 0b10100,
    3: 0b10101,
    4: 0b01010,
    5: 0b01011,
    6: 0b01110,
    7: 0b01111,
    8: 0b10010,
    9: 0b10011,
    10: 0b10110,
    11: 0b10111,
    12: 0b11010,
    13: 0b11011,
    14: 0b11100,
    15: 0b11101,
    'S1': 0b11000,
    'S2': 0b10001,
    'S3': 0b00110,
    'RST1': 0b00111,
    'RST2': 0b11001,
    'EOP': 0b01101}

Hopefully soon I will have the 2 talking to each other, I think I have most of the pieces... 

It's great that MicroPython is being used, it's ideal for experimentation like this.

MicroPython is not bad at all for data manipulation for protocols! I was stuck on a CRC issue a while back (I cant recall the specifics), and it was possible to find a normal Python library, and edit it slightly to function with MicroPython, so there's actually a wealth of potentially useful code that can be used with it, with a bit of tweaking occasionally.

I hope MicroPython gets closer to real Python so that microcontroller projects benefit more from a lot of regular Python libraries.