sending 25 bit ook signal.

[adminy]

transmit only takes bytes and I'd like to send 25 bits of information about 4 times,

my parameters are the following:

[~ (50kHz) ]            # define a base frequency
[_ (2100us) ]             # define a long gap (6 clks)
[0 (~344us) (1238us) ]   # define a short pulse and long gap (1:3)
[1 (~1032us) (344us) ]   # define a long pulse and short gap (3:1)

And the key is 0011011101100111101111000.

code = '006ecf78'

code = int(code, 16).to_bytes(4, byteorder='big')

print(code, len(code))

import cc1101, math


MESSAGE_BITS = 25
MESSAGE_REPEAT = 4

SYNC_WORD = bytes([255, 168])  # 168 might be sender-specific


with cc1101.CC1101() as transceiver:
    transceiver.set_base_frequency_hertz(433.92e6)
    transceiver.set_symbol_rate_baud(2048)
    transceiver.set_sync_mode(cc1101.SyncMode.TRANSMIT_16_MATCH_15_BITS, _carrier_sense_threshold_enabled=True)
    transceiver.set_sync_word(SYNC_WORD)
    transceiver.disable_checksum()
    
    transmission_length_bytes = math.ceil(MESSAGE_BITS * MESSAGE_REPEAT / 8)
    transceiver.set_packet_length_mode(cc1101.PacketLengthMode.FIXED)
    transceiver.set_packet_length_bytes(transmission_length_bytes - len(SYNC_WORD))

    transceiver._set_filter_bandwidth(mantissa=3, exponent=3)

    print(transceiver)
    transceiver.transmit(code)

    packet = transceiver._wait_for_packet(timeout=0, gdo0_gpio_line_name=b"GPIO24")
    print(packet)

Also not sure that this is the correct way to both receive and transmit at the same time. I suspect this makes sense in a callback way of doing this.

[fphammerle]

cc1101.transmit uses cc1101's "synchronous serial mode". as far as I understand cc1101's official docs that mode does not support sending fraction of bytes (see PKTCTRL0.PKT_FORMAT=1).
if you are using on-off-keying modulation (OOK) without checksums you could just append low bits (signal off) at the end of each payload to fill up incomplete bytes.
alternatively, you could use with transceiver.asynchronous_transmission() as pin: … (see PKTCTRL0.PKT_FORMAT=3 in cc1101's official docs), but then you will need to send your signal manually to pin GDO0.

_wait_for_packet would work as specified in your code sample above. however, that method is still private cause the interface is unstable (might change in future). callback is not implemented yet.

[adminy]

for _wait_for_packet I had to use the libgpiod python package. I have the code changes if you'd like a PR. Can there be multiple fixed values for packages received or would I have to use variable mode for that? Also I noticed some packages are not showing up. I wonder what I can do to receive all packages, maybe have less message repeats and count repeats another way? maybe automate the set_packet_length_bytes function.

[fphammerle]

for _wait_for_packet I had to use the libgpiod python package. I have the code changes if you'd like a PR.

Thanks, I am already using libgpiod, PR isn't needed for my purposes.
https://github.com/fphammerle/python-cc1101/blob/v3.0.0/cc1101/_gpio.py#L65

Can there be multiple fixed values for packages received or would I have to use variable mode for that?

As far as I know, in fixed length mode CC1101 only supports a single length.

Also I noticed some packages are not showing up. I wonder what I can do to receive all packages, maybe have less message repeats and count repeats another way?

Sorry, I can't provide support here (I would need to analyze the signal).

[adminy]

The GPIO was missing the library call in the dll/so lib, because it seems I'm using a newer version of libgpiod. So this worked for me:

I'll try see if I can improove the parsing in case the signal repeats, I'll post my solution here. see if we can improve on the receiving code.

[adminy]

Ok, so I've exhausted all options here, still not receiving anything at all.

import cc1101

with cc1101.CC1101() as transceiver:
    transceiver.set_base_frequency_hertz(433.92e6)
    transceiver.set_symbol_rate_baud(2048)
    transceiver.set_sync_mode(cc1101.SyncMode.NO_PREAMBLE_AND_SYNC_WORD)
    transceiver.disable_checksum()
    transceiver.set_packet_length_mode(cc1101.PacketLengthMode.VARIABLE)

    transceiver._set_filter_bandwidth(mantissa=3, exponent=3)
    transceiver._enable_receive_mode()
    print(transceiver) # CC1101(marcstate=startcal, base_frequency=433.92MHz, symbol_rate=2.05kBaud, modulation_format=ASK_OOK, sync_mode=NO_PREAMBLE_AND_SYNC_WORD, packet_length≤255B, output_power=(0xc6,0))

    while True:
        packet = transceiver._get_received_packet()
        if packet and packet.payload: print(packet.payload)

... and ... radio silence .... (except b'\xff\xff' appearing out of nowhere with no radio involved)
any ideas what I could try @fphammerle ?

[fphammerle]

To verify that the settings above are correct, I would 1. record the original signal (e.g. with a RTL-SDR dongle), 2. transmit with your settings above & record the transmitted signal in the same way as 1. and then compare if 1. and 2. look similar (same base frequency, symbol rate etc.)

b'\xff\xff' are probably noise

[adminy]

the two variables i'm not sure about is the symbol rate and filter bandwidth. I didn't know the rtl_sdr dongle reports back a symbol rate, is this perhaps the sample rate?. I guess that's something I can check.

[fphammerle]

rtl_sdr dongle does not report the symbol rate. You need to (manually) derive the symbol rate from the signal captured by the rtl_sdr dongle.

the sample rate is the configured rate that the rtl_sdr dongle records in

[adminy]

I scanned with rtl sdr.
here are the results: https://triq.org/pdv/#AAB0210306015003EC28108190908190909081818181819090818190818181819090818255+AAB0120301015003EC28108190908190909081818255
I have:

• 119 bytes or 119 * 8 bits of data.
• Duration is 279.16 ms
• sample rate is 250khz.
• 69971 samples
• 160 pulses

ASK bit_rate is the same as the baud_rate.

bits_per_second = (119 * 8) * (1 / 0.279)

3410 baud samples per second

Receiver getting nothing still.

[adminy]

I did a little sanity check test by doing this:

    transceiver._enable_receive_mode()
    while True:
        packet = transceiver._get_received_packet()
        if packet and packet.payload:
            print(packet.payload)
            transceiver._enable_receive_mode()
            

So it looks like packet payload only changes if you call _enable_receive_mode() in a loop continuously after receiving packets. Also the GPIO rising EDGE only gets called once, perhaps I've got to listen to both RISING and FALLING edges?

[fphammerle]

Personally, I use _wait_for_packet (calls _enable_receive_mode before each _get_received_packet).
Sorry, I can't provide any more support here.