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Which lora chip is used in RFM69HCW (rfm9x lora) ?
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Which lora chip is used in RFM69HCW (rfm9x lora) ?

by raspadafruit on Mon Jul 01, 2019 4:12 am

Hi,

I'm using a Lopy4 (it's a developpement board using LoRa https://docs.pycom.io/.gitbook/assets/specsheets/Pycom_002_Specsheets_LoPy4_v2.pdf) and I'm trying to communicate with an "Adafruit RFM95W" (https://www.adafruit.com/product/3072). As it didn't succeed, I looked into datasheets to see if the LoRa chips were the same.

    - Regarding the Lopy, it uses a Semtech SX1276 (Sigfox and Lora).
    - For the RFM95W, on the description it is written "SX1276 LoRa® based module with SPI interface" but on the datasheet page it says SX1272, or SX1231 so I'm confused.

Which LoRa chip is actually used in the breakout module and could it be the reason I can't communicate with the Lopy ?

Thanks.

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by adafruit_support_mike on Mon Jul 01, 2019 4:28 am

Are you sure you've matched the frequency and antenna on the LoPy with the frequency of the packet radio module you got from us? From what I can see in the datasheet linked above, the LoPy can span frequencies from 137MHz to 1.02GHz.

raspadafruit wrote:but on the datasheet page it says SX1272, or SX1231

The non-LoRa packet radio modules use the SX1231, and we generally call them RFM69 boards. The LoRa modules use the SX1272, and we generally call them RFM95 boards.

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by raspadafruit on Mon Jul 01, 2019 4:39 am

Thanks for clearing the chip question out.

Regarding the frequencies, both devices have a range from 868 to 915MHz so I tried to set them to 868 or 870MHz (software part).
But as you mentioned 137MHz to 1.02GHz, maybe we aren't talking about the same thing ?

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by adafruit_support_mike on Mon Jul 01, 2019 11:16 pm

Are you in the US or in Europe?

The FCC allows devices operatings at 915MHz to run unlicensed in the US, while the EU alllows unlicensed devices to use 868MHz.

The datasheet linked above shows connectors for a 433MHz to 510MHz antenna and an 868MHz to 915MHz antenna. The LoRa radio specs further along say the radio has a tuning range from 137MHz to 1.02GHz, which matches the specs for the radio chip.

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by raspadafruit on Tue Jul 02, 2019 3:34 am

I'm in Europe that's why I'm using 868 MHz (on both devices).
I'm using the correct antenna connectors (the one on the right of the led that is for 868-915).

I'm sending packets from the lopy every 5 seconds and reading continuously on the rfm9x.

    - After one minute one packet appeared (and was for the most part unreadable but I recognized the packet).
    I guess, it means that they can communicate but something's wrong it doesn't work correctly (+ the rssi was -60 dB).
    - I tried a second time and the rfm9x received the following :
    Code: Select all | TOGGLE FULL SIZE
    Received (raw bytes): bytearray(b'\x02\xf3\x12E\xe1\xdb_m60S\x8b\\\x854\x1a\xd6\x92\x00\xb6\x8bU\x83\x9d\xb1\x02\x9a\xd5\xac\x97\x18\xae\xa2iQ\
    x8b\xca\x04\n\xc6C\xf6\x9e\x0b\x91\x88
    \xe5\x0e\xf6Q`\x00P\x17]\xff\xd9\x88\x80\xaeB6H\x88\xd8|\xea\x9b\xd2\xe3\x9a\x98\xb33\n/\x15\xdd\x16W\x9fd\xf8\xd3\xa2\t\
    xb0\xfd\x17\x1e\xa5\xe5\xffE\x8d\xc9\x16\x03\xae9\xadm\xde\xbf\xdc\xdd\x99Z\x1eT&\xaf\x03\xd9\\\xcdKq1Hp\x1c\x8ft\x90\xa6)xd\xfd\x9c\xc6W\x01\xf9S\xfaC\x8a\xd8\x9c\x08
    \xe4\x86a\x81AP\xc5\x90Rz\xd7\x1af\xc1\xa8H
    \xc4\xdaC\xa6\xdeY\xd8g\xcf\x8dy\xcc\xbc\xcb\x96\t[82\xb9\xe3\x8d\xc1\x8at\xb0^\xb9\xf2\x8fy\xbdm\xb9\x13\x1ep\xf6\xb4\xee\xd6\x9fJ\x93\xd3\xd3P\x1e]x\xa1\xa1t\
    x02\xcaT\x07\xb0\xa8x/T\x0e\xd80\x8cKbH$\x91\xb4\xee`\x93x\xf2\x08\xbe`\xc1\x93\xd3\xf9N\x048g')
    Traceback (most recent call last):
      File "test.py", line 25, in <module>
        packet_text = str(packet, 'ascii')
    UnicodeDecodeError: 'ascii' codec can't decode byte 0xf3 in position 1: ordinal not in range(128)
    and just crashed

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by adafruit_support_mike on Tue Jul 02, 2019 11:33 pm

Hmm.. that output looks like a baudrate mismatch between the receiver and the computer it's talking to. Things like this:

Code: Select all | TOGGLE FULL SIZE
\x8b\\\x854
with the two extra backslashes looks like it should have been a sequence of 4 bytes, but lost the data for two of them. There are also variable-width sequences like this:

Code: Select all | TOGGLE FULL SIZE
\xe1\xdb_m60S
which look like a garbled signal. The text around it is normal though, which is confusing.

You might want to check with the folks at PyCom and see if they have any idea what that kind of output means:

https://www.pycom.io/contact/

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by raspadafruit on Wed Jul 03, 2019 2:54 am

Thanks, I'll ask them and put the answer here if I got one !

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by raspadafruit on Thu Jul 04, 2019 3:39 am

For those who are interested I actually found an answer : (I posted the same question on pycom's forum https://forum.pycom.io/topic/4962/lora-communication-lopy-rfm9x/7)

Here's the answer that worked :

Hi, i have a look at lora source code from pycom and adafruit( https://github.com/adafruit/Adafruit_Ci ... t_rfm9x.py ) , i'm don't very familiar with their coding style but in my humble opinion adafruit lib they don't do all init stuff for the lora chip (sx1276), and worst they doesn't allow fine grained frequency selection.

In particular for your usage, they don't set a value for lora sync word, so sx1276 use it's reset value 0x12 (private lora), but it's seem that pycom init value is 0x34 (public lora aka lorawan).
I suggest you to test on your pycom device with
Code: Select all | TOGGLE FULL SIZE
lora = LoRa(mode=LoRa.LORA, region=LoRa.EU868,frequency=868000000,public=False)

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Re: Which lora chip is used in RFM69HCW (rfm9x lora) ?

by adafruit_support_mike on Thu Jul 04, 2019 11:50 pm

Glad to hear you goto things working, and thanks for posting the follow-up!

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