Hello again,
Just a small update in case someone wants to try this out. I have two
patches to apply to get this working for me. The first,
RFM69-Library-AVR-syncword.patch, is to apply against
fermitron2048/packetdemod and the second, RFM69.patch, is to apply
against nayem-cosmic/RFM69-Library-AVR. My thanks to both
nayem-cosmic and fermitron2048 for their work writing these pieces of
software.
Take care.
Chris
On Thu, Feb 3, 2022 at 12:40 PM Chris Gorman <chrisjohgor...@gmail.com> wrote:
>
> Hello All,
>
> I have two rfm69 boards [1] connected to two avrs and they are sending
> messages to each other over the airway. Once I got this working I
> thought it would be fun to inspect the messages being sent with my
> rtl_sdr. I can confirm the message is being sent over serial on the
> receiver.
>
> I went searching on the internet for a way to decode the transmission
> and found some scripts to use gnuradio to do packetdemod on rfm69
> boards [2]. The problem with this setup is it requires me to modify
> the code to the rfm69 [3] to prevent whitening. My software to run
> the avrs isn't the same as the author of the packetdemod's and I can't
> apply his patch. I have looked at the code to see if I am using
> whitening, but as far as I can tell I am not. Regardless when I run
> the packetdemod script, I get 'Invalid packets" instead of my message.
>
> In my inbox this morning I found an email with a reference to packet
> communications with gnuradio [4] and am wondering if I should be using
> this method to decode the transmission between the two rfm69's? I
> will try it out anyway as it seems interesting, but is this the
> correct direction to analyze the transmission between two boards like
> the rfm69s?
>
> Thanks in advance,
>
> Chris
>
> [1] https://www.sparkfun.com/products/12775
> [2] https://github.com/fermitron2048/packetdemod
> [3] https://github.com/nayem-cosmic/RFM69-Library-AVR
> [4] https://wiki.gnuradio.org/index.php?title=Packet_Communications
diff --git a/packetdemod.py b/packetdemod.py
index 1825c64..bdaf828 100644
--- a/packetdemod.py
+++ b/packetdemod.py
@@ -126,7 +126,7 @@ def parsepacket(bits):
invalid_packets += 1
return
syncword = (ord(bytes[0])<<8) + ord(bytes[1])
- if(syncword != 0x2d21):
+ if(syncword != 0x2dd4):
print("Invalid packet")
invalid_packets += 1
return
@@ -192,7 +192,7 @@ def decode(values = []):
# Align to sync word for beginning of packet
for i in range(1,50):
- syncword = [0,0,1,0,1,1,0,1,0,0,1,0,0,0,0,1]
+ syncword = [0,0,1,0,1,1,0,1,1,1,0,1,0,1,0,0]
tmpbits = bits[i:]
if(cmp(syncword,tmpbits[:16].tolist()) == 0):
bits = bits[i:]
diff --git a/radio.py b/radio.py
index df67922..25e366f 100644
--- a/radio.py
+++ b/radio.py
@@ -81,7 +81,7 @@ def parsepacket(bits):
invalid_packets += 1
return
syncword = (ord(bytes[0])<<8) + ord(bytes[1])
- if(syncword != 0x2d21):
+ if(syncword != 0x2dd4):
print("Invalid packet")
invalid_packets += 1
return
@@ -147,7 +147,7 @@ def decode(values = []):
# Align to sync word for beginning of packet
for i in range(1,50):
- syncword = [0,0,1,0,1,1,0,1,0,0,1,0,0,0,0,1]
+ syncword = [0,0,1,0,1,1,0,1,1,1,0,1,0,1,0,0]
tmpbits = bits[i:]
if(cmp(syncword,tmpbits[:16].tolist()) == 0):
bits = bits[i:]
diff --git a/RFM69.c b/RFM69.c
index 1a52fc3..83ba45f 100644
--- a/RFM69.c
+++ b/RFM69.c
@@ -59,11 +59,11 @@ void rfm69_init(uint16_t freqBand, uint8_t nodeID, uint8_t networkID)
const uint8_t CONFIG[][2] =
{
/* 0x01 */ { REG_OPMODE, RF_OPMODE_SEQUENCER_ON | RF_OPMODE_LISTEN_OFF | RF_OPMODE_STANDBY },
- /* 0x02 */ { REG_DATAMODUL, RF_DATAMODUL_DATAMODE_PACKET | RF_DATAMODUL_MODULATIONTYPE_FSK | RF_DATAMODUL_MODULATIONSHAPING_00 }, // no shaping
- /* 0x03 */ { REG_BITRATEMSB, RF_BITRATEMSB_55555}, // default: 4.8 KBPS
- /* 0x04 */ { REG_BITRATELSB, RF_BITRATELSB_55555},
- /* 0x05 */ { REG_FDEVMSB, RF_FDEVMSB_50000}, // default: 5KHz, (FDEV + BitRate / 2 <= 500KHz)
- /* 0x06 */ { REG_FDEVLSB, RF_FDEVLSB_50000},
+ /* 0x02 */ { REG_DATAMODUL, RF_DATAMODUL_DATAMODE_PACKET | RF_DATAMODUL_MODULATIONTYPE_OOK | RF_DATAMODUL_MODULATIONSHAPING_00 }, // no shaping
+ /* 0x03 */ { REG_BITRATEMSB, RF_BITRATEMSB_1200}, // default: 4.8 KBPS
+ /* 0x04 */ { REG_BITRATELSB, RF_BITRATELSB_1200},
+ /* 0x05 */ { REG_FDEVMSB, RF_FDEVMSB_5000}, // default: 5KHz, (FDEV + BitRate / 2 <= 500KHz)
+ /* 0x06 */ { REG_FDEVLSB, RF_FDEVLSB_5000},
//* 0x07 */ { REG_FRFMSB, RF_FRFMSB_433},
//* 0x08 */ { REG_FRFMID, RF_FRFMID_433},
