SX126x LoRa modules !

manuka

Senior Member
Agreed -narrower BW will certainly improve range if you are using Dorji''s DRF1268DM modules (best confirm). Refer attached table -organised by SRNET & myself some years ago with SX127x modules. I'd settled then on 62.5kHz BW for reliability.

The crystal oscillator on 2nd generation SX126x based LoRa offerings has superior matching & temperature stability than the xtall on initial SX127x modules. Dorji's setup tool is quite involved however so you may well be able to stay with what's working! Mmm -aside from Oaks in full leaf do you experience heavy rain signal fade ? Stan.
 

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geezer88

Senior Member
Here is a bit of an update. I set my Dorji SX1268 modules BW31.25, SF12, and CR 4/5. With only a few tests, RSSI varies from 142 to 150, about the same as where it has been the last couple of weeks. Besides the leafing out of the oaks, I do see signal levels drop in heavy rain. So far, I have not had a total failure to communicate, and I think the leaves have pretty much done their thing.

I haven't worked any more on antennas, except this afternoon I put the little coil antenna that came with the modules in the nanoVNA and got a resonant frequency of 455Mhz, and SWR of 1.2.

Thanks for your tips. I need to reread the SX1268 manual to find out how to get SNR. It would be interesting to see what the backround noise is like out here.

tom
 

srnet

Senior Member
SNR does not help you much to identify the actual noise level, since it just tells you relationship between the strength of the received signal and the noise level. So unless the received signal level is a known constant .............

There is a command for the SX126X that tells you the instantaneous noise level (RSSI) , the noise level the device is seeing at that instant. Thus if there is no packet in progress you can use this command to see what the background noise level is.

I would not trust the RSSI reported from the LoRa devices to be definative however, Semtech have altered the calculation in the datasheets over the years, with no hardware changes.

Incidently, quoting RSSI values as positive numbers makes no sense at all, better for everyone if you convert the readings you might get from some bit of incorrect software into the real world numbers. I, and most passing readers of the forum, have no idea whatsoever what an RSSI of '142 to 150' means.
 

geezer88

Senior Member
Time for a quick update. The signal strength, RSSI, has been increasing for the last week or so. I think the newly opened leaves and the rain blocked the signal more effectively than when dry. That seems intuitively right, as more water content the blocking effect would be increased.

In his last comment, srnet made the comment that "RSSI values as positive numbers makes no sense at all". Previously he said, "Semtech have altered the calculation in the datasheets over the years".

The last statement is precisely why I prefer the raw number, straight from the hardware; it hasn't been monkeyed with. I can expect a number from someone else to be comparable to one I have gotten.

tom
 

BillBWann

Member
I recently ordered a couple of DRF1268DS modules from Dorji to have a play with them. They were promptly delivered only a week or so later from China which came as a pleasant surprise and they have worked well.

I’ve used the configuration program to alter some parameters like baud rate and bandwidth and again, it all worked as expected.

I then tried using the picaxe to change the configuration and read the RSSI but I’ve run into problems.

As I understand it, to put the module into AT mode, I simply send the sequence FF,FF,02,0B,0D to the DRF1268DS which should then go into command mode and confirm that by responding with the sequence FF,FF,02,0C,0E. But I’m not getting any response and the sequence is simply being transmitted to the other module - but interestingly, the last char transmitted (0D) isn’t received although it’s clearly sent.

DRF1268DS.png

I’m not sure how the DRF1268DS distinguishes this Enter AT Mode sequence from such a sequence being part of a transmitted binary file but I’m assuming that the sequence needs a pause before and after but I didn’t see that in the manual.

Where am I going wrong?
 

AllyCat

Senior Member
Hi,

$0D (decimal 13) is the "Carriage Return" character which is often paired with "Line Feed" ($0A, decimal 10) and there are various options in most terminal emulators to add or remove the LF character. "Windows" may also do unexpected things with these characters, so I wondered if that was related to your problem.

But first, you appear to be sending (decimal) 29 which is $1D and previously 27 which is $1B . Is your issue just "a slip of the finger" (mind) ?

Cheers, Alan.
 

BillBWann

Member
Is your issue just "a slip of the finger" (mind) ?
Thanks Alan for your reply. Yes, it was a slip of the finger but not what was sent to the DRF1268DS. It was my typing in #45 where I listed the Set AT Command. It should have been FF,FF,02,1B,1D and get a reply of FF,FF,02,1C,1E. The picaxe program had the correct string so that was not the problem.

However, I've just discovered what was the real problem and that was that I was sending out the characters too slowly with gaps between characters of about 3 msecs. This was because the program assembles the string in RAM and then uses a For...Next loop to serout the @bptr values. When I increased the frequency to M8, it all worked as expected.

So it may be that a pause of more than 2 msecs or so is enough for the DRF1268DS to think that its the end of a Command sequence.
 

manuka

Senior Member
Bill -thanks for this detective work. I've run into diverse AT timing issues before & your finding is a handy heads up on the matter! Stan.
 

AllyCat

Senior Member
Hi,
SNR is a better indication of how good the signals are when reception is close the the limit, as discussed here;
https://www.loratracker.uk/lora-signal-quality-rssi-or-snr/
Researching another project, I see that Stuart's "loratracker" domain (which is linked from several PICaxe forum threads) has now expired and he hasn't logged in here for almost 9 months. At the moment most of the PICaxe files still appear to be on DropBox , but I wonder for how long ?

Cheers, Alan.
 

John West

Senior Member
A heads up for Semtech's updated SX126x LoRa engines.These were announced 2018 but complete setups are now arriving. See DORJI's SPI =>https://www.tindie.com/products/DORJI_COM/433mhz-sx1268-tcxo-module-drf1268t/.

Features abound compared with existing SX127x based LoRa modules -check Chengdu EBYTE's SX126x E22 range -
* cheaper (< US$10 for UART), smaller, lighter
* wide supply range
* allow remote config.
* RSSI
* channel "listen before talk" carrier sense
* WOR (wake on radio -greatly enhances battery drain
* relay feature
* low RX current drain (~half that of SX127x)
* configs. over a wider freq. range (410-493MHz apparently 1MHz spaced )
* simple UART or SPI
* GUI setup
* AT command friendly
* work with SX127x

Several of these features look "smell of an oily electron" goldmines for energy sniffing IoT applications!

EBYTE'S E22 pinouts however are 1.27mm spaced (half the normal .1" = 2.54mm) which means breadboard issues. However at least pins are not cussed 2mm, & only a handful are needed anyway.

I've ordered some E22-400T22S 433MHz UART versions,but delivery influenced by the present CNY (Chinese New Year) shut down. Stay tuned -Stan.

Extra: If new to LoRa perhaps refer my mega (! ) popular 2015 PICAXE slanted Instructable => https://www.instructables.com/id/Introducing-LoRa-/
Thanks for this, Manuka. I always like your highly detailed work.
 
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