SX126x LoRa modules !

manuka

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-/
 

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manuka

Senior Member
Chinese firm Shenzen Dorji recently kindly supplied me several of their new UART friendly SX1268 based 433 MHz modules, & these have been tested to very good effect here in NZ. Several quick points -

* The associated V 2.2 configuration tool is very involved & perhaps needs simplification -advanced tweaks often need NOT be shown for basic setups.

* The RSSI reporting feature is marvellous & offers all sorts of IoT prospects !

* Due to crystal matching tolerances, temperature & aging drift the initial SX127x based modules were usually limited to 62.5 kHz BW. An apparently superior Rakon crystal (~1ppm) is now used, implying tighter BW could be beneficially employed. Such more closely matched Rx & Tx freqs suggest range improvements of perhaps 50 -100% could arise with narrower BW. (Refer the attached table -organised in conjunction with SRNET back in 2015.)

Note: Dorji's ever friendly (& Queen's English speaking) Mark Yao has been offering DRF126xDS evaluation modules (433 or~900 MHz) on more popular micro forums, & I'm posting as an alert for legacy PICAXE fans who may also want to put their hands up. Refer Dorji's site => http://www.dorji.com/products.php
 

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techElder

Well-known member
I've been trying to get something working on LoRa in my area ever since you first started discussing it. 433 MHz is crap here, but ~900 is still available and especially for amateur radio.
 

manuka

Senior Member
I've been trying to get something working on LoRa in my area ever since you first started discussing it. 433 MHz is crap here, but ~900 is still available and especially for amateur radio.
Unsure what you mean -does "trying" relate to LoRa configuration, UHF technology, your noisy local RF environment or just micro interfacing ? The latter is straight forward enough with an 08M. Stan.
 

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techElder

Well-known member
Unsure what you mean -does "trying" relate to LoRa
Well, I must have been short of words that day. :D What I meant was that it was difficult to find the hardware at my price point at my usual suppliers (such as Mouser) as easy as it was to find the surplus stuff on eBay.

I set down my interest in LoRa, based on your interest in LoRa, for the development value of the HC-12 modules. I got something to develope with for as little as $2US.

Now, in looking on eBay, I find that there are some LoRa modules that are below $20US, but still $20 seems to be the norm and is still ten times more. I did quickly find a pair for less than $12US. Perhaps I need to do another sweep?
 

manuka

Senior Member
OK ! Wise choice on HC-12 as they're dirt cheap, versatile & very reliable performers. However "horses for courses" -LoRa ranges are ~an order of magnitude greater.

Those single chipper LoRa modules you spotted are the popular HopeRF SPI interfaced ones. UART interfaced Tx & Rx two chippers are probably easier to work with.

Semtech's recent release of 2nd generation SX126x LoRa engines predictably lowered prices on the initial SX127x range. I focused on Dorji's DRF1278DM modules in my 2015 Instructable, & they're probably still good LoRa starters. You could maybe get a pair for US $20 from the usual Asian outlets. I've several spare here in fact too! Stan.
 

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manuka

Senior Member
DRF1268DM RSSI reporting & Cayenne display. Sample of an ongoing 433 MHz LoRa "heat map" signal coverage quest.
 

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srnet

Senior Member
The performance of the TCXO equipped SX1262 is reported on here;


In summary, operation out of the box at 7.8khz, even if one device is at +20C and the other is at -20C.

Its true that the SX1262 has half the receive current, but the device thats really wanted in a easy to use module is the SX1261, that promises half the TX current as well, and that could have a major impact on battery life .................

There are now of course 2.4Ghz LoRa devices, and they are not performance slouches at all;

 

manuka

Senior Member
Thanks Stuart for these test findings, with the thermal stability indeed VERY appealing ! 2.4GHz LoRa would struggle in NZ's "bush", which tends rainforest dense. This is a significant reason why 433 MHz devices are favoured by many here. There's even better signal penetration at lower VHF freqs. of course, with diverse animal trackers here using ~170MHz .

Re the SX1261 -I'd not appreciated the TX benefits - thanks! Have you run across the attached (German) module? Best get samples before Brexit bites!
Stan.
 

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srnet

Senior Member
Well the SX1280 is no slouch, high data rates at longish distance and no duty cycle limits.

Not keen on the modules that put a UART in front of the device, that Micromo module might provide direct access, but they want you to register to see the datasheet ................

I do have a 'SX1261 module' here, I swapped the RF part on one of the SX1262 modules I have, it works, but its not yet clear what I need to do to make the DCDC converter work on TX too.
 

geezer88

Senior Member
These modules look very promising. For my next project I would like to make a mailbox alert system. My mailbox is about 800M from my house, but the forest is dense between for about half the distance. Were it not for the trees, it would be line of sight.

My plan is to send a few bytes of qualifier text when the mailbox is opened. At the house the picaxe would record the time of arrival and blink a light to alert me. All very simple, but I'm not too confidant these 433 MH devices will get through the oak trees.

If this is do-able, I'd like recommendation on which modules to buy and what settings to use. Time is not of the essence, so a very low bit-rate should help.

thanks, tom
 

manuka

Senior Member
800 metres thru' such vegetation has been found 433 MHz LoRa doable here in largely evergreen New Zealand. Oaks of course tend deciduous so you may get a performance hit when the trees are in full leaf !
Consider a quick check with a pair of UHF CB voice sets, which typically have Watts of TX power = several orders of magnitude more than LoRa data modules. Naturally their Rx is deaf beside LoRa but overall coverage tends similar. Stan.
 

srnet

Senior Member
My mailbox is about 800M from my house, but the forest is dense between for about half the distance. Were it not for the trees, it would be line of sight.
Read this;


This was at 1562bps, the summary is that @ 50mw you should get around 2km, when the TX is lying on the ground in the forest ......
 

geezer88

Senior Member
My first whack at this used a family radio service transmitter. It worked fine all winter, but when the oaks leafed out in spring it was all she wrote.

Since the whole works was powered down except for a few seconds six times a week, a small lead acid battery floated across a 100 mm square solar panel worked fine, even in the gloomy Oregon winters.

tom
 

techElder

Well-known member
What's your year round solar resource like ?
Well, in Texas, we don’t have much of a solar problem, but the solar panel will create a vandalism problem by making it all too visible.

I’ve been using 18650 power with regulation, but it isn’t efficient enough for general use. Also, I’m not using LoRa yet.
 

Hemi345

Senior Member
Well, in Texas, we don’t have much of a solar problem, but the solar panel will create a vandalism problem by making it all too visible.

I’ve been using 18650 power with regulation, but it isn’t efficient enough for general use. Also, I’m not using LoRa yet.
I ran across these power gating timers by Texas Instruments: DATASHEET

I'm designing little remote boards to monitor my yard's gate statuses and send updates with an HC-12. I picked a very efficient (both running and while in shutdown) LDO. The timer can periodically enable the LDO and the PICAXE will tell the timer to shut it back down. All can happen very quickly, so battery life, by my calculations, should last many months with the timer and LDO sipping nA most of the time.
 

techElder

Well-known member
Keeping an HC-12 in a "transceiver" mode is power hungry (relatively), and I assume to some extent so is LoRa but much less consuming. If you only use the HC-12 as an intermittant "transmitter", then, yeah, power off is zero power consumption.
 

srnet

Senior Member
One benefit of using LoRa radio devices for remote monitoring is appreciated when you realise that most all LoRa devices allow you to reduce the transmitted power level, you dont need to run on 100mW max all the time.

An SX1262 running at 1mW transmit power will probably have a longer range that a module such as HC12 running at 100mW, so the battery power savings could be considerable for the LoRa setup.
 

geezer88

Senior Member
I have used the Dorji DRF1268DM modules with great success for my mailbox alert. I've been watching the RSSI numbers to see how much the leafing out oak trees will impact the results. I have scoured Semitech's website and documents, but haven't been able to find out just what the "RSSI" signal strength measures. Can someone point me in a direction to a source of more information?

On a related note, has anyone actually used the lower cost (US ~$6) modules from Ebyte? They use the same Semitech SX1268 as the basic device, but documentation is sadly lacking. The Ebyte module model is E22 400 30s.

thanks, tom
 

geezer88

Senior Member
After looking at the data sheet in your post, I see I screwed up. The modem I have is an SPI interface, and I thought I was getting a uart version. I guess I will have to figure that out. If someone else has blazed the trail, I would love to see your code.

I guess the adage about older and wiser doesn't work in my case.

tom
 

srnet

Senior Member
I have used the Dorji DRF1268DM modules with great success for my mailbox alert. I've been watching the RSSI numbers to see how much the leafing out oak trees will impact the results. I have scoured Semitech's website and documents, but haven't been able to find out just what the "RSSI" signal strength measures. Can someone point me in a direction to a source of more information?

On a related note, has anyone actually used the lower cost (US ~$6) modules from Ebyte? They use the same Semitech SX1268 as the basic device, but documentation is sadly lacking. The Ebyte module model is E22 400 30s.

thanks, tom
Well RSSI (Received Signal Strength Indicator) reports signal strength and is mentioned as such in the LoRa device datasheets.

SNR is a beter 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/

The E22 400 appears to be a standard SPI based LoRa module using the SX126x, with the addition of RX\TX enable switching. There is code for Arduino and Mbed, but good luck writing a full PICAXE compatible library .......

Although why you would want a 1W LoRa device I cannot imagine, the range would be stupid, and the power level likley to be illegal in a lot of places in the World.
 

geezer88

Senior Member
Thanks for the idea of SNR. I didn't see that as an option on the Dorgi configuration tool, so I didn't search further. I did find it in the semtech manual. I'll have to see how hard it is to enable and use it.

As far as the Ebyte 1 watt module is concerned, that was purchased as a backup if I can't get through the oak trees when they leaf out. They are getting bigger each day, and in about 6 more weeks I think they will be at their peak. Currently, the RSSI has not decreased, so maybe it won't be a problem.

My signal is three bytes long, and repeated at most three times if the base does not respond. This happens once per mail delivery day. I have monitored the frequency and not found anything else going on. We are ten miles from town, so I'm not worried about buggering up someone else's day.

One other option for the summer "leaf season" is to build a repeater. It would be located about half way and because of the dogleg path, avoid most of the trees. A solar panel could keep it alive.

While looking for the SNR in the manual, I found the definition of the RSSI:

Actual Rssi in dB = -SignalRssiPkt/2

And for SNR:

Actual SNR in dB =SnrPkt/4

I observe that RSSI goes up with shorter range, so why is there a minus sigh on the right side of the equation?

tom
 

srnet

Senior Member
RSSI is a negative value. As signals get weaker it get more negative.

For you application speed would appear not to be a problem, so on long range settings the standard 100mW LoRa module should reach through 5 - 10km of (flat) forest, perhaps more, and with simple wire antennas.
 

geezer88

Senior Member
Thanks for taking the time to respond.

"RSSI is a negative value. As signals get weaker it get more negative."

That is what I get from reading the manual. But, walking with a receiving Dorji DRF1268 I get raw RSSI numbers that decrease as I walk further from the transmitting unit. In the same room I get numbers like 220. At 100 meters I get 180. At 800 meters I get 150. At 900 meters and more trees I get 140 and barely legible results.

If RSSI was a negative function, it should increase as I walk further from the transmitter. I don't get it. Also when I get down in the 140 range, the connection gets sketchy. Above 150, it seems reliable. This would refute the datasheet minus sign. So, I'm still confused.

In the next few weeks I will try to get a SNR reading going. Maybe the area I walk to has more noise, so even if the signal is going up, my signal can't compete.

tom
 

manuka

Senior Member
Dorji's SX126x modules return a POSITIVE signal strength "RSSI" value, with a maximum of 255. It seems a non linear scale (binary related as recall 2^8 =256), since 433 MHz trials here in rural NZ showed ~220 for strong signals in the same room with ~140 being almost lost in the noise when distant from the transmitter.

FWIW: A group of fellow Kiwis have been using Dorji's DRF1268DS TTL friendly modules to great effect, particularly with micros like RPi. For educational breadboard trials DIY pinout adaptors have suited well -further details available if interested. Stan.
 

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AllyCat

Senior Member
Hi,
If RSSI was a negative function, it should increase as I walk further from the transmitter.
Why? If you increase the range (from the transmitter) then the RSSI value decreases. To me, that is a negative(-going) function, even if the actual value is (still) a positive number.

Cheers, Alan.
 

geezer88

Senior Member
Why? If you increase the range (from the transmitter) then the RSSI value decreases. To me, that is a negative(-going) function, even if the actual value is (still) a positive number.

Cheers, Alan.
Right. Except in the Semtech manual it says:


Average over last packet received of RSSI
Actual signal power is –RssiPkt/2 (dBm)

Doesn't that minus sign make it a negative number, whose value would get larger as the signal increases?

Maybe the Dorji folks do something to it. Anyway, I think their modules are great. As I mentioned above I'm currently getting around 158 and that hasn't changed in the past week as the trees are looking greener and greener. Stan mentions above that the signal is getting lost in the noise when rssi is in the lower 140s. So far, that seems to be my experience as well. He also says the value seems non-linear. As the equation above shows, it is a log function. I've ordered another pair of the Dorjis. The Ebyte pair will sit in a box of stuff waiting for the proverbial rainy day.

tom
 

srnet

Senior Member
I can assure you the datasheets for the SX126x and SX127X and SX128X have the correct calculations.

You will get RSSI of circa -40dBm for a strong signal and circa -122dBm for a weak one on the very limit of working.

RSSI is power relative to 0dBm, so an RSSI of 158 would be 6,309,573,444,801 Watts !
 

geezer88

Senior Member
Yikes! Now I know why mine came with water jacket cooling connections.

Taking your numbers from above: 220 is a good signal, 140 barely works. By the formula in the Semtech manual, 220 becomes -110dBm and 140 becomes -70dBm. -70 is bigger than -110. I'm still missing something. Maybe I'm mis-interpreting their formula?
 

manuka

Senior Member
Geezer88: Best just consider Dorji's returned "RSSI" numbers (which relate to 8 bit values - recall 2^8 =256) as a "reversed" way of indicating the traditional -dBm RSSI.

It's akin to perhaps fuel economy being expressed in Imperial miles per gallon (10 mpg is poor while 50 is great !) beside metric litres/100km ( 3 l/100km is wonderful while 15 would be a gas guzzler ). Just get to know what's most useful in your situation!

Stan. (in totally metricated New Zealand!)
 

geezer88

Senior Member
The oaks have leafed out, and reception between the mail box has been interrupted. Before I build a repeater, I figured I'd spend more time on antennas. The mailbox has a two element Yagi and the house has a Yagi with three elements. They are both from plans found on internet, and have had no tuning. So I built a nine element Yagi, and spent a day tuning it with a nanoVNA. For the interested, there is quite an active forum that discusses these low-cost open-source vector network analyzers. The original antennas were sketchy when the RSSI got down to about 140. With the 9 element up a the house and the 2 element in the mailbox, even with the trees leafed-out, I'm getting 150 and consistent operation. There is enough room in the mailbox for a three element Yagi, so that will be the next step.

The Ebyte one watt spi modules are collecting dust. I haven't taken the time to figure out how to use them with Picaxe yet.

tom
 

geezer88

Senior Member
The new nine element Yagi is at my house. So far, the mailbox, made of plastic, conceals a two element Yagi, but there is room for one more element. Around here, mailboxes get clouted by kids, so I don't want anything to attract attention to mine. The only exception is the 100mm square solar panel that keeps the transmitter battery charged. It is pretty much the same color as the mailbox, so mostly inconspicuous.
 

geezer88

Senior Member
Here's my settings: Band width=125khz, Spread factor=11, Code rate=4/5

Each transmission consists of: two byte qualifier and a single byte data.

I tried a spread factor of 12, but that didn't seem to work. I may have screwed up in using the setting tool. I went back to 11, and quit messing with it. I'd be grateful for your feedback.

The mailbox unit is powered down completely after each use. The house unit is run off the mains, and is powered up all the time.

tom
 

srnet

Senior Member
Using a bandwidth of 20khz should be workable, long packets maybe, but together with SF12 should give you 3 times the range over your current settings.

There are no LoRa settings I have found that dont work when properly configured, but at higher than SF11 with bandwidth lower than 125khz, low data rate optimisation will need to be set.
 
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