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Topic: Help on details about different Low Power communication modules (Read 283 times) previous topic - next topic

edugimeno

Hi There.
I'm ready to develop a system involving some sensors distributed which would be sending their reading to a "central" node and after investiganting the different options I am a little confused.

Options I see: RF24L01 (w and w/o PA+LNA), RFM22, ZigBee, and LoRa, mainly.

I see they are all basically Low Power modules that would let me send and receive some payload

But my confusion comes here in the differences between them all.

Are they a point to point (like a transparent serial line) RF line? Or can they receive from different modules at the same time?

I see Lora is mainly used in LoRaWan protocols, which seems to work to connect singular devices (mostly IoT) to a main gateway (like in the city, unfortunately in mine there's no endpoints). Can I still use LoRa as a normal device "interconnection" system so all the devices talk to a central point (and then the centrl point has the WAN interface -Wifi or Sigfox- to the world)?

In my scenario, where I would have like 5-10 devices reading a parameter every 10 minutes and a central gateway which would listen to the remote devices and forward the reading to "the cloud", which system would you use to communicate them all? I'm now biased towards nRF+PA+LNA but I don't understand the channels/pipes relationship and whether it would be able to LISTEN at the same time to several clients or it's only for a PTP link. It seems like I could listen to 5 pipes at the same time? Do I need to set up same channel and pipe# on both ends?

Any clarification on these would be really appreciated

Thanks guys!

srnet

Hi There.
I'm ready to develop a system involving some sensors distributed which would be sending their reading to a "central" node and after investiganting the different options I am a little confused.

Options I see: RF24L01 (w and w/o PA+LNA), RFM22, ZigBee, and LoRa, mainly.

I see they are all basically Low Power modules that would let me send and receive some payload

But my confusion comes here in the differences between them all.

Are they a point to point (like a transparent serial line) RF line? Or can they receive from different modules at the same time?

I see Lora is mainly used in LoRaWan protocols, which seems to work to connect singular devices (mostly IoT) to a main gateway (like in the city, unfortunately in mine there's no endpoints). Can I still use LoRa as a normal device "interconnection" system so all the devices talk to a central point (and then the centrl point has the WAN interface -Wifi or Sigfox- to the world)?

In my scenario, where I would have like 5-10 devices reading a parameter every 10 minutes and a central gateway which would listen to the remote devices and forward the reading to "the cloud", which system would you use to communicate them all? I'm now biased towards nRF+PA+LNA but I don't understand the channels/pipes relationship and whether it would be able to LISTEN at the same time to several clients or it's only for a PTP link. It seems like I could listen to 5 pipes at the same time? Do I need to set up same channel and pipe# on both ends?

Any clarification on these would be really appreciated

Thanks guys!

A good idea when decribing a project is to give an overview of the situation and location, we know you want to connect 'sensors', but what are the 'sensors', where are they and how far apart might they be ? 
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

edugimeno

Thanks, the sensors are not really relevant at this moment and they are not actually fully determined, let's say they could be temperature, air humidity, soil humidity, battery level, etc... Just normal stuff that can be measured and translated into a BYTE and sent along with other readings to a ThingSpeak server.
The distance would be in the range of 100-300 meters (~yards), in open space, or option 2, 30m in a house.

Thanks

Robin2

The nRF24L01+ modules are cheap (and work well).  I think for ranges over 100m you would probably need at least one of the pair to be a high-power module with the external antenna. That could probably be at the base station. The ability to cover 30m indoors will be affected by the building construction so you probably need to do some tests.


One option that you have not mentioned are the HC12 433MHz modules which have received very favourable comment on the Forum for their range and ability to penetrate buildings. But I have no personal experience of them.


Whichever option you choose you will need to think carefully about the system control logic to minimise and to deal with data collisions if the slave modules are asleep most of the time (to save energy) and wake up at intervals to send data to the master.

...R
Simple nRF24L01+ Tutorial
Two or three hours spent thinking and reading documentation solves most programming problems.

edugimeno

Very very good tutorial Robin ( I saw it was yours). Thanks for linking to it. I rad a bunch of other tutorials but this one was clearly the best one.

I understand you have solid experience working with these modules. So would you suggest them to be used as a way to interconnect some remote devices to the WAN-Connected device that acts as a bridge? How are they about power? I've seen amazing specs about some LPWAN devices in terms of power.

I see the gateway would be listening to a specific channel and then the different end-points would have a different address, so my gateway would have 5 listening pipes into listen mode, but what if I have more than 5 remote devices? Can I have them all use the same address, rely on the "integrity detecion" in the RF24 to discard the "garbled" data due to simultaneous communication, and have the station ID embedded in the payload so I can put as many remote stations as I want? Would this work?

Thanks!

srnet

The distance would be in the range of 100-300 meters (~yards), in open space, or option 2, 30m in a house.
Outdoors, in open space should not be a particular problem for the nRF24L01 or HC12 modules, but 30M in a house might be, it rather depends on the house.

I have no particular experience of the nRF24L01 indoors but do with 433Mhz modules of which the HC12 is a type type. At the standard licence excempt (legal) power of 10mW the HC12 might struggle in a large house, depending on where the sensors are.

Before planning and how to stitch the modules together in a network, I would get a pair of nRF24L01 and HC12 modules and test them in your situation first.
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

srnet

Can I still use LoRa as a normal device "interconnection" system so all the devices talk to a central point
Yes LoRa does point to point rather well, you dont have to use in a LoRaWAN\TTN setup.
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

edugimeno

Thanks Stuart, I've seen your work on the $50 sat and it¡s amazing, definitely in my TODO list since more than 5yr ago
Knowing the scenario I would be working in (let's figure one particularly out, 10 acres field which needs 10 soil humidity sensors distributed along the land sending measurements to a center Lora/nRF to SigFox network. Would you go for Lora, nRF or HC12, from your own experience? Cost is also a factor here,  nRF may be the cheapest here right?

Thanks!

srnet

Well, in terms of module cost then the NRF24L01s are hard to beat; as low as £1 each.

RFM22s (Si4432) around £2, HC12 £2.50, LoRa £5.

But is module cost really any significant part of the overall installation cost, I doubt it myself.

I did some tests recently using a LoRa transmitter placed on the ground in a very wet forest the receiver was handheld, see;

Lost in a (wet or dry) Forest.pdf

At 1500bps I got the equivalent of 1km on simple wire antennas at ground level, for sensor applications you could drop the data rate to 100bps and the distance would increase to circa 3km.

Now the point to be made here is that LoRa is clearly fairly undemanding as to the installation, a simple bit of wire in a box that is resting on the ground is enough for sensors.

For other modules you may need to elevate the central receiver and antanna and depending on the terain you may need to elevate the transmitter antennas also, all of which has cost implications.

I would again recommend you experiment .................

   
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

Robin2

I would again recommend you experiment .................
+1 +20

And, while nothing will work if the wireless doesn't,  the capability of the wireless is not the only factor in a successful project where there will be multiple transmitters.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

edugimeno

Ok I'll do my homework. I'm pretty sure I have a bunch or nRF modules around (does it matter whether they are + or not?). Which LoRa modules should I get (Im in Spain, in case the bands matter)

Thanks!

Robin2

I don't think the absence of the + on the nRF24s will make much difference, but I have only used the + versions. have a look at the Nordic datasheets.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

srnet

Which LoRa modules should I get (Im in Spain, in case the bands matter)
433Mhz is popular in Europe, TTN\LoRaWan uses 868Mhz. Hope and Dorji do 433mHz and 868Mhz.

There is link test software that will run on the SPI based LoRa modules here.

There is an explanation of how to use it to compare locations and antennas and provide real world results, as apposed to data sheets and calculations.
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

edugimeno

Ok, I found 4x nRF24L01+ modules. The one with the builtin antenna onboard. Yes I know what to expect from those...
Tried a simple TX->Incremental integers on one side, RX->Echo to serial on the other side

1st attempt: MIN power at the nRF module. Good signal at the same room. Nothing at all next room
2nd attempt: MAX power. Good signal same room, good signal next room, half packets lost 2 rooms away, no Rx at all 3 rooms away

I know, I need to test the ones with LNA+PA+"real antenna", but I need to order those, these others I already had them sitting in a box, never used

Thanks

Robin2

Two or three hours spent thinking and reading documentation solves most programming problems.

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