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I'm working with a project to collect temperature data from about 50 cabins that are located close together. It therefore seems easiest to use 50 Lora nodes with temperature sensors and one gateway.

So I'm searching for a way to use multiple Lora nodes to create a sensor network. From what I've gathered it might be more cost and time effective to buy a readymade gateway such the Dragino. But I can't seem to find any good guides on how to create a small Lora node? I live in Europe and therefore want to use 433Hz frequency. I'm thinking something like a RFM96 and an Arduino nano should do the trick? Or is there easier solutions?

Since there is little documentation about this I hope others can find this useful as well.

Thanks in advance!

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  • \$\begingroup\$ All you need is an RFM96 or RFM95, any microcontroller with SPI, a suitable antenna and power source + sensors. You don't have to implement the whole LoRaWAN protocol. You can treat the RFM96 just as a "stupid" radio and send custom frames using LoRa modulation. \$\endgroup\$
    – filo
    Feb 28, 2018 at 14:11
  • \$\begingroup\$ @filo This sounds great! Could you please send some documentation for this or point me in the right direction? I think I solve the "RFM96/95 + MCU + battery + sensor" part but to where do these sensor nodes send their data? \$\endgroup\$
    – Lamar
    Feb 28, 2018 at 14:20
  • \$\begingroup\$ Have you got a supply of power in the cabins or do you intend the transmitting radios to be battery powered? \$\endgroup\$
    – Andy aka
    Feb 28, 2018 at 14:32
  • \$\begingroup\$ @Andyaka They are to be battery powered. \$\endgroup\$
    – Lamar
    Feb 28, 2018 at 14:39
  • \$\begingroup\$ And do you only require data to be sent in one direction? If so how often and what size of data? I.e. if you only need to transmit temperature (3 bytes of data) once per hour then there will be a better solution for battery power rather than LoRa \$\endgroup\$
    – Andy aka
    Feb 28, 2018 at 14:41

1 Answer 1

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Maybe if......

The 50 cabins each send temperature data once every 10 minutes using battery power this could be handled by a system that does not rely on a receive protocol to tell the "transmitter" when to transmit. This could massively sustain battery life because you are not wasting several mA of current continuously keeping the radio listening.

In the 9 minutes, 59.9 seconds between transmissions your battery consumption could be as low as a few microamps. During transmission (0.1 seconds) you might need 20 mA so the average current is: -

Background (say 10 uA) plus 20 mA/6600 = 10 uA + 3 uA = 13 uA.

Channel usage per cabin transmitter is 0.1 seconds every 660 seconds so, with 50 transmitters this means the channel average utilization is 5/660 = 0.75%. Each transmitter could randomly time its transmission based on a unique address so that on average it was ten minutes (with plus or minus 5 minutes as the random factor).

Collision probability would be low but you'd get a cabin's temperature the next time in all probability. It's all down to how you want to play it.

This type of system would use 50 transmitters and one receiver. The receiver does all the data collection for the 50 cabins.

Quite cheap (I would use FM) transmitters could be used but each would need a little MCU to format the transmission with preamble, address, payload data and checksum. The little MCU would also do the random timing thing.

The receiver (AC powered) would convert a received transmission back to the payload data (having proven that the checksum tallied) and the address of the cabin would also be detected in the transmission.

Similar question.

Maybe a LoRa module could be put into shut-down mode to conserve battery life thus you get a similar solution that wouldn't require an MCU to format the data to make it suitable for a transmission?

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  • \$\begingroup\$ This could absolutely work! What do you recon the range of such FM transmitters to be? And what FM receiver that could receive multiple transmissions could you recommend for a start? \$\endgroup\$
    – Lamar
    Feb 28, 2018 at 15:06
  • \$\begingroup\$ Firstly, you can't receive multiple transmissions. This idea is based on a transmission getting through to the receiver because the overall channel occupancy is low and each transmitter randomly times its transmission. I got 100 metres from quite small FM modules. I'll try and find a recommendation.... \$\endgroup\$
    – Andy aka
    Feb 28, 2018 at 15:09
  • \$\begingroup\$ I don't think they make the Tx and Rx I used back in the 1990s but here's a link to their current portfolio. Basically you choose a transmitter and a receiver. See what you think then come back if you need more selection help. I think you should look at the TX2 and RX2 that they offer. \$\endgroup\$
    – Andy aka
    Feb 28, 2018 at 15:13

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