Which wireless technology should I use?

Projects Networking, Protocols, and Devices
1

So I want to implement a room occupancy detection system at my institute. The idea is to create multiple sensing nodes consisting of a PIR sensor, a microcontroller, some form of wireless transmitter and a battery. Many of these nodes would be placed throughout my institute and all of the data(which area shows activity) from the nodes should be available on some central monitoring system, over the internet

This is exactly what we want to create: OccupEye

The problem I am facing right now is in deciding what form of wireless should we use? We do not want to depend on the institute's WiFi network and want to create an independent network.

Here is a rough outline of a floor at my institute:

Roughly 4-5 nodes would be placed in each Lab/Classroom.

Points that I'm concerned about:

  • Should not cause interference with existing WiFi network/devices
  • Low power
  • Range

I've thought about using the ESP or nRF24 modules, or some kind of hybrid network, but I'm not able to decide. What do you guys suggest?

2

possible worth considering is a XBee mesh

or a Lora mesh
http://www.nicerf.com/product_149_203.html

3

Xbee is a good option and is robust, but it will drive up the cost per node by a significant amount and I don't want to go for it unless absolutely necessary.

Whereas in case of LoRa, isn't it best for outdoor applications? Would something like this module be good in my case?

4

you can use Lora anywhere - make sure you have the correct frequency for your country
I think the module linked in post #2 is just a transceiver - you would require a host microcontroller

have a look at these devices which you can program using the Arduino IDE
32u4 lora

I have several 32u4 Lora devices I will try the code from

clearly the development of the Lora mesh is in its early days!
Unlike (the more expensive) XBee which works off the shelf!

5

@Horace,

Did you find some docs for this 32u4 Lora device ?

Is the onboard ATmega used only to control the Lora transceiver ?

I suppose it needs a library to do that and that very few space is left ?

Thanks for any infos,
Patrick.

6

it appears to be the same device as
Adafruit 32u4 lora

you have access to ATmega IO pins
pinout

you use the library
arduino IDE setup

also have a look at this thread on The Things network forum
Got Adafruit Feather 32u4 LoRa Radio to work and here is how
I had to modify all four 32u4 boards I have (two from UK two from China)

the code to connect to a LoraWAN gateway is large, e.g. my ttn-otaa code shows
Sketch uses 22868 bytes (79%) of program storage space. Maximum is 28672 bytes.
this is a run talking to The Things Gateway

Starting
CFG_eu868
Packet queued
0
282043: EV_JOINING
977597: EV_JOINED
1178551: EV_TXCOMPLETE (includes waiting for RX windows)
Packet queued
5129588: EV_TXCOMPLETE (includes waiting for RX windows)
Packet queued
12349299: EV_TXCOMPLETE (includes waiting for RX windows)
Packet queued
19568726: EV_TXCOMPLETE (includes waiting for RX windows)

a simple Rx-Tx test program for a peer-to-peer connection between two 32u4 devices gives
Sketch uses 9506 bytes (33%) of program storage space. Maximum is 28672 bytes.

if you require more memory there is the Adafruit Feather M0 Lora

7

Thank you for all that info @horace. Since I have to create a deployable system and not merely a hobby type device in the span of about 2 months, I think I'll probably go with a tree-type network using the nRF24l01 modules. Or maybe if the range causes issues, I can use LoRa as well at some points of my network.

All the walls are fully reinforced concrete, with many cables running all around the 8-storey building, I'll first have to do some range testing. Meanwhile, I'd really appreciate any input that you guys have!

8

I think range testing various devices in the building is the first step
fully reinforced concrete rooms end up like a Faraday cage!

9

@Horace,

Thanks for infos.

This library leaves little free space in the ATmel... Not enough for my own Arduino sketch.

A nice thing would be to have a sketch on this board that would emulate AT commands via the serial port.
The board would be considered as a modem and would simplify the use.

Thanks,

10

tk5ep:
A nice thing would be to have a sketch on this board that would emulate AT commands via the serial port.
The board would be considered as a modem and would simplify the use.

Well volunteered, do make it open sourced when its ready.
.
There is however already a module specifically designed for LoRaWAN and addressed via the serial port, the RN2483.

11

srnet:
Well volunteered, do make it open sourced when its ready.
.
There is however already a module specifically designed for LoRaWAN and addressed via the serial port, the RN2483.

and there is a module with onboard RN2483
LoRaGo Mote