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  • Author Author: ralphjy
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LoRa Experimental Environmental Sensors (LoRaXes) - Introduction

ralphjy

I recently connected my Things Gateway to the Things Network and this Project14 challenge seemed like a good opportunity to do some experiments with the two MKR WAN 1300 boards that I received with the gateway.

 

I'd like to build a pair of portable outdoor LoRa sensors and I came up with a set of requirements:

  1. Small size - something that can be handheld
  2. Battery operated - would like at least a month of runtime
  3. Weather resistant - usable in the rain
  4. Expandable - capable of adding internal/external sensors

 

The type of testing that I'd like to do initially:

  1. LoRa sensor range - using the gateway indoors with the stock antenna
  2. Battery life - try to optimize
  3. Reliability - uptime of Things server, gateway, and sensor
  4. RSSI variation - received signal strength vs channel and time at a fixed position

 

Sensor capability:

I haven't decided yet what sensors to implement.  The MKR WAN 1300 boards are already capable of running with a 3V battery source and there is an onboard resistor divider to allow battery voltage monitoring on pin PB08.  The SAM D21 processor has up to six configurable serial communication interfaces (SERCOM), so I should be able to implement SPI, I2C, and/or UART for the sensor interface.  There are also 15 digital pins, 7 analog inputs and 1 analog output.  I'll need to map which pins and sercoms are still available in the MKR WAN 1300 implementation (e.g. the LoRa interface consumes a sercom).

 

Here's a list of sensors that I'm currently considering.

  1. GPS - (UART)
  2. Temperature/humidity/pressure (I2C)
  3. Ambient light (analog in)
  4. Water level (analog in)
  5. PIR (digital in)

 

The two units would probably have different capabilities

I thought for range testing it would be useful to add a GPS to one of the units to track RSSI vs location.  Both would have the temperature sensor.  I'll need to figure out the final application for each sensor unit to determine what other capability to add.

 

Here is the common hardware for the sensors:

  1. MKR WAN 1300
  2. 3.5dBi omni-directional antenna w/cable
  3. 3V battery pack w/2 AA batteries
  4. Plastic case w/cover, 9.6 x 5.6 x 2.1 cm

image

 

And the gateway with the stock antenna (looks like the 3.5dBi antennas that I'm using with the sensors):

image

 

I thought I would call the system LoRaXes in loose reference to the Dr. Seuss character in his book about the plight of the environment in the industrial age.

  • in reply to fmilburn

    Hi Frank,

     

    Thanks for the link.  It is unclear whether or not I have an updated board.  An updated schematic exists (MKRWANV1.1 vs MKRWANV1.0)  with the Murata VDD_TCX0 pin disconnected from +3V3 and connected to pin PA12.  There is no version on the PCB silkscreen and the date codes look like 4517 and 0318, so I probably have old boards.  I'll verify that when I get around to testing.  I also just realized that the battery pack I have in the picture is a AAA pack, so I probably won't get anywhere near the battery life that I wanted if the sleep current is ~2mA.

     

    Ralph

  • Hi Ralph,

     

    Very interesting!  I hope to get back to LoRa again one of these days.  In my project I was able to get GPS and a number of sensors working but was not able to get low power - It draws a milliamp + even when the board is in deep sleep.  There is a thread here on the Arduino forums that states it is a hardware problem and a revision to the board will be released. I would be interested if you received revised boards or otherwise find a solution to lower the power requirements.  Also interested in how well the gateway works.

     

    Frank