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:
- Small size - something that can be handheld
- Battery operated - would like at least a month of runtime
- Weather resistant - usable in the rain
- Expandable - capable of adding internal/external sensors
The type of testing that I'd like to do initially:
- LoRa sensor range - using the gateway indoors with the stock antenna
- Battery life - try to optimize
- Reliability - uptime of Things server, gateway, and sensor
- RSSI variation - received signal strength vs channel and time at a fixed position
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.
- GPS - (UART)
- Temperature/humidity/pressure (I2C)
- Ambient light (analog in)
- Water level (analog in)
- 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:
- MKR WAN 1300
- 3.5dBi omni-directional antenna w/cable
- 3V battery pack w/2 AA batteries
- Plastic case w/cover, 9.6 x 5.6 x 2.1 cm
And the gateway with the stock antenna (looks like the 3.5dBi antennas that I'm using with the sensors):
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.