Alvaro Prieto has published a write-up of his latest weather station board, the Chaac v4.0, which adds Bluetooth connectivity to his existing XBee-based design.
The Chaac project has been ongoing for some time: Prieto documented his original efforts to build a weather station a year ago, walking through a range of improvements that went from an nRF52-based Bluetooth Low Energy prototype through to a breakout board for the Nucleo development board, and the integrated Chaac board versions 1.0 through 1.2 — the latter adding in solar panel voltage monitoring.
In the year since, Prieto has been working on upgrading the Chaac design — and has gathered all the improvements into a single write-up, beginning with the Chaac v2.0 which combined the existing XBee-based communication system with an nRF52811 for Bluetooth connectivity.
The Chaac v3.0, meanwhile, was primarily designed to reduce the size of the system. "The main goal was to make the enclosure smaller and the overall system more compact," Prieto explains. "I decided to split the project into two separate PCBs, which allowed me to use the slightly more expensive 4 layer board on the radio section and the cheaper 2 layer board for the larger base board. This also allowed me to try out double-sided surface mount soldering. I had been using stencils and solder paste, but had never done it on a double-sided board."
"The last new feature I wanted to try out was a different RF connector. Previous boards used an RP-SMA connector but I wanted to try something more compact. I decided against using a u.FL connector due to the low number of insertion cycles, and went with the MMCX connector instead. Another interesting topic I learned a bit about was waterproof RF connectors."
Following some modifications to the external sensors — the addition of a solar radiation shield and a new BME280 temperature, humidity, and pressure sensor — the Chaac v3.1 board received a conformal coating to protect it against the elements. Following the flooding of an original v1.2 installation, Prieto developed Chaac v4.0 — adding LoRaWAN connectivity with support for The Things Network or point-to-point connectivity to a Raspberry Pi.
"[The] next change was to get rid of the solar panel and battery charger," Prieto continues. "From similar projects, I estimate I can get the average power consumption in the low tens-of-microamps range or even single digit microamps. With some alkaline AA batteries or rechargeable AA batteries, the devices should last well over a year."
"This simplifies the circuit and makes installation much simpler, since no direct sunlight will be required. The final change is to split the pressure and humidity sensors and somehow shield the pressure sensor from the elements. I’ve had a few ideas bouncing around in my head, so I’ll have to try a few and see what works."
Prieto's full write-up is available on his blog.