Recently I added an environmental sensor to a rooftop solar meshtastic node. This provides telemetry of temperature, humidity, and air pressure. In this article I describe what was required to accomplish this.
The starting point was that recently I deployed a rooftop solar meshtastic node.
Meshtastic (Wikipedia article, community web site) is an open-source volunteer-supported protocol and platform.
The device requires no cell towers, no internet, and no electrical power. It provides meshtastic connectivity to some twenty square miles of a rural area. It is a SenseCAP Solar Node P1-Pro (manufacturer’s web page, Amazon page).
After some time I realized that this device is made so that one can add a sensor for temperature, humidity and air pressure. The sensor is a BME280 (manufacturer’s web page). It is astonishingly small (2.5 mm by 2.5 mm) and draws astonishingly little electrical power (3.6 μA) and is strikingly inexpensive at less than $8 for a complete development board.
You can see the development board (called “GYBMEP”) here. At left is the sensor side of the board. The sensor (a small silver-colored square) is at top right. Across the bottom of the board, four terminals may be seen — VIN (5 volts), GND, SCL (clock), and SDA (data).
You can see a schematic of the GYBMEP board at right.
It turns out that there is a sort of informal industry standard called “Grove” (sponsor web page) for a four-wire bus permitting one or more sensors to be connected to a device. What I needed to do is find a Grove cable and solder it to this circuit board. This required that I learn which Grove pin performs which function. The answer turns out to be:
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- Grove pin 1 – ground (customarily black)
- Grove pin 2 – 5 volt power (customarily red)
- Grove pin 3 – SDA (I2C data, customarily white)
- Grove pin 4 – SDC (I2C clock, customarily yellow)
So I soldered the four wires of a Grove cable to the sensor board, as shown at right. The result was a sensor cable assembly as seen here.
My next step was to open up the solar meshtastic node. You can see the battery B which is four 18650 cells, each 3350 mAh at 3.6 V. This provides around 48 watt-hours of energy. (They get charged up by a five-watt solar panel.) You can see the GNSS chip G which is a L76K GPS module, and its GNSS antenna E. You can see the Wio-SX1262 LoRa transceiver C. You can see the XIAO nRF52840 processor F. And, importantly for this discussion you can see the Grove port D. And you can see that I added the sensor A.
Having added the sensor A, I closed up the housing and powered up the node. And I was delighted to see the temperature, humidity, and air pressure information as shown at the start of the article.
Have you worked with meshtastic? Please post a comment below.