Raspberry Pi Weather Station: Hardware

This is the hardware part of a project I built while volunteering with a research group at a physics lab. I was tasked with using two Raspberry Pi’s to monitor temperature, pressure, and humidity in various places throughout two rooms. To see the software portion of the project, including a simple web app for displaying graph of the data, click here.

Specs

  • 2 Raspberry Pi’s, one in each lab room
  • Up to 8 sensors per Pi
  • 50m max cable runs from sensor to Pi
  • Sensors read temperature, pressure, humidity all from one I2C breakout board
  • Data is sent over ethernet to a database server on the host computer via LAN

Here’s my hardware setup in 5 steps:

Step 1: pick a sensor board

 

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This is the Adafruit BME280. It has temp, pressure, and humidity all on one breakout board. It uses I2C to talk to the Pi.

Step 1 1/3: realize I2C only has a range of ~1 meter after already building half the project

:'(

Step 1 2/3: buy cheap I2C buffer chips to extend the range up to 50 meters

:)

I used this one from TI. I also had to mess around a lot with pull-up resistor values to get it to work through a 10m cable.

 

Step 2: build sensors

 

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I Used AutoCAD and a laser cutter for most of the enclosures for this project.

Step 3: multiplex sensors into Pi

 

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Unfortunately the BME280 sensor boards have a fixed I2C bus address. This multiplexer, also made by Adafruit was a very easy fix. A multiplexer is like a digital selector switch which lets us choose which sensor to read.

Step 4: put pi in a box

 

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I found a really cool website where you just enter your box dimensions and it generates a laser cutter design. All I had to do was add in all the cutouts and epoxy it together.

Step 5: put it all together while attempting to not create an octopus monster of cables

 

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Result

Overall this setup seems to work pretty well. The Pi can handle powering and reading 8 sensors no problem. If I were to redo this in the future I probably wouldn’t use I2C and instead pick a protocol better designed for long distances. Either that or look into making it wireless by sticking a cheap micro at each sensor.

That’s the hardware side of things. Here is how the software came together.

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