Shameless Self Promotion

— The Aaron Brady Story

Weather

Just a quickie project, mostly consisting of smushing Adafruit modules and eBay modules together in hardware, and a few choice libraries in software.

I’ve moved to Canada and I have a garage with mains power. I’ve never been through this kind of winter before, so I thought it would be interesting to log the inside and outside temperature and outside barometric pressure.

While there is power, there’s no connectivity in the garage, so I’m following in the footsteps of some of my friends back in England, and using a pair of Nordic nRF24 modules to establish a reliable radio link.

The source code to the whole thing is on GitHub, and it depends on the RF24 and Adafruit Sensor libraries.

I tested my set up by starting with low power amplifier settings on the radios and using an example sketch provided with the library. It might seem like setting power to the maximum is the best, but that also puts the most load on your 3.3V voltage regulator, and some Arduinos and clones don’t deal well with that.

Luckily, I was able to verify that mine does, and use that. I also only transmit at 250Kbps, which results in acceptable performance at higher ranges.

Sensor Node

Arduino PinBMP180 PinnRF2401+ Pin
GNDGNDGND
VCCVCC-
3.3-VCC
7-CE
8-CSN
11-MOSI
12-MISO
13-SCK
A4SDA-
A5SCL-

Receiver Node

Arduino PinnRF2401+ Pin
GNDGND
3.3VCC
7CE
8CSN
11MOSI
12MISO
13SCK

Reading the Output

As long as the Receiver node can pick up the signal from the Sensor node, you’ll get regular data output over the USB serial:

picocom --baud 9600 /dev/ttyUSB0
...
OHAI
P1022.41T4.30

That’s 1022.41 hPa and 4.30C outside.

Because I have a local Graphite install, I can just send metrics to 127.0.0.1:2003 with a tiny Ruby script, which parses the serial output and spits Carbon formatted data over TCP to my Graphite install.

It's not cold ... yet

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