Public Lab Research note

Remote temperature sensing

by cfastie | September 14, 2012 22:28 14 Sep 22:28 | #3822 | #3822

When I went public with my home compost pile four days ago, I sort of challenged the participants of next week’s LEAFFEST to rescue me from my 25 year old thermometer device that I use to monitor the temperature inside the pile. The Pioneer Valley Open Science crowd was up to the challenge and already has a prototype which could beam temperature data from four locations in the pile direct to my PC 300 feet away. There it could automatically update a graph maybe at This a better solution, although it has been a pleasure walking over to the garden first thing and last thing every day this week to check the temperature. Venus and Jupiter were brilliant as the crescent Moon was rising at dawn, and it was clear enough in the evening to adjust the sundial gnomon by making sure it was pointed exactly at the North Star. That might be a bit more connecting to the cosmos than I really need.

Here is a shopping list for Don Blair's prototype that he deftly illustrates above. The total cost will be about $100:

It might be obvious to some that the sensor side of this wireless setup (the JeeNode and battery) is sufficiently small and lightweight to ride nicely on a kite or balloon camera rig. It could carry temperature, humidity, H2S, and barometric pressure sensors and describe the air column. It might not be necessary to beam the data live, so it could be saved to a memory card on board. This would require slightly different hardware, which of course is also available, because there are now inexpensive tiny computers and sensors that will do just about any kind of remote control and sensing you can think of. Some of these devices could be programmed to take every other photo after zooming in a bit for more detail, or alert the people on the ground that the camera is no longer shooting.

These are some of the topics we plan to spend the weekend of September 22 and 23 thinking about and trying out. If you would like to join us, sign up here for LEAFFEST in the next few days so we know when you are coming.

Below is the time course of temperature at the center of my compost pile. This is a live graph and will update whenever I walk out to the garden and report additional readings. Someday, maybe this will happen automatically, and I can just stay inside.


Great post, Chris! Addendum -- in addition to the Jeenodes, I think Craig Versek is going to be able to bring a WiFi-enabled Raspberry PI ($30-ish) taking snapshots (perhaps from a kite?) via a small webcam. Still in development, but he's kind of obsessed with it, so ...

-- I think you've told me this > 1,000 times, but: how heavy a payload can your KAP rig carry? Wondering if we can add a PI on top of everything else to send snapshots / live video down to earth.

-- Super cool graph! The temp seems to have peaked, then came down and settled into a plateau ... do you know from prior piles what to expect for the temperature behavior over the long term? What the heck is going on down in that buggy gooey mess? Can you use that energy to heat your home / fry a terribly smelly egg?

-- We'll be trying to give an overview at LEAFFEST of the various Arduino-like solutions out there, what they might be good for, and how they might be combined with Raspberry PI - type devices. So far as any of us understand any that. If anyone else has a nice overview / feature matrix / set of opinions on the matter, please come up North and join the convo ... and/or post here ...

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Having a choice of full-fledged computers for $30 is kind of astounding. LEAFFEST will be a really good opportunity for me to learn which will be most useful for various projects. That is really cool that Craig might be able to beam down webcam stills. That could be really useful for framing shots. Or point the webcam at the Powershot so you can tell that it is still operating.

As far as a kite lifting them, if there is enough wind, there is always room for PI! A Canon Powershot weighs 125 to 250 grams, and adding another 100 to 200 grams should be doable with sufficient wind.

The end of the temperature rise in the compost pile indicates that the aerobic bacteria have used up all the oxygen and are dying by the millions. They are no longer releasing metabolic heat, so the pile will slowly cool off. This will take a while because the hot center of the pile is insulated by the outer layers which have not been rotting or heating up. Turning the pile now will remix everything and incorporate oxygen and the pile will once again be good substrate for an exponentially growing culture of aerobic bacteria. If it is not turned, anaerobic bacteria will continue to decompose the material, but they work and reproduce much more slowly and give off little heat. After it is turned, the pile will be smaller (the pile has already shrunk in volume by 25%), and the center will include both fresh and rotted material so will not heat up as much as the first round unless a lot of new, rich material is added. I might turn it in the next couple of days.

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