Researched a bit. Found some interesting websites– Basics of Composting and Magic Soil, which looks kind of goofy but actually has tons of good info. Looks like we're going to need to monitor temperature, oxygen & maybe CO2 levels, and moisture content. As of now we haven't put much thought into air filtering- smelliness may be an issue since the bins are to go inside the greenhouse, so we'll have to come up with a plan for that. One possibility may be to do negative-pressure (suction) instead of positive, but I read that that method is less efficient.
To do this week: order/find sensors, begin building a tester compost bin, decide what airflow method to use & buy/find it. One website uses a leaf blower, we may be able to find a cheap one on Ebay or something.
I think this link will be useful for figuring out how to turn the leaf blower on and off using the arduino.
things obtained: leaf blower, temperature sensors. Things ordered: moisture sensors.
It has been a long time since the last entry… but a lot has happened. Essentially, I put together a prototype, which failed… so I'm working on a second try. Here's what happened with the first.
First, I built a contained area for the compost to live in out of some old pallets. I lined it with some landscaping cloth to keep everything in. I found an old leafblower and hooked up the front to 7ft of PVC pipe which I drilled holes into. This is what forces the air through the compost! Now for the arduino…
To turn the leaf blower on and off based on temperature and other factors requires two basic components: sensors and a relay. With some research I found and bought this relay. After some fiddling, I couldn't get it to turn anything off and on… a bust. I then got a recommendation for a more user-friendly– and more expensive– piece of equipment, the Adafruit PowerSwitch Tail. This thing is great and simple, just wire in a signal from the arduino and plug in whatever needs turning off and on. Now I could turn the leafblower on and off with the arduino.
Next came the sensors- these are mostly plug-and-go, but the temperature sensor was slightly more complicated. It requires the OneWire library. After a bit of searching I found the sample code and modified it slightly to send a signal to the leafblower when the temperature reached a certain point. Here's the code!
I decided the simple on/off at a certain temperature would be enough for the prototype, and decided to set up. So, with help, I mixed up some compost using food waste from McClurg and some horse manure from the Equestrian Center, and filled the bin with compost. Once the pile was completed we monitored the temperature for a few days, manually turning on the leafblower just to see how it effected the temperature before plugging in the arduino.
The first pile collapsed the first time the blower was turned on. The structure of the compost was off: it needs a kind of bulking agent to make sure that it has porous space, and the woodchips we added to achieve that effect were too old and degraded. The second pile did not collapse, but when I manually turned on the leaf blower, I did not see a visible effect on temperature in the pile. It didn't seem smart to set up the arduino on the pile when the blower didn't have an effect on temperature: the blower would end up turning on too often, even if programmed in intervals; and if the blower didn't have an effect it seemed futile. For a short time, the compost kept itself at the perfect temperature naturally; see the last picture.
So, now troubleshooting is in progress. I suspect there aren't enough holes in the pvc pipe, not allowing enough air through: the motor does seem to strain a bit. In some way, air is not reaching the compost, so I just have to figure out why.