Mr. Compost is an appliance which heats and agitates food scraps collected in your kitchen. This accelerates decomposition before you put the compost outside (in a worm bin or compost pile) to finish breaking down.
My own goal was to build something that would break things down enough that once transferred to my worm bin, the compost won't draw flies. This will allow me to move the worms inside during the winter without an entourage of flying insects.
Agitation helps add oxygen to the mix and mechanically break things down while allowing moisture to escape, and high temperatures (we'll be shooting for 140F) are ideal for the voracious thermophilic bacteria which take over naturally when outdoor compost piles build up enough internal heat on their own. As a bonus, flies stay away from things at that temperature.
Doesn't this waste energy? It does use some electricity, but if you're a city dweller who can use this and a worm bin instead of curbside yard waste collection, then disposing of kitchen scraps this way saves energy! I'm still working on getting 1.21 gigawatts back out of it though....
Sound complicated? We're just replacing the computerized controller in another appliance that holds, heats, and agitates things: a bread maker!
My own goal was to build something that would break things down enough that once transferred to my worm bin, the compost won't draw flies. This will allow me to move the worms inside during the winter without an entourage of flying insects.
Agitation helps add oxygen to the mix and mechanically break things down while allowing moisture to escape, and high temperatures (we'll be shooting for 140F) are ideal for the voracious thermophilic bacteria which take over naturally when outdoor compost piles build up enough internal heat on their own. As a bonus, flies stay away from things at that temperature.
Doesn't this waste energy? It does use some electricity, but if you're a city dweller who can use this and a worm bin instead of curbside yard waste collection, then disposing of kitchen scraps this way saves energy! I'm still working on getting 1.21 gigawatts back out of it though....
Sound complicated? We're just replacing the computerized controller in another appliance that holds, heats, and agitates things: a bread maker!
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Signing UpStep 1: What You'll Need
Parts:
- a bread maker ($5-$25). I used a Zojirushi BBCC-V20 that I found at a thrift store; I'd highly recommend this brand because of the way it's clearly designed and labeled internally, as you'll see later.
- a microcontroller ($0-$30) with at minimum several digital I/O lines. At least one analog-to-digital input and one PWM output is preferable. I used a Basic Stamp II (only digital I/O), but I highly recommend using something newer and easier to program such as an Arduino USB Board ($30 at SparkFun)
- (optional) an LCD ($0-$20), 2x16 character or so, so that Mr. Compost can tell you what he's doing
- miscellaneous resistors and connecting wire
-a coat hanger for upgrading the bread machine's stirrer/kneader into more of an auger that will thoroughly turn the compost
My total cost: $25 for a bread maker; everything else was laying around. If you have to buy everything, you should still be able to do this for under $50.
For a fun comparison, the NatureMill Plus Edition is $299 - but keep in mind that Mr. Compost doesn't replicate all the same functionality.
Tools:
- a soldering iron and solder
- wire strippers/cutters and pliers
- screw drivers
- a logic probe or voltmeter (preferred)
- vinyl (electric) tape and a sharpie
- a breadboard is very helpful for assembling intermediate test circuits
- a computer for developing the programming for your microcontroller
- a drill or dremel tool and small drill bit to make holes for coat hanger wire (5/64" worked for me)
- a beer bottle to help shape the coat hanger
Helpful Skills:
- comfortable going beyond "Warranty Void If Broken" stickers
- solid understanding of circuits & some experience reverse-engineering circuit boards
- comfortable working around live circuits with potentially lethal voltages
- experience soldering, especially in tight places
- basic understanding of PID feedback control using Pulse-Width Modulation (PWM)
- whatever programming language is required by your microcontroller
This is a fairly technical project. I've focused on covering all the high-level aspects that are important while also selectively including details that will save you time, hopefully without being too long-winded.
- a bread maker ($5-$25). I used a Zojirushi BBCC-V20 that I found at a thrift store; I'd highly recommend this brand because of the way it's clearly designed and labeled internally, as you'll see later.
- a microcontroller ($0-$30) with at minimum several digital I/O lines. At least one analog-to-digital input and one PWM output is preferable. I used a Basic Stamp II (only digital I/O), but I highly recommend using something newer and easier to program such as an Arduino USB Board ($30 at SparkFun)
- (optional) an LCD ($0-$20), 2x16 character or so, so that Mr. Compost can tell you what he's doing
- miscellaneous resistors and connecting wire
-a coat hanger for upgrading the bread machine's stirrer/kneader into more of an auger that will thoroughly turn the compost
My total cost: $25 for a bread maker; everything else was laying around. If you have to buy everything, you should still be able to do this for under $50.
For a fun comparison, the NatureMill Plus Edition is $299 - but keep in mind that Mr. Compost doesn't replicate all the same functionality.
Tools:
- a soldering iron and solder
- wire strippers/cutters and pliers
- screw drivers
- a logic probe or voltmeter (preferred)
- vinyl (electric) tape and a sharpie
- a breadboard is very helpful for assembling intermediate test circuits
- a computer for developing the programming for your microcontroller
- a drill or dremel tool and small drill bit to make holes for coat hanger wire (5/64" worked for me)
- a beer bottle to help shape the coat hanger
Helpful Skills:
- comfortable going beyond "Warranty Void If Broken" stickers
- solid understanding of circuits & some experience reverse-engineering circuit boards
- comfortable working around live circuits with potentially lethal voltages
- experience soldering, especially in tight places
- basic understanding of PID feedback control using Pulse-Width Modulation (PWM)
- whatever programming language is required by your microcontroller
This is a fairly technical project. I've focused on covering all the high-level aspects that are important while also selectively including details that will save you time, hopefully without being too long-winded.
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I'm lazy, and electronically clueless, so this contraption is way too complicated for me.
Why not just put a small worm bin on the porch, or even in the house, and let the worms and microbes do the work?
When I first started my worm bin , it was in the house for the first few months I had it due to cold weather, and no shelter outside. It didn't take up much space, and had not detectable odor unless I was right next to it with the lid off. Even then, the odor is not objectionable; though I wouldn't put it on my kitchen counter.
I did offer worm encouragement when I first started my bin by making a food scrap puree in the blender, but I only did that a few times.
I have since build a self-harvesting continuous-flow vermicomposter from a 50-gallon plastic barrel that I was very happy with. I nearly made an instructable and still might, but there are several designs on the web as well.
In short, you want to create a grating maybe 12" above the base of your barrel or other container, and an opening below the grating to shovel out finished compost. While most designs call for about 1-inch spacing between bars in the grating, I found that with 1.5" spacing, the weight of the whole mess would push the finished stuff through at some point and maintain a good equilibrium. This is in Seattle where it's relatively humid and cool all the time; elsewhere you may have difficulty with the very bottom layer drying out if exposed to the air. You could probably make a cover for the acces opening to keep the bottom nice and moist.
I also tried a scaled-up version of the bag design that has a very well-written instructable but wasn't very happy with it - I think that one is more high-maintenance.
Again, congratulations!!
Thanks!
Nice project, too!
We're not supposed to compost meat scraps. Otherwise, your design sounds fascinating!
Best part about this is that there are abandoned bread makers by the dozen in just about every yard sale, thrift store, front stoop, junk pile in America. I'd be SO doing this right now except I have ZEEROW knowledge of deconstructing circuit boards.
Any way you can just make it not bake your compost? Like lobotomize the circuit board with a blunt object(?)
As it stands, these kitchen cluttering bread machine things make good compost bins by themselves. Here's mine... and some tomatoes from our garden....and one of the garden...
You may not be able to find this out without either looking up the bread maker's manual online or turning it on and playing with it, but my (and many?) bread makers allow a custom baking program in addition to all the built-in ones. I was able to set up a custom baking program that did a lot of pre-heating and rising (the optimal rise temperature is pretty close to the temp range we want) and only 'baked' for 1 minute. This meant that my bread machine would do approximately what I wanted, including agitation every hour or so, for about 4 hours at a time with some annoying beeps every so often. (Maybe you're at least comfortable finding the piezo speaker and duct taping its mouth shut?)
That being said, I still feel compelled to warn you about this whole approach - the vessel is so small that you tend to dessicate your compost or have to put up with a nasty smell and condensation. I plan on very shortly building a vermicomposting 'sock' system, beautifully documented in http://www.instructables.com/id/Worm_bin_bag_for_indoor_vermicomposting_and_easy_s/ this instructable, and then maybe adding a heated vessel at the bottom to help dry out the results and break down anything the worms didn't want to eat. I'm thinking of using an electric blanket to provide the heat.
If you're vermicomposting or just outdoor composting, it helps to keep your collection container in the freezer so that everything gets broken up a bit at the microscopic level from the water crystallizing and expanding.
When I do come up with a solution I'm happy with, I'll post an epilogue page to this instructable. In the meantime, read the comments =)
In fact, research has been done to discover the 'optimal' particle size for composting. I remember coming across the number 1.5-3cm but I can't find that document now; however, here's a general discussion of compost particle size considerations: http://whatcom.wsu.edu/ag/compost/fundamentals/needs_particle_size.htm
If you emptied the larger bits from a blender into a compost appliance, either mine or NatureMill's, I think the particles would already be so small that the stirring mechanisms would be ineffective and you'd get a dense buildup or sludge.
By the way, after using my composter with added filter for a few weeks (I actually ordered the same one as NatureMill uses), I found that with the small container volume and filter airflow required to contain bad smells, my appliance tends to desiccate (dry out) the material too quickly for it to compost well. However, it does reduce the volume of material and eliminate excess moisture from the worm bin.
I also bought a NatureMill at Costco out of curiosity, and while the general design is brilliant, they have some component choice problems that need to be ironed out. The stirrer motor in the one I bought jammed against a piece of ginger and stripped one of its gears, rendering it useless. The air pump for the filter was also quite loud, louder than a refrigerator compressor, and runs continuously. And, it leaked a fair amount of disgusting liquid into the plastic tray at the bottom (like a cheap flower pot). This was a 'Plus' model, and NatureMill just announced a new 'XE' line that is advertised as having stronger motors and other improvements.