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A cheap oven with a programmable temperature range.  This could be useful for making a controlled temperature area for tempeh, yoghurt or drying out wet electronics, shoot, I don't know your life.

Our problem: We need to know the % of moisture in each batch of manure to determine how much carbon material (sawdust, coffee hulls, etc) to add to achieve 50-60% moisture (typical ideal moisture for aerobic decomposition).  We didn't have an oven that could accurately maintain temperatures between 221-230 F (and we didn't really want to put manure samples in our oven).

It costs about $8 to send a sample to the lab to determine moisture, but we wanted a cheap way to determine it ourselves so that we could see if our moisture assumptions were right.

Our solution:
For our "oven" we lined a cardboard box with tinfoil.  Then we controlled an incandescent light bulb with a Solid State Relay (SSR) to turn on if the temperature is less than 105 C and make it turn off if the temperature is more than 109 C.

We followed standard protocol's for moisture tests:

Calculate the % moisture for each of the materials you plan to compost.
a) Weigh a small container.
b) Weigh 10 g of the material into the container.
c) Dry the sample for 24 hours in a 105-110 C oven (221- 230 degrees Fehrenheit)
d) Reweigh the sample, subtract the weight of the container, and determine the moisture content using the following equation:
Mn = ((Ww-Wd)/Ww) x 100(in which:(Mn = moisture content (%) of material n(WW = wet weight of the sample, and(Wd = weight of the sample after drying.
This is from Cornell's division of Science and Engineering.

Step 1: Materials Needed

container for oven: we used a cardboard box, tin foil and tape to adhere the tin foil to the box.

For heat source: and incandescent light bulb (we used a 75 watt bulb) with fixture and plug.

To control the temperature:

-one Ground Fault Interruptor (GFI or GFCI), the kind of plug you have in your bathroom.  You should always use one of these while playing with AC power, because dying sucks.

-one standard electrical outlet and a junction box to house it's wires.

-14 gauge wire for AC electronics

-Wire nuts for AC wire junctions

-one solid state relay (Sharp S202S02, DigiKey part # 425-2403-5-ND).

-a microcontroller development board like a Teensy, Arduino, Freeduino, etc. We like to keep it local (and cheap) here in Portland, OR so we used the Teensy.

-microUSB to regular USB cable

-Arduino 21 software download at http://arduino.cc/en/Guide/HomePage

-power supply for your microcontroller so you don't have to keep it plugged into your computer (we used LadyAda's breadboardable power supply).

-We used a breadboard for DC electronics DO NOT BREABOARD AC POWER!


To measure the temperature:
 Dallas OneWire  DS18B20
These things are awesome and pretty cheap. In bulk they drop below $4 each. They are self-calibrating, low-power devices, and the DS18B20 has 1/2 degree Celsius accuracy. They are easily wired up for parasitic or independent power. The official Arduino guide to OneWire    describes how they work and gives you links to libraries.
Mat created his own printed circuit board (pcb) to attach long strings of temperature sensors to microcontrollers, but you really don't need these.  we just have 100 of them.

So I understand you connected the GFI and the lamp in series? What is the purpose of that? In fact I am not even sure what your GFI is. Is that a switch? otherwise i do not really see the purpose of it.<br><br>Isn't this just an arduino measuring a temperature and then switching on a lamp in a box to maintain temperature, or am i missing something significant here?
I understand nothing in electronics, but looks fine.
Great idea. As a person minimally talented in electronic innovations, I am envious. I have an idea I would like to implement, (also for animal leavings), I got as far as purchasing the arduino and sensors etc. However I find I don't have the background to proceed. Can you recommend a place to look for a mentor to help?
The center terminal of the light socket should be the live wire.<br><br>Also the ribbed side of the wire is usually the neutral wire.
When I saw &quot;Pooven&quot; in the thumnail I had to check this out.<br>Nice and &quot;Science-y.&quot; Thanks.
Neat!!!! Can not wait to set that idea up using my pc.

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Bio: Cloacina is the Roman Goddess of the sewers, we've enlisted her help to develop ecological sanitation solutions for the urban US.
More by mollyd:Moisture Test: Build an Arduino Controlled Low Temp Oven Rodent Resistant Composter 
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