User:Boohyabuddha/ENES100/Project0

Project Preference
1) Disaster Toilet 2) XY Coordinator 3) Printer Diagram

Problem Statement
We are tasked with developing a portable, budget (<$100) toilet that can be used for 30+ days in a disaster/relief scenario. We must make it with materials that are easily available, and can be trasnported easily and quickly when needed.

Project Plan
For the next 4 weeks we will conceive of what the best means for disposing of human waste, or means to handle it while minimizing exposure to pathohgens and other health hazards. We will determine what mechanisms are essential to meet the assigned restrictions (budget, functionality, etc.), and concieve of a design that will meet these needs while serving its ultimate function as a toilet. For the first two or three weeks, we will focus on researching what means we will handle waste within our toilet, and after deciding on the best mechanism, we will begin the initial designs based on research that was done regarding size, portability, cost, materials, ergonomics, etc.

Week1 Narrative
During the first week of this project, I was tasked with researching the dimensions and ergonomics of toilets, and using that data to determine a basic size for our initial designs. I also took into consideration the weight/cargo limits of planes used by the U.N. to transport relief, and considered the average person's carrying capacity, both weight and volume.

The dimensions of toilets varies greatly, and, upon reflection with the team, I came away with the thought that the height and depth of the toilets I reviewed were not essential to consider in our conceive stage since these dimensions are based on the water/flush mechanism that we will probably not be using. However, I did discover that the average toilet height compare to, say, the average desk chair height had about a 3-4" difference, with the toilet seat being lower. This was intriguing to me, because it meant that as we design the toilet, we can take liberties with the seat height while refusing to sacrifice comfort. In other words, we can raise the seat height by, theoretically, about 5-6" without disrupting the users' familiarity with using the toilet, and the extra height enables us to gain about 1/3 extra space to work with designing a mechanism for dealing with the waste. Also learned during research was that the toilet, in its final form, mustn't be too bulky or unwieldy. The toilet must be in a shape that can be easily handled by one person; whether this means a handle, or a making its size manageable within the arm span of one person, it must, in the end, allow the person transporting it to comfortably carry it (volume and weight considered) down a road for a substantial distance (up to a mile).

As far as the research into the U.N. planes used for relief transportation, the size and max. cargo liftoff weights were in the 100,000lbs, and combining that fact with the assumption (again, based on research) that the average person (between 180-200lbs) can carry about half their weight comfortably (90-100lbs), even assuming there is a pallet with 100 toilets on them at the max weight of 100lbs, this adds a 10% change. While 10% is a lot, this is postulating that our design will indeed be that heavy or that that many will be shipped at once, both of which is highly unlikely.

Once we sat down and shared our research results, we determined the best means to handle the waste was through the use of a bacteria which Anya would research more of. Jacob took the lead on designing a toilet in which the bacteria would be inside to handle waste, and, in the end, my task was to develop an Arduino-based system for monitoring important data streams from the toilet and the bacterial waste conversion: NOx content, methane, DO2, temperature, pH. This was my next task.

Week2 Narrative
I researched initially into what kind of sensors we could use in the toilet system. The obvious ones I thought about were: methane, dissolved O2, pH, and temperature. Of course, as I learn more about the waste conversion process and how to sustain the bacterial growth and reproduction, I can add/remove/tweak what we need, but those were the sensors I initially worked with.

Methane: There are heating coil-based methane sensors for <$5 on www.adafruit.com (Links to an external site.), which is ultimately not the rock bottom of electronic component prices, and you also have to consider that the price/unit comes down with bulk orders. This unit runs off of a Vcc between 2.2-5.5V, which is perfect for the Arduino. The only caveat is that because it requires an initial voltage output other than ground, it will require a 10k Ohm pull-up resistor, but those are literally <$0.01 a piece at high volume. This sensor seemed very feasible from the beginning when I began researching it.

Temperature: I found a PVC tube-encased thermistor for <$5, with ranges -55-105C. Since this already carries an impedance, it won't require a pull-up resistor, and can be plugged directly into the breadboard/PCB. However, since we need to measure the voltage and the Arduino doesn't have a resistance meter built in, I'll have to create a resistor series with the thermistor and put the analog input into the middle of the series and measure the change in resistance to get the voltage conversion. (See here for tutorial: https://learn.adafruit.com/thermistor/using-a-thermistor (Links to an external site.))

pH Monitor: This is where my component research began to break down. A pH probe, circuit, BNC breakout circuit, and the solutions to calibrate the probe were about $80-100. Even when I began exploring hackable alternatives, such as creating a BNC circuit from an op-amp and connecting that to a $16 aquarium pH probe, this still left me with a pH monitor in the range of about $20-30, and that's still before calibrating. It seems financially unfeasible to incorporate a pH monitoring system into individual toilets. However, this did get me thinking that perhaps there's a toilet monitoring kit we could develop that could be used on a regular basis to test the toilets, or, if we decide to create a disposal tank to convert the waste into compost, can be integrated into that instead of the toilets.

DO2 Monitor: Again, same situation as the pH monitor: kits ran around $120-135. This was even more difficult to hack since it appears that the circuits used convert the voltage outputs into a 13 character or less ASCII string that's sent from the circuit to the display (LCD, computer, etc.) I couldn't find much information initially on how to take the voltage readings from the DO2 probe and convert it into a reading using the Arduino programming language (in ways similar to converting thermistor readings into actual temperatures), but I can continue to research if we decide that a monitoring kit is part of our design program. Otherwise, it seems as infeasible for individual toilets as the pH monitor.

All of this considered, I believe that the only sensors that can easily and cheaply integrated into an individual toilet are thermistors and methane sensors. The other sensors, specifically pH monitor and DO2 monitor, are too expensive to be used in each individual toilet. As it stands, it would take a complete CDIO of the individual components to meet the price and function needs as I see them (submersible, cheap, voltage, etc.) That being said, if we decide to create a storage or "fermentation" tank (for lack of a better term) which will be a dumping unit for the toilets' waste for further bacterial conversion, a pH and DO2 monitor would be feasible since the amount of toilets it would be serving compared to the cost is a more reasonable ratio. There's also a possibility of creating a mobile kit for testing the individual toilets, not dissimilar to a kit used to test the chemical composition of a pool or spa.

I also still need to devise a way to communicate the data stream from the sensors and Arduino: LCD display, LED array for each sensor, plug'n'play mobile device? These are ideas I'll bring to the team to discuss. I will also consider the designs that Jacob came up with to figure out the best way to implement these sensors. Ultimately, the basic mechanisms of our toilet will rely on Anya's findings regarding this bacteria and the feasibility of using it in individual toilets, or in a larger storage unit, perhaps. These will all influence our next step in the design process, but I feel like I have ideas on how to handle either way, and I'm ready to help engage in the next design step, whether that's further developing the Arduino sensor array, or the fundamental mechanisms and design of the toilet itself.

Week3 Narrative
I finished a small prototype for developing an Arduino-based temperature sensor. The basic way this thermometer works is as follows:

The Arduino has the conversion formulas programed into it (I'll post the script and formula/coefficients on the wiki before Wednesday), and it's set (right now) to display temperatures in Celsius and Fahrenheit onto a computer running the Arduino IDE. It updates roughly every 5 secs and, as far as I can tell, is accurate withing a degree or so. Since we're only concerned with a general monitoring of the composting process and not reliant on maintaining any specific temperature, this should be fine unless you see an issue.

With regard to the thermistor/temperature monitoring, the only other things I'd like to continue to do are: 1) integrate an LCD display screen that will allow the sensor to not be tethered to a computer; 2) Integrate a solar cell array and battery to allow it to run autonomously; and, 3) Measure the exact degree difference between the readings and actual temperature (ie, test against ice, boiling water, etc.). These are listed in roughly the priority I have for these different parts. This also doesn't address one issue: the thermistor I bought isn't a ready-made waterproof probe--it measures surface/air temperature. This is fine for now just as I'm developing the prototype, but unless we want to wait for an waterproof thermistor, I'll have to wire the thermistor legs, wrap them in shrink-tubing and also seal the tip of the resistor since it's a ceramic compound. The issue with this is that it'll negate the coefficients I've been working with for the programing formula, and I'll have to either find a way to mathematically compensate for the sealant, or I'll have to take a bunch of temperature readings and define a cubic linear regression model based on those readings; those temperatures would have to range from roughly 0C - 100C though, and would be a lot of data-basing. This is something we can address in class though.

With regard to other components and parts of the composting tank:

I found an adequate humidity/temperature monitor: DHT22. It is simple and would work well to monitor the humidity of the composting tank within 5% and within the 0-100% humidity range. Since, as far as I know, the compost has to be within 0-50% humidity or risk breeding odor-causing coliform bacteria, regardless of temperature, this is probably the most important component to integrate into our tank. Unfortunately I wasn't able to find it or any other humidity monitors while i was shopping this weekend, but I'll talk to you guys about either purchasing it online or researching appliances that might have it integrated into them that we can hack out of if it's been junked. The sensor is only $10, and seems reliable.

As far as dealing with odors, I've also stumbled upon an idea for the tank. I know that convection and an outlet tube is probably the best and mechanically simplest way to deal with it, but if we wanted another option to consider, I was thinking of an ozone generator. Ozone is a natural deodorizer, and the only negative byproduct is nitric acid, but that mixed with composting waste would become nitrates, unless my organic chemistry is way off. The system could be made with a small, cheap 9V transformer, ceramic/insulated plates, two probes, and a computer fan to blow the ozone into the tank, or as an exhaust that would "sterilize" the air as it's being pulled out of the tank.

Next will be to acquire female/male pin leads for I can insert an LCD display sheild into the design without inhibiting the access to the other unused analog pins and digital pins; also, I still need to find a reliable, long-term energy source that can provide the current and voltage necessary to power this array without relying on generators or the power grid.

((Link to Wikimedia picture of Adruino/Breadboard, or Fritzing))