Fart Intensity Detector Using Atmega644

INTRODUCTION

Our project is a fart intensity detector which ranks fart magnitude on a scale from 0-9 according to sound, temperature, and gas concentrations.

The inspiration for this project was to determine who could generate the worst flatulence measurable in a personally unbiased manner. To do so, however, requires measuring the intensity of these emissions. Therefore, a multitude of sensors were used in conjunction with a microcontroller to coordinate and analyze these sensor readings. Sound, temperature, and gas sensors were chosen for this purpose.

As a readout itself is not very user friendly, additional functionality was added with an LCD screen, speaker, LEDs, fan, and playback button. The LCD screen alerts the user to the status of the device as well as displaying rankings from each sensor and an overall ranking, as do flashing LEDs. Overall rank is stated by the speaker, with beeping of varying intensity signifying fart rank. If the fart is ranked high enough, a fan turns on to blow it away. A playback button is also added to allow the user to hear his previous fart. All of these components were assembled in a component box on a tripod, or a Fart Intensity Detection Station, for ease of use.

HIGH LEVEL DESIGN

Rationale
The idea to design a fart detector came from the fact that any device that can sense farts would require us to actually make use of the capabilities of the MCU, integrate hardware and software for the sensors, and on top of being a nontrivial project, it would be an enjoyable and certainly unique project to take on.
The truth is that farts are something recurrent in everyday life. Just like we breathe, we fart. From the reader of this webpage to the designers of this device, we all do it. This device might not be a innovative proof-of-concept gadget, but it certainly fulfills its two functions:
1. It creates an opportunity for the designers to show their expertise in hardware to software integration, since the project is based on chemical, sound and temperature sensing, data processing and conditional output. Likewise, it is not a device with a straight-forward design. Since it has never been done, it certainly poses a lot of research challenges, such as ultra-low H2S detection, super-sensitive temperature detection, and coming up with user-friendly ways to tell the user of the severity of the fart.
2. It is a device that everyone, from a PhD student to a little kid, can feel eager to play with. It is a fascinating idea that something that induces so much laughter in society can be actually measured and objectively ranked. In fact, it is a project that shows the world out there that electrical engineering can indeed be simply deliciously FUN!

Background math

The first step in determining the feasibility of this project was to find out what distinguishes a common weak fart from a mighty intense one. Upon doing some background research (see References section at the end of the page), we found out that intense farts could be best described as those that are the most unpleasant to others (for the one responsible for the emission, perhaps an inversely proportional scale applies, but that is out of the scope here). Farts are gaseous emissions of hydrogen, oxygen, nitrogen and other trace gases. The sulphur-containing trace gases, such as Hydrogen sulphide and mercaptans, are the ones accountable for the smell. Bacteria breaks down organic components inside our stomachs into hydrogen sulphide (H2S), which gives the infamous ‘rotten eggs smell’.
For us, this meant that we needed to detect trace amounts of hydrogen sulphide. A fart contains from 0.001 PPM to 1 PPM of H2S (indeed, the human nose is very sensitive). The human odor threshold is above 0.005PPM and prolongued exposition of more than 1 hour to H2S above 1 PPM is a health hazard (those are truly killer farts). To make sure that it was feasible to measure such amounts we obtained the breakdown of gases found in room temperature air:

According to wikipedia, there is about 0.0001 PPM of H2S in the air. Since the amount of H2S found in the atmosphere is way below that in a fart, we determined such low-level sensing would be possible. After some negotiations, we were able to have a 4mA-20mA transmitter board with a H2S sensor sampled. Such board is commonly found on toxic detectors in factories. For our custom designed board, 4mA was the output when there was absolute 0 PPM in the air and 20mA when the maximum detectable 20 PPM was detected.
This meant that unless the voltage went up by around 2.5 mV (0.8mA/330ohms), the fart could be ranked to 0. On the other hand, a 150mV change would be ranked at the top. This was great news since the ADC is accurate up to around 1mV on 10-bit mode with an A_ref of 5V (5V/1024 is roughly 1mV).

However, the most dangerous farts are not just those with containing hydrogen sulfide, but those that on top of this chemical, are warmer. This is because as the temperature goes up, the environment for this H2S producing bacteria becomes more encouraging, increasing the amount of the H2S in the fart and also amplifying the range of the fart, since gases move faster when they are hotter as dictacted by:

Sound is another factor that makes farts unpleasant to the bystanders. There is certainly something we have built-in that makes us feel uncomfortable when a fart noise is emitted next to us (of course, that is excluding the laughing riot it might ensue afterwards). As a sound-to-voltage transducer, we used a simple electret microphone. This cheap microphone does not do any filtering, and so low frequency noise had to be extracted out.

Parts List:

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