The 48 hour burn in of both sensors has now been completed and I have been able to do some initial measurements of the sensors characteristics. So far both the sensors does seem to react to acetone but that is not rely surprising. The sensor resistance range (Rs) does vary a lot between them, the TGS822 has a span of 300Ω – 78 kΩ while the MQ-3 has a more narrow resistance span of 22.6 – 1.5 kΩ. Since I am interested in low concentrations of gas I want to have as wide range as possible and have therefor selected to go on working with the TGS822 sensor first.
One aspect of the sensors that makes the them a bit annoying to work with is that they have a warmup period of 3-5 minutes before the resistance has stabilized it self and they also take quite a long time to return back to the initial value after a measurement has been done. The time it takes for the sensor to reset is related to how high the gas concentration was.
- Rs = 78 kΩ, 22 degrees C, 20% Humidity, normal air.
- Rs = 300 kΩ when blowing into the sensor.
- Rs = 300 kΩ after ail polish remover puff.
A good value for voltage divider resistor with the TGS822 should be 10k. A 10k resistor would give an output to the Arduino of just above 0.5 V at no gas detection up to a full 5 V for high gas concentrations.
Reset time, Resistance in kΩ/time after acetone puff.
- 32 kΩ after 7 minutes
- 41 kΩ after 10 minutes
- 51 kΩ after 13 minutes
- 54 kΩ after 15 minutes
- 58.4 kΩ after 18 minutes
- 62 kΩ after 21 minutes
- Rs = 22.6 kΩ, 22 degrees C, 20% Humidity, normal air.
- Rs = 15 kΩ when blowing into the sensor.
- Rs = 1.05 kΩ after ail polish remover puff.
Reset time, Resistance in kΩ/time after acetone puff.
- 10.5 kΩ after 8 minutes
- 14.5 kΩ after 16 minutes
- 17.9 kΩ after 26 minutes
- 18.9 kΩ after 31 minutes
Blowing at the sensor with clean air did not seem to have any effect on the reset time.
I came across a much inspiring video about some scientists at UCLA who successfully made some graphene and using only commercially available equipment doing it.
After watching this I just had to look in to what it would take to make some graphene and perhaps a super capacitor or two of my own. Graphene is a fascinating material and I believe there are hundreds of uses for it yet to be discovered, but again to be able to discover something to use it for I need to have some. So what do I need to rustle up some graphene?
Shopping list for DIY graphene
- Graphite oxide
- Light scribe capable DVD burner
- Light scribe DVD
Additional items for super capacitor
- Ion-porous separator
In the report written by Maher F. El-Kady & co they stated that they used a mix of 3.7mg graphite oxide in 1 mL water.
I did some empirical testing on how much water it takes to cover an area as large as a CD and it was around 10ml. So to make a piece of graphene the size of a CD we need 37 mg graphite oxide.
I have found one supplier, although it wasn’t easy, that sells graphite oxide for 120$ per gram and is willing to ship it to me. The price for the graphite oxide per CD would be somewhere around 0.12 * 37 = 4.4$.
Light scribe capable DVD burner / Light scribe DVD
This is probably the object on the list that would be the easiest to get a hold of. A Light scribe capable DVD-writer cost about 40$ here in Sweden and the Light scribe media is about 1$ a piece.
Although it would be possible to make the graphene straight on to the DVD media it would not be very practical since one of the properties of graphene is that it is thin and flexible and a DVD is pretty far both from thin and flexible. What makes a bit more sense is to have some material between the DVD and the graphite oxide that acts as a carrier and also perhaps as an electrode. Maher F. El-Kady & co tried a bunch of different substrates and here I belive there is plenty of room to experiment.
Substrates tried by Maher F. El-Kady & co
- polyethylene terephthalate (PET)
- aluminum foil
- a porous nitrocellulose membrane
- regular photocopy paper
To state that the researchers at UCLA used only commercially available equipment while making their Light scribe graphene (LSG) is a bit of a stretch. Although graphite oxide is water-soluble you can’t just put some graphite oxide powder in water and give it a stir like it was a cup of Nescafé, that would not disperse it good enough. What you need to do is to smash the graphite oxide powder with ultrasound using a sonicator probe and that is not something everyone has in their kitchen drawers at least not me.
However using a proper sonicator probe might not be rely necessary in this case it might suffice using a ultrasonic cleaner instead and those are both much easier to obtain and also a lot cheeper (around 45-55$).
Perhaps not so hard to get but I have to remember to get one. It might be possible to get the graphite oxide solution on to the substrate using some other thing but I think a pipette is a good investment.
So far it feels like making your own graphene is far from impossible but at the same time it is not super easy. I would have to make some investments as well. 0.5 g of graphite oxide would in theory allow me to make 13 ”graphene DVDs” but I would say that a more reasonable number is 8-10 DVDs.
0.5 g graphite oxide, 60$
Light scribe DVD writer, 40$
Light scribe DVD (10 pieces), 10$
Ultrasound cleaner, 50$
A total of 165$ and then add some stretch to that budget brings it to a grand total of 200$.
Update: To see videos where the process described in this post is put into practice check out my another post ”DIY Graphene Videos” about some of the other people online who are working hands on with DIY Graphene experiments.
Yesterday the sensors I had ordered arrived, I had ordered the Figaro TGS822 and the MQ-3 from Hanwei Electronics. Since this type of sensors require a burn-in of 24-48 hours I wired them and applied some power. I had a suspicion that the sensors were actually going to be identical in function but perhaps I was wrong since they do actually use different amounts of current. The TGS822 sensor draws 117 mA while the MQ-3 draws 102 mA. It might just be that different individuals use different amount of current, further experimenting will tell if they also measure differently.
One thing that I didn’t expect was that the pins of the sensors are placed along the side of the round sensor following the curvature. This makes it impossible to stick them into a breadboard, since the pins will not line up with the holes in the breadboard, so I had to solder some wires to the connectors.
There are a bunch of different sensors out there, based on price and sensitivity I have chosen to buy two different sensors the TGS822 from Figaro sensors and the MQ-3 from HANWEI ELETRONICS. If i wasn’t on a budget I would also have ordered a WSP2110 – air polution detection since I believe that a combination with on of the TGS882 or MQ-3 with the WSP2110 could be a good match where the WSP2110 is has a sensitivity range between 1-50 ppm and the other two has a range between 10-1000 ppm. So the combined result of both could give us a more granular scale at lower concentration levels.
TGS822 – Alcohol (ethanol) gas sensor, gas sensors is a tin dioxide (SnO2) semiconductor.
HANWEI ELECTRONICS CO.,LTD
MQ-3 – Alcohol Gas Sensor, is also a SnO2 sensor so it should have similar detection abilities as the TGS822 but acetone is not mentioned in the data sheet. According to one manufacturer this sensor has a detection range between 10-1000 ppm for alcohol and then about the same apply for acetone.
MQ303A – Alcohol Gas Sensor, is essentially the same sensor as the MQ-3 however it works on a lower voltage. One serious disadvantage with this one is that a manufacturer states that the sensitivity of this sensor is 20-1000 ppm.
When you compare the MQ303A with the MQ-3 sensor’s range of 10-1000 ppm I think I will go with the MQ-3 sensor instead of the MQ303A since the concentrations we want to measure is between 0-200 ppm.
WSP2110 – air polution detection, this sensor has a different ceramic substrate of subminiature Al2O instead of th SnO2 used in the other sensors and is more sensitive but also has a smaller detection range then the others, 1-50 ppm. it is also a lot more expensive as the other sensors.
ME3A – C2H5OH – This sensor works with a completely different type of chemical process.
”Detects gas concentration by measuring current based on the electrochemical principle, which utilizes the electrochemical oxidation process of target gas on the working electrode inside the electrolytic cell, the current produced in electrochemical reaction of the target gas are in direct proportion with its concentration while following Faraday law”
It seems to be very sensitive and detects between 0-1.000mg/L alcohol per liter, however it also have a price of /piece. Since this sensor works with a completely different technique I am not even sure if it detects acetone as well as ethanol and it is also way to expensive so just forget about this one.
After doing some Google searching I found several different studies on the concentration of acetone in a persons breath and here I will look in to some of them.
I found a Study published in the paper ”The American Journal of clinical nutrition” where the concentration of breath acetone was measured after every hour for persons while eating a ketogen diet for 12 hours which states. ”Changes in breath acetone, plasma acetoacetate, plasma β-hydroxybutyrate, and urinary acetoacetate over the 12-h dietary study period are illustrated in Figure 1⇓. By the end of the study, breath acetone increased 3.5-fold (from 33 ± 13 nmol/L at 0 h to 116 ± 19 nmol/L at 12 h).”
This gives an indication for what concentration of acetone that can be expected, however the persons in the study had not been eating a ketogen diet before the study so I don’t know what levels a person that has been eating a ketogen diet for a longer while will have but I suspect it will be higher then the 116 ± 19 nmol/L the participants in the study showed. Since most sensors give the sensitivity to different gasses in their data sheets as ppm i need to convert the 116 ± 19 nmol/L to ppm.
Found concentration in breath = 116 ± 19 nmol/L, nmole = (10-9) of a mole.
To convert nmol/L to ppmv we need to know the volume of 116 ± 19 nmol/L of acetone. This can be done by using the Ideal gas law.
V = nRT/P
P = atm = 1
V = Liters
R = 0.08206 L·atm·mol−1·K−1
n = measured in moles
T = in kelvin (273.15 Kelvin = 0 C)
At 23 degrees and at 1 atm that amounts to: ((116 * 10-9) * 0.08206 * 296) / 1 = 2.81761×10^-6 liter = 2.8176 µL (microliters) parts per million in a gas system is equal to µL/L So the concentraion for the subjects in the study was 2.8176 ppmv.
In this study a prototype of a ”acetone breach detector has been built and the engineers tested it by fasting for 17 hours and then blowing in to it.
”Results indicate acetone concentrations of 2.5ppm and 0.7ppm. Notably, the author (‘Steve’) had fasted for 17 hours and recorded a slightly high breath acetone value. When the sensor is recently calibrated and has been optimized properly, acetone sensitivity for breath measurements is conservatively estimated at several tenths ppmv, and it is appropriate for breath acetone measurements of healthy, metabolically stressed, and diseased individuals.”
”The daily average acetone concentration of the dieters during this period was 290 nmoI/L (SD 8.1, range 280-300 nmol/L). The control subjects showed a daily average breath acetone concentration of 15 nmoIJL (SD 11 nmol/L) .”
(((300 * (10^(-9))) * 0.08206 * 296) / 1) * liters = 7.286928 microliter = 7.286928 ppmv
Some rats on a ketogenic diet reached 500 nmol/(L*kg)
So all studies I have looked at indicated that the breath acetone concentration should be around 2-7 ppm. When it comes to sensor sensitivity that i very low and it will be difficult to find a sensor that has that level of sensitivity.
However I think the concentration of a acetone in a persons breath that has been on a ketose diet is significantly higher. Since many people report that the smell of aceton is noticeable and the required concentration of acetone for it to be detected by smell is 200 ppm according to the CDC I have decided to go set as a hypothesis that the sensor range should be around 0-200 ppm.
Based on Steves posts it looks like it is actually possible to detect if a person is in a ketose state or not by analyzing that persons breath. But what are the signs of ketosis?
After doing some researching on Wikipedia I concluded that what we are looking for is acetone.
|Molar mass||58.08 g mol−1|
|Odor||Pungent, irritating, floral|
|Density||0.791 g cm−3|
|Melting point||-95–93 °C, 178-180 K, -139–136 °F|
|Boiling point||56-57 °C, 329-330 K, 133-134 °F|
|Vapor pressure||24.46–24.60 kPa (at 20 °C)|
|Refractive index (nD)||1.35900|
From the Wiki page about Ketone Bodies
Ketone bodies are three water-soluble compounds that are produced as by-products when fatty acids are broken down for energy in the liver. Two of the three are used as a source of energy in the heart and brain while the third (acetone) is a waste product excreted from the body. In the brain, they are a vital source of energy during fasting. Although termed ”bodies”, they are dissolved substances, not particles.
The three endogenous ketone bodies are acetone, acetoacetic acid, and beta-hydroxybutyric acid, although beta-hydroxybutyric acid is not technically a ketone but a carboxylic acid. Other ketone bodies such as beta-ketopentanoate and beta-hydroxypentanoate may be created as a result of the metabolism of synthetic triglycerides such as triheptanoin.d
Individuals who follow a low-carbohydrate diet will also develop ketosis, sometimes called nutritional ketosis, but the level of ketone body concentrations are on the order of 0.5-5 mM whereas the pathological ketoacidosis is 15-25 mM.
From the Wiki page about Ketosis
Steve also published a post at a newsgroup were he presented some more details about his ”KetoFlute”. He also included a picture of his creation.
Date: Jun 12 2012 21:12:02
I've been silent for the past week while I've been pushing to
get a prototype ketone breathalyzer finished
I've never worked with USB at the hardware/software level
before. So I didn't appreciate that the USB HID (Human Interface
Device) was inherently low-bandwidth, or at least low polling
rate... fixed at a minimum of 16 milliseconds per packet
Since my whole effort has been toward determining as quickly as
possible whether I CAN detect exhaled ketones, and differentiate
their effect on the gas sensor from the extreme effects of
temperature and humidity, I have wanted to race to reach that
conclusion as fast as possible. That meant NOT placing any
processor out on the data collection end... just using a "dumb"
solution that could talk to ultra-high-resolution analog to
digital converters. But THAT meant that the USB HID polling
rate severely limited my possible transactions with the ADC's.
Consequently, I was forced to scrap my first iteration base upon
the USB HID spec and switch to mainstream USB data exchange.
THAT second-generation solution is now FINISHED and WORKING:
In the photo, you can see the mouthpiece at the lower right,
the gas collection chamber, and its connection to the pair of
22-bit ultra-high-resolution SPI-interface surface mount ADC's.
The large green button allows the "user" to signal to the
software, though I'm unsure that it will be necessary since
there is NO DOUBT when someone is blowing into the gas
The two large power-transistor-looking things near the top are
a P-Channel Power MOSFET which I use to switch the USB's 5 volt
supply to the pair of gas sensors, and an adjustable voltage
regulator which I use to drop the USB's 5 volt supply down to
3 volts for the gas sensors. (If this should ever evolve into
a limited production run build of KetoFlutes, it would run on
a pair of AA cells, so 3 volts is my operating target.)
The circuit board at the far left is an FTDI USB-to-Serial
protocol bridge which, among other things, supports the SPI
protocol used by the pair of Microchip MCP3553 ADC's.
The left-most trimpot adjusts the sensor voltage to 3vdc, and
the other four trimpots adjust the gain and offset for each of
the two data acquisition channels.
It's all working and able to collect a pair of high-precision
22-bit samples at about 22.5 samples per second, which is more
than adequate for my purposes.
And I have a prototype console app that reads and displays the
data from both channels, but I don't have anyone handy who is
NOT in ketosis. For ME, I'm seeing a DEFINITE "common-mode"
signal difference between the "signal" sensor that IS supposed
to respond to volatile gasses and the "control" sensor that
should NOT respond. But I don't yet know that I might not
just be seeing a difference in, for example, the channel gain.
(Though I don't really think I am, since I swapped channels and
the response moved with the sensor.)
I have the podcast tomorrow that I need to switch over to now.
So it will be for another day or two before I'm able to bug my
NON Ketogenic friends and have them blow into the mouthpiece
while I collect and log the data for subsequent analysis.
I may well remain in a fat-burning ketogenic state for the rest
of my life. So I would LOVE to have a handy ketone breathalyzer
that can yield both qualitative and quantitative realtime
appraisals of my body's ketone status. I've been poking my
fingers and drawing drops of blood for test-strips several times
per day, but at kr31.73 () per test it's not really affordable over the
long term, and my fingers are getting a bit chewed up.
So... If I can make this work, I will DEFINITELY build at least
one standalone AA battery-powered "KetoFlute" for myself. And
if there appears to be sufficient interest among our podcast
listeners, then I'll likely do a single production run of these
devices to equip everyone who wants one.
This all began when I heard of Steve Gibsons work of building a ”KetoFlute” and I decided to look in to if I could build one as well. I use this blog as a note book for my initial research. From what I have found Steve talked about his ”KetoFlute” twice at the Security now! podcast.
From the transcript of theSecurity now! podcast ep 356, June 6, 2012.
STEVE: That's the little prototype for the ketone breathalyzer. LEO: [Laughing] You madman. You've done it. Does it work? STEVE: It's on its way. LEO: He's breadboarding a ketone analyzer. Well, it's about time. STEVE: Yeah, exactly. LEO: Wow. STEVE: Because I don't have enough things on... LEO: What chip do you use to detect the presence of ketones? Is there a sensor? STEVE: There are volatile gas sensors which will detect ethanol and also acetone. The problem is that they all - they're very sensitive to temperature and humidity, and our breath is both hot and moist. So the signal I'm looking for is minuscule compared to the noise, which is temperature and humidity. So I have a second sensor which is exactly the same technology, but designed to detect methane instead. And so the idea is that the common mode response will be humidity and temperature, and the differential response will be the content of gases that differ between the two sensors. So anyway, I'm just at the beginning of... LEO: What a fun challenge. STEVE: ...of experimenting. It may be that I cannot find - it may be that breath is just too hostile because of its temperature and humidity. But I'm going to - I'm working to very quickly determine, one way or the other, because I am just so tired of - my hands are just raw from poking them in order to take blood several times a day, which I have been doing. LEO: Several times a day? STEVE: Oh, yeah, yeah, because I'm spending serious money on these ketone blood tests in order to monitor my ketones and get a sense for where they are. I would - I can't wait to be able to, you know, to blow into something. And if it works, we'll, I mean, I'm not going to go into production. People don't have to worry about me disappearing...
From the transcript of theSecurity now! podcast ep 358, June 20, 2012.
LEO: Ho ho ho, he's building it, ladies and gentlemen. STEVE: Yeah. LEO: You put that on your head? What the hell? STEVE: You blow in there. LEO: For those listening, it is breadboarded. Lots of - I see six, five pots on there. I see a bunch of circuitry, wires. And there is a little - there's a USB interface. Oh, that's cool, so it's USB. And a thing, I see a thing, I guess that you could buy that off the shelf, that you blow into. STEVE: Oh, no, that's a made-from-scratch... LEO: You made that, too. STEVE: It's a chamber that has the sensor located inside... LEO: Dude, you rock. STEVE: ...which is measuring - anyway. So the point is... LEO: You're calling that the Ketoflute, right, as I remember. STEVE: The Ketoflute, yeah. And I've invested heavily. I've had friends blowing in it. I mean, it's working. But I still don't know... LEO: Hey, come here. Can I get you to blow into this? STEVE: I still don't know if I'm going to have anything. LEO: Right, this is research. STEVE: Yeah, it's pure R&D. LEO: Steve, this is why we love you. I'm getting tears in my eyes. This is amazing. STEVE: I need to answer the question. Maybe it'll work; maybe not. But again, if I have to go, well, okay, now I know, at least I've satisfied my curiosity without needing it to be something it isn't. So... LEO: You see? STEVE: It's important to be a pure researcher. LEO: And everybody needs to have that. If people could develop that mentality, it'd be so great. If you don't know, investigate. And you probably don't know. That's the problem. Smart people think they know. STEVE: Well, and that was the lesson from the Portable Dog Killer. I just encourage people to go build something because, oh, the act of doing that teaches you so much.