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.