in video number 300 i postulated that
each classroom should have a co2 center
against sleepiness
for a few days we have a second reason
that probably created a better business
case for your project the fear of a next
lockdown might convince the shule
managers more because co2 measurements
in rooms can also reduce aerosols in the
air
as usual we want more
we want the kids to be involved in the
build of the sensors and we will also
learn how the different co2 and eco2
sensors behaved during the last 6 months
besides that i will show you an
innovative new co2 sensor great
youtubers here is the guy with the swiss
accent
with a new episode and fresh ideas
around sensors and microcontrollers
remember if you subscribe you will
always sit in the first row one typical
way of transmitting cov19 is via the air
this time not over-the-air updates but
ota infections
last week here in switzerland we had a
super spreading event that made it into
the new york times
the infection was transported because
the air was not correctly exchanged
maybe our innovative sensor could have
helped
latest since video number 300 we know
how to detect used air by measuring its
co2 content
but as said before we want more
the sensor should be visible but not
disturbing during class
it has to be fancy enough to be accepted
by the kids
preferably it should be possible to
build one by the students
like that they can learn something about
sensors and microcontrollers
or would work if they are interested
it has to measure co2 not eco2
i will show you the difference and the
reason
it should be extendable and adaptable
there are other proposals for such
sensors for example this german project
as its name says it shows the result
optically
i wanted to go another way because
moving numbers can distract the students
and here is my proposal a cuckoo clock
which does not announce the hour but the
time to open the window or otherwise
exchange the air
this clock is a complete fake
first cuckoo clocks are no swiss thing
they are german
second this bird is for sure no cuckoo
and third
arnold schwarzenegger does not live in
this small house
in addition he is not swiss nor german
even if he speaks like me he is austrian
the only non-fakes are the co2 values
anyway you can comment if you have a
better idea for visualizing the need for
air cleaning
let's start with the build
we need five things
a bird's house disabled people made this
one and i think they did a great job
a co2 sensor and a microcontroller
i will use a professional sensor from
syntherion and an esp32 mainly because
it runs on 3.3 volts
it is also extendable if you want to
create a dashboard for your schule for
example
a 3d printed bird including a linear
servo to move it a voice generation
module including amplifier and
loudspeaker
and the voices of a cuckoo
and the terminator
my bird's house can be accessed from the
top
it is not made for breeding it is made
for feeding the birds in winter
building a similar house should be
within reach of most woodworking classes
so we can continue with the sensor and
the microcontroller i choose one of
those esp32 mini boards because it is
small and all peripheral components run
on 3.3 volts
i also need two serial connections
a 3.3 volt arduino mini with software
serial would do it too
but its programming with an ftdi board
is a little more complicated
and you would lose the possibility to
connect it to the internet if you want
now to the sensors selection if you are
not interested in co2 sensors you can
skip this part and go to the next
chapter this is a new youtube feature
in video number 300 we saw that we could
buy real co2 sensors and so-called eco2
sensors
what is the difference
the first is the price
real co2 sensors are much more expensive
than eco2 sensors eco2 sensors measure
different gases emitted by humans
and the theory goes that they can be
used instead of the more expensive co2
sensors
so should we use eco2 sensors for our
meter
here is an example of measurements of a
few days
while the real co2 sensors show little
differences in their reading they move
very parallel
the eco2 values sometimes follow the co2
values and sometimes not so they are not
very dependable i strongly suggest using
real co2 sensors for your project
sensors like the
sgp30 the
cc811 and the bme 680 therefore are out
for this purpose
let's now focus on the co2 sensors
i have the following selection
the cheapest is the chinese
mhc19 it has a serial connection and
about the same size as the sunrise
sensor from senseir
the next is the scd-30 from sincerion
the latter two have i square c
connectors
all three sensors use the same principle
non-dispersive infrared or ndir
they use the fact that co2 blocks light
with a wavelength of around
4.26 micrometer
a diode emits infrared light which
travels through the air towards a
detector
usually with a filter for those 4.26
micrometers in front of it
that's all the more co2 in the air the
lower the light level for the sensor
but because the light changes are
minimal these parts must be produced
with high precision
in spring i got an innovative new sensor
a scd-40 also from sensarian it uses an
entirely different principle
the photo acoustic effect
as in the ndir sensors an ir emitter
emits light at the wavelength absorbed
by the co2 molecules
when molecules absorb energy they
increase their movement and therefore
increase the pressure inside the sensors
nearly closed room
this principle was known for many years
but the devices were quite big and
expensive
sincerion was able to miniaturize the
principle to this small size
you can imagine that the pressure
increase is not high and hard to detect
this is why they use a trick
the ir light is modulated now the
pressure increases and reduces with the
frequency of the modulation
a microphone can measure this sound and
determine the amount of co2 molecules in
this small room
cool
because this effect also depends on
humidity and temperature they included a
sensor for those values too
these sensors are not yet sold i got an
early version for my tests directly from
sincerion
the next question which accuracy do we
need for our purpose
one thing is essential the outside co2
concentration is around 410 ppm at sea
level it is reduced by 3
for every 300 meters altitude
so it's easy to calibrate the sensor
for long term stability it has to be
calibrated from time to time
the sensorian and the sunrise sensors
have an automatic adjustment
for the
mhc19 i'm not sure
anyway it should be possible for most
rooms to determine the minimum value for
example during the night and set it to
410 ppm
the next question is what co2
concentration is dangerous
here we can have a look at two extreme
situations
submarines and the space station
both have to save on air and cannot
exchange it often
nasa has set the maximum allowable 24
hour average co2 on board of the iss at
5200
ppm
data collected on nuclear-powered
submarines indicate an average co2
concentration of 3500 to 4100 ppm with
maximum values of 11 300 ppm
we see the accuracy needed is not too
important
but we have to be sure that we measure
co2 i suggest putting the limit at
around 1000 to 1500 ppm and above that
value the cuckoo should remind us to
open the windows for a short time
by the way just opening a window or two
is not good
much better is to open the windows and
the door like that the chance the air is
wholly exchanged is much higher
now we should be able to select our
sensor
after nine months of usage all four
sensors still work and deliver values
with compensation all sensors were
accurate enough for our purpose
i choose the scd30 because it uses i
square c and is small i square c was
important because i needed the second
serial connection for the sound system
of my clock
i mounted the sensor below the house
because co2 is heavier than air
the next component of our co2 cuckoo
clock is the moving bird of course i
printed a linear servo which translates
this servo rotation into a linear
movement of about four centimeters
enough for our purpose
and the mini servo is strong enough
i found a more professional looking
linear servo but its tolerances are
quite tight and i had to help it with a
little silicone lubricant
both thingiverse links are in the
description
the bird also comes from thingiverse i
just had to reduce its size with
simplify 3d prusa slicer has the same
feature and i think other slicers have
it too
now i mounted the bird on the rail using
super glue and the moving bird is ready
add the servo library and adjust the
servo as well as the linear actuator the
servo moves 180 degrees
the last part is the sound
as said before i choose an acoustic
alarm because the alarm system of humans
is acoustic
with this concept nothing interesting
happens as long as the air does not need
to be exchanged and the students can
study
only if the air is used too much the
bird becomes visible and announces the
event
i'll be back
as announced it comes back every 30
seconds until the co2 value is lowered
of course you could add a second
announcement if the value is below 500
for example to close the windows
the sound is produced by this small mp3
player an amplifier and a loudspeaker
you can also use the player used in
video number 259
i search for wave files with cuckoo
clock sounds and stored it on the sd
card
the naming is not essential the sequence
is solely defined by in which sequence
the files are copied to the sd card not
a very good idea but okay if you know it
and i added the terminator as a surprise
for kids i'll be back
but of course here your and the kids
imagination is the limit
now i put everything together for that i
need this small 3d printed mount for the
mechanics
i suggest to power the clock with a usb
power brick because it consumes too much
energy for a battery
now i can place it here in my lap to
protect me from sleeping too much
before you start with your build i
summarize
we finished a unique cuckoo clock which
announces two high co2 values in a room
it uses a real co2 sensor because the
eco2 sensors are not reliable in
detecting exhaled air
i compared three conventional and one
new eco2 sensors and saw that they were
all okay for our purpose
outside co2 values are very stable at
around 410 ppm at sea level they can be
used to calibrate our sensors from time
to time
fixing a maximum allowed co2 level is no
science
knowing that the guys in the space
station have a maximum of 5000 ppm i
suggest going for a limit of 1000 to
1500 ppm
also because of the current corona
discussions
the alarm is done with a moving cuckoo
and its typical sound
such a clock can be built with kits if
you are a teacher or father watching
this channel if you want to get a kit i
suggest looking at guido workers project
called
co2 traffic light
as always you find the relevant links in
the description i hope this video was
useful or at least interesting for you
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thank you
bye