radar is a valuable technology because
of its unique features
it not only helped to win world war ii
it also can solve many problems in our
projects
gritsy 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
these are the questions answered in this
video
which radar sensors exist and how do
they have to be connected to our boards
how do they compare how can we use them
in our projects which other technologies
exist
to solve similar problems and finally we
should have a comparison chart
also including pir and lidars
we do not have to invent everything in
video number 135
i showed cheap and practical radar
sensors to detect presence
in video number 181 we tried to measure
speed with radar today we will add a new
class of sensors
fmcw radars to measure distances
but first how does radar work
usually a transmitter emits ultra high
frequency waves in one direction
our typical radar sensors work on either
3
10 or 24 gigahertz only 24 gigahertz is
an
ism band that can be used without
licenses
the 3 and the 10 gigahertz bands seem to
be illegal to use
these waves are reflected by metal or
water for example
and can be received by the sensor's
receiver
the radar module then does some magic
and finally we get a proper output
signal for our projects
at 24 gigahertz the wavelength is only
1.2 centimeters which allows us to use
small antennas building microwave
devices is not easy
and usually extremely expensive
fortunately
we get ready-made sensors produced in
high series
and therefore also good for our budgets
the first type of sensors was shown in
video number 135
they are small and incredibly cheap they
can be used as presence detector
with a range of up to about 5 meters for
a person
bigger metal structures like a car
probably could be detected further away
like all radars they even work through
plastic
wood or thin walls but they are blocked
by metal also coated windows can block
or
reflect radar waves because they contain
metal
there were many discussions on the net
on how they work
it seems they do not contain a
transmitter
they are regenerative receivers like the
tube receiver we built in
video number 355 run on 3.3 volts
and resonate a little below 3.2
gigahertz
if enough conducting materials appear in
their
vicinity they change their behavior
because
human bodies contain lots of salty water
they conduct
this change is then amplified in a b0001
chip
and compared with a threshold because
they do not contain a transmitter
most of them are sensitive in all
directions
if you need more information i suggest
watching video number 135
where you see different versions of
those sensors
the next sensors are called hp 100
or ctm 324 they are
doppler sensors and detect speed
like the police radar sensors how do
they work
they use the doppler effect let's go
back in time
and see our experiments in video number
135
we mounted the sensor on the camera and
you should hear the sound coming out of
the loudspeaker
and again you see that the creator of
this video does not spare
any effort for a good video i am the
driver of the speeding vehicle
my assistant marvin acts as a police
officer
as you see his dress code today is
on the cover you clearly hear the
movement of the bicycle
when i drive by and the signal is
already picked up from quite far away
do you recognize the difference between
a fast
and a slow movement the frequency you
heard in the loudspeaker was produced by
the built-in mixer
which subtracts the frequency of the
transmitter from the incoming signal
the resulting frequency can be
calculated with this
formula as you see the frequency is
higher
the higher the speed is and also the
higher the frequency of the sensor
on which frequencies do those sensors
work
the hp 100 should work on 10 gigahertz
i have no instrument to measure it but
rumors say that its frequency varies
considerably
from sensor to sensor the cdm324
works on the open 24 gigahertz ism band
as we saw before the frequency change of
a particular speed
depends on the working frequency so the
cdm324 has more resolution
the sensor is also smaller because of
its higher frequency
definitely the better choice if we can
measure the output frequency for these
sensors we can determine the object's
speed in front of it this is what we did
in video number 181
the idea is to amplify its signal and
measure its frequency
unfortunately we were only able to get a
maximum range of about 5 meters
so the hopes to create a cheap speed
display
were not fulfilled and we abandoned the
project
i leave you a link to an excellent page
about these two sensors
we could connect an esp32 to the
amplified signal
and run a fourier transformation or fft
sketch
to measure its frequency this worked
quite well for us
i leave a link to such an fft sketch in
the description
it can also be used for other
applications
you get sensors with more reach on the
market
but unfortunately their prices are much
higher
because such devices are used in cars
maybe their prices will drop over time
or we even will be able to repurpose
car sensors please tell us if you know
if somebody already did such a project
this device is an abuse of such a speed
sensor
they use a cheap hp 100 amplify its
output signal with an op
amp and compare the amplitude with a
fixed value
they do not measure its frequency like
that they get a presence sensor with
variable sensitivity this can be an
important difference
from the small and simple rcwl sensors
all these sensors have in common that
they are not
influenced by light a deciding factor
for
outdoor applications most of their
competitors
work with light that in full daylight
competes with powerful sunlight
that is why most of those sensors do not
work outdoors
or at least only in a very small range
one of the earliest and today's most
essential radar applications is
aviation where it is used to detect
airplanes
there we are not too much interested in
the presence or speed of the planes
we are interested in their positions so
radar has to be able to measure distance
this was not possible with all the
sensors we looked at
up till now the engineers had to keep
their heads crooked
to concentrate all their brains in one
place
to find a solution for this problem
finally they came
up with the following proposal if we
continuously change the signal frequency
we create an artificial frequency
difference to the reflected signal
which can be measured like the doppler
effect
why is that the emitted signal has to
travel
to the target and back even at the speed
of light
this takes a while during this time our
transmitter frequency changed slightly
but the frequency of the reflected
signal still is the same
because it was generated a little bit
earlier
so the longer the travel and therefore
the distance to the target
the bigger the frequency difference cool
idea
it is called frequency modulated
continuous wave
short fmcw but
does it work it seems to work in air
traffic control
and i also found such sensors on
aliexpress
they are not as cheap as the ones we had
before
but they have everything integrated the
transmitter
the receiver as well as an mcu for
evaluation
their output is a serial signal which an
arduino can easily
read now we have to test it
in particular it's promised range of 20
meters
to make it more difficult i do it
outdoors
where fortunately the sun shines i
mounted the sensor and arduino uno
to this pole and placed it in free space
i already learned that a congested area
could lead to wrong results because also
non-moving parts can create
reflections and so screw up the
measurement
so pay attention if you want to use them
indoors
because the output signal is 3.3 volt
you easily can also use an esp for the
purpose by the way
the first test is with the human body
even it is before noon i drank a beer to
get more reflection coefficient
in my belly beer is much better than
water because it conducts
but does it help you see not very much
after two to three meters i'm no more
detected
and the detection angle gets smaller
with increasing distance
a sign of very directive antennas so we
have to get a bigger object
i choose my neighbor's car because after
the beer i want it to stay legal
obviously i cannot move it so i have to
move the sensor
here we see that it is good to about 11
meters
also here the detection angle is small
if i move the direction of the sensor
with my feet
it stops detecting the car and
no need to comment on my shoes this was
already done
in recent videos so the last step
is to compare what we have here are
the different sensors and here their
properties
the first five are radar sensors i
compare them with other sensors
used for similar purposes the pir and
the lidar sensors all sensors can
measure presence
speed only with the two doppler radars
and the lidars
lidars measure only distance but
subtracting two distances can be used to
calculate
speed the distance sensors can also be
used
to determine the direction of the
movement the doppler sensors always
produce a positive
frequency and cannot determine direction
only a more expensive version of the
cdm324
has two outputs and so provides
directional information
all radar sensors work through thin
walls and so can be hidden
this is of course not possible for
sensors using light
and finally pirs and lidars are heavily
influenced by light
and therefore better for indoor usage
where nearby metal can
irritate radars pirs are not
good in heated environments because
temperature differences
trigger them with this chart you have
the information to decide on the
suitable sensor for your next project
as always you find all 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