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STM32 TIMERS #2. PWM Input
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Jul 31, 2021
Purchase the Products shown in this video from :: https://controllerstech.store ________________________________________________________________________________________ STM32 TIMERS PART1 :::: https://youtu.be/OwlfFp8fPN0 STM32 TIMERS PART 3 :::: https://youtu.be/xqzWQgpqHmI STM32 TIMERS Playlist :::: https://www.youtube.com/playlist?list=PLfIJKC1ud8gjLZBzjE3kKBMDEH_lUc428 STM32 Playlist :::: https://www.youtube.com/playlist?list=PLfIJKC1ud8gga7xeUUJ-bRUbeChfTOOBd DOWNLOAD THIS PROJECT FROM :::: https://controllerstech.com/pwm-input-in-stm32/ ________________________________________________________________________________________ ******* SUPPORT US BY DONATING****** https://paypal.me/controllertech *******Join the Membership******* https://www.youtube.com/channel/UCkdqtSMnhYuMsJkyHOxiPZQ/join
View Video Transcript
0:00
[Music]
0:10
hello
0:10
everyone welcome to controllers tech
0:14
this is second video in the stm 32 timer
0:17
series
0:18
and today we will see how to use the pwm
0:22
input mode i covered the pwm
0:25
output in my previous video about the
0:27
timers and that's why i decided to go
0:29
with the pwm input today
0:32
we will see how to measure the input
0:34
frequency and the duty cycle
0:36
using the pwm input mode
0:40
so let's start by creating the project
0:42
in cube id
0:44
i am using stm32f446re
0:49
give some name to the project and click
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finish
0:53
so first of all i am selecting the
0:55
external crystal for the clock
0:58
let's see the clock configuration
1:01
type in the crystal frequency of your
1:03
controller
1:05
choose this as per your board don't just
1:07
use what i am using
1:09
my board have eight megahertz crystal
1:12
choose the hse for external crystal
1:16
choose pclk for pll clock
1:20
type the frequency you want to run the
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controller at
1:23
and hit enter that's all about the clock
1:26
configuration
1:28
now let's configure the timer i am
1:31
choosing timer 1 to provide the pwm
1:34
signal pwm output has already been
1:37
covered
1:38
and you can watch the video on the top
1:40
right corner
1:42
timer 1 is connected to a pb 2 clock
1:45
which is running at 180 megahertz
1:49
i am choosing the auto reload period of
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1800
1:52
so the output frequency will be 100
1:55
kilohertz
1:59
this is it for the timer 1.
2:03
now timer 2 is going to be used for the
2:05
pwm input
2:11
choose the clock source as internal
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clock and choose the combined channels
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as pwm
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input timer 2 channel 1 will be our main
2:20
channel
2:21
where we will provide the input clock
2:24
you can see here the pin p-a-0 got
2:27
selected
2:28
now comes the parameters
2:33
here i am keeping the prescaler zero so
2:36
the timer clock will be same as a-p-b-1
2:39
and that is 90 megahertz
2:43
the auto reload is set to maximum value
2:47
this is a 32-bit register and that's why
2:50
this value is very high
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if you have 16-bit register this will be
2:57
65535
2:58
so leave it to default next is the
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internal clock division to understand
3:04
this
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we need to check the reference manual
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here in the control register 1 we have
3:22
the clock division
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this clock division basically sets up
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the dead time and sampling clock
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the dts clock decides how fast we want
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to sample the input signal
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here are the settings for the dts clock
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i am keeping it to no division and that
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means the dts clock will be same as the
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internal clock
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we can skip the rest and come to the
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channel configuration
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here the input trigger is t i 1 f p 1
4:01
which means that the input from channel
4:03
1 after the filter and polarity
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selection
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will be connected to the capture 1. next
4:09
we have is the parameters for channel 1.
4:13
the polarity is set to rising edge which
4:15
means that this channel is going to
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measure the rising edges of the signal
4:20
i-c selection is direct and we will
4:23
connect the input signal directly to
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this channel
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this channel is our main channel and it
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will measure the frequency
4:32
now for the prescaler division ratio
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let's see the reference manual again
4:40
here we are interested in the capture
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compare register
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we have the input capture prescaler and
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as you can see
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it basically controls the capture
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frequency
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these bits controls how often we want to
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do the capture
4:59
let me explain this in detail
5:02
let's assume that this is the input
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clock and we want to capture the rising
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edges
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a rising edge would be counted as an
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event
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now suppose we use the prescaler
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division 8 that would mean that
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interrupt will trigger after the 8
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events
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and that means here this will keep
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happening after
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every eight events remember that
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if we do the captures at very high
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frequency then the interrupts will
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trigger very often
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and this will leave the rest of the code
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useless
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so this is an important parameters
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i am going with the highest possible
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value and that means
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the capture will be done once every
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eight events
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but the issue is that the cube m-x is
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not letting me choose this one
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don't worry about this we can set it in
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the code itself
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next comes the filter i am not going to
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use it
6:00
but let me explain it anyway here we
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have the input capture filter
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the filter configures the frequency at
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which the input signal will be sampled
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it is also used as low pass filter but i
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couldn't find more information on the
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topic
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for now we will keep the filter zero and
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that means the sampling frequency will
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be d t
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s and that is the internal clock
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i will update you if i find more
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information on how to use these filters
6:32
now comes the parameters for channel 2.
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the polarity should be opposite to the
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first channel and that's why it's
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falling
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edge the ic selection is indirect
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and this means we don't need to give the
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input to this channel
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it's internally connected to the channel
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1 and it is used to calculate the duty
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cycle
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all right let's enable the interrupt for
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the timer 2.
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this is it for the setup click save to
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generate the code now
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let's create few variables where we can
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store the results
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now in the main function start the timer
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in input capture mode for channel 1.
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channel 2 can be used in the normal mode
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since we only need the interrupt from
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channel 1.
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after the input capture has been started
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we will start the pwm
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for timer 1.
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and finally set the value of capture
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compare register for the duty cycle
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everything related to pwm output has
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been covered in the previous video
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so if you don't understand pwm output
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please watch the video on the top right
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corner
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once the input capture actually does the
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capture
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an interrupt will be triggered and this
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input capture callback will be called
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now we will write the rest of the code
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inside this callback function
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here we will check if the interrupt was
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triggered by the channel 1
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that is due to the rising edge of the
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input signal
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if it is then we will read the input
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capture value for the channel 1.
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then we will read the capture value for
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the channel 2
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and use it to calculate the duty cycle
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i will explain this in a minute
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next calculate the frequency
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this 90 megahertz is my timer 2 clock
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now let's understand this calculation
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let's see the pwm input mode in the
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reference manual
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well we are mainly interested in this
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figure
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here you can see when the first rising
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edge is captured
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the counter is reset and so do the
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captures values
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when the second rising edge gets
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captures the capture value read
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this value is actually this time
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difference between the first
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and second edges so the period of the
10:01
signal
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in the callback we also read the capture
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value for the falling edge
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using that value we can determine the
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pulse high time
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as a percentage of the total time
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this will be the duty cycle for the
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signal
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similarly using the clock frequency we
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can determine the frequency of the input
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signal
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i am just giving this delay in the while
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loop to test if the control enters the
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loop or not
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all right let's test this
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i have added all three variables to the
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live expression
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ok you can see the frequency is around
11:01
100 kilohertz
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and the duty is around 50 percent also
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note that the input capture value is
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pretty consistent
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let's put a break point in the while
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loop to check if the control
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enters the loop so the loop is also
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working all right
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since it's working fine for now let's
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test the higher frequencies
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now the auto reload is 450 making the
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output frequency 400 kilohertz
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and let's change the capture compare to
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225
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making the duty cycle 50.
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and there we have it around 400
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kilohertz frequency
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and 50 duty cycle but
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the while loop isn't running anymore
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this is because the interrupts are
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getting triggered at very high rate
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making the rest of the code impossible
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to run
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this is where the input capture
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prescaler comes in
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right now it's set to division 1 but we
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will change it to highest
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and this will make the capture to be
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performed every 8 events
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let's test this
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and now you can see the while loop is
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running pretty well
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let's see how high air can we measure
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with this setup
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this time the auto reload is 180
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making the frequency equal to 1
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megahertz
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let's change the capture compare to 60
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so the duty cycle will be 33 percent
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i would say the result is approximately
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correct
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the frequency is around 1 megahertz and
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the duty is 31
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the while loop is still running so we
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can test even higher range
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now the frequency will be 2 megahertz
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and the capture compare is still
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60 making the duty cycle equal to 66
14:00
percent
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this is still working all right
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surprisingly
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the while loop is still running honestly
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i wasn't expecting it
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but let's go even higher
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now the auto reload is 60 making the
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frequency equal to 3 megahertz
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and i am keeping the auto reload at 30
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so the duty would be 50 percent
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here we do have approximate to what we
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need but the while loop is not running
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anymore
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i guess this is the limit for the while
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loop with the current setup
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even though it was able to measure the 2
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megahertz clocks
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i would suggest that you keep the
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measurement below 1 megahertz
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for those frequencies the rest of the
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code can run
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pretty well too if you want to measure
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high frequencies
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well then you won't be able to run the
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rest of the code
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you can play with some other settings to
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improve the accuracy of the frequency
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measure
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before finishing this video i want to
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share one more thing
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it's quite possible to measure the high
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frequencies also
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in fact i did some tests and you can see
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the result in the picture
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the accuracy even at 10 megahertz
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frequency is quite phenomenal
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this is a different method by the way i
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was able to measure up to 18 megahertz
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input frequencies
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and even then the while loop was still
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able to run
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i was going to make the video on that
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method but as i was about to start
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i saw the cube mx has deprecated some
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settings that are needed for it
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anyway i will post the video on that
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method soon
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and if the cube mx allows you to do the
15:55
setup
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you can use it this is it for the
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today's video
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i hope you understood the process and
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its explanation
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you can download the code from the link
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in the description
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leave comments in case of any doubt
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keep watching and have a nice day ahead
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