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welcome to controllers tech I made a
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video about HCS a zero for ultrasonic
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sensor to find distance this video will
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cover the HCS a zero force sensor but
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this time we will use a different but
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better approach towards it we will see
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how can we use input capture to measure
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the pulse width and which will be used
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to find the distance let's start with
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cube ID I am using stm32 f103 c8
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controller give the name to the project
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and click finish let's set up the clock
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first I am selecting external crystal do
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this if you have cortex m3 only let's
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run the system at maximum clock I am
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going to use timer 1 for this project
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select the input capture mode I have
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made a video on input capture a few
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months ago you can watch it by clicking
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the top right corner timer 1 is
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connected to a PB 2 clock and which is
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clocked at 72 megahertz if you are using
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any other timer check the datasheet to
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know where it is connected to prescaler
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in my case will be 71 this will bring
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the timer clock to 1 megahertz
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and we will get a time a period of 1
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microsecond per count this is important
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because HCS are 0 for sends the pulse of
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few microseconds so in order to read the
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we need the timer working in
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microseconds range now a r r will be the
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maximum possible value for a 16-bit
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timer it would be 65535
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make sure you enable the timer capture
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compare interrupts let's assume that you
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used another timer like timer two and
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you don't see the capture compare
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interrupts then in that case enable the
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global interrupt pin PA it is selected
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by default and we will connect the echo
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pin here select the pin pa9 as the
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output for the trick pin everything is
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set now click Save to generate the
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project let's start now first of all I
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will create a delay function which can
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provide us the microsecond delay I have
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already made a video on it check the top
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here are the variables defined which
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will be used this callback function will
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be called whenever a rising or falling
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edge will be captured first on detecting
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a rising edge the timestamp will be
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stored in the IC Val one variable now we
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will set the polarity for capturing the
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falling edge when the falling edge is
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captured another timestamp will be
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stored in the IC Val two variable now
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the counter will be reset and we will
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calculate the difference between two
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captured timestamps this difference will
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be in microseconds as our timer is
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running in that range based on this
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difference the distance will be
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calculated by using the formula provided
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in the sensors datasheet after finishing
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up all the calculations we will change
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the polarity in order to capture the
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rising edge again and this loop will
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keep repeating if you are using any
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other timer channel make sure you update
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it at all the respective positions this
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is the function to trigger the HC SR 0 4
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to start capturing data
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let me quickly define the trick pin and
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to trigger the HCS are 0-4 we have to
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pull the trigger pin high for around 10
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microseconds and then pull it low for
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I created a delay function to give delay
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now in the main function we will start
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the timer in input capture interrupt
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and in the while loop we will read the
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HCS a zero for every 200 milliseconds
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we got a lot of errors here I have
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defined the pin in a wrong way
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we still got few errors this error is
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actually present in the default
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generated code you can also click the
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error in the console and you will
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directly reach here click at this end
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and delete this bracket I didn't got
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this error in f4 series controllers you
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may or may not get this based on your
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software version if you are not looking
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for the LCD this is it you will get the
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distance accurately within plus minus 2
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let's include the i2c for the LCD I am
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using i2c one for this purpose that
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arrow got generated again
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let me quickly fix it now let's include
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the LCD library files
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refresh the code so that you can see
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them if you are using another eye to see
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make sure you change here initialize the
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LCD first let's print this string on the
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display now inside the while loop we
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will print the distance values on the
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display let's say the distance is 23
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then 23 divided by 10 will give us 2 and
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plus 48 is to convert to the respective
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similarly 23% 10 will give us three
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let's build it looks like I forgot to
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include the head of file
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include I to see LCD H
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everything is good now let's flash it to
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you can see the distance shown is as
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expected this is it for the video I hope
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you understood the concept and the
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procedure you can download the code from
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the link in the description keep
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watching and have a nice day
