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Hello.

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Welcome back.

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We started by learning how to measure the time between events using timers.

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And as I mentioned the excellent application for use in timers to measure the time between events is

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when you are programming the drivers for ultrasonic sensors.

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So we're going to learn about ultrasonic sensors in this lesson and then we'll go ahead to write our

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own drivers an API and we would apply.

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Time is to do that.

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So back here our cortex and dot com and I'm gonna go to lessons and when the page opens I'm going to

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select over here interface and we sense or so I'm going to select ultrasonic module see as SRO for when

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I click.

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There are some very nice article that we wrote some time ago on write in drivers for ultrasonic sensors.

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So I'll just take you through the arm.

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The ultrasonic sense or here.

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This is a very nice summary of what a data sheet says.

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So you don't need to read a data sheet of this component after this lecture.

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Yeah.

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So the H.C. CSR all for ultrasonic sensor is a very popular low cost ultrasonic sensor used for non

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contact distance measurement.

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The module comes with a separate transmitter and receiver to determine the distance of an obstacle in

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front of the module.

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That transmitter which is known as the trigger pin automatically transmits eight 40 heads ultrasonic

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signals the signals or the bursts hit the obstacle and then bounces back to the module.

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When and if the module when and if the ultrasonic sense IV gets back the receiver which is known as

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the echo pin automatically turns high for a duration of their some of the time taken to send and receive

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deep or trust sonic burst.

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That time is then multiplied by a constant to get that distance.

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So that's how the ultrasonic or works.

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So the module we're using it for this experiment has four pins it's got pin one as far as CCD the second

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being as their Trig trigger pin and then the third as the echo pin and then the fourth as they can D

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deficiency which are connect to our microcontrollers two point three volt.

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We shall try to put a three point three volt if it's not enough 42 to power the V.C. we're going to

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do next or five fivefold and then a trigger pin which would enable us a digital output pin remember

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that trigger pin sends out the ultra sonic burst and then the echo pin we use as the digital input to

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pin the echo Bean the pin that receives the bounced back signal when the signals hits when the signal

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hits an obstacle it bounces back and then it is detected by the echo pin.

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So we would enable this as an input pin and then we will connect the ground to the ground.

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Right.

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So this is this schematic we're going to use we're going to put 200 K resistor between the echo p and

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now what P B6 we still use in the same microcontroller team for C 1 2 3 TVC Launchpad yes more about

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the specifications of the board of the ultrasonic module it draws about 15 merely umpires the maximum

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range is four meters.

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That is very long and the minimum range is two centimeters.

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The work and frequency as we said is 400 hertz and a trigger signal.

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The signal is triggered at least 40 microseconds.

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Let's see how do we pyramids these six steps to program.

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This is just a summary would go into details when we start writing the actual code.

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Over here it says set a trick pin of the ultrasonic module high.

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Wait for a signal to bounce back Necco and then start a timer when equities detect it stop time.

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When echo pain goes low.

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So this how we measure the time between the event read the time value converts value to a distance.

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So to even give you more details you can come back to this article and read it at your own convenience

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but I would still summarize and tell you how it works yet.

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It's called X and dot com.

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You can check it out.

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It's the the official site for all the cortex courses we have on all our you know our online schools.

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How do you detect the echo.

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So remember from the Peanuts above which we've seen we have said the echo pin as an input.

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So to detect echo we can simply check whether the state of the inputs pin is high or not in the circuit

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diagram above.

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We have connected the echo into PBS six or four of our microcontroller to detect if p B6 is high and

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it starts a timer.

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So all we have to do is detect if P6 is high and it starts a timer.

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And this is a very short pseudocode.

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We can check with a simple logical comparison and then keep incrementing account of variable while the

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condition is true.

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A simple us while P B6 is not equal to zero.

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Therefore it's high current plus plus distance cause counter times are constant.

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We would have to derive this constant that would help us convert this counter value to our appropriate

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time unit.

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So that's one way of doing it and then converting the value of their counter to distance by more to

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plan it to a constant.

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That's what I've just said over here.

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This method is straightforward but it's not very precise.

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The more precise and efficient with which I highly recommend is by set in a general purpose timer to

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detect the rising and falling edge of P6.

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That's where you can detect exactly when P B6 gets high and when it's course low.

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Nice.

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So that is what we are going to do.

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And this is a so getting your time is right.

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Like I said when I come to this website I just read a blog post a bit like you know back in the days

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at school.

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Yeah.

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So just bear with me.

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It's very important to understand this stuff.

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And what is written here is just yes.

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A blog post I wrote so it's just like my script to write a more robust piece of code to interface with

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ultrasonic sense or we need to set two timers.

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If you refer back to the specifications of our H.R. off our HECS are all for addressing an excess or

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in the table above.

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You'll find that it says trigger signal at least 10 microseconds long.

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This means this means that when we set our Trig up in high we have to wait for 10 microseconds and then

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turn its back too low.

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To achieve this microsecond delay we have to set a time to create this precise delay for us and we already

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learned how to create delays using timers so that it's already covered.

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Let's call this time a time a one for the sake of this example we shall call this time a time of 1.

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As we mentioned earlier we need to detect the rise and fall in Edge of the Echo speed.

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We shall need another time for this.

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Let's call this time a time of zero the first and you should know about time as is that they are directly

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affected by the run and frequency of the microcontroller.

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You already know this course we've been right in time and drivers throughout this lesson or try this

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course.

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So yeah I'm glad you already know that.

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Let's say we are running our team for C 1 2 3 2 C launchpad which by default runs at a 16 megahertz

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to set the microsecond delay timer.

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After performing the necessary initialization requirements such as enabling the clock for the time a

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block sets and a bit option and selecting the running mode with a periodic or one shot or down counter

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you will have to load the number sixteen minus one into their time into file load value.

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This is how we derive 16.

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You already know this with this example.

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For a second delay we loaded 16 million into the interval load register and for a millisecond delay

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we load it sixteen thousand into the interval load register now for a microsecond early we load just

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16 into the interval load register and this is how it's derived.

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You already know this suggests the same calculations we did at a time.

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So let's see what we've got here.

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Therefore at 16 megahertz our microcontroller Ryan 16 clocks runs this thing clock cycles in one microseconds

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so 16 clock cycles is run in y and microseconds hence we load 16 so this is this is right up the border.

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This is a delay function a very simple delay function microsecond delay function were written for this

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very same thing like we did in our previous lessons.

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We initialize the arm that propagates in mechanism of the time a block we disable the timer.

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We can forget everything we loaded 16 into the time up.

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Time a load register.

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And then we initialize the timer back and then we created a loop and then we pulled for the time.

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This is the same as the time delay functions we've been right.

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Just that this is a microsecond version because we are lowered in 16 over here.

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Now we are in a position to create microsecond delays to create a 10 microseconds delay as required

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by the trigger pin.

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We simply need to call our delay microsecond function like this delay microseconds.

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Don't worry about all of this we are going to write all of the code and we are going to see its work.

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So just hold on with me.

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Now let's take a look at how we are going to use time as Europe to get the rise and fall in urge of

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our equipping.

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Again using our second diagram above as an example we can see the echo penis connected to p B6 of our

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microcontroller in our function for initializing this timer.

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We have set p p six alternates function so let's register.

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We've said the appropriate PTL value of the pin.

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This can be found in data sheet and we showed this in the very end an example we did for count an event.

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We have said the bit option and finally set the running mode as both edges inputs capture mode again

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for details you can check the data sheet or just wait until we start writing the code.

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Yeah this is what the initialization function looks like.

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We've initialized the function here.

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This these are the clock gate initialization is initialized the timer with initialized the deport b

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over here and then we've just said it would be disposed to be put to be direction register we set in

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it as input by the direction the IRS admitted here and then we set the PTO CTO with the alternate function

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as well.

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So then we come here and then we disable the timer before we start configuring it and then we do the

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configurations.

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We set a time on mode register in the mode register we decide that we want to detect both edges discord

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corresponds to that if you if we start code and you would see what I mean.

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And then and then that's it we enabled a timer.

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So this is just a very quick summary of how this is done to prepare you before we write the actual code.

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So if there is something you do not understand please leave it in a comment section.

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So how do we really measure the distance of an object.

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Let's see to measure the distance of an object in front of the ultrasonic module we have to set a trick

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below to just make sure it is low wait for about 10 microseconds for it to take effect set a trip in

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high with 410.

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Wait for at least 10 microseconds set a trip in low again start time of zero captured a timestamp of

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the rising edge capture the timestamp of the falling edge get a difference of the two timestamps calculate

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the distance in centimeters and then formula is time difference multiplied by six two point five we've

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taken the time difference this formula.

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The time difference multiplied by one period.

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You know we run that 16 megahertz in one period is sixty two point five nanoseconds.

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That is this sixteen point five race to the power minus nine.

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This sixty two point five nanoseconds and then we're more to play by this constant.

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I'm going to get into the details of derive and this constant this constant is derived from the speed

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of sound.

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And when we multiply this we get that distance in centimeters and we are going to verify that we will

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do that.

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And good to see it's working.

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So this is what the code looks like this the function we are going to write.

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We've called it measure D and then we stop by.

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We'll connect the trigger pen to put a X terror.

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I wouldn't go into this.

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We would just go and write the actual code instead.

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So we'll write the code.

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And still if you still want to read this you can come to cortex.

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Dot com go to lessons and then you can select interface interfacing H.S. S R O for all trust on extend

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source and then you see all of this here.

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It's all free of charge and we keep updating our lessons with free lessons to help students and professionals

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get updated their new standards and new ways of coding the cortex architecture.

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Yeah.

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So I'll see you in the next lesson.

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We will go to you vision and write the actual code for this lesson.

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See you.