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Welcome back.

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Let's continue where we left off in the previous lesson we created the initialization of function for

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our time like zero which is in charge of detecting the echo and then measuring the time.

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In this lesson we're going to stop by create an not delay microsecond and then go on to write the rest

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of the driver.

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So let's stop by writing the function it takes one argument.

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It takes a you end argument and this is the time delay we want to program and then we start by unlocking

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it with a clock source by activating the clock gate and mechanism for timer what your 0 uptime on what

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you're 1 Sorry we use in time at 1 year we use time of zero up there and then we stop by disabling the

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time up before making any changes by access in that time a control register.

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After that we go to the timeout configuration register and set it to the sixteen bits mode right.

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The next thing will be to go to that timer a mode register and choose it's us a periodic timer.

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We'll do this by writing two X two or two into this register.

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The next step will be to load the interval file into the Interpol load register and we've already said

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in order to get it microsecond delete.

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We have to load 16 into the interval a load register and minus one cause it begins content from zero.

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And also because 16 because we're running at 16 megahertz.

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If we were to run a 24 make hour load twenty four hundred megahertz we load a hundred.

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The next thing will be to access the ICR register and set it high.

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And then the next one would be to activate the time by going back to the time control register like

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this said to me.

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Finally we pull and wait for the time out to occur.

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We used to loop to pull to create our delay like we did before and we forgot to to up this local variable

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declaration.

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We can just declare the int I up here like this right and our delete functions set and then next thing

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as we initialize the port and write the final function which will be the function that actually measures

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the distance of the obstacle in front of the ultrasonic sensor.

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So this next function we're going to call it a port in it and this function is just going to perform

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basic initialization of the pins and ports.

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We are using for this particular project so we stopped by initialize in the cheapest I O port a course

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we've connected a trig up into Port a then we can also initialize to keep an eye O port F test to initialize

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the blue only to make the project more fun provide some outputs on the c we don't need to initialize

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points bu cos we've initialized it over here it's working with a timer set trigger pin US output it's

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like this because we've already defined trigger remember defined it so the code knows what trigger means

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and then we've set the direction of the blue which is also an output thing

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then we can digitally enabled the

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condition enabled the pin.

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We don't need this here this echo echo is connected to p p p.

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So that's a mistake over there.

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We need to do is enable this then enable that to wrap up this function we need to enable that then for

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the blue early D like this.

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Right.

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So the third function is complete the next function is going to be the function that does the calculation

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and outputs that distance of the object on the object close to the ultrasonic essential.

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And this function is going to return a new end 32 and it's going to take no argument.

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This what it looks like.

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I'm going to call this function measure D measured distance and stuff like this.

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Right.

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So the first thing to do is to disable the trigger pin.

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Remember when we spoke about the steps to detect the distance from the ultrasonic sense or we said you

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first disable the trigger pin just to make sure it is disabled.

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And then after that we give at least a 10 millisecond delay.

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So let's do the first to disable the trigger pin like this this one here disables is just the trigger

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pin and then we use our new delay function that delay microsecond and it says at least 10 milliseconds

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so we can give twelve milliseconds to find and then after that we enable the trigger pin right and then

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we delay at least 10 milliseconds again 10 microseconds sorry delay at least 10 microseconds again which

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is 12.

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Then finally we disable a trigger pin

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right.

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So this how we we send out the ultrasonic burst remember it sends aid 40 hertz or sonic bursts to this

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how we send it refers first to say would trigger pin.

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We wait for about 10 microseconds 10 microseconds and then we enable the trigger pin and then we wait

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for another 10 microseconds and disable it.

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Then the next thing we have to do is capture the return of the signal on the equipment.

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We have to clear a time a capture flag by right and a one to the ICR register.

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If you check the data sheet it says when you write a one two bits two of the ICR register you cleared

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a time of capture flag and this base is known as the CCI entry bit.

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It's an data sheet and we have to poll just like we did for the delay function.

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We have to pull over.

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We have to pull the raw interrupt the raw interrupt status register the right s and see if the second

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bit is high and I've put a comment here.

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I said Wait till captured by checking the C E R S which is the bit to check in.

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That too is high.

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That shows that an interrupt hustle can mean and capture has occurred.

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And when that capture occurs or you have to do is stored it timestamp in a variable so we can store

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it in this variable here known as high edge.

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And we've not declared its variable.

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That's why we we get getting this red marks.

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But let's declare the variable.

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Now we are going to have two of such variables one is high end and the other is low high edge sorry.

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And the other is little H.

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So yeah.

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So we pull to see whether the B2 is high which indicates that there's been a capture and then we store

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it in the T R and A T R is basically this statement basically means that time at which the last edge

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event took place should be stored in high edge.

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Right.

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Because that timestamp is stored in our in a t r register because we've with the course we've configured

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the timer to edge time mode.

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It stores the timestamp when we did the edge count mode.

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It stores the number of H counted in the T R because we can't forget earlier on to each time it stores

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the timestamp.

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And now we have timestamp stored over here in this variable.

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So that's what we.

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We want to do is get the next edge.

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Remember when a rise in your cast the next one is at fault an age when a fallen angel cast the next

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one is a rise in age.

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So we just need to do the same thing basically.

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And then we'll get food and age.

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So in fact I'll post a video and see if you can do that.

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Could you post a video and try it out and see whether you can write the rest of the code to detect the

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full edge.

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All right.

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Welcome back.

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OK let's do it together.

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I trust you tried your best.

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It's very straightforward and I'm sure most of you got it.

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So the next day and I'll just put a comment to a cop just take an edge which

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like this to fall in edge.

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And what we have to do is exactly the same thing first.

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We cleared a capture flag like we did above after we've cleared a couple to flag we've pulled the low

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interrupt status register to see whether the second bit is high.

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Good to see Coach hustle kid right.

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It's the same thing then.

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If it is high because we have it wild appear the program is going to freeze onto the cultural cars.

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If it's high we store it in the other variable which is the low edge.

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Now we have the.

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We have.

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We have detected the high edge and the low edge.

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The next thing we have to do is declare a variable to store the difference between the high edge and

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the low edge and then declared a variable that would return the results to what I'm going to do next

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is declare some constants and some yeah some new variables.

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So let's declare a new variable.

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I'm going to call this variable D distance.

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You can call it whatever you want to call it the distance.

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I don't know why that would be easier but could the distance.

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This one is going to start a distance in centimeters.

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We're going to create a constant and this constant is going to hold our period in the period of our

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run and frequency is sixty two point five.

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None of seconds and this is how you write.

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You're right sixty two point five E minus nine sixty two point five nanoseconds and then we need and

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multiply a constant.

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So this number here was derived from the speed of sound.

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We need this to multiply our timestamp and our run frequency in order to get a distance in centimeters.

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Right.

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So we have these new variables.

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Let's see what we use them for too.

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The next thing would be to store the difference between the low edge and high edge in the distance.

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Right.

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Since the low edge bulkhead latest you can just look up the H minus high edge like this.

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And then we have the difference of the two timestamps stand here and to get a distance.

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Finally we just multiply the distance by the multiplier and then by 0 60 megahertz one clock.

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Then we have the distance and because the function returns in that two would just return the distance.

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This is a straightforward yes.

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This function is complete.

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This function would return the distance of an object right in front of the ultrasonic sensor.

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And this is able and this program is able to do this by measuring the time between two events that rise

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in age in the fall and age.

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This one application of time is was used in designing drivers and signal processing.

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So I will pause here and continue.

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Later we continue the next lesson that we write the application to test this.

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We just write we basically complete the main function in the next lesson.

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So see you in the next lesson.