140 lines
4.3 KiB
Markdown
140 lines
4.3 KiB
Markdown
# Object Near?
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## Introduction @unplugged
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The digital Ultrasonic Sensor generates sound waves and reads their echoes to detect and measure distance from objects in centimeters. Build a program that will detect when an object is nearby.
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## Step 1
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Open the ``||variables:Variables||`` Toolbox drawer. Pull a ``||variables:set item to||`` block onto the Workspace and place it into the ``||loops:forever||`` block.
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```blocks
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let item = 0
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forever(function () {
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item = 0
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})
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```
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## Step 2
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Go to the ``||variables:set item to||`` block and click the variable name dropdown and select "Rename variable...". In the window that pops up, rename the variable to ``nearness`` and click **Ok**.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = 0
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})
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```
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## Step 3
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Open the ``||sensors:Sensors||`` Toolbox drawer. Drag the ``||sensors:ultrasonic distance||`` out and use it to replace the `0` in the ``||variables:set nearness to||`` block.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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})
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```
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## Step 4
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Get an ``||logic:if then||`` block from the ``||logic:Logic||`` drawer and place it below ``||variables:set nearness to||``. Find the ``||logic:0 < 0||`` conditional block and replace the ``true`` value of the ``||logic:if then||`` condition with it.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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if (0 < 0) {
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}
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})
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```
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## Step 5
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In the ``||logic:0 < 0||`` conditional, put the ``||variables:nearness||`` variable from the ``||variables:Variables||`` drawer in the first slot. Change the value of `0` in the second slot to `50`. This sets our range for a near object.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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if (nearness < 50) {
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}
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})
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```
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## Step 6
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Go get a ``||brick:show value||`` block from the ``||brick:Brick||`` Toolbox drawer and put it inside the ``||logic:if then||``. Set the string in the first slot to `"Distance (cm)"`. Get another ``||variables:nearness||`` and drop it into the second slot.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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if (nearness < 50) {
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brick.showValue("Distnace (cm)", nearness, 1)
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}
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})
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```
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## Step 7
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Now, let's add a sound as an alert when something is near. In the ``||music:Music||`` drawer, get the ``||music:play sound effect||`` and put it just below the ``||brick:show value||``.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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if (nearness < 50) {
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brick.showValue("Distnace (cm)", nearness, 1)
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music.playSoundEffect(sounds.animalsCatPurr)
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}
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})
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```
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## Step 8
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In the ``||music:play sound effect||`` block, use the drop-down menu to select the ``information detected`` sound effect.
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When an object is near, our brick will display the distance away that the object is detected in centimeters and then say `"detected"`.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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if (nearness < 50) {
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brick.showValue("Distnace (cm)", nearness, 1)
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music.playSoundEffect(sounds.informationDetected)
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}
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})
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```
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## Step 9
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To give a little time to see the message, put a ``||loops:pause||`` after the ``||music:play sound effect||`` block. Change the time from `100` to `1500` milliseconds. Pull out a ``||brick:clear screen||`` and put it after the ``||loops:pause||``.
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```blocks
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let nearness = 0
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forever(function () {
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nearness = sensors.ultrasonic4.distance()
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if (nearness < 50) {
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brick.showValue("Distnace (cm)", nearness, 1)
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music.playSoundEffect(sounds.informationDetected)
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pause(1500)
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brick.clearScreen()
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}
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})
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```
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## Step 10
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Now, plug your EV3 Brick into the computer with the USB cable, and click the **Download** button at the bottom of your screen. Follow the directions to save your program to the EV3 Brick.
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Attach an Ultrasonic Sensor to Port 4 of your EV3 Brick. Test your program by putting an object at different distances in front of the Ultrasonic Sensor – an object 50 centimeters or closer should be detected.
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