pxt-ev3/docs/tutorials/object-near.md

Object Near?

Introduction @fullscreen

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.

Step 1

Open the ||variables:Variables|| Toolbox drawer. Pull a ||variables:set item to|| block onto the Workspace and place it into the ||loops:forever|| block.

let item = 0
forever(function () {
    item = 0
})

Step 2

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.

let nearness = 0
forever(function () {
    nearness = 0
})

Step 3

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.

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
})

Step 4

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.

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
    if (0 < 0) {

    }
})

Step 5

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.

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
    if (nearness < 50) {

    }
})

Step 6

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.

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
    if (nearness < 50) {
        brick.showValue("Distnace (cm)", nearness, 1)
    }
})

Step 7

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||.

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
    if (nearness < 50) {
        brick.showValue("Distnace (cm)", nearness, 1)
        music.playSoundEffect(sounds.animalsCatPurr)
    }
})

Step 8

In the ||music:play sound effect|| block, use the drop-down menu to select the information detected sound effect.

When an object is near, our brick will display the distance away that the object is detected in centimeters and then say "detected".

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
    if (nearness < 50) {
        brick.showValue("Distnace (cm)", nearness, 1)
        music.playSoundEffect(sounds.informationDetected)
    }
})

Step 9

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||.

let nearness = 0
forever(function () {
    nearness = sensors.ultrasonic4.distance()
    if (nearness < 50) {
        brick.showValue("Distnace (cm)", nearness, 1)
        music.playSoundEffect(sounds.informationDetected)
        pause(1500)
        brick.clearScreen()
    }
})

Step 10

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 brick.

Attach an Ultrasonic Sensor to Port 4 of your 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.