140 lines
4.3 KiB
Markdown
140 lines
4.3 KiB
Markdown
# Object Near?
|
||
|
||
## Introduction @unplugged
|
||
|
||
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.
|
||
|
||
```blocks
|
||
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**.
|
||
|
||
```blocks
|
||
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.
|
||
|
||
```blocks
|
||
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.
|
||
|
||
```blocks
|
||
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.
|
||
|
||
```blocks
|
||
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.
|
||
|
||
```blocks
|
||
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||``.
|
||
|
||
```blocks
|
||
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"`.
|
||
|
||
```blocks
|
||
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||``.
|
||
|
||
```blocks
|
||
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.
|