pxt-ev3
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LEGO MINDSTORMS EV3 for Microsoft MakeCode
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# Line Following
## Introduction @unplugged
Make your @boardname@ robot follow a line using the Color Sensor's Reflected Light Intensity Mode.
## Step 1
In the ``||logic:Logic||`` Toolbox drawer under the **Conditionals** section, drag out an ``||logic:If then else||`` block onto the Workspace, and drop it into the ``||loops:forever||`` loop.
```blocks
forever(function () {
if (true) {
} else {
}
})
```
## Step 2
Open the ``||logic:Logic||`` Toolbox drawer again. From the **Comparison** section, drag out ``||logic:0 < 0||`` comparison block and drop it into the ``||logic:if then else||`` block, replacing ``true``.
```blocks
forever(function () {
if (0 < 0) {
} else {
}
})
```
## Step 3
Open the ``||sensors:Sensors||`` Toolbox drawer. Drag out a ``||sensors:color sensor light||`` value block and drop it into the second slot of the ``||logic:0 < 0||`` comparison block, replacing the second `0`.
```blocks
forever(function () {
if (0 < sensors.color3.light(LightIntensityMode.Reflected)) {
} else {
}
})
```
## Step 4
If the value of the reflected light is greater than 40% (white or very light), our robot is outside the line, so steer to the left. In the ``||logic:0 < 0||`` comparison block change the first compared value from `0` to `40`.
```blocks
forever(function () {
if (40 < sensors.color3.light(LightIntensityMode.Reflected)) {
} else {
}
})
```
## Step 5
Open the ``||motors:Motors||`` Toolbox drawer. Drag out **2** ``||motors:tank motors||`` blocks and drop one of them into the ``||logic:if||`` part, and the other into the ``||logic:else||`` part of the ``||logic:if then else||`` block.
```blocks
forever(function () {
if (40 < sensors.color3.light(LightIntensityMode.Reflected)) {
motors.largeBC.tank(50, 50)
} else {
motors.largeBC.tank(50, 50)
}
})
```
## Step 6
In the first ``||motors:tank motors||`` block in the ``||logic:if||`` clause, change the speed values of the motors from ``50%``, ``50%`` to ``5%``, ``15%``. This slows down the robot and steers it to the left (because the **C** motor is driving faster than the **B** motor).
```blocks
forever(function () {
if (40 < sensors.color3.light(LightIntensityMode.Reflected)) {
motors.largeBC.tank(5, 15)
} else {
motors.largeBC.tank(50, 50)
}
})
```
## Step 7
In the second ``||motors:tank motors||`` block in the ``||logic:else||`` clause, change the speed values of the motors from ``50%``, ``50%`` to ``15%``, ``5%``. This slows down the robot and steers it to the right (because the **B** motor is driving faster than the **C** motor).
```blocks
forever(function () {
if (40 < sensors.color3.light(LightIntensityMode.Reflected)) {
motors.largeBC.tank(5, 15)
} else {
motors.largeBC.tank(15, 5)
}
})
```
## Step 8 @fullscreen
Use the EV3 simulator to try out your code.
Move the slider under the Color Sensor to change the reflected light intensity and check that motors are moving as you would expect.
## Step 9
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.
Attach a Color Sensor to Port 3 of your EV3 Brick, and attach your brick to a driving base with large motors attached to Ports B and C. See the instructions for building a _Driving Base with Color Sensor Down_. Test your program by positioning your robot to the right of a dark, thick line and then let it drive!