# case 01 Fixed Parking

## Our Goal

 Make motor:bit smart car realize fixed parking function.


## Material

 1 x [motor:bit smart car kit](https://www.elecfreaks.com/motor-bit-acrylic-smart-car-kit.html)

## Background Knowledge

### Principle of Line Tracking

 The line tracking module in this kit has adopted an infrared sensor. It consists of a **transmitter** and a **receiver**. The transmitter emits infrared light, while the receiver collects the infrared light reflected by the ground. 
 When contacting with black ground or other infrared light absorbing materials, the receiver can't receive the infrared light, then the light tracking module returns to 1. 

![](./images/uPsoeBB.jpg)


## Hardware Connection


Connect the left sensor(S1) on line tracking module to the 4th pin on motor:bit.
And connect the right sensor(S2) to 3rd pin. See picture below.

![](./images/BOpsVvF.jpg)

![](./images/kzPngGo.jpg)

## Software

[Microsoft MakeCode](https://makecode.microbit.org/#)

## Programming

### Step 1
Click **Advanced** in the code drawer of MakeCode to see more options. 

![](./images/LjMR5IU.png)

To program for motor:bit, we have to add a package. Find **Add Package** in the bottom of code drawer and click it. This will pop up a dialogue box. Search for "motorbit" and then click to download this package.

![](./images/XDlSfIS.png)

***Note:*** If you get a hint that some packages will be deleted due to the problem of incompatibility, you can either follow the prompts, or create a new project in the project menu. 

### Step 2

 Insert a `move forward with speed` block below `on start`. Set the speed parameter to 80, which means the car will move forward at the speed of 80 when being powered on.
 Create two variables: `left` and `right`. They are used to collect the return values of the left or right sensor. set their initial value to 1. 

![](./images/tYJS1aY.png)

### Step 3

 Within forever block, read digital pin P3 and P4, which are correspond to the left or right sensor on line tracking module separately. 
 Assign value to`left`and `right` variable.
 Judge if `left` or `right` is 0, which means one of the two sensors has detected black line. 
 If `left` or `right` is 0, set the motor speed to 0 and stop the car. 

![](./images/p2WuniN.png)

### Program

Link of the whole program: [https://makecode.microbit.org/_1gXfr9fdA6LH](https://makecode.microbit.org/_1gXfr9fdA6LH)

You can also download it from the page below.

<div style="position:relative;height:0;padding-bottom:70%;overflow:hidden;"><iframe style="position:absolute;top:0;left:0;width:100%;height:100%;" src="https://makecode.microbit.org/#pub:_1gXfr9fdA6LH" frameborder="0" sandbox="allow-popups allow-forms allow-scripts allow-same-origin"></iframe></div>  


***Note:*** Due to the effect of inertia, the car will rush out a certain distance before stop when a black line is detected.


## Result

 Once powered on, the car moves forward at the speed of 80. When a black line is detected by the line tracking module, the car stops immediately. 


## Think 

 Create more black lines to allow the car complete fixed turning and slow down speed. How can we program? 


## FAQ



## Relative Readings