# 1.7 Flowing LED

Today, we will use LED, Raspberry Pi and scratch to make a Water Lamp.

The LED will light up in order with the direction of the arrows on the stage.

![](./img/1.7/1.7_header.png)

## Required Components

![](./img/1.7/1.7_list.png)

## Build the Circuit

![](./img/1.7/1.7_fritzing.png)

## Load the Code and See What Happens

By clicking on **Arrow1**, the LEDs  are lit in sequence from the left to the right (one at a time) and then off. Click **Arrow2** and the LEDs light up in the opposite order.

## Tips on Sprites

Delete the default sprite and choose the **Arrow1** sprite.

![](./img/1.7/1.7_sprite.png)

Here we will need 2 **Arrow1** sprites, which can be done with the duplicate button.

![](./img/1.7/1.7_sprite1.png)

Click on the **Arrow 2** sprite and change the direction of the arrow by selecting arrow1-b.

![](./img/1.7/1.7_sprite2.png)

Now let’s make a variable.

![](./img/1.7/1.7_code.png)

Name it as **num**.

![](./img/1.7/1.7_code1.png)

Follow the same method to create a list called **led**.

![](./img/1.7/1.7_code2.png)

After adding, you should see the **num** variable and the **led** list on the stage area.

Click **+** to add 10 list items and enter the pin numbers in order (17,18,27,22,23,24,25,2,3,8).

![](./img/1.7/1.7_code3.png) ![](./img/1.7/1.7_code4.png) ![](./img/1.7/1.7_code5.png)

## Tips on Codes

![](./img/1.7/1.7_code6.png)

This is an event block that is triggered when the current sprite is clicked.

![](./img/1.7/1.7_code7.png)

The initial value of the **num** variable determines which LED is lit first.

![](./img/1.7/1.7_code8.png)

Set the pin corresponding to **num** in the led list to low to light the LED, and then set the pin corresponding to **num-1** to high to turn off the previous LED.