pxt-calliope/docs/lessons/flashing-heart/activity.md
Sam El-Husseini e3975e65e5 pxt-microbit Accessibility PR ()
* Accessibility changes
2017-09-07 13:42:08 -07:00

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# flashing heart blocks activity
Control images with a variable.
## ~avatar avatar
In this activity, you will learn how to blink an image on the LED screen.
## ~
Let's start by adding code that plots a heart image on the screen using `show LEDs`. Once you are done coding, don't forget to run your code in the simulator or the @boardname@.
```blocks
basic.showLeds(`
. # . # .
# # # # #
# # # # #
. # # # .
. . # . .`);
```
We want to leave the image on the screen for 0.5 seconds (500 milliseconds), then clear the screen. We can use `pause` to wait and `clear screen` to turn off the LEDs.
```blocks
basic.forever(() => {
basic.showLeds(`
. # . # .
# # # # #
# # # # #
. # # # .
. . # . .
`)
basic.pause(500)
basic.clearScreen()
})
```
Finally, we can surround this code with a `forever` loop to repeat it and add a pause after `clear screen` to keep the screen off for a little while. Modify your code so that your code looks like this.
```blocks
basic.forever(() => {
basic.showLeds(`
. # . # .
# # # # #
# # # # #
. # # # .
. . # . .
`)
basic.pause(500)
basic.clearScreen()
basic.pause(500)
})
```
## ~avatar boothing
Excellent, you're ready to continue with the [challenges](/lessons/flashing-heart/challenges)!
## ~