pxt-calliope/docs/lessons/strobe-light/challenges.md
2016-04-13 08:27:45 -07:00

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# strobe light challenges
Coding challenges for strobe light.
## Before we get started
Complete the following [guided tutorial](/lessons/strobe-light/activity), your code should look like this:
```blocks
for (let i = 0; i < 5; i++) {
for (let j = 0; j < 5; j++) {
led.plot(i, j)
basic.pause(200)
}
}
```
### Challenge 1
### @video td/videos/strobe-light-1
Make the LEDs light up faster by changing the **pause** from 200 to 100 milliseconds:
```blocks
for (let i = 0; i < 5; i++) {
for (let j = 0; j < 5; j++) {
led.plot(i, j)
basic.pause(100)
}
}
```
* Run the code to see if it works as expected.
### Challenge 2
### @video td/videos/strobe-light-2
Make the board light up by rows instead of by columns by swapping the `i` and `j` variables in `plot(i, j)`.
```blocks
for (let i = 0; i < 5; i++) {
for (let j = 0; j < 5; j++) {
led.plot(j, i)
basic.pause(100)
}
}
```
* Run the code to see if it works as expected.
### Challenge 3
### @video td/videos/strobe-light-ultimate
Now that all the LEDs are lit up, let's make them turn off by reversing the strobe light pattern! You can use `unplot` to turn off a single LED.
```blocks
for (let i = 0; i < 5; i++) {
for (let j = 0; j < 5; j++) {
led.plot(j, i)
basic.pause(100)
}
}
for (let k = 0; k < 5; k++) {
for (let l = 0; l < 5; l++) {
led.unplot(4 - l, 4 - k)
basic.pause(100)
}
}
```