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

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# Fireflies
## ~ avatar
Turn your @boardname@ into fireflies.
## ~
https://youtu.be/ZGvtnE1Wy6U
## How do Fireflies synchronise?
Go to http://ncase.me/fireflies/ and read about the fireflies synchronization phenomenon.
## Code
We want to create virtual fireflies using multiple @boardname@ (each @boardname@ acts as a firefly).
Let's review some of the key points of the article:
## "Each firefly has its own individual internal clock"
A clock in this case is like a counter, so we will start by adding a ``clock`` variable to our program.
```block
// the clock ticker
let clock = 1
```
## "and every time the clock “strikes twelve”, it flashes."
We can use a [forever](/reference/basic/forever) loop to repeat code that increments the clock.
When the clock reaches "noon" (let's pick `8`), we turn on the screen briefly (by using the game score animation)
```block
// the clock ticker
let clock = 0
basic.forever(() => {
// if clock "hits noon", flash the screen
if (clock >= 8) {
// flash
game.addScore(1)
// wait for 2 ticks
basic.pause(200)
// reset the clock
clock = 0
} else {
// just wait a bit
basic.pause(100)
// increment the clock
clock += 1
}
})
```
## Step 1: when you see a nearby firefly flash, nudge your clock a little bit forward.
The @boardname@ can send radio messages to neighbor @boardname@.
We can use these messages to simulate the "flashes" of light.
* When a firefly flashes, it also sends a number over radio using [radio send number](/reference/radio/send-number).
```block
// the clock ticker
let clock = 0
basic.forever(() => {
// if clock "hits noon", flash the screen
if (clock >= 8) {
// notify neighbors
radio.sendNumber(0)
// flash
game.addScore(1)
// wait for 2 ticks
basic.pause(200)
// reset the clock
clock = 0
} else {
// just wait a bit
basic.pause(100)
// increment the clock
clock += 1
}
})
```
* When a firefly receives a radio packet, it increments its clock by one.
```block
// the clock ticker
let clock = 0
radio.onDataPacketReceived(() => {
// advance clock to catch up neighbors
clock += 1
})
```
## Putting all together
https://youtu.be/XzZeB4yYnEw
Download this program on as many @boardname@ as you can find and try it out in a dark room!
(We've added a [radio set group](/reference/radio/set-group) block to specify which group the firefly will communicate on).
```blocks
// the clock ticker
let clock = 0
radio.onDataPacketReceived(() => {
// advance clock to catch up neighbors
clock += 1
})
basic.forever(() => {
// if clock hits noon, flash the screen
if (clock >= 8) {
// notify neighbors
radio.sendNumber(0)
// flash
game.addScore(1)
// wait for 2 ticks
basic.pause(200)
// reset the clock
clock = 0
} else {
// just wait a bit
basic.pause(100)
// increment the clock
clock += 1
}
})
radio.setTransmitPower(1)
radio.setGroup(12)
```
```package
radio
```