pxt-calliope/docs/projects/fireflies.md
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Radiodocsupdate (#1430)
* a few updates

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2018-10-15 15:32:09 -07:00

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# Fireflies
## ~ avatar
Turn your @boardname@ into fireflies.
## ~
https://youtu.be/ZGvtnE1Wy6U
## How do Fireflies synchronize?
Go to http://ncase.me/fireflies/ and read about the fireflies synchronization phenomenon.
## Code the firefly
We want to create virtual fireflies using multiple @boardname@s (each @boardname@ acts as a firefly).
Let's review some of the key points from 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 ``||basic:forever||`` loop to repeat code that increments the clock.
When the clock reaches "noon" (let's pick `8` as noon), 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
}
})
```
### When you see a nearby firefly flash, nudge your clock a little bit forward
The @boardname@ can send radio messages to a 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: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.onReceivedNumber(function (receivedNumber) {
// advance clock to catch up neighbors
clock += 1
})
```
## Put it all together
https://youtu.be/XzZeB4yYnEw
Download this program on as many @boardname@s as you can find and try it out in the dark!
**Note:** We've added a ``||radio:radio set group||`` block to specify which group the firefly will communicate on.
```blocks
// the clock ticker
let clock = 0
radio.onReceivedNumber(function (receivedNumber) {
// 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
```