Fireflies

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 micro:bit (each micro:bit 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.

// the clock ticker
let clock = 1

“and every time the clock “strikes twelve”, it flashes.”

We can use a 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)

// 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 micro:bit can send radio messages to neighbor micro:bit. 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.

// 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.

// the clock ticker
let clock = 0
radio.onDataPacketReceived(() => {
    // advance clock to catch up neighbors
    clock += 1
})

Putting all together

Download this program on as many micro:bit as you can find and try it out in a dark room!

(We’ve added a radio set group block to specify which group the firefly will communicate on).

// 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)

radio