RS Components - Tweet Race

The design winner is only 18 (Tom Speller)! Here's his design (not necessarily the final version?):


Source: blog

Source: Twitter

and fwiw, the code on his blog (not the final version):
CODEint track1 = 10; // track 1 PWM pin
int input1 = 0; //this is a interrupt input not a digital number (digital pin 2)
volatile int count1 = 0; // tweet counter for track 1
int car1Speed = 0;

int setReset1 = 1;

long track1Time = -500;

int speedSet1 = 0;

int track2 = 11; // track 2 PWM pin
int input2 = 1; //this is a interrupt input not a digital number (digital pin 3)
volatile int count2 = 0;
int car2Speed = 0;

int setReset2 = 1;

long track2Time = -500;

int speedSet2 = 0;

int carTime[] = {500, 450, 400, 300, 150}; // the amount of time the car will run on each tweet.

int carSpeed[] = {120, 160, 190, 210, 230};

int serialValue[] = {0,0};

int changeSet[] = {30, 60, 120, 250};

void setup(){

pinMode(track1, OUTPUT);
attachInterrupt(input1, track1input, FALLING);

pinMode(track2, OUTPUT);
attachInterrupt(input2, track2input, FALLING);

Serial.begin(9600);

}

void loop(){

if(Serial.available() > 0){

int data = Serial.read();
int currentNumber = 0;

if(data == '<'){

while(data != '>'){

data = Serial.read();

if(data >= '0' && data <= '9'){
serialValue[currentNumber] = serialValue[currentNumber] * 10 + data - '0';
}

if(data == ','){
currentNumber = 1;
}
}
Serial.flush();
}
}

if(serialValue[0] > 0){
count1 = count1 + serialValue[0];
serialValue[0] = 0;
}
if(serialValue[1] > 0){
count2 = count2 + serialValue[1];
serialValue[1] = 0;
}

if(count1 > 0){
Serial.print(count1);
Serial.print(" , ");
Serial.println(count2);

if(count1 > changeSet[3]){
speedSet1 = 4;
}else if(count1 > changeSet[2]){
speedSet1 = 3;
}else if(count1 > changeSet[1]){
speedSet1 = 2;
}else if(count1 > changeSet[0]){
speedSet1 = 1;
}else{
speedSet1 = 0;
}

if(setReset1 == 1){
analogWrite(track1, carSpeed[speedSet1]);
track1Time = millis();
setReset1 = 0;
}

if(setReset1 == 0){
if(millis() > track1Time + carTime[speedSet1]){
analogWrite(track1, 0);
count1 = count1 - 1;
setReset1 = 1;
}
}

}

if(count2 > 0){
Serial.print(count1);
Serial.print(" , ");
Serial.println(count2);

if(count2 > changeSet[3]){
speedSet2 = 4;
}else if(count2 > changeSet[2]){
speedSet2 = 3;
}else if(count2 > changeSet[1]){
speedSet2 = 2;
}else if(count2 > changeSet[0]){
speedSet2 = 1;
}else{
speedSet2 = 0;
}

if(setReset2 == 1){
analogWrite(track2, 120);
track2Time = millis();
setReset2 = 0;
}
if(setReset2 == 0){
if(millis() > track2Time + carTime[speedSet2]){
analogWrite(track2, 0);
count2 = count2 - 1;
setReset2 = 1;
}
}
}

}

void track1input(){
count1 = count1 + 1;
}

void track2input(){
count2 = count2 + 1;
}