String voz;
int
led1 = 9,
led2 = 10,
led3 = 11,
led4 = 12,
led5 = 13;

void allon(){
digitalWrite(led1, HIGH);
digitalWrite(led2, HIGH);
digitalWrite(led3, HIGH);
digitalWrite(led4, HIGH);
digitalWrite(led5, HIGH);
}
void alloff(){
digitalWrite(led1, LOW);
digitalWrite(led2, LOW);
digitalWrite(led3, LOW);
digitalWrite(led4, LOW);
digitalWrite(led5, LOW);
}

void setup() {
Serial.begin(9600);
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(led3, OUTPUT);
pinMode(led4, OUTPUT);
pinMode(led5, OUTPUT);
}

void loop() {
while (Serial.available()){
delay(10);
char c = Serial.read();
voz += c;
}
if (voz.length() > 0) {
Serial.println(voz);

if(voz == "ligar tudo" ) {allon();}
else if(voz == "desligar tudo"){alloff();}


else if(voz == "ligar lâmpada 1") {digitalWrite(led1, HIGH);}
else if(voz == "ligar lâmpada 2") {digitalWrite(led2, HIGH);}
else if(voz == "ligar lâmpada 3") {digitalWrite(led3, HIGH);}
else if(voz == "ligar lâmpada 4") {digitalWrite(led4, HIGH);}
else if(voz == "ligar lâmpada 5") {digitalWrite(led5, HIGH);}

else if(voz == "desligar lâmpada 1") {digitalWrite(led1, LOW);}
else if(voz == "desligar lâmpada 2") {digitalWrite(led2, LOW);}
else if(voz == "desligar lâmpada 3") {digitalWrite(led3, LOW);}
else if(voz == "desligar lâmpada 4") {digitalWrite(led4, LOW);}
else if(voz == "desligar lâmpada 5") {digitalWrite(led5, LOW);}

voz="";}}

http://arduinoetecnologia.com/?p=201