c - Arduino 开发环境 : Print once inside loop

Question

我正在使用 LDR 告诉我 Arduino 是否有光。我的代码非常简单，但与其发送垃圾邮件“light light light light”，我希望它说一次“light”，然后如果灯熄灭，让它说一次“No light”。从“readanalogvoltage”编辑的代码:

void setup() {
    // initialize serial communication at 9600 bits per second:
    Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
    // read the input on analog pin 0:
    int sensorValue = analogRead(A0);

    // Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 5V):
    float voltage = sensorValue * (5.0 / 1023.0);

    // print out the value you read:
    if (voltage > 1.5)
    {
        Serial.print("Light");
        Serial.println();
        delay(5000);
    }

    if (voltage < 1.5)
    {
        Serial.print("No Light");
        Serial.println();
        delay(50);
    }

}

Answer 1

保留一个保存最后状态的变量:

void setup() {
    // initialize serial communication at 9600 bits per second:
    Serial.begin(9600);
}

int wasLit = 0;

// the loop routine runs over and over again forever:
void loop() {
    // read the input on analog pin 0:
    int sensorValue = analogRead(A0);

    // Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 5V):
    float voltage = sensorValue * (5.0 / 1023.0);

    // print out the value you read:
    if (!wasLit && voltage > 1.5) {
        wasLit = 1;
        Serial.print("Light");
        Serial.println();
        delay(5000);
    } else if(wasLit && voltage <= 1.5) {
        wasLit = 0;
        Serial.print("No Light");
        Serial.println();
        delay(50);
    }
}