Maybe one day…
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I will use RFID technology for my project.
Here I found a base code of connecting Arduino and RFID reader.
P.S. Currently, the code generates an error yet.

#include
NewSoftSerial mySerial(8, 10);
int cardPresent = 9;
int led_pin = 13;
void setup()
{
Serial.begin(57600);
Serial.println("RFID Reader Active");
pinMode(cardPresent, INPUT);
pinMode(led_pin, OUTPUT);
mySerial.begin(2400);
}
void loop()
{
if (digitalRead(cardPresent)==HIGH) {
digitalWrite(led_pin, HIGH);
} else {
digitalWrite(led_pin, LOW);
}
if (mySerial.available()) {
Serial.print((char)mySerial.read(),HEX);
}
}
Here I documented the instruction for making sound by a piezo speaker while an LED is blinking.
/*
* LED attached from digital pin 9 to ground.
* spk attached from pin 13 to ground
* pressuresensor attached to pin 2 from +5V
* 10K resistor attached to pin 2 from ground
*/
const int buttonPin = 2; // the number of the pushbutton pin
const int spkPin = 10; // the number of the blinking spk pin
const int ledPinf = 9; // the number of the fading LED pin
int fadeValue = 0; // variable for the brightness of the fading LED
boolean fadeUp = true; // variable to keep track of if the LED is fading up or down
int buttonState = 0; // variable for reading the pressuresensor status
int spkState = LOW; // ledState used to set the blinking spk on or off
long previousMillis = 0; // will store last time LED was updated
// the follow variable is a long because the time, measured in miliseconds,
// will quickly become a bigger number than can be stored in an int.
long interval = 1700; // interval at which to blink (milliseconds)
boolean blinkOn = false; // variable to keep track of if blink spk should be blinking or not
int blink2 = 0; // variable to keep track of how many times the spk blinks
void setup() {
// initialize the blinking spk pin as an output:
// initialize the pressuresensor pin as an input:
pinMode(buttonPin, INPUT);
Serial.begin(9600); // you only need this to send data to the serial port
}
void loop() {
// ------- LED fading ---------------
if (fadeUp == true) { // if we are making it brighter
fadeValue +=5; //increase the brightness by 5
if (fadeValue >= 255) { // if the brightness gets too high
fadeUp=false; // we are not fading up
}
analogWrite(ledPinf, fadeValue); // send the brightness to the LED
delay(15);
}
else { // if we are fading down
fadeValue -=5;
if (fadeValue <= 5) {
fadeUp=true;
}
analogWrite(ledPinf, fadeValue);
delay(15);
}
// --------- check the button ------------------
// read the state of the pressuresensor value:
buttonState = digitalRead(buttonPin);
// check if the pressuresensor is pressed.
// if it is, the buttonState is HIGH: we need to blink
if (buttonState == HIGH) {
blinkOn = true;
}
// ------------ blink the spk ------------------------
/*
This next statement asks if the current time minus the time of the last blink
is greater then the blink interval AND has blinkOn been set to true
*/
if (millis() - previousMillis > interval && blinkOn == true) {
// save the last time you blinked the spk
previousMillis = millis();
// if the spk is off turn it on and vice-versa:
analogWrite(spkPin, fadeValue);
blink2 += 1; // count the number of blinks
}
if (blink2 >= 3) { // after we do three blinks stop blinking
blink2 = 0;
blinkOn = false;
analogWrite(spkPin, 0);
}
// you can uncomment these to watch the values change in the monitor
//Serial.print(millis());
//Serial.print(" blinkOn = ");
//Serial.print(blinkOn,BIN);
//Serial.print(" blink2 = ");
//Serial.print(blink2);
//Serial.print(" spkState = ");
//Serial.print(spkState);
//Serial.print(" FadeUp = ");
//Serial.print(fadeUp,BIN);
//Serial.print(" FadeValue = ");
//Serial.print(fadeValue);
//Serial.println("");
}