Remote Audio Relay Kit (Phone Decoder)

This awesome kit includes everything needed, except for the microcontroller of preference, to implement a custom remote audio-controlled set of relays by easily detecting & decoding audio signals (the buttons that the person on the other side is pressing) into numerical values to be used in code. This can easily be used for the development of custom telephone switching boards.   //*******************************************// #include <FlexiTimer2.h>   int STD = A0; int Q1 = A1; int Q2 = A2; int Q3 = A3; int Q4 = A4;   int CH1 = 2; int CH2 = 3; int CH3 = 4; int CH4 = 5;   ....   //Check once every 5 ms void dtmf_decode(void) {   ....   }   void setup() { ..... }   void loop() {   //Complete the decoding   if(Decod_finished) { Decod_finished = 0;   switch(Q_dat){ case 1 : Serial.print(" Activate : Channel 1 \n" ); digitalWrite(CH1, LOW);delay(delay_time);digitalWrite(CH1, HIGH); break; case 2 : Serial.print(" Activate : Channel 2 \n" ); digitalWrite(CH2, LOW);delay(delay_time);digitalWrite(CH2, HIGH);break; case 3 : Serial.print(" Activate : Channel 3 \n" ); digitalWrite(CH3, LOW);delay(delay_time);digitalWrite(CH3, HIGH); break; case 4 : Serial.print(" Activate : Channel 4 \n" ); digitalWrite(CH4, LOW); delay(delay_time);digitalWrite(CH4, HIGH);break; default : Serial.print("Invalid channel \n" ); break; }   .....   //****************************************************************************//