#include <TM1637.h>

TM1637 TMx0;

char buffer[5];

void setup() {
  Serial.begin(9600);
  Serial.println("Type your text for the third display.");
  Serial.println("Now displaying \"----\".");

  TMx0.begin(4, 5, 4);       //  clockpin, datapin, #digits
  TMx0.displayClear();
  TMx0.setBrightness(7);     // full brightness, default is 3
  TMx0.displayPChar("----"); // Initial text on third display

}

void loop() {
  unsigned long currentMillis = millis();
  // -----------------------------------------
  // Third display
  // -----------------------------------------
  if (Serial.available() > 0)
  {
    int inChar = Serial.read();
    if (isprint(inChar))
    {
      for( int i=0; i<3; i++) // shift buffer to the left
        buffer[i] = buffer[i+1];

      buffer[3] = (char) inChar; // add new character
      buffer[4] = '\0';      // add zero-terminator
    }
    TMx0.displayPChar(buffer); // display the new text
  };

}