3x4 matrix tenkey -> ADC input

analogtenkey.ino

// analog matrix-tenkey
// 20170410

const int analogInPin = A0;  // Analog input pin that the potentiometer is attached to

int sensorValue = 0;        // value read from the pot
char ankey;

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}

void loop() {
  // read the analog in value:
  sensorValue = analogRead(analogInPin);
  ankey = an3x4value(sensorValue);
  // print the results to the serial monitor:
  if (ankey!='\0') Serial.print(ankey);
  // Serial.println(sensorValue);
  // wait 2 milliseconds before the next loop
  // for the analog-to-digital converter to settle
  // after the last reading:
  delay(2);

  delay(100);
}

char an3x4value(int an) { // analog value = 1...1023
  if (1020<an && an<1024) return '#';
  if (942-3<an && an<942+3) return '9';
  if (865-3<an && an<865+3) return '6';
  if (767-3<an && an<767+3) return '3';
  if (561-3<an && an<561+3) return '0';
  if (527-3<an && an<527+3) return '8';
  if (491-3<an && an<491+3) return '5';
  if (445-3<an && an<445+3) return '2';
  if (346-3<an && an<346+3) return '*';
  if (325-3<an && an<325+3) return '7';
  if (304-3<an && an<304+3) return '4';
  if (275-3<an && an<275+3) return '1';
  return '\0';  
}