#include <Servo.h>

Servo servo1;
Servo servo2;
byte servo1pin = 5, servo2pin = 6;
int servo1home = 180, servo2home = 0;
int servoCount = 0, dir = 1, speedControl = 9;
int speedMax = 3, speedMin = 9; // delay

#define ENC_CK 2 // encoder
#define ENC_DT 3
#define ENC_SW 4 // button

void setup() {
  Serial.begin(115200);
  pinMode(ENC_CK, INPUT);
  pinMode(ENC_DT, INPUT);
  pinMode(ENC_SW, INPUT_PULLUP);

  servo1.attach(servo1pin); // start the servos
  servo2.attach(servo2pin);
  servo1.write(servo1home);
  servo2.write(servo2home);

  attachInterrupt(digitalPinToInterrupt(ENC_CK), readEncoder, FALLING);

  while (digitalRead(ENC_SW)); // wait for switch press
}

void loop() {
  if (servoCount > 180 || servoCount < 0)
    dir = -dir;
  delay(speedControl);
  servo1.write(servoCount);
  servo2.write(180 - servoCount);
  servoCount += dir;
}

void readEncoder() {
  Serial.print(speedControl);
  int dtValue = digitalRead(ENC_DT);
  if (dtValue == HIGH) {
    speedControl++;
  }
  if (dtValue == LOW) {
    speedControl--;
  }
  if (speedControl > speedMin)
    speedControl = speedMin;
  if (speedControl < speedMax)
    speedControl = speedMax;
}