#define GREENBTN 3
#define LEDPIN 2
#define REDBTN 4

int led_delay = 1000;
int led_voltage = LOW; //LOW
int last_changed = 0;

int gbt = 0, gbt_past = 0;
int rbt = 0, rbt_past = 0;
void setup() {
  // put your setup code here, to run once:
  pinMode(LEDPIN, OUTPUT);
  pinMode(GREENBTN, INPUT);
  pinMode(REDBTN, INPUT);

}

void loop() {
  if (millis() >= last_changed + led_delay){
    led_voltage = !led_voltage;
    digitalWrite(LEDPIN, led_voltage);
    last_changed = millis();
  }

  gbt_past = gbt;
  gbt = digitalRead(GREENBTN);
  if (gbt == LOW && gbt_past == HIGH){
    led_delay -= 100;
  }

  rbt_past = rbt;
  rbt = digitalRead(REDBTN);
  if (rbt == LOW && rbt_past == HIGH){
    led_delay += 100;
  }

  delay(50);
}