Isotactic Polypropylene

// Living-hinge flex counter - batch 97, US 3,112,300
// Flexes a hinge 0 -> 90 degrees and back, and stops every BLOCK cycles for you to inspect it.
// Servo signal -> D9, servo + -> 5V, servo - -> GND. Microswitch between D2 and GND.
#include <Servo.h>

Servo flexer;
const int SERVO_PIN  = 9;
const int BUTTON_PIN = 2;             // microswitch to GND, internal pull-up
const int OPEN_DEG   = 0;
const int CLOSED_DEG = 90;
const unsigned long MOVE_MS = 350;    // an SG90 needs roughly 0.3 s for 90 degrees
const unsigned long BLOCK   = 1000;   // cycles between inspections; make it smaller near failure
unsigned long cycles = 0;

void waitForButton() {
  while (digitalRead(BUTTON_PIN) == HIGH) {}
  delay(50);                          // debounce
  while (digitalRead(BUTTON_PIN) == LOW) {}
}

void setup() {
  Serial.begin(115200);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  flexer.attach(SERVO_PIN);
  flexer.write(OPEN_DEG);
  Serial.println(F("Mount the hinge, then press the switch to start."));
  waitForButton();
}

void loop() {
  flexer.write(CLOSED_DEG); delay(MOVE_MS);
  flexer.write(OPEN_DEG);   delay(MOVE_MS);
  cycles++;
  if (cycles % BLOCK == 0) {
    flexer.detach();                  // rest the servo while you look
    Serial.print(cycles);
    Serial.println(F(" cycles - inspect the crease. Intact? press the switch. Cracked? note it."));
    waitForButton();
    flexer.attach(SERVO_PIN);
  }
}