Stroboscope

// LED stroboscope - batch 99, after US 2,186,013
// WARNING: flashing light can trigger seizures in people with photosensitive epilepsy.
// NeoPixel strip DIN -> D6 (5V, GND). Potentiometer wiper -> A0 sets the flash rate.
#include <Adafruit_NeoPixel.h>

const int PIN = 6, COUNT = 8;
const unsigned int FLASH_US = 300;          // flash length: shorter = sharper, dimmer
Adafruit_NeoPixel strip(COUNT, PIN, NEO_GRB + NEO_KHZ800);
const uint32_t WHITE = Adafruit_NeoPixel::Color(255, 255, 255);

void setup() {
  Serial.begin(115200);
  strip.begin();
  strip.setBrightness(255);
  strip.clear(); strip.show();
}

void loop() {
  // 5 to 105 flashes per second from the knob
  float hz = 5.0 + analogRead(A0) * 100.0 / 1023.0;
  unsigned long period = (unsigned long)(1e6 / hz);
  unsigned long t0 = micros();
  strip.fill(WHITE); strip.show();
  delayMicroseconds(FLASH_US);
  strip.clear(); strip.show();
  static unsigned long lastPrint = 0;
  if (millis() - lastPrint > 500) { lastPrint = millis(); Serial.print(hz, 2); Serial.println(F(" Hz")); }
  while (micros() - t0 < period) {}
}