LedFade.ino

Fades the green LED (D1) in and out with PWM while the red LED (D2) does the opposite, so one brightens as the other dims. One full cycle, in and out, takes about 2 s.

Jumpers

JP3 at 3.3 V.

Output

The LEDs only; nothing is printed.

Notes

Both LEDs are active low: the anode goes to VDD and the pin sinks the current, so a lower analogWrite() value gives a brighter LED. setBrightness() writes 255 - brightness, so 0 is off and 255 is full brightness.

/*
 * LedFade
 * Fades the green LED (D1) in and out with PWM while the red LED (D2) does
 * the opposite, so one brightens as the other dims. One full cycle, in and
 * out, takes about 2 s.
 *
 * Jumpers: JP3 at 3.3 V.
 * Output: the LEDs only; nothing is printed.
 *
 * Both LEDs are active low: the anode goes to VDD and the pin sinks the
 * current, so a lower analogWrite() value gives a brighter LED. setBrightness()
 * writes 255 - brightness, so 0 is off and 255 is full brightness.
 */
#include <AnalogShield.h>
 
using namespace AnalogShieldPins;
 
static AnalogShield Shield;
 
constexpr uint32_t STEP_MS = 4;  // time per brightness step; 2 × 256 steps ≈ 2 s
 
// Sets an active-low LED from 0 (off) to 255 (full brightness)
void setBrightness(uint8_t pin, uint8_t brightness) {
  analogWrite(pin, 255 - brightness);
}
 
void setup() {
  Shield.begin();
}
 
void loop() {
  // D1 fades in, D2 fades out
  for (int brightness = 0; brightness <= 255; ++brightness) {
    setBrightness(LED1, brightness);
    setBrightness(LED2, 255 - brightness);
    delay(STEP_MS);
  }
 
  // D1 fades out, D2 fades in
  for (int brightness = 255; brightness >= 0; --brightness) {
    setBrightness(LED1, brightness);
    setBrightness(LED2, 255 - brightness);
    delay(STEP_MS);
  }
}