Printed Morse Decoder Card: Hand-Wired LEDs Light Your Letter on Dave Nathanson's Chart

// Printed Morse decoder card: firmware for an Arduino Pro Mini 3.3 V / 8 MHz on a CR2032.
// Chart after Dave Nathanson's "Morse Code Receive Decoder Chart (a-z)" (KG6ZJO, copyleft 2010); codes per ITU-R M.1677-1.
// Press the key: short = dot, long = dash. The LED of the letter reached lights; a pause ends the letter.
// Generated by make_firmware.py together with wiring.md. Every timing below is ours: change it to suit you.
#include <avr/sleep.h>
#include <string.h>

const uint8_t KEY_PIN = 2;                      // INT0, key to GND, internal pull-up
const uint8_t NETS[6] = {3, 4, 5, 6, 7, 8};     // each through its own 150 ohm resistor
const unsigned long DEBOUNCE_MS = 15;
const unsigned long DASH_MS = 250;              // a press this long or longer is a dash
const unsigned long END_MS = 700;               // a pause this long ends the letter
const unsigned long BLINK_MS = 150;
const unsigned long IDLE_MS = 30000;            // then sleep until the key is pressed

struct Led { const char *code; const char *label; uint8_t a, k; };
const Led LEDS[] = {
  {"", "Start", 0, 1},
  {"-", "T", 1, 0},
  {".", "E", 1, 2},
  {"--", "M", 2, 1},
  {"-.", "N", 2, 3},
  {".-", "A", 3, 2},
  {"..", "I", 3, 4},
  {"---", "O", 4, 3},
  {"--.", "G", 4, 5},
  {"-.-", "K", 5, 4},
  {"-..", "D", 0, 2},
  {".--", "W", 1, 3},
  {".-.", "R", 2, 0},
  {"..-", "U", 2, 4},
  {"...", "S", 3, 1},
  {"--.-", "Q", 3, 5},
  {"--..", "Z", 4, 2},
  {"-.--", "Y", 5, 3},
  {"-.-.", "C", 0, 3},
  {"-..-", "X", 1, 4},
  {"-...", "B", 2, 5},
  {".---", "J", 3, 0},
  {".--.", "P", 4, 1},
  {".-..", "L", 5, 2},
  {"..-.", "F", 0, 4},
  {"...-", "V", 1, 5},
  {"....", "H", 4, 0},
};
const uint8_t COUNT = sizeof(LEDS) / sizeof(LEDS[0]);

char code[8] = "";
uint8_t len = 0;
bool down = false;
unsigned long changed = 0, lastActivity = 0;

void allOff() {
  for (uint8_t i = 0; i < 6; i++) { pinMode(NETS[i], INPUT); digitalWrite(NETS[i], LOW); }
}

void light(int8_t i) {
  allOff();
  if (i < 0) return;
  pinMode(NETS[LEDS[i].a], OUTPUT); digitalWrite(NETS[LEDS[i].a], HIGH);
  pinMode(NETS[LEDS[i].k], OUTPUT); digitalWrite(NETS[LEDS[i].k], LOW);
}

int8_t find(const char *c) {
  for (uint8_t i = 0; i < COUNT; i++) if (strcmp(LEDS[i].code, c) == 0) return i;
  return -1;
}

void blink(int8_t i, uint8_t times) {
  for (uint8_t n = 0; n < times; n++) { allOff(); delay(BLINK_MS); light(i); delay(BLINK_MS); }
}

void restart() { len = 0; code[0] = 0; light(find("")); }

void wake() {}

void sleepNow() {
  allOff();
  ADCSRA = 0;                                   // ADC off while asleep
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  noInterrupts();
  sleep_enable();
  attachInterrupt(digitalPinToInterrupt(KEY_PIN), wake, LOW);
  interrupts();
  sleep_cpu();                                  // wakes when the key pulls INT0 low
  sleep_disable();
  detachInterrupt(digitalPinToInterrupt(KEY_PIN));
  while (digitalRead(KEY_PIN) == LOW) {}        // the waking press does not count
  delay(DEBOUNCE_MS);
  restart();
  down = false;
  changed = lastActivity = millis();
}

void setup() {
  pinMode(KEY_PIN, INPUT_PULLUP);
  restart();
  changed = lastActivity = millis();
}

void loop() {
  unsigned long now = millis();
  bool pressed = digitalRead(KEY_PIN) == LOW;
  if (pressed != down && now - changed >= DEBOUNCE_MS) {
    if (!pressed) {                             // released: a dot or a dash
      code[len++] = (now - changed >= DASH_MS) ? '-' : '.';
      code[len] = 0;
      int8_t i = find(code);
      if (i < 0 || len >= sizeof(code) - 1) { blink(find(""), 3); restart(); }
      else light(i);
    }
    down = pressed;
    changed = lastActivity = now;
  }
  if (!down && len > 0 && now - changed >= END_MS) {   // the letter is finished
    blink(find(code), 3);
    restart();
    lastActivity = millis();
  }
  if (!down && millis() - lastActivity >= IDLE_MS) sleepNow();
}