Fix ATtiny85 watchdog register timing with atomic ASM writes; handle WDRF resets with early watchdog disable and recovery delay.
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@@ -1,31 +1,39 @@
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/*
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=============================================================================
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FireFly Morse Throwie
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- a light controlled (LED as Sensor) morse blinker throwie with ATTiny85
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=============================================================================
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FireFly Solar / 日輪蛍 – Nichirin Hotaru / a Solar Morse Throwie
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太陽を宿し、夜にモールスを灯す蛍。
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Taiyō o yadoshi, yoru ni Mōrusu o tomosu hotaru.
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A firefly carrying the sun, lighting Morse in the night.
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=============================================================================
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Project definitions, sources
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-----------------------------------------------------------------------------
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Version: 0.4 - ATTiny85, 1 MHz, BOD fuse disabled
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gitea : https://gitea.togo-lab.io/tgohle/0001-FireFly
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Date : 2026-11-08
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Version : 0.5 - ATTiny85, 1 MHz, BOD fuse disabled
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used Flash: 1284 bytes
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Key changes Version 0.4 (goal: lowest possible average current):
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gitea : https://gitea.togo-lab.io/tgohle/0001-FireFly
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Date : 2026-11-10
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Key changes Version 0.5 (goal: lowest possible average current):
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- No delay(), no millis(): Timer0 and Timer1 are not needed any more and
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are switched off in PRR.
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- ALL timing (Morse units, sensing window, 8 s sleep) is done by the watchdog
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in interrupt mode while the CPU is in POWER-DOWN. The CPU runs only for a
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few microseconds per wake-up. LED pins keep their state in power-down.
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- Darkness sensing no longer polls digitalRead() in a busy loop (that was
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- Darkness sensing by LED no longer polls digitalRead() in a busy loop (that was
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~0.3-1 s awake per cycle). The LED junction is charged, then the CPU sleeps
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in 16 ms steps and checks the pin: bright light exits after the first step.
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- ADC is disabled BEFORE it is gated off in PRR (order matters).
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- After a power-on / external reset the sketch waits RECOVER_CYCLES cycles
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before it blinks again, so a nearly empty supercap can recharge first.
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Default ~16 minutes, therefore added a debug option.
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- After a power-on, external, brown-out or watchdog reset the sketch waits
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RECOVER_CYCLES cycles before blinking, allowing the supercap to recharge.
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Default ~13 min 20 s (nominal); the debug option bypasses recovery.
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- Startup code saves MCUSR and disables the watchdog early (.init3), avoiding
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a watchdog-reset loop before setup() can execute.
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- Optional: BOD disable during sleep (only useful if BOD fuse is enabled).
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Not tested yet.
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But found out that also BOD Fuse for 1.8V shorten unnecessary blinking time,
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will still work ~1V, meaning ~20 min longer blinking time.
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- Field Test: After a sunny day in Winter, outdoor -1 ... 8°C, with a payload
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of 10 signs) it blinks for >> 12h.
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@@ -58,7 +66,9 @@ Inspired by Karl Lunt's FireFly project:
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'.', ".-.-.-" ',', "--..--" '?', "..--.."
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'!', "-.-.--" ':', "---..." ';', "-.-.-."
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'(', "-.--." ')', "-.--.-" '"', ".-..-."
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'@', ".--.-." '&', ".-..."
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'@', ".--.-." '&', ".-..." '-', "-....-"
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'/', "-..-." ''', ".----." '+', ".-.-."
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'=', "-...-" '_', "..--.-"
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-----------------------------------------------------------------------------
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@@ -77,7 +87,7 @@ Inspired by Karl Lunt's FireFly project:
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// ---------------------------------------------------------------------------
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// DEBUG_TEST 1 = bench testing: no reset-recovery wait, a blink attempt every
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// 8 s, and a short flash when the sketch thinks it is BRIGHT.
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// SET TO 0 FOR THE FIELD (48 s cycle, 16 min recovery wait after a reset).
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// SET TO 0 FOR THE FIELD (40 s idle sleep, ~13m20s reset recovery).
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#define DEBUG_TEST 0
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#ifndef cbi
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@@ -104,7 +114,7 @@ Inspired by Karl Lunt's FireFly project:
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// ---------------------------------------------------------------------------
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// Sleep interval between two sensing/blink attempts: sleepCycles x 8 s.
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// 6 x 8 s = 48 s. Goal ~ 1 blink/min.
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// 5 x 8 s = 40 s. Goal ~ 1 blink/min.
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#if DEBUG_TEST
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const uint8_t sleepCycles = 1;
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#else
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@@ -116,16 +126,16 @@ const uint8_t sleepCycles = 5;
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// After charging the LED junction the CPU sleeps step by step. If the pin
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// reads LOW within the window the LED discharged quickly = bright = no blink.
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// Still HIGH after the full window = dark = blink.
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// Longer window = triggers in brighter conditions (like the old threshold).
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// Longer window = triggers in darker conditions
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// The window costs almost no energy (CPU sleeps), so it is only a threshold.
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// Calibrate at real dusk. Old threshold 17000 loops: measure the old
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// sensDarkness() time with micros() at your dusk level and divide it by 16 ms.
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const uint8_t darkSteps = 40; // ~640 ms
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// ---------------------------------------------------------------------------
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// After a power-on / external reset (e.g. supercap was empty, DC/DC restart)
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// do not blink for this many cycles (x ~48 s) so the supercap can recharge.
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// 20 -> ~16 min. Set to 0 while testing/uploading (upload = external reset).
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// After a power-on / brown-out / external / watchdog reset, do not blink for
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// this many cycles (each has 40 s of sleep) so the supercap can recharge.
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// 20 -> ~13 min 20 s nominal. Set to 0 for bench testing/uploading.
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#if DEBUG_TEST
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#define RECOVER_CYCLES 0
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#else
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@@ -166,6 +176,19 @@ volatile bool f_wdt = false;
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// Remaining cycles without blinking after a reset.
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static uint8_t recoverCycles = 0;
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// Preserve the reset flags before Arduino startup and stop a watchdog left
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// running by a previous reset. AVR-libc's recommended .init3 pattern.
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// .noinit is not cleared by C runtime initialization.
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static uint8_t resetCauseEarly __attribute__((section(".noinit")));
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void earlyWatchdogInit(void) __attribute__((used, naked, section(".init3")));
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void earlyWatchdogInit(void)
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{
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resetCauseEarly = MCUSR;
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MCUSR = 0; // Clear WDRF before disabling WDT.
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wdt_disable(); // Prevent repeated ~15 ms watchdog resets.
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}
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// ---------------------------------------------------------------------------
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// Forward declarations.
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static void sleepWdt(uint8_t ii);
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@@ -182,10 +205,10 @@ void dah(int LED_P);
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// ===========================================================================
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void setup()
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{
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// Remember why we restarted, then clear the flags.
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uint8_t resetCause = MCUSR;
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MCUSR = 0;
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if (resetCause & ((1 << PORF) | (1 << BORF) | (1 << EXTRF))) {
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// Reset cause was captured before C/Arduino initialization in .init3.
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// Include WDRF: a watchdog reset also needs supercap recovery time.
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if (resetCauseEarly & ((1 << PORF) | (1 << BORF) |
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(1 << EXTRF) | (1 << WDRF))) {
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recoverCycles = RECOVER_CYCLES;
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}
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@@ -280,11 +303,19 @@ static void sleepWdt(uint8_t ii)
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f_wdt = false;
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cli();
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wdt_reset();
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MCUSR &= ~(1 << WDRF);
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// Timed sequence: the two writes must follow each other within 4 cycles.
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WDTCR = (1 << WDCE) | (1 << WDE);
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WDTCR = cfg;
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// WDCE/WDE unlock and configuration: two consecutive OUT instructions.
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// The second write is guaranteed to occur within the required four cycles.
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const uint8_t unlock = _BV(WDCE) | _BV(WDE);
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__asm__ __volatile__(
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"out %[wdt], %[unlock] \n\t"
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"out %[wdt], %[config] \n\t"
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:
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: [wdt] "I" (_SFR_IO_ADDR(WDTCR)),
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[unlock] "r" (unlock),
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[config] "r" (cfg)
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: "memory"
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);
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set_sleep_mode(SLEEP_MODE_PWR_DOWN);
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@@ -438,7 +469,7 @@ void morse(int LED_N, int LED_P)
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case '9': dah(LED_P); dah(LED_P); dah(LED_P); dah(LED_P); dit(LED_P); symbolSent = true; break; // ----.
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case '0': dah(LED_P); dah(LED_P); dah(LED_P); dah(LED_P); dah(LED_P); symbolSent = true; break; // -----
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// ----- Punctuation -----
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// ----- Punctuation & Specials -----
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case '.': dit(LED_P); dah(LED_P); dit(LED_P); dah(LED_P); dit(LED_P); dah(LED_P); symbolSent = true; break; // .-.-.-
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case ',': dah(LED_P); dah(LED_P); dit(LED_P); dit(LED_P); dah(LED_P); dah(LED_P); symbolSent = true; break; // --..--
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case '?': dit(LED_P); dit(LED_P); dah(LED_P); dah(LED_P); dit(LED_P); dit(LED_P); symbolSent = true; break; // ..--..
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@@ -450,6 +481,12 @@ void morse(int LED_N, int LED_P)
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case '"': dit(LED_P); dah(LED_P); dit(LED_P); dit(LED_P); dah(LED_P); dit(LED_P); symbolSent = true; break; // .-..-.
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case '@': dit(LED_P); dah(LED_P); dah(LED_P); dit(LED_P); dah(LED_P); dit(LED_P); symbolSent = true; break; // .--.-.
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case '&': dit(LED_P); dah(LED_P); dit(LED_P); dit(LED_P); dit(LED_P); symbolSent = true; break; // .-...
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case '-': dah(LED_P); dit(LED_P); dit(LED_P); dit(LED_P); dit(LED_P); dah(LED_P); symbolSent = true; break; // -....-
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case '/': dah(LED_P); dit(LED_P); dit(LED_P); dah(LED_P); dit(LED_P); symbolSent = true; break; // -..-.
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case '\'': dit(LED_P); dah(LED_P); dah(LED_P);dah(LED_P); dah(LED_P); dit(LED_P); symbolSent = true; break; // .----.
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case '+': dit(LED_P); dah(LED_P); dit(LED_P); dah(LED_P); dit(LED_P); symbolSent = true; break; // .-.-.
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case '=': dah(LED_P); dit(LED_P); dit(LED_P); dit(LED_P); dah(LED_P); symbolSent = true; break; // -...-
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case '_': dit(LED_P); dit(LED_P); dah(LED_P); dah(LED_P); dit(LED_P); dah(LED_P); symbolSent = true; break; // ..--.-
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// Space handling:
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// Previous symbol already ended with 1 unit OFF and then received the
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