Blink text as morse code to the Raspberry Pi built-in LED

morse_echo.sh

#!/usr/bin/env bash

# Blink out text using the Pi's built-in status LED
# Example usage: ./morse_echo.sh hello world
# Requires root for the Raspberry Pi

DIT_SPACE="0.2"
INTER_CHARACTER_SPACE="0.4"  # 2xDIT_SPACE for normal timing (3 total)
INTER_WORD_SPACE="0.8"  # 4xDIT_SPACE for normal timing (7 total)
# Increase INTER_WORD_SPACE and INTER_CHARACTER_SPACE more than "normal" for Farnsworth timing


# This may break in the future:
# Check if we are a Pi by the OUI
ifconfig eth0 | grep -q 'b8:27:eb' || ifconfig eth0 | grep -q 'dc:a6:32'
IS_RASPBERRY=$?
ifconfig eth0 | grep -q 'dc:a6:32'
IS_PI4=$?
if [ $IS_PI4 -eq 0 ]; then
    ON=1
    OFF=0
else
    ON=0
    OFF=1
fi

if [ $IS_RASPBERRY -eq 0 ]; then
    echo none > /sys/class/leds/led0/trigger
fi

signal_on() {
    if [ $IS_RASPBERRY -eq 0 ]; then
        echo $ON >/sys/class/leds/led0/brightness
    else
        echo -n "******"
    fi
}

signal_off() {
    if [ $IS_RASPBERRY -eq 0 ]; then
        echo $OFF >/sys/class/leds/led0/brightness
    else
        echo -ne "\b\b\b\b\b\b      \b\b\b\b\b\b"
    fi
}


finish() {
    if [ $IS_RASPBERRY -eq 0 ]; then
        echo "mmc0" >/sys/class/leds/led0/trigger  # Default configuration
    else
        echo "finishing"
    fi
}
trap finish EXIT

encode() {
    declare -A morse
    morse[A]=".-";
    morse[B]="-...";
    morse[C]="-.-.";
    morse[D]="-..";
    morse[E]=".";
    morse[F]="..-.";
    morse[G]="--.";
    morse[H]="....";
    morse[I]="..";
    morse[J]=".---";
    morse[K]="-.-";
    morse[L]=".-..";
    morse[M]="--";
    morse[N]="-.";
    morse[O]="---";
    morse[P]=".--.";
    morse[Q]="--.-";
    morse[R]=".-.";
    morse[S]="...";
    morse[T]="-";
    morse[U]="..-";
    morse[V]="...-";
    morse[W]=".--";
    morse[X]="-..-";
    morse[Y]="-.--";
    morse[Z]="--..";
    morse[1]=".----";
    morse[2]="..---";
    morse[3]="...--";
    morse[4]="....-";
    morse[5]=".....";
    morse[6]="-....";
    morse[7]="--...";
    morse[8]="---..";
    morse[9]="----.";
    morse[0]="-----";
    morse[" "]=" ";

    text="$*"  # All arguments as a single string separated by $IFS (space)
    text="${text^^}"  # Capitalize all letters
    # Loop through the characters by index
    for (( k = 0; k < ${#text}; k=k + 1 )); do
        char="${text:$k:1}"
        mchar="${morse[$char]}"  # Morse lookup
        # echo "$mchar"
        # Loop through morse characters
        for (( i = 0; i < ${#mchar}; i=i + 1)); do
            case "${mchar:$i:1}" in
                "-")
                    signal_on
                    sleep "$DIT_SPACE"
                    sleep "$DIT_SPACE"
                    sleep "$DIT_SPACE"
                    signal_off
                    sleep "$DIT_SPACE"
                    ;;
                ".")
                    signal_on
                    sleep "$DIT_SPACE"
                    signal_off
                    sleep "$DIT_SPACE"
                    ;;
                " ")
                    sleep "$INTER_WORD_SPACE"
                    ;;
                *)
                    sleep "$INTER_WORD_SPACE"
                    ;;
            esac
        done
        sleep "$INTER_CHARACTER_SPACE"
    done
}

encode "$*"