Arduino Morse Decoder




About: Goeroe.

This device reads hand keyed Morse code from a signal key (or an ordinary switch) and translates it to plain text and show the Morse code you're keying on an LCD. I use it to train my own Morse keying skills.

The decoder automatically corrects itself for your keying speed.

Step 1: Requirements

1x Arduino UNO
1x Buzzer
1x LCD with I2C connector and 4 lines of text

And a switch (or Morse key), breadboard and wires.

Tip: you could create it without an LCD and then output the decoded text on the serial monitor of the Arduino IDE.

Step 2: Hardware Setup

Setup the hardware by hooking up everything as shown in the schematic diagram.

Connect the buzzer between GND and pin 8 of the Arduino and the Morse key (I use a tactile switch) between GND and pin 7.

Besides the GND and +5V pins the LCD has an SCL and SDA connection that you connect to the pins with the same names on the Arduino. I didn't use pull-up's to connect the LCD, but you could if you want to.

Step 3: Software

Upload the sketch (Seinsleutel2.ino) in the Arduino. I also included the library that I needed to use to control the LCD.

And start keying (see the video for a demonstration).



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    36 Discussions


    2 years ago

    Leuk project, ik ga dit eens uitproberen. Ik ben bezig voor het Museum Engelandvaarders waar we een seinsleutel hebben uit de 2e wereldoorlog. De bezoeker mag straks letter voor letter morsecode nadoen in de hoop dat er wat leesbaars op het scherm komt. Ik heb wel de timing een beetje aangepast. Een dot is 200ms.

    1 reply

    Reply 4 months ago

    "Nice project, I'm going to try this out. I am working for the Museum Engelandvaarders where we have a key from the 2nd World War. The visitor may later copy letter by letter morse code in the hope that something readable on the screen. I have adjusted the timing a bit. A dot is 200ms."

    I had to translate it to understand this


    6 months ago

    Funny story... I tried to burn this to a Wemos board ESP-WROOM-02 without thinking enough. On that board, pins 7 & 8 aren't brought out but actually used to communicate with the module's flash. Setting buzzer(8) to an output led to a shoving match that the flash lost. I replaced the flash and the Wemos talks again.. Lesson learned: sometimes software problems aren't fixed by powering down. (that and I should think more)


    1 year ago

    Hi Sir, Thanks a lot for this lesson, can you send me the code? because i did not find it

    1 reply

    Reply 1 year ago

    the code inside the .ino file. Download the file-> open the arduino IDE -> file-> open-> chose the file that you had been downloaded


    1 year ago

    May I use this code as the basis for a geocache? I will, of course, refer to your name and work in my modified code. The object of the cache would be for the finder to translate a specific word into the dots and dashes of morse code. When the program recognizes the correct word, a servo will release a lock and provide access to the cache container. Please let me know if I may do this.


    2 years ago

    For those who do not have the I2C type liquid crystal display it should be easy to change this to use a standard 1602 style parallel interfaced LCD. Also possible to use Serial.print() to send text information to either the terminal screen that is built into the IDE or to an attached PC running a terminal emulator that is capable of connecting via tty/USB mode.

    The I2C LCD library is in the zip file and can be installed in your IDE once the file has been unzipped.

    It makes no difference whether variables are named in German or some other language. The compiler just converts them to numeric tokens and compiles them as defined. An example of this might be the define "int x = 5", where x is neither English or German, or both, and the compiler handles this variable name with no problem.

    3 replies

    Reply 2 years ago

    Just to be more precise, I had to use a different library for the 1602A:

    #include <LiquidCrystal.h>

    Initializing the LCD with pins:

    LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

    Then take into account it has 2 rows and 16 columns in the setup

    lcd.begin(16, 2);

    And also in the upd function

    x++; if (x >= 16) {

    if (y >= 2) {

    I hope it helps!


    Reply 2 years ago

    Are you able to post the entire code with your updates? I am new to this and am not sure why nothing is coming up on the LCD. Thanks!!!


    Reply 2 years ago

    Hi kangetsu

    sorry for late reply, I am not sure how to upload the entire code, check the connections between the Arduino and the LCD, they should be smthg like:

    LCD Arduino/protobrd

    K GND

    A 100ohm resistor to vcc (5V)

    D7 D2

    D6 D3

    D5 D4

    D4 D5

    E D11

    RW GND

    RS D12

    V0 100ohm resistor to GND

    VDD Vcc - 5V


    Resistor values could be changed to adjust the backlight and char light to your needs

    hope it helps!!


    2 years ago

    im getting more questionmarks than letters - is something wrong with my setup ?


    2 years ago

    Hi Hackertie,

    I am studying your source code and I have a question about the algorithm you use to identify a Pause and start decoding the "Kar"achter. Why do you use

    if (tijd > StreepDuur - StreepDuur / 40 ) ? is it a spece between two letters?


    if (tijd > StreepDuur * 2) ? is it the space between two words?

    Many thanks


    2 replies

    Reply 2 years ago

    StreepDuur == the duration of a dash
    tijd == time

    The statement "if (tijd > StreepDuur - StreepDuur / 40): decodes a space between two letters.
    And "(tijd > StreepDuur * 2)" is for decoading a space between words.

    Som more explanation:
    PuntDuur == Duration of a dot
    starttijd == Start time


    3 years ago

    I dont have the lcd display, so how can I display the reading into the monitor serial?

    1 reply

    Reply 2 years ago

    Serial.print(variable_name); or Serial.print("text string");

    CW transmits much further than just a few mile, and good luck getting perfect unobstructed line of sight.


    Reply 2 years ago

    Actually there are several commercial providers of laser-beam communications systems. Th ones I installed in San Francisco area in the 1996 era are still being used today with satisfactory service. Key seems to be using dual-beam layout separated by at least 2 meters to avoid the bird blockage situation. Fog that is prevalent in that area does not seem to be a problem. System orientation does have to be observed to avoid sunrise or sunset interference with the light beam.

    Hams have been experimenting with light-beam communication since the 1960's with some remote transceivers and repeaters being monitored and controlled via optical Ethernet links.

    In the nineties, there were a lot of ideas for comercial telecommunication equipment with laser that failed with a little of fog of when a bird crossed the laser beam. It already was made... and didn't work...

    Could be as an indoor experiment only.

    BTW: Hacketje, good job and I'll try to modify to your code for numbers as well

    Best regards to both and all contributors.