![]() Now that we have encoding Morse pretty well nailed down, how 'bout decoding Morse code, which is a little more interesting. THIS TABLE INCLUDES ALL CHARACTERS ENCODED IN THE 'a_decode' LOOKUP TABLE 'DECODE' THIS LIST OF MORSE CHARACTER STRINGS #define NUM_ENTRIES(ARRAY) (sizeof(ARRAY) / sizeof(ARRAY)) The version encoded here is a six element encoding to include some punctuation characters. If you're interested I can post the code the generates the 'a_decode' table based on the 'morse' table which would allow you to add or remove the morse characters you wish to allow. Original thread: morse decoder problem - #9 by nickgammon - Programming Questions - Arduino ForumĮxample of decoding a morse 'C' string using a lookup table. It auto-adjusts to the sending speed after a bit of time "learning" the length of a dot and dash. (millis () - lastPulse) >= (dotLength * 2) & If (pinState = HIGH & width >= (wordLength - FUZZ_FACTOR)) If (pinState = HIGH & width >= (dashLength - FUZZ_FACTOR)) Volatile unsigned int widths īyte pinState = digitalRead (SIGNAL_PIN) Here it is from my sketches folder: // Morse code decoderĬonst int SIGNAL_COUNT = 6 // maximum number of dots/dashes in a letter I am going to start by building the Danish solution next.I seem to remember writing a decoder a while back. WV2YAU uses the LM567 external tone decoder together with Budd’s software, as described in this video.You can find details on his web site, or watch this video for a demonstration. Budd Churchward, WB7FHC has another popular solution.Then, digital signal processing detects and filters the tones. Rather, it uses the Arduino analog input to sample audio from the receiver. Danish ham, Hjalmar Skovholm Hansen, OZ8SMA provides a Arduino Morse Decoder that does not require external hardware. ![]() It makes more sense to reuse rather than reinvent. Here are some choices for “ready made”, open source solutions. Arduino Morse Decoder – Choices Available In other solutions, software does it all. In some solutions, steps 1-3 can be done using external hardware, such as the LM567 tone detector. That’s the algorithm for a Morse decoder. Finally, after the characters are decoded, they are displayed on a screen. Machine generated Morse decodes perfectly human sent code, not so much. By understanding this pattern, your software converts on-off data into characters. This pattern holds relatively steady regardless of the speed. The duration of Morse elements, and the spacing of letters and words, follows a standard pattern, as explained on Wikipedia. Filtering is also used remove noise spikes in the audio. Since you will be detecting the tones faster than they are actually being sent, you need a filter to smooth out the data between samples. If a signal at the right frequency exceeds threshold, the switch is turned on. A strong signal at the right frequency indicates a tone. The other is to use software to adjust the threshold automatically. One approach is to set the threshold manually with a knob. ![]() You set a signal threshold so the detector can differentiate between tone and noise. Normally, the tone is stronger than the noise. Also, you need to ignore the broadband noise and select the narrow band tone. Even with automatic gain control, the signal level varies. A Morse Code tone exists in a sea of noise. An example of an ADC is the input side of your computer’s sound card. This is called analog-to-digital conversion, or ADC. Computers need data, not signals. Convert the audio signal into data.
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