[GreenKeys] Precise Baud Timing

[Harold Hallikainen]

I am doing something similar in the DSP TU (
https://w6iwi.org/rtty/DspTU3/ ).

https://github.com/HaroldHallikainen/DSP_TU2/blob/master/src/dds.c
generates the AFSK using simple DDS.

https://github.com/HaroldHallikainen/DSP_TU2/blob/master/src/BaudotUart.c
does ASCII to Baudot conversion, Baudot to ASCII, and transmit and receive
uarts.

DDS AFSK to a file is also described at https://w6iwi.org/rtty/audio/npr/ .

Harold
https://w6iwi.org


On Wed, November 12, 2025 1:09 pm, Zach Tumbusch wrote:
> I went through a few iterations testing with Node, PHP, and C# but
> settled on this example. The bigger challenge was sorting the popping on
> the fast frequency transition. I tested this up to 9600 baud with my
> ST-8000. The
> bit stream is 8 bit characters  "A": "01100011" 11000 with 1 start bit and
>  2 stop bits. The actual bitrate at 45.45 baud is around 22ms. but since
> I
> am directly converting points to a wav file I keep track of that based on
> how many samples. Prints well on all my machines. Model 28 / UGC-136BX /
> Hal. See the working example. https://w8zjt.net/itty
>
>
> 73, de W8ZJT
>
>
> async generateAFSKWav(bitstream: string, baud, mark, space): Promise<
> Blob> {
> const sampleRate = 16000;  // Sample rate in Hz const fadeDuration = 50;
> // Number of samples for smooth
> frequency transition const samplesPerBit = Math.round(sampleRate / baud);
> const totalSamples = bitstream.length * samplesPerBit; let audioSamples:
> Float32Array = new Float32Array(totalSamples);
> let phase = 0.0; let currentFreq = bitstream[0] === "1" ? mark : space; let
> currentPhaseIncrement = (2 * Math.PI * currentFreq) / sampleRate ;
>
>
> for (let bitIndex = 0; bitIndex < bitstream.length; bitIndex++) { const
> newFreq = bitstream[bitIndex] === "1" ? mark : space; const
> newPhaseIncrement = (2 * Math.PI * newFreq) / sampleRate;
>
> for (let i = 0; i < samplesPerBit; i++) { if (i < fadeDuration) { // Smooth
> frequency transition (interpolation) const fadeFactor = i / fadeDuration;
> const interpolatedFreq = currentFreq * (1 - fadeFactor) + newFreq *
> fadeFactor; currentPhaseIncrement = (2 * Math.PI * interpolatedFreq) /
> sampleRate; } else {
> currentPhaseIncrement = newPhaseIncrement; }
>
>
> // Generate waveform sample
> audioSamples[bitIndex * samplesPerBit + i] = Math.sin(phase );
> phase += currentPhaseIncrement;
>
> if (phase >= 2 * Math.PI) { phase -= 2 * Math.PI; }
> }
>
>
> currentFreq = newFreq; }
> // Convert to WAV format
> const wavBuffer = await WavEncoder.encode({ sampleRate: sampleRate,
> channelData: [audioSamples] // Mono channel
> });
>
>
> On Wed, Nov 12, 2025 at 1:57 PM Steve <zarco at sonic.net> wrote:
>
>
>> Much easier to do in hardware with just a few chips.
>> 555 timer and shift register. A couple more chips and
>> send R-Y test. You can use a scope or period counter to accurately setup
>> the 555 clock. Can be implemented in Baudot or ASCII.
>>
>> With a uP, use the programmable timer which in most these
>> days is internal. This should be largely independent of the code if done
>> right.
>>
>> Projects like this are fun...enjoy!
>> Steve W6SSP
>> ______________________________________________________________
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>>
>>
>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>>
>> https://teletype.net/gksearch
>>
>>>>> 2002-to-present greenkeys archive:
>>>>>
>> http://mailman.qth.net/pipermail/greenkeys/
>>
>>>>> 1998-to-2001 greenkeys archive:
>>>>>
>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>
>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>>
>> http://comcents.com/tty/greenkeyssearch.html
>>
>>
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>> Message delivered to zach.tumbusch at gmail.com
>>
> ______________________________________________________________
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>
>
>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>> https://teletype.net/gksearch
>>>> 2002-to-present greenkeys archive:
>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>> 1998-to-2001 greenkeys archive:
>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to harold at w6iwi.org


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