Hi Hans, Kiste, You can still by DTMF decoders and I assume also DTMF encoders. Just look at for example Aliexpress and type DTMF.
But another suggestion. Many, many years ago I had built an Apple II and I used cassette tapes to store and load games which was using tones generated by the Apple II itself using two tones, one for high, one for low and one as a lead-in tone (not sure in the lead-in tone was another tone) to synchronze the start of the recorded program. You would not need this lead-in tone in your case So I think it may not be that complex: -) For recording on casette, generate this dual tone by the PIC via PWM or maybe it is also sufficient to generate one tone in case of a 1 and no tone in case of a 0 but I think this will be less reliable. -) For playback, measure the length of the recorded PWM tone. If is is within a certain range you accept it as a one and in case of two tones the lower tone could be zero and the higher tone is one. As long as the tone frequency is not too high, I think this could work. A more advanced solution would be to use a phase locked loop (PLL) but I am not sure if it will work. The PLL locks to the input signal so the voltage that controls the oscillator goes up and down to follow (lock on to) the input signal and this oscillator voltage signal could then be used by a comparator of the PIC to detect a high or low tone. You can also use the oscillator of the IC to generate the two tones by controlling the oscillator voltage by the PIC. A typical IC for that is the HEF4046. I have used this IC many many years ago too. This solution may be bit over the top since you only want a kind of trigger signal But maybe the first solution is more doable. Just give it a try. Kind regards, Rob ________________________________ Van: 'Oliver Seitz' via jallib <[email protected]> Verzonden: woensdag 23 februari 2022 09:58 Aan: [email protected] <[email protected]> Onderwerp: Re: [jallib] PWM serial audio transmission Hi Hans, 20 years ago I would have suggested using DTMF, but the decoder chips are rare these days... PIC controllers include various peripherals which can be used to encode and decode DC-free signals (which, apart from the frequency below, say, 10kHz, is the requirement to be recorded as audio). On/off keying or frequency shift keying are the easiest, I think. Which chips are you going to use? Greets, Kiste Am Mittwoch, 23. Februar 2022, 09:15:43 MEZ hat hans <[email protected]> Folgendes geschrieben: Hello everyone, I have been trying for a long time to place a serial signal on one track of an audio recording which I can read afterwards. To make all kinds of things happen at the same time as the audio is played. I have now tried to do this with the old modem system ( TCM3105) but it failed hopelessly. I read that there are also systems to do this using PWM. Does anyone have an idea? regards Hans -- You received this message because you are subscribed to the Google Groups "jallib" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To view this discussion on the web visit https://groups.google.com/d/msgid/jallib/773ca37b-9bed-4349-a8eb-32a5d8973df6n%40googlegroups.com<https://groups.google.com/d/msgid/jallib/773ca37b-9bed-4349-a8eb-32a5d8973df6n%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "jallib" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To view this discussion on the web visit https://groups.google.com/d/msgid/jallib/201142693.752814.1645606718467%40mail.yahoo.com<https://groups.google.com/d/msgid/jallib/201142693.752814.1645606718467%40mail.yahoo.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "jallib" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/jallib/DB6P195MB01835C6FD6A58A5598BC8C6AE63C9%40DB6P195MB0183.EURP195.PROD.OUTLOOK.COM.
