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  • My version of the TM808 finalized and revised with the schematic :

    Click image for larger version

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    [ATTACH]n412688[/ATTACH]
    Attached Files

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    • Gerber
      Attached Files

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      • I still can't find the xtal 26.37khz or 211.2....

        How did you solve it?

        These are my TM808 files

        TM808 BERREIZETA.rar

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        • Calculation of the resonance circuit of a coil, online :

          https://ekalk.eu/lc_es.html

          Click image for larger version

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          • Solution with 555 :

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            • Your crystal problem could be solved by using a 420 kHz ( or 429 kHz ) ceramic resonator, and dividing it by 16.
              This gives equivalent crystal freq and operating freq of:
              420 kHz > 26250 Hz > 6563 Hz ( and 429 kHz > 26813 Hz > 6.703 Hz ) These resonators are used in TV remote controls, mainly, but also some radio IF circuits instead of 455 kHz.

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              • OK, I will searching for one, thx

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                • The resonators should be easily obtained, I checked eBay, there were several sellers. The oscillator circuit is similar to that of a quartz crystal, with some component value changes ( lower resistances, etc ) , so you should be able to use the existing 4011 NAND gates.
                  And the divide-by-16 can be done with any CMOS counter, such as the CD4024.

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                  • I found an active crystal of 25600Hz.
                    25600/4= 6400
                    psync 1600,
                    800 and 400
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                    • With Active Xtal 25.60 Khz :

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                      • The poor availability of custom cut quartz crystals these days was discussed on here before. One solution was MEMS based oscillators, some of which are programmable, some are fixed ( pre-programmed? ). I see that some have quite low operating frequencies, below the usual "quartz crystal range".
                        Here are some made by Microchip, as examples:
                        https://www.digikey.co.nz/en/product...5K600/12811287
                        https://www.digikey.com/en/products/...DSC6001/254165

                        https://www.sitime.com/support/resou...stal-resonator

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                        • I have been playing with an active crystal of 1.8432 Mhz (the lowest I have) and a 4060.

                          On pin14 (Q8*/256) it gives 7200Hz, and stays nailed for ever!.

                          As I can't find any 6600Hz multiplier I think I'll try the 25.6Khz (= 6400Hz), and adjust the coils to that frequency.

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                            • The only common quartz crystal frequency that divides down to nearly the right frequency is 6.7458 MHz, which divided by 256 gives 26351Hz / ( and 6588 Hz operating f ). It's used in some 433 MHz ISM band RF transmitters, and is readily available cheap.
                              But whether 6.7MHz is a bit 'hot' for 4000 series operating at a low voltage, I can't say. There's always 74HC.. equivalents.

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                              • In case you were unaware of it, there is a 4000-series IC that combines an inverter-based oscillator and a binary divider / ripple-counter, the CD4060. This can be used as a crystal oscillator ( or an R-C based one ), and just use the appropriate divided output .
                                It would be OK to do the ceramic resonator oscillator, but I think 6.7MHz is too hot for 5V operation. So the better choice is the much faster HC version, the 74HC4060, restricted to 3V to 6V supply rails, though.

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