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Post by Deleted on May 24, 2017 12:05:01 GMT -5
Several voltage dividers (trimmers) will be selected through the CD 4051 (or 4067), the output will be connected to a transistor via an unity gain follower (I don't want some current to "go back" to the voltage dividers and interfere : CD 4051 and 4067 are bidirectional) and then a resistor ; one connection will provide the full stop. There will be a freewheel diode and the output will be followed by the inverting relay. Perhaps I will build several sections, each section with its own controller, but only one central trimmer "bank" to preset the speeds.
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Post by Deleted on May 25, 2017 0:38:38 GMT -5
Thank You Greg. But because, as You wrote, only one input/output is active at once and the 4051 seems to have a very high impedance when pins are "off", there is really only VERY LITTLE current between the various trimmers (if the trimmers themselves are not several MOhms, this could not really interfere ! ). And in case of problems, I could add an "unity gain follower" to each trimmer too, but I think it won't be necessary. My main problem could be the base current of the transistor and therefore I will use the unity gain follower, it will by an impedance adapter. To the principle : there will be several presets for each train : full for "uphill", full for "downhill" (perhaps several steps between them for an amount of "progressivity"), slow for switching (and off for all) ; so it's correct if only one speed is selected at once, according to the present train running on the section (and its direction). Because there will be only 2 train configurations (passenger Budd's in MU and 2 freight with GP7/9, at almost the same speed), I think 15 different preset speeds would be sufficient. Another system, replacing the trimmers, would be a "daisy chain" of resistors ...
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Post by Deleted on May 25, 2017 3:16:00 GMT -5
The "voltages" (trimmers or daisy chain) will be each connected individually to one of the 8 (16) inputs (they are exclusive, like a rotary switch, as You wrote, and there is a VERY LITTLE leakage current between them at normal temperature), the "common" pin of the IC will then go to to unity gain follower. So the voltages will be individually selected and never connected together. For two controllers, the 8 (16) inputs of the multiplexers would be connected pairwise to the same voltages, but the common pins will go to different Op-Amps and then to a different resistor and transistor...
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Post by Deleted on May 25, 2017 10:48:18 GMT -5
Thank You Greg, an "integrating" capacitor would smoothen the transitions. But I think it would be better to connect it between Gnd and the output of the Op-Amp, or Gnd and the "base" connexion of the transistor ("after" the resistor) . Here is testing the best way of doing. Now I am still waiting for my locos (customs are very slow, everywhere) ; and the first version for the controller will be built on Veroboard, all the way, before I design my PCB ...
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Post by Commodore on May 25, 2017 15:09:12 GMT -5
Thank You Greg, an "integrating" capacitor would smoothen the transitions. Now I am still waiting for my locos (customs are very slow, everywhere) ; and the first version for the controller will be built on Veroboard, all the way, before I design my PCB ... Thanks, Alberich: and ...If if works good, be sure to make enough for everyone!!!
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Post by Commodore on May 25, 2017 18:18:39 GMT -5
You do realize this is a multi-step dc output device to be connected to and driven by a computer? (It won't work without a computer) Greg Yep I'm counting on getting one of the cheap laptops you mentioned. (well, anything is better than my old blue box marklin transformers)
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Post by Deleted on May 25, 2017 22:42:52 GMT -5
1) I think the features of my interface will be WORSE than the Märklin "blue" transformer ... 2) For Windows, Mac or Linux users, there are some readymade USB to parallel adapters (CodeMercs, FTDI, ... ) ; those can drive every homebrew circuit, and can be controlled from every high level language (for my other application , I used Delphi/Lazarus).
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