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3 aspect model RR signalling help plse

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by angie1199, Nov 15, 2009.

  1. angie1199

    angie1199 New Member

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    Yellow on other block works fine too. You called the detect the input but it's an output isn't it? positive is grounded by the detect? Or are you talking about electrons flowing opposite direction to the way it is perceived?
     
  2. Raiway Pete

    Raiway Pete New Member

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    Hi Angie,

    It is relative. I was focussing on the signal controller and its needs. The 'detect' is the input. When we focus on the Twin-T then the detect is the output. It's simple really.

    However given that your signal controler works fine with a fake detect input (ground) I am now optimzing the Twin-T as best I can. Here is what is going on. The Twin-T works fine. The output voltage swing that operates the detect level is approx from 0.01 volts (conducting) to 9.5 volts (almost off).
    Somehow I think your sig controller is demanding too much from T4. I think you will need to weigh your options here.

    1/ You can try and place diodes into the emitters to your transistors. That will raise the emitters level to where a non-perfect 'detect' can cut them off at their bases. It might just work.

    2/ You can try adding a pull up resistor to the detect signal. ie connect the detect to 12v with a 2K resistor.

    3/ Best bet. For a nice clean solid ground that's proven, use a relay. The site you gave me had some for 65p when you buy 25. And that is what you need for your 25 detectors. Go buy a 12v one with a coil resistance of at least 650 Ohm at Maplins just to try and play with. If they don't have one then I'll get one here and ship it in a Xmas card.

    I have revamped the circuit diagram, filed in new component values and attached new drawing.

    Pete
     

    Attached Files:

    Last edited: Dec 24, 2009
  3. angie1199

    angie1199 New Member

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    Ok, I think this isn't going to work without a relay. I have some JD2-1A relays on an old microwave circuit board I could use to try.

    They are 12V 16A 2125/240VAC. Not sure if they're suitable or would work as a test.

    Now, I know you're gonna kill me. I think I got the wrong optoisolator :(

    The circuit says 4n25 or 4N33. These are six pin, led +/-, collector, emitter and base

    The one I got was a 4 pin, led +/- and collector/emitter.

    I'm thinking the base assists with full switchover. Gonna get one to try.
     
  4. dave

    Dave New Member

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  5. MrDEB

    MrDEB Active Member

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    the circuit I posted does not use relays but it seems to work in sim.
    it is basically the same circuit that Pete has.
    at least give it a try.
     
  6. angie1199

    angie1199 New Member

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    This is soooo close to working with one loco (loco1), red nearly out without loco, green nearly out with loco.

    But another loco (loco2), not so good, greens and reds 50% lit when loco present :(

    I think this is a non starter. Seems like it's impossible to get the balance just right.
     
  7. MrDEB

    MrDEB Active Member

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    correct me if I am wrong but didn't the orginal signaling circuit use larger resistors on the LEDs.
    but then in my schematic I have 18v, should be 12? for the signals.
    perhaps a larger resistor instead of the 500 ohm ones on the LEDs.
    at 18 v I was showing 32ma per led when on.
    with the 500 ohm resistors "track clear"I show 32 ma green, 774.34fa yellow and 3.07pa on the red.
    what leds are you using as ths may be why they are dim when supposed to be off.
    as far as loco, I put 10, 5k and 10k resistors across the track.
    I just may have to build this circuit but then I need a power supply.
    perhaps we need to step back and really think what this simple circuit is dong.
     
  8. angie1199

    angie1199 New Member

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    Ok, just found this and had a look at it.

    http://home.cogeco.ca/~rpaisley4/SimpleSignalCKopto.GIF

    Not quite the same signalling circuit but I added the transistor after the optocoupler. Connected the 12V through the LED side of the optocoupler to gnd via a 1K resistor. Signals worked as they should. This was with 12V DC as supply and 1K resistor.

    Ok, so we need enough V and A to light the led in the optocoupler, then this will work. So how do we get that V and A?
     
  9. MrDEB

    MrDEB Active Member

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    I would stay with the signaling circuit you have. WHY change?
    IMHO if you change direction you are going to run nto some different problems.
    Right now the signaling circuit works?
    the track block detection circuit works?
    its just getting the two to work together, correct?
    thinking just go to Radio Shack and buy the transistors and resistors.
    as for supply, I have a 12v dc but no ac for the track simul;ation. perhaps a dc supply should work?
     
  10. MrDEB

    MrDEB Active Member

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    did you look at the reed switches I posted?
    these would work nbut need to test.
     
  11. MrDEB

    MrDEB Active Member

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    MAYBE reason the output transistor on the twin t won't go to ground is due to the fac that the ac from the track via the diodes are producig a square wave thus the transistor is switching from on to off?
    let me take a pic of LT spice
     
  12. MrDEB

    MrDEB Active Member

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    here is a pic of output measurments

    the input is at 20hz ( easier to read instead of 10khz)
    principal the same
    this is just theory. maybe way in left field?
    perhaps this is why most go with relays or comparator circuits?
    could also be reason for opticouplier not working and dim LEDs
     

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  13. Raiway Pete

    Raiway Pete New Member

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    Angie,

    The relays may be OK. But their coils should have a resistance of 650 ohms or higher. The 16 Amps at 230VAC is what the contacts can handle. For your application they will work fine. (but they will be under-employed. :) )

    Try the opto-isolator and mess around with the base bias. See what happens. But I still don't think it can provide all the current needed to drive the LEDs. ????
     
    Last edited: Dec 24, 2009
  14. Raiway Pete

    Raiway Pete New Member

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    Try and input a square wave across the track. A sine wave will prob generate those squares at the cross over. A square wave 'may' produce spikes depending on the DCC manufacturer.

    P.
     
  15. Raiway Pete

    Raiway Pete New Member

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    OK Angie.

    You can put the opto coupler in the Twin-T booster collector circuit. It will be on (LED lit) until a detect occurs. If you now take the output of the isolator and feed it to a transistor not only will the voltage levels have a bigger wiggle and drive the transistor into saturation but the 'detect' will be inverted. And that is what you want to drive you signal controller.

    Have you done anything with the latest updated circuit I sent you?

    PS. Question. You said that you tried one loco and then two. Were they moving and drawing near two amps? OR were they just put on the track. Thing to note. With DCC a standing engine draws little current. The low motor resistance is not across the track, it's across the decoder.
     
  16. Raiway Pete

    Raiway Pete New Member

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    DC will work fine, but only one of the Twin-T transistors will be conducting depending on the flow of current. I suggest rigging up a reversing swich so that the DC 'engine' can 'travel' in both directions. For testing only one Twin-t needs to work anyway. It's the last transistor stage that counts. If that last stage (open collector ???) does not produce a good solid ground while delivering the right amount of current LEDs won't be driven rail to rail either.

    Angie,

    The last circuit I sent you is working fine. It drives an old reed relay that I ripped off a computer PC board. It operates from 20 ohms across the track thru 10K and 'damp fingers'. Also DCC need not be connected.

    P.
     
  17. MrDEB

    MrDEB Active Member

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    yes but the dcc outputs ac ??
    so inputing AC to simulate correctly?
    this I think (now there's a thought) that the opti couplier is pulsing as is the transistor switch.
    as I said, maybe thje way to go is a voltage comparator?? of add one to the twin t. let the twin t do its thing and the comparator or opamp smooth out the voltage??
    just a thought.
     
  18. Raiway Pete

    Raiway Pete New Member

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    MrDeb.

    I'm using two almost exhausted 9v batteries in series as a test power supply. They produce barely 12 volts. Try that.
     
  19. Raiway Pete

    Raiway Pete New Member

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    Hm?

    DCC does not put out AC. AC implies a nice sine wave. Your diagram shows nice square 'zero cross over' pulses. These pulses are caused by the low voltage threshold across the diodes when going from positive to negative and back. In actual fact by using square waves these pulses are extremely narrow and are in the sub-microsecond area. These can be shorted out by placing a very small capacitor either across the diodes, or a larger one after the booster output that is part of the debouncing RC delay circuit (as per my last updated post).

    Angies's idea of playing around with opto-isolator in the booster transistor is a good one. The spikes can be made to bypass the LED via a 0.01 (or abouts) microfarad cap across the LED

    However there is also a practical aspect to this. The spikes are very narrow. At 20 Khertz (one for positive to negative and one for the negative to positive. The time of LED flicker is about 2%. this is not enough to be noticed by the human eye. I have a hand held scope but the frequency of the spikes is at the limit of its capability. So I might have misread the display.

    P.
     
  20. angie1199

    angie1199 New Member

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    I didn't mean change the signalling circuit. I meant build a detect circuit that controls the optocoupler using the base detect circuit we have currently got to to light the optocoupler properly.

    Just need some way of getting proper V and mA through the LED side of the optocoupler, then I can add a transistor on the detect, signalling circuit side of the optocoupler which I didn't try.
     
  21. angie1199

    angie1199 New Member

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    The last circuit (http://www.electro-tech-online.com/attachments/twin-t-prototype-pdf.36646/) works but I have R3 as 2.2k and no connection from R3/R4 to ground via the cap as I don't havee a cap.

    Loco1 detects fine, appears to be nearly full brightness. Loco2 is detected but LED is slightly dimmer.

    When no loco present, LED has a very faint glow, not going off completely.
     

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