Some type of pulse detection circuit?

Discussion in 'The Projects Forum' started by Cold Turkey, Oct 26, 2010.

  1. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    G'day, I'm building a car completely from the ground up as well as designing all of my own wiring and circuits.

    Currently I'm working on a circuit for the electric windows and I've nearly finished but, I have one last hurdle to overcome.

    I have made my circuit so that it can accept a pulse input through one of two lines which will automatically wind the windows up or down (depending on the wire the pulse is input to).

    I would like to take the pulse from the central locking actuator so that windows will do their thing on the doors lock or unlock. The problem is that I want it to happen on the second input pulse and not the first.

    EG. I want to be able to press the lock button on the remote and my windows will stay down, but with a second press wind them all up.

    I have attempted to do this myself a couple of times with the materials I have available but unfortunately I haven't yet figured it out and I don't want to outlay more for components until I know it will work for sure.

    Cheers for any and all help.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    So what do u want us to do?
     
  3. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    Crap sorry,... Yeah basically I was wondering if anyone had an idea on how I could make a circuit that could identify between the first press of the button and the second.

    The door actuator has two wires that switch between positive and negative depending on their state (locked / unlocked) I want to use the output from those two wires to drive the circuit.

    If there is only one press of the lock / unlock button then there will be no output from the circuit. But if the button is pressed a second time, I'd like the circuit to output a single pulse.

    I am very new to circuits and I'm not entirely sure I've provided enough information. If I haven't please let me know.

    Cheers.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Show us what u have.
     
  5. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    I don't have any of the circuits saved on this computer unfortunately and the best I could find on here was paint so please excuse the poor drawing.

    I can tell you that the window circuit I have designed has a single input to automatically roll all of the windows up and a single input to roll all of the windows down (call them W1 -for up, and W2 -for down).

    These can both be activated by a single pulse of +12V (I also have momentary switches hooked to these so I can roll them up or down with the press of a button inside the car).

    The actuator I will be pulling the signal from has two lines (call them A1 and A2). When the lock button is pressed A1 will momentarily be positive and A2 will be negative. On unlock the opposite will occur.

    If the doors are locked and the lock button is pressed a second time the wires on the actuators will still provide the same result.

    I am trying to design the circuit so that it will register the initial positive output from A1 and then wait for (for about 2 seconds) to see if there is another output. If it receives a second output from A1 within the 2 second time period then I want it to send a single +12V pulse to W1 and the windows will roll themselves up. If the circuit does not receive a second pulse within 2 seconds then I'd like it to reset and wait for its initial input again.

    The opposite will occur on unlock being pressed twice. The circuit will monitor A2 for +12v pulses and relay what is required to W2

    Really appreciate the help, hope I've explained it well enough.

    [​IMG]
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I am having a hard time trying to wrap my head around that.

    Could u simplify it.
    Try to tell in point forms.
    like
    # Initial condition
    # button pressed, what button
    # what should happen when pressed..

    Something like tht.
     
  7. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    I can try but it may be even more confusing :)

    Outputs from actuator - A1 and A2

    Initial state - (A1) nothing, (A2) nothing

    Button pressed - Lock Button

    When pressed - A1 becomes positive, A2 becomes negative. (momentary)

    When pressed again - A1 becomes positive, A2 becomes negative. (momentary)

    ----------------

    Button pressed - Unlock Button

    When pressed - A2 becomes positive, A1 becomes negative. (momentary)

    When pressed again - A2 becomes positive, A1 becomes negative. (momentary)

    -----------------

    Window Circuit - 2 inputs, (W1, W2)

    When +12V pulse is applied to W1 - windows go up

    When +12V pulse is applied to W2 - windows go down


    Hope that makes sense of it.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Ok..why are u always implying tht it shud be momentary.
    Is it tht u have an original window actuator and locks.
    And u want to tap into them.
     
  9. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    The window motors are designed for hotrods and custom cars to lift flat glass. The circuit that came with them is nothing more than some wiring and some 20A switches. You have to hold the switch down to wind the window up and down, there is no auto up or down and there is no way to lock out the passengers from using them.

    I have made my own circuit to replace the window wiring kit that provides auto up and down to all of my windows (5 in total) and the other functions I want. The circuit uses relays to latch closed after a momentary input (rom a 2 way rocker switch - (hold the switch down a little and the window goes down, press it all the way down and release and the widow auto travels down) The relays will unlatch once the window has reached the end of its travel and tripped a circuit breaker.

    The reason the input is momentary is because the circuit does the latching, not the switch. By simply adding an extra wire to all of the up switches and another to all of the down switches, I can control all of the windows with a 2 way momentary rocker switch (or, by inputting a momentary +12v signal from another source eg. a pulse from the door being locked or unlocked)

    The door lock actuators are an off the shelf eBay item. The car will also have an off the shelf security and keyless entry system (don't feel confident enough to build that part) The actuators work by momentarily applying a positive charge to one wire and a negative to the other. They will go up or down depending on which wire has the positive and negative charge. If they have constant power applied to them they will either always be locked or unlocked and they will burn out. So they only ever see power for a moment.

    The reason I am tapping into the actuator is because that is the only part of the system I know will be constant, no matter which alarm system I choose to install they will all provide power to the actuators the same way.

    At the end of the day, the window circuit needs to see a momentary input. If it is a constant input it will keep attempting to wind up the windows after they have run out of space to move and burn something out.

    To me the easiest solution was to take the information being provided to the door lock to produce the input required for the windows.

    That's pretty much all the info I have, but if there is anything else you'd like to know please let me know. Cheers.
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Let me see. Will take a couple of hours as I have to get to work u know.
    Check later.
     
  11. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    Thanks heaps.
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You are stopping it by having a circuit breaker disconnect from current load when the motor stops, or is there a physical limit switch that the window closes in the path?
     
  13. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    I'm using something called a PTC fuse. The circuit will switch positive power and earth to one wire or the other on the window motor depending on whether it's going up or down. The PTC fuse is always on the postive line to the motor and when the motor starts to draw more power (when it's reached the end of travel) the PTC fuse trips, breaks the latching circuit with the relays, and then resets.
     
  14. eblc1388

    Senior Member

    Nov 28, 2008
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    I would advise not to use a protective element to function repeatedly as an end stop limit.

    These fuses has certain operating life and is not supposed to be actuated repeatedly.
     
  15. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    I searched everywhere on the net to see if I could find a circuit that I could build to give me the auto up and down function without a physical end of travel switch. The only thing I could find in the end was a company producing PCMs that showed they could be used in that particular way.

    http://www.circuitprotection.com/catalog/app/F07_power_(176-178).pdf

    That is where I got the information from. I then adapted it to allow for auto up and down.

    If you do know of a better way please let me know.

    Cheers.
     
  16. eblc1388

    Senior Member

    Nov 28, 2008
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    The article you have mentioned does not seem to have the name of the author. Well, who would be brave enough to put his name on the line.

    I also found additional information in Raychem's data sheet, here:

    PolySwitch

    Its your call as to who you would believe, depending on what "occasional overcurrent" really means.

    [​IMG]
     
  17. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    Well.... That sucks. Looks like it's back to the drawing board. Thanks for that though, it would have really been bad if it had of kept burning out.

    Any ideas on how I can perform a similar function without adding a physical switch to break the current?
     
  18. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    A way to implement the limit switches without contact would be a magnet on the moving window, and reed switches on the frame to detect the limits and activate/deactivate the relays.

    A more elegant solution would involve either hall effect sensors in place of the reed switches, or a current sense on the motor power line, controlled by a small circuit that runs the relay, or an H-Bridge in an all solid state solution (no relays).
     
  19. Cold Turkey

    Thread Starter New Member

    Sep 15, 2009
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    I like the sound of sensing the current on the motor and the whole solid state thing. Unfortunately up until a week or two ago my experience with electronics didn't extend pass relays, light bulbs and switches.

    I'm not asking you to do the project for me but would you be able to shed a little more light on how I would be able to sense the current on the motor? Keeping in mind that the positive and negative will switch for up and down motions.

    Some info on a "H-Bridge" would be awesome to.

    I've attached a section of what I have so far. The resistor in the circuit is where I was going to put the PTC fuse because that line will be the power feed for both up and down on the motor. The LEDs are just to indicate the direction of the window and that is how I built it on my breadboard. Worked really well.

    Let me know what you think.
    Cheers for the help

    [​IMG]
     
  20. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The current measuring is usually done by inserting a precision small value resistor, such as 0.1Ω into the power supply line to the motor, then measuring the voltage drop across it. The result, through ohms law, gives you the current.

    This would require a complete redesign of the current layout you have that is all relays, and if you aren't very comfortable working with protoboards/semiconductors, it would be rather large for a first project. Use the forum search for "H-Bridge" to see the designs and complexity some systems reach. Usually a microcontroller is involved, at least in late model production cars.

    I'd suggest attempting to work in the Original intention of controlling the windows as the first project, then work the rest in.

    The only warning is that sometimes PTC's fail closed, so be sure to have the proper rated fuse in power to the windows, and take a good warning from it if it blows!

    --ETA: On subject of the windows, you don't have a -12V supply, so it needs to be in terms of +12V and GND (- of battery/chassis). Might want to clear the confusion up a bit. You are essentially creating an H-Bridge with the relays already by swapping motor polarity.
     
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