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Design an adjustable voltage switch

Discussion in 'General Electronics Chat' started by stuhagen, Sep 27, 2008.

  1. Roff

    Roff Well-Known Member

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    One pot symbol is all you need. You change the value and the percent rotation.once it's on the schematic.
    Pot.asy is 699 bytes, pot.sub is 195 bytes.
    Show us the complete path to each file on your computer (C:\program files\...).
     
  2. stuhagen

    stuhagen Member

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    I have only the one, but I do not have the 195byte .sub.

    I have "pot" in c:/programs/LTC/LTspiceIV/lib/sub and again in/sym. Problem I guess is I am unable to unzip it for some reason. Says something about it being "empty" yet it has properties.

    Stu

     
  3. stuhagen

    stuhagen Member

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    OK here is a screen shot of the issues I have trying to open this "zip" file

    Stu
     

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  4. dave

    Dave New Member

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  5. Roff

    Roff Well-Known Member

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    Not sure why you're having trouble with Zip files. My computer recognizes them and apparently unzips them automatically.
    Here's another way. Copy and paste the following to Notepad. Save it as pot.asy in C:\Program files\LTC\SWcadIV\lib\sym\misc.
    Code (text):
    Version 4
    SymbolType CELL
    LINE Normal 16 88 16 96
    LINE Normal 0 80 16 88
    LINE Normal 32 64 0 80
    LINE Normal 0 48 32 64
    LINE Normal 32 32 0 48
    LINE Normal 16 16 16 24
    LINE Normal 16 24 32 32
    LINE Normal 40 64 64 64
    LINE Normal 40 64 48 56
    LINE Normal 40 64 48 72
    WINDOW 0 36 32 Left 0
    WINDOW 3 36 88 Left 0
    WINDOW 39 36 128 Left 0
    SYMATTR Value Rtot=10K wiper=.5
    SYMATTR Prefix X
    SYMATTR SpiceModel potentiometer
    SYMATTR Description Resistor Potentiometer, must include potentiometer.sub
    SYMATTR ModelFile pot.sub
    PIN 16 16 NONE 0
    PINATTR PinName A
    PINATTR SpiceOrder 1
    PIN 16 96 NONE 0
    PINATTR PinName B
    PINATTR SpiceOrder 2
    PIN 64 64 NONE 0
    PINATTR PinName C
    PINATTR SpiceOrder 3
     
    Copy and paste the following into Notepad and save as pot.sub in C:\program files\LTC\SWcadIV\lib\sub.
    Code (text):
    * This is the potentiometer
    *      _____
    *  1--|_____|--2
    *        |
    *        3
    *
    .SUBCKT potentiometer 1 2 3
    .param w=limit(wiper,1m,.999)
    R0 1 3 {Rtot*(1-w)}
    R1 3 2 {Rtot*(w)}
    .ENDS
     
  6. Roff

    Roff Well-Known Member

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    You should definitely have a regulator for the LM393 and the zener. I would use 8 volts. If you can get them, LM78L08 or LM317L (programmable) are good.
    Change the zener bias resistor from 1k to 220Ω or 240Ω.
    Automobile DC power can be very noisy, with high voltage spikes which can destroy a regulator.
    Attached is one way to protect the regulator.
    I'm not sure if the regulator will solve your problem, but it might.
     

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  7. stuhagen

    stuhagen Member

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    WOOT~! That worked.

    Thnks

    Stu


     
  8. stuhagen

    stuhagen Member

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    I have found what I need for the hysteresis. I have a circuit I just tested that was made by others (professional). ALthough I would love to just use it because it works, it is way too big. So after my testing this other circuit, it does not oscillate at all. When I bench test it at a 4.5v trigger, it drops to 3.65v. Best I can get on mine is from 4.5v to about 4.1v. Not enough. I am wondering now If it is even possible to get this large of a drop. By the way, the "range" for this circuit will never be below 4.0v. More like the range will run at 4.3v to 4.7v. Which it works great for this. If I can "lick" this 4.5v--> 3.65V drop it will work.

    So I tried working this LTspice and I am stumbling a bit. Have to read more. I tried your math on calculating the hysteresis and stumbled there as well. So I hope I can figure this out, but if you have a quick suggestion for acheiving this hysteresis, i am all ears (-:

    Stu


     
  9. Roff

    Roff Well-Known Member

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    Too much information here.:confused: What range do you want for the threshold when the input voltage is rising? How much hysteresis do you want? Or do you want the threshold to drop to 3.65V, independent of the rising threshold?
     
  10. stuhagen

    stuhagen Member

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    OK.... My Vset will always be from 4.5 to 4.7v. No less, no more. The Vsrc (sensor) range is from 3.0v to 5.v.
    Now, assuming a Vset at 4.5v I need a hysteresis of 3.65 once it has triggered. This is a critical bottom threshold to acheive. If not, it will oscillate (loop)
    What happens, is when it triggers at 4.5v, the Vsrc immediatly drops to 3.7v. (just the way it is)
    So all my previous circuits do not have this great of hysteresis range for my Vsrc drop. So it was going to a "loop" cycle. 0n-off-on-off-on. I want it t go on and stay on until I start over (back to car idle)
     
  11. Roff

    Roff Well-Known Member

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    The definition of hysteresis is a delta (change in) voltage.
    With a Vset of 4.5V, do you want it to drop to 3.65V? And if Vset is 4.7V, do you want it to drop to 3.85V?
     
  12. stuhagen

    stuhagen Member

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    With a vset at 4.5v I do not want the circuit to go "off" until the Vsrc has gone below 3.7v. I will always keep the 10K pot at this desired Vset (ref). To answer the question, if I "raise" the Ref Vset to 4.7v, do I still want the 3.65v?. If possible, yes. I do not know if this is possible being this requires a greater drop? Basically, it appears that no matter what Vset I choose, it will always drop to 3.65v. which is why when I select a real low Vset (ref) if starts to not loop because the 3.65 gets closer to the Vset.
     
  13. Roff

    Roff Well-Known Member

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    I still don't understand.
    With the threshold set at 4.5V, when the sensor voltage reaches 4.5V, what voltage do you want the threshold voltage to drop to?
    With the threshold set at 4.6V, when the sensor voltage reaches 4.6V, what voltage do you want the threshold voltage to drop to?
    With the threshold set at 4.7V, when the sensor voltage reaches 4.7V, what voltage do you want the threshold voltage to drop to?
     
    Last edited: Jun 23, 2010
  14. stuhagen

    stuhagen Member

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    ALL Above need to be at a threshold drop of 3.65v. I assume making the 4.7v at 3.65v, the other lower 2 will fall into the same range.
     
  15. Roff

    Roff Well-Known Member

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    So, independent of the threshold voltage, you want the relay coil current to go off when the sensor voltage goes above the threshold voltage, and stay off until the sensor voltage drops below 3.65V. Am I interpreting this correctly?
    I know I sound stupid, but you and I don't interpret electronics language exactly the same way, and i hate spending a lot of time designing something, only to find that I misunderstood the specs.
     
  16. stuhagen

    stuhagen Member

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    YES SIR~! EE to dumb EE ha..ha.. that is exactly what I want.

    BTW, if your interested in seeing the circuit that "does" work, I can send it to you as a PM. It is too elaborate and more universal. Hence why I prefer to make mine simpler and more specific.
     
  17. Roff

    Roff Well-Known Member

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    OK, I looked at the PDF you PM'ed. Have you noticed that it is very similar to your circuit? If you add the voltage regulator, which I recommended, it is even closer. You could get rid of the zener if you add the regulator.
     
  18. stuhagen

    stuhagen Member

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    I will eventually add that into the final design ONCE i figure this damn drop voltage I need. Any luck or ideas so far? Did you note the 1M in-line resistor after the Vref? There resistance for hysteresis is from the 1M pot. I should take that pot out and read it's resistance. I suppose I could copy there 2 values. But it is enough different, that may not be all in the equation.

    Stu
     
  19. Roff

    Roff Well-Known Member

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    I'm working on it. I've been busy on other stuff today. I might get back to it tomorrow afternoon.
     
  20. Roff

    Roff Well-Known Member

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    OK, here's what I came up with. I'm hoping you aren't using the other half of the LM393 for anything. I used it so we can get full output swing on the first one, making the hysteresis easy to attain. If the other section is not available, there are other possible solutions.
    I think you were trying to build this with parts on hand. Let me know what you don't have. If it is not difficult to get parts, I recommend the values shown - except for the 2N2222, which might be susceptible to CE breakdown due to spikes on the car's battery rail. Something like 2N5550 would be much better. A small MOSFET could also work, which would also eliminate the need to use the 2nd half of the LM393.

    The adjustment labels probably look like they are swapped, but they are not.
     

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  21. stuhagen

    stuhagen Member

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    Ron,

    Thanks for spending time on this. I am well aware of ones "spare time"

    If you go back to the beginning of this thread, these components were given to me by various people. I think Eric might have been the guy who rec'md the 2N2222.
    I will use my own 8V Vreg, or the one posted a page back. (Although not sure why I need an adj one.)

    I think using both sides of the LM393 is just as good. A MOSFET would require adding in another component which takes away board real estate.

    I am going to start over and make all new boards. I will order any new stuff from digikey. So if you feel that other components are worth changing, LMK and I will order those as well.

    Please verify components:

    U1 = POT 1K?
    U3 = POT 500K? (adj Hysteresis )
    LM393 Vcc = 8V ? ( I assume since you have an "8" below the Vreg symbol.

    Lastly, I do not see any Zener's here. Does this new design eliminate them? Since adjusting the Vsrc is so limited for my usage (4.0 to 4.7 range)

    Lastly, this new circuit above, is it totally complete? I ask because the configuration on R1 and R2 is different than my original that has caps and Zener's to the left.

    Stu
     

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