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Momentary lockout Solenoid

Discussion in 'Homework Help' started by syntax_x, May 21, 2013.

  1. syntax_x

    syntax_x Member

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    Hello, New user here with a simple little problem.


    [​IMG]

    This is the circuit I am working with, it emulates the recoil of a pistol and allows a signal from the trigger to be used. (the black square is a relay..)

    The problem I am having at the moment is if the trigger is held down, the solenoid stays engaged, no-brainer right?

    So I am trying to make the solenoid receive power for only the duration needed to send it into a fully engaged position.

    That way the solenoid recoils before the trigger is deactivated.

    I can post up some videos of my progress so far if it helps.
     

    Attached Files:

  2. Mr RB

    Mr RB Well-Known Member

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    Firstly, Hi and welcome to the forum. :)

    And thank you for posting clear information on exactly what the circuit does and providing your circuit diagram! Lots of first-time posters leave out critical information.

    OK, your diode is connected wrong. it should be connected across (parallel with) the solenoid coil, woth the diode ANODE (white stripe) at the + end of the solenoid coil (not the GND end). After that your diode will do it's job, and protect things against the solenoid induced back-EMF spike.

    Next, to get the "one shot" result you need, there are a few solutions involving monostable timers, which adds complexity.

    You might be able to get away with a simple solution, and just put a large cap (2200uF) in series with the solenoid wire (where you show the diode in post #1).

    The cap will make a current pulse while it charges, that will "fire" the solenoid. Then when the cap is charged there is little/no current and the solenoid will drop out. That will require a resistor across the cap, to discharge the cap when the user is not firing. The discharge time will need to be shorter than the time between user firings. Maybe try a 1000 ohm resistor, but have a few values handy if it needs a higher or lower value resistor.
     
  3. WTP Pepper

    WTP Pepper Active Member

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    Using caps is guessing when the solenoid is fully engaged. I would use something like a simple magnet on the solenoid triggering a reed switch to disable the drive current to the solenoid.

    It then makes it a closed loop control system where you definately know the solenoid has engaged.
     
  4. dave

    Dave New Member

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  5. Mr RB

    Mr RB Well-Known Member

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    That will oscillate! :)
     
  6. WTP Pepper

    WTP Pepper Active Member

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    With a bit of careful design with a few flip flops, it won't.
     
  7. alec_t

    alec_t Well-Known Member Most Helpful Member

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    How much current does your solenoid draw at 24V?
     
  8. syntax_x

    syntax_x Member

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    Hmmm... It seems the Administration team did not like my response...
    Lets try again (for the 3rd time...)

    Thanks for the warm welcome Mr RB. Nice to have a long time member give me a hand straight up.

    Concerning the diode, yes i had it in the wrong spot, the solenoid actually came with 2 diode already inplace, 1 is where you stated.

    I have looked into using a 555 timer in momentary mode as a one shot, but im not sure where to start with resistor and cap values, and im pretty sure ill need a pot to tune the response rate.

    WTP Pepper, thankyou for your input, its greatly appreciated, but my thoughts were the same as Mr. RB, i feel it would oscillate.
    I'm sure with a few flip flops and the magnetic reed it would in theory work, but the solenoid itself has a very violent action and would probably introduce different forms of interference and false inputs.

    I WILL post up some links to videos on what i have done thus far.

    I would like to add that I am not a student, and that this is not for profit of any kind, except my own enjoyment and maybe others.
    If i manage to get this working ill be posting a write-up on how to, and anybody who has helped here will be getting the credit.

    Im just a guy with a soldering iron..

    Cheers again on the input thus far , ill check the current draw @ 24v right now alec_t.
     
  9. syntax_x

    syntax_x Member

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    If Admin allows it, here is a more in-depth picture of my project.

    Circuit2.jpg
     
  10. syntax_x

    syntax_x Member

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    When the solenoid is first engaged the current pull is 1.4 A. If i keep it held it slowly drops past 1.2A. Didn't hold it on any longer than that.
     
  11. alec_t

    alec_t Well-Known Member Most Helpful Member

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    What is the foot pedal for?
     
  12. syntax_x

    syntax_x Member

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  13. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Here's a suggested driver for the solenoid:
    SolenoidDriver.gif
     

    Attached Files:

  14. syntax_x

    syntax_x Member

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    Hey alec_t, Did you just throw that together for me?

    Thanks champ!

    2 questions, what is m1?, and what does the pot change?
     
  15. Mr RB

    Mr RB Well-Known Member

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    Nice machine! I feel a bit silly now, my original comments were with the idea to keep the parts count down, as I thought you were fitting this inside a small device like a laser tag grip.
     
  16. syntax_x

    syntax_x Member

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  17. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Those caps will be fine.
     
  18. syntax_x

    syntax_x Member

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    Cheers Roman, I'm pretty happy with the cab myself :)

    alec-t, ive built the 555 circuit but I'm pretty sure M1 on your diagram is a transistor. Im not sure what to do there:confused:...sorry.

    hopefully i wired the pot up correctly too, i soldered to the outside legs, which is wrong hey, i should of used the middle and left leg i think...:confused:
     
  19. syntax_x

    syntax_x Member

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    My bad, just wired up the pot correctly, but still unsure of M1.

    Also the pot showed it only went to 420k on my multimeter.
     
  20. WTP Pepper

    WTP Pepper Active Member

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    1. 24V is way too high for an NE555 to operate.
    2. What is R4 used for?
     
  21. syntax_x

    syntax_x Member

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    I could attack the 5v feed to the relay instead.
     

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