1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Problem with 555 not discharging.

Discussion in 'Homework Help' started by syntax_x, Aug 25, 2015.

  1. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    So awhile ago with the help of this forum i built a 555 timer to control an arcade lightgun solenoid.

    Im no longer using it for the arcade and decided to wire it up to a playstation controller

    Now the rapid fire 555 is running fine but the single shot one for some reason is missing input/output for the solenoid if the trigger
    switch is pressed too fast (even so the game being used to test is picking up every input as can be heard in the video)

    This 555 drives the solenoid for 45ms
    The 555 should only be powered when the trigger is pulled and grounds the circuit.


    [​IMG]
    I have a feeling the 555 is being kept powered and not allowing the solenoid to fire again.

    So whats a good way to ensure the circuit discharges as soon as possible??
     
    Last edited: Aug 25, 2015
  2. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    deleted
     
  3. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,315
    Likes:
    1,230
    Location:
    Cardiff, Wales
    That's a rather unusual way of triggering the single shot 555. Any particular reason you're not doing it the conventional way by keeping pin 1 grounded and using the gun trigger to pull pin 2 to ground temporarily? If the 555 is not powered then cap C2 can't discharge rapidly via pin 7, and cap C1 has no obvious discharge path to enable the 555 to be re-triggered.
     
    Last edited: Aug 25, 2015
    • Thanks Thanks x 1
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia

    I just tried keeping Pin 1 grounded, connecting the Pin 2 to my controller trigger feed (+5v) which is one side of the trigger and the other side is ground.
    i didnt remove c1 or r1. but did cut the trigger wire from them.

    All it did was stay open with trigger held in like a relay would...

    Funny thing is it does do a 45ms fire when i first plug it in...
     
    Last edited: Aug 25, 2015
  6. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,474
    Likes:
    191
    Location:
    Lancashire UK
    If my understanding of your phrase " if the trigger switch is pressed too fast" means that it fails to work when the trigger is held closed for less than 45ms but works if the trigger if the trigger is held for more than 45 ms is correct then because you are removing the power from the circuit when the trigger is released there is no power to drive the relay. If you power the circuit permanently and trigger the monostable in the normal way as others have suggested it should work .

    Les.
     
    • Thanks Thanks x 1
  7. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    No it fails when there is less than around 45ms BETWEEN presses. Like it never turned off.
    In the video you can hear the game input still registering the keypress but the solenoid is missing. Its a very muffled noise sorry.
    I dont know why it worked fine on one system but not the other.
     
  8. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,315
    Likes:
    1,230
    Location:
    Cardiff, Wales
    The trigger is not connected to +5V in your schematic! Connecting pin 2 to +5V is not what I suggested and it won't work.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,573
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    A 555 monostable timer will not "time out" if its pin 2 is low when it is trying to time out. When it times out then its output goes low, then it is ready to be triggered again.
     
  10. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    What about connecting it to +5v which is then grounded every time the trigger is pulled?

    I can't avoid this as the game board trigger wire is +5v.
     
  11. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,315
    Likes:
    1,230
    Location:
    Cardiff, Wales
    No. That will short out the +5V supply. You need a pull-up resistor to +5V (i.e. the R1 you already have).
     
    • Thanks Thanks x 1
  12. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    So something like this should work?
    Sorry its been so long since i played with these timers and it gets a little overwhelming at times.

    (Forgot to put a cap on CV sorry)

    [​IMG]
     
  13. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    Diodes, Oh glorious diodes....
    I isolated the game board trigger wire with a diode and guess what? Everything is as it should be!

    Thanks again for all the fast help guys!
     
    Last edited: Aug 26, 2015
  14. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,474
    Likes:
    191
    Location:
    Lancashire UK
    I think the value of C1 in your original circuit is too large. Try changing C1 to 47nf (The time constant with R1 being 100K will be 47 mS) I think the the flip flop in the 555 may be still be held in the set state at the time C2 reaches the threshold level. Also C1 may not discharge quickly enough when the trigger button is released. (So that the 555 may not be forced into the set state when the trigger button is next pressed.) I suggest putting a diode in parallel with R1 with the negative end to C1. (So C1 discharges quickly.) Also adding a resistor (Say 1K) between the ground and vcc on the 555 would help to discharge it.

    Les
     
    • Thanks Thanks x 1
  15. JoeJester

    JoeJester Active Member

    Joined:
    Nov 6, 2009
    Messages:
    699
    Likes:
    105
    Location:
    Grand Prairie, TX
    Why aren't you taking advantage of the RST pin. Two inverters, one for each circuit, then all your design is a straight forward astable oscillator and relay drivers.
     
  16. syntax_x

    syntax_x Member

    Joined:
    May 21, 2013
    Messages:
    39
    Likes:
    0
    Location:
    Australia
    Because keeping the circuit powered all the time is not an option.
    Working fine regardless, no input lag, no missed presses, and the solenoid fires at the same time as the trigger.
    Every now and then i press the trigger for such a short time the solenoid doesn't fully fire but i can live with that it
     

Share This Page