SCR Driving a 555 Time Delay

Discussion in 'Homework Help' started by drmanmachine, Mar 19, 2016.

  1. drmanmachine

    Thread Starter New Member

    Mar 12, 2016
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    Is there a way to keep the 555 output running when I let go of the momentary switch?
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    How long do you want it to stay on after the switch is pressed? Why are you using an SCR to trigger the timer?
     
  3. drmanmachine

    Thread Starter New Member

    Mar 12, 2016
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    I was hoping to make it a one shot. The idea was to connect the 555 output to one of the two inputs on an h-bridge to rotate a motor.

    The project we're working on is a sorting system of different colored balls. The balls would roll down a ramp into a cart attached to a conveyor belt. At the bottom of the ramp, we would attach a limit switch for the balls to make contact. When the first ball makes contact, the limit switch would send a signal to the 555 to delay the motor from rotating. When the motor begins to rotate, the balls will be transported in the cart. That cart will make contact with a second limit switch to stop the motor from rotating.

    The SCR was an idea from a fellow classmate of mine. He thought that by using the SCR, we could latch the current to keep the motor rotating until it reaches the second limit switch.
     
  4. dl324

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    Mar 30, 2015
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    Post your schematic so we can see the R and C values you're using.

    If you only post pieces of your problem, you'll only get pieces of a solution.

    BTW, is this homework?
     
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  5. drmanmachine

    Thread Starter New Member

    Mar 12, 2016
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    It's a part of a project.
     
  6. dl324

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    A school project for which you will receive a grade?
     
  7. drmanmachine

    Thread Starter New Member

    Mar 12, 2016
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    Yes.
     
  8. dl324

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    In that case, you need to post your ideas (schematics, block diagrams, etc) and your understanding of how they work or don't work. You will be guided to solutions. The rate of progress will depend mostly on your ability to do your work.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The top switch should be "normally closed" and can be reset by breaking the connection. You should also have a resistor between the bottom switch and the scr gate to limit current (check the datasheet to the scr you will use).

    I think that will solve one problem but you will notice a second problem.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    It is customary to keep a 555 monostable permanently powered and use pin 2 to trigger it, pin 4 to reset it.
     
  11. drmanmachine

    Thread Starter New Member

    Mar 12, 2016
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    I didn't add it to this thread because of how long and lengthy it would be to read. If you'd prefer me to write it all out, I'd be happy to.
     
  12. dl324

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    Mar 30, 2015
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    You mentioned that one of the ideas was to use the SCR to drive the motor, but you didn't show how the SCR is your circuit was driving the motor.

    You also didn't mention the type of SCR you were using. Most SCR's require power to be removed or current to be reduced below the holding current before they stop conducting. Some have sensitive gates that can be used to turn them off. Giving more context in how the devices are being used will generally yield more useful answers.

    The way you've connected the 555 timer is not a typical OS configuration. Normally the trigger input would be used to trigger the one shot and the discharge pin would be used to discharge the timing cap.
     
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