Timer Circuit Problem

Discussion in 'The Projects Forum' started by kauffjd3, May 3, 2009.

  1. kauffjd3

    Thread Starter Member

    May 3, 2009
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    First off hello all! I'm a computer programmer and am new to electrical circuit board development. I have been searching google and playing around with a bread board for a few days now and need some help.

    Project:
    Temperature driven motor

    Example:
    Set temperature to 60 degrees

    1. If temperature is below 60 degrees run the motor clockwise for 1 second.

    2. If the temperature is above 60 degrees run the motor counter clockwise for 1 second.


    I didn't do anything with the temperature yet because I may just order a kit.

    Anyway I currently have a 556 timer ic setup i monostable mode like this (this is for either clockwise or counter clockwise then the second time will be for the opposite direction):
    http://www.eleinmec.com/figures/004_02.gif


    I plugged in a 12v blue bulb to the output and hooked up a 9v battery to test it. Nothing happened but then I realized I needed to trigger it.

    So I gave the trigger wire 9v power and nothing. So I grounded it and to my surprise it worked. When I quickly touched the trigger wire to the ground and removed it the blue light would stay on for a split second after I ungrounded the trigger wire. Hence the 1 second.

    Finally my question:
    My temperature kit is going to power all the time so how am I suppose to hook it up to my trigger? Currently if I keep the trigger wire grounded the light stays on.

    Thanks in advance for all your help! And if there is an easier way of doing this I am all ears.


    Justin
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Where are the specifications of the kit?
     
  3. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
    0
  4. mik3

    Senior Member

    Feb 4, 2008
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    First note that the kit is not able to measure 60 degrees celcious (5-30).

    If you hold the trigger of the 555 always pressed then the 555 will re-trigger and the output will be always high. You need to depress the trigger switch before the timing cycle ends.

    To solve the problem replace the trigger switch with a 100nF capacitor and a 10K resistor in parallel with it and use the output relay of the kit to power the whole 555.
     
  5. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
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    60 degrees F.

    So I removed the battery from the 555 and hook the output of the kit into where I removed the battery? What do I use to trigger the timer?
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Leave the battery which powers the 555 and use the relay output of the kit to switch the 555 on/off. To trigger it replace the trigger push button with a 100nF capacitor in parallel with a 10K resistor.
     
  7. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
    0
    thanks for your help Mik3. I'm still confused.


    If I run a 100nF capacitor and a 10k resistor from pin 2 on the 555 where does the other end go? ground?

    When you say use the relay to switch the 555 on/off where do I feed it if I leave the battery?

    Sorry I'm such a newbie. I can program all day but I have a lot more learning to do for this stuff.
     
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    The other end goes to ground.


    Connect the relay common (C) and normally open (NO) between the batteries positive and pin 8 of the 555.
     
  9. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
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    for the time being since i dont have the thermostat kit, I added one end of a 10k resistor to pin 2. Then the other end into a blank spot in the bread board. Hooked the 100nF capacitor from the end of the resistor and the other end to ground. When I give it power the blue light just stays on. Did I do something wrong?
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    Connect the capacitor between pin 2 and ground, connect a 10K resistor between pin 2 and Vcc (positive supply) and finally connect another 10K resistor between pin 2 and ground.
     
  11. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
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    with them all hooked the blue light doesn't turn on. removed the resistor from pin 2 to the powersupply and the blue light just stays on again.
     
  12. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
    0
    double post
     
    Last edited: May 3, 2009
  13. mik3

    Senior Member

    Feb 4, 2008
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    Use a bigger capacitor, like 10 uF.
     
  14. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
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    I don't have anything that big here at the house. I will pick some up and give them a try. Thanks for all the help Mik3! Can you explain what this is actually doing or trying to do so I understand?

    Thanks again!
     
  15. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    The capacitor will be uncharged. When you power the 555 pin 2 will see 0V and will trigger the 555. After a few ms the voltage across the capacitor will rise at Vcc/2 (pin 2 will be at the same voltage too) and the 555 will not trigger again.

    Try more than one capacitor in parallel for now to see if it works.
     
  16. kauffjd3

    Thread Starter Member

    May 3, 2009
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    I have 2 .1uF capacitors 1 10k resistor going from pin 2 to ground. And 1 10k resistor going from pin 2 to power source. The blue light doesn't come on.

    When I remove the 10k resistor from pin 2 to power source the light comes back on but stays on...
     
  17. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
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    just hooked up a 1uF capacitor from pin 2 to ground also same thing light just stays on.
     
  18. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Do you have a resistor from Vcc (positive supply line) to pin 2?

    What is the voltage on pin 2 after 1 sec?
     
  19. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
    0
    Yeah I have the resistor from pin 2 to positive. Looks like 9.3v at pin 2 when I hook the battery up.
     
  20. kauffjd3

    Thread Starter Member

    May 3, 2009
    15
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