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Need a timer diagram?

Discussion in 'General Electronics Chat' started by zone97, Jan 28, 2009.

  1. KMoffett

    KMoffett Well-Known Member

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    Verify the lead configuration of the transistors by looking at its datasheet. Also, the polarity of your diodes, and the polarity of the capacitor (your Sim shows a non-polar one, but 100uF will be polarized). Some relays have flyback diodes built-in, so their coil polarity is important. Also, you didn't say what the coil current of the relay is. It might be too high for the drive transistors. Otherwise, double and triple check your wiring. Highlight lines on a schematic as you verify each connection.

    Ken
     
  2. KMoffett

    KMoffett Well-Known Member

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    Duffy,

    After taking another look at your circuit, I also don't see a discharge path for the capacitor after the power is removed. Does it just depend on leakage?

    Ken
     
    Last edited: Feb 10, 2009
  3. zone97

    zone97 New Member

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    Specs on the relay are

    coil voltage nominal 12vdc max 15.6vdc
    coil current 30ma
    coil resistance 400 ohms +-10%
    pickup/dropoff 9.0/.06vdc
     
  4. dave

    Dave New Member

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  5. zone97

    zone97 New Member

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    ??? I do not know.. sorry.

    BTW, how much current can this circuit tolerate. As the source is 12vdc 2amps.
     
    Last edited: Feb 10, 2009
  6. duffy

    duffy New Member

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    No, it depends on Vcc going to ground. That's why I mentioned adding the 1k resistor across the power supply. D1 discharges it, and bypasses the timing resistor for a quick reset on power off.
     
    Last edited: Feb 10, 2009
  7. KMoffett

    KMoffett Well-Known Member

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    OK, I couldn't keep away from the bench. Duffy's circuit works as advertised...but it takes a long time for the circuit to reset after power-down...the relay will dropout at power-down, but will pickup immediately on power-up.

    Ken
     
  8. duffy

    duffy New Member

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    Depends on the size of the filter caps. OP said once an hour, so it shouldn't be a problem.
     
  9. KMoffett

    KMoffett Well-Known Member

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    The 1K resistor make sense, because if the +12v is disconnected by a switch, as opposed to a power supply being shut off, there is no discharge path through the transistors' collectors to ground (to D1 or R1/R2).

    ken
     
  10. zone97

    zone97 New Member

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    That's kinda what I am looking for, but i need the relay to fire at power on and go for about 15 seconds, then off, after 60 seconds power will be removed at which time everything needs to reset. and wait for another hour before repeating.
     
  11. duffy

    duffy New Member

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    Yes, originally I was assuming there were other things on the 12V supply that would discharge it (because of the 60 second dwell time) but now I see that's just a minimum setting for the timer.

    Zone97, what are you making with this? I was guessing a fish pump or a plant-watering device.
     
    Last edited: Feb 10, 2009
  12. zone97

    zone97 New Member

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    That is correct, the +v will be connected to circuit and a pump. The relay on its 'NO' side will switch the ground, which is attached to -v of the pump.
     
  13. duffy

    duffy New Member

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    Pump for fish or plants?
     
  14. zone97

    zone97 New Member

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    Its actually a universal water pump for the sprayer in your car, its connected to a water tank, to keep a terrarium watered. I have live plants and tropical geckos and a frog.
     
  15. duffy

    duffy New Member

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    Very cool! Hope the frog appreciates the effort. Can you water the terrarium without misting up the glass and obscuring the view?
     
  16. zone97

    zone97 New Member

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    the misting jets I use, are more like foggers. I have a fan in the front of the terrarium blowing down which helps keep the front from fogging. I'll attach an image.
     

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  17. KMoffett

    KMoffett Well-Known Member

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    Have you tried using the windshield washer pump? I tried using these for an automatic Christmas tree stand watering system. All the replacement ones from the auto parts stores have nylon bearings. These are made to run only for "very" brief periods. I tried several brands and they all melted the bearings trying to refill an half an inch or so of water in the stand.

    Ken
     
  18. zone97

    zone97 New Member

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    That's what it is... A washer sprayer. and hence the need to only run it for 15 seconds, every hour or so.. :)
     
    Last edited: Feb 10, 2009
  19. duffy

    duffy New Member

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    Oh man is this weird - a guy at work was showing me that exact temperature and humidity gauge not three hours ago.
     
  20. zone97

    zone97 New Member

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    So with the motor and wiring in mind, do i need to do anything else to the circuit. As I now have batteries and will try to build the circuit again.
     
  21. zone97

    zone97 New Member

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    Ok built it on a protoboard, all but the motor is connected. When power is applied, the relay turns on but never turns off? It will if i remove power.
     

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