Help with a momentary circuit

Discussion in 'The Projects Forum' started by stf5060, Oct 5, 2011.

  1. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    Hi,

    I have never really built anything too complicated from scratch, only followed pre-made guides and I'm looking for some help. Basically I bought a 12V 15RPM motor that I will have hooked up to a remote activated outlet plug. I want to make a circuit that will, when the power is activated from the plug, turn the motor on for somewhere between 1-5 seconds (I haven't decided yet) and then turn it off. Can someone help me figure out a method for doing this? Your help is much appreciated. Thanks
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    This forum (and google) are full of "555 timer circuits" that should do what you need.

    The 555 timer is a small easy to use IC that lets you make a time delay.

    The 555 can drive a relay or transistor that controls the motor power. So try "555 timer with relay" or "555 timer control DC motor" or similar searches. :)
     
  3. Georacer

    Moderator

    Nov 25, 2009
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    Don't forget that this site doesn't allow circuits connected directly to the mains.
    If you post any circuits, make sure they are electrically isolated from the wall plug through a 1:1 transformer.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    For remote activation of a power outlet, look into X10 modules. Off the shelf and safe. No need to mess with power line interfacing.

    Google:X10

    Depending on how much current the motor draws, you can power the motor and a 555 timer circuit from a 12V wall wart plugged into an X10 receiver.

    Ken
     
  5. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    This is what I already got for the remote activation:
    http://www.amazon.com/gp/product/B000G80V28

    I was thinking about a 555 timer but won't that just turn the motor on for 5 then off for 5 and then back on for 5 and keep repeating? I just want it to turn on, then off and stay off.
     
  6. KMoffett

    AAC Fanatic!

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  7. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    Thanks for the link. So I will try and build the monostable circuit. The only problem is I was planning on using 24v .3 amps, which I see is too much for a 555 timer. Would this work to downgrade the voltage? http://www.ebay.com/itm/5-x-L7812-7...735?pt=LH_DefaultDomain_0&hash=item20bd48a377

    So I'm assuming if I drop the voltage to 12v the current is doubled to .6 amps, correct? Now what can I use at the end to bring the voltage back up to 24v? And I'm having trouble finding a 100k resistor like the one in the diagram that is suitable for 24v .3 amps (~8watts), anyone have any ideas? Thanks for the help guys
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I'm missing something. If the circuit and the motor are 12V, why will you be using 24V?

    Ken
     
  9. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    I forgot to mention I need to make 3 of these circuits. 1 for the motor which is 12v and the other 2 for actuating solenoid valves at 24v
     
  10. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    OK, how much current does the 12V motor draw maximum, in the start/stalled condition? How much current does each of the solenoid valves draw? Are there any other things attached to this we will need to take into account.

    The devil's in the details!

    Ken
     
  11. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    I'm waiting on the specs for the 12v motor, but I'm not as concerned about that. The solenoids will be operating on 24v 0.3Amps. There won't be anything else attached to the circuit. I just simply need them to open for a short amount of time, and then shut, and the circuit to not retrigger them to open. And then power will be cut from the circuit after a short amount of time
     
  12. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    Bump......
     
  13. KMoffett

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    Thought I posted this last night. Must have not hit Submit. :(

    Ken
     
  14. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    Wow! Thanks so much for the diagram, much appreciated! I just have a few questions if you don't mind. For the 24v circuit, you used a 1N4742A zener diode, but it says its only rated for 1W, isn't that too small? Doesn't everything have to be rated for like ~8W? And Which of the capacitors/resistors do I have to adjust to adjust to output time? Could you recommend a good site to order all or most of this stuff? Instead of hunting around for each part. Thanks again for all your help!
     
  15. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    The zener only supplies current to the timer circuit that draws very little, so 1W should be sufficient. R3 is a potentiometer used as a variable resistor to adjust the time. I'll take a look at the components and give you a vendor.

    Ken
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    Ken,
    Shouldn't use a Zener like that. You need the circuit voltage regulated, not the drop from 24v down to the timer voltage. You take a chance that a spike will zap the circuit; and you're using a CMOS timer and a MOSFET for a driver. Odds are that one spike will kill them both.
     
  17. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    ...So, what would you suggest? And since the zener is only rated for 1W does that mean I can use capacitors and resistors for 1W as well? I was under the impression I needed something that parts that could support about 8W for everything. Thanks again for all the help guys
     
  18. SgtWookie

    Expert

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    Steven,
    In the right-hand schematic, D2 and R1 need to be exchanged. R1 needs to be reduced to allow between 10-20mA current to flow through it. That's 600 to 1.2k Ohms.

    Also, 0.1uF and 1uF or larger caps need to be connected across the Vcc and GND terminals of both 555 IC's.
     
  19. stf5060

    Thread Starter New Member

    Oct 5, 2011
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    How did you know my name??
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    I must be psychic. ;)
     
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