20 second delay on switch.

Discussion in 'The Projects Forum' started by Maloney, Jan 15, 2010.

  1. Maloney

    Thread Starter New Member

    Jan 7, 2010
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    so i have a project where a sensor turns a servo, but i need a 20 second delay on the servo. but i am not sure of how to do this. It would have to take the voltage coming in, and pass it through, but only after 20 seconds has passed. Kind of like a transistor, but with a 20 second delay. How would i go about doing this?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Google 555 monostable.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Since a "servo" requires a continuous stream of PWM pulses it would require some way to store a particular width for the 20 seconds...and any changes during that 20 seconds. Kind of like a 20 second long bucket-brigade. Can you post a schematic of what you have now? And maybe a little more about the entire project?

    Ken
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    How were you planning on controlling the servo?
     
  5. Maloney

    Thread Starter New Member

    Jan 7, 2010
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    The servo is modded, its just a motor and the gearbox now. so it only needs voltage in and ground, all that prt is done i just need the delay. a monostable will not work here, that delays it after the signal is detected. I need it to be delayed from 20 seconds on turn on, and then it open the bridge and connects the positive line on the motor.
     
  6. Maloney

    Thread Starter New Member

    Jan 7, 2010
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    pirmotor.jpg
    thats the current setup, i just need to add the delay on the imput to the motor, after the transistor.

    pirmotor with delay.jpg
    It needs to work the way it is drawn here. currently i have a switch in that possition, but it is for an airsoft claymore. I want to be able to just place it, flip one switch and go. Instead of turning it on, and waiting 20 seconds then flipping another swith. I need it because the PIR is learning its environment for the first 20 seconds, and the servo turns randomly, this would set off the tripmine. so i need to bypass it for 20 seconds.
     
    Last edited: Jan 16, 2010
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Maybe this will do. At power turn on, 555 P 2, held lo 1/4 sec, P3 hi holding PNP off, motor inhibited. After 20 sec, PNP on, PIR pulses control motor. R depends on motor current, NPN gain, & PIR output V , output resistance.[ 300Ω ?].
     
  8. Maloney

    Thread Starter New Member

    Jan 7, 2010
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    that may work, not entirely sure. However I am running it on a 9v now, sorry about not changing the diagram i attached. I will have to buy the parts and test it out. Seems like it would work though. Thanks alot.

    new to this stuff, not exactly sure what you mean by 1M by the resistors? or 20m for the one capacitor? another thing i have always been stumped by, was the voltage of a capacitor, does it really matter? what would i use in the case of your schematic.
     
    Last edited: Jan 16, 2010
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Yesterdays post went to the great memory bank in the sky; so will try again: 1M= 1 meg ohms, 1000000 ohms, 20 uF @ 25V, u= micro in Quick Reply, much better u in Post Reply. Cap. V is operating voltage, operating much above might result in failure of cap. I like to rate caps at 150% of circuit voltage V. The .1 & .01 are uF.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Something like this might be modified to work, it was drawn for another project....

    [​IMG]

    The 1st timer sets the delay, the second turns on Q1 for a preset amount of time.
     
  11. Maloney

    Thread Starter New Member

    Jan 7, 2010
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    Using the diagram that bernard posted, what would i change so it has a 60 second delay? it is also running off of 9v instead of 6, thats my fault however. What all would i change for a 20 second delay on 9v and a 60 second delay on 9v? also range of what the missing resistor would be?
    Also isnt a 20U capacitor extremely huge for use in a small circuit like this? i cant even find any online.
     
    Last edited: Jan 19, 2010
  12. Wendy

    Moderator

    Mar 24, 2008
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    555 timers are immune to voltage. The formula I listed on my schematic also work for Bernards, so I suspect you're good to go.

    On the one I drew there is a delay from the push button, and the second timer controls how long the relay would be on.
     
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