1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Need a timer diagram?

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

  1. duffy

    duffy New Member

    Joined:
    Dec 22, 2008
    Messages:
    2,618
    Likes:
    73
    Location:
    nortern 'sconsin
    Not THAT robust or it wouldn't... wait, how far is the circuit from the power supply and what kind of wire are you using?

    KMoffett - Yes, I thought of those - the Schmitt trigger seems the most likely and that's why I asked about the relay contacts. I'm thinking there might be a way to weasle a cap in there so the relay shifts the charge from the cap.

    Say it's an spdt to ground, motor on the NO, on the NC a parallel RC back to the base of the Darlington. Relay drops out, cap yanks charge off the base. Turns off and solidly so.
     
    Last edited: Feb 10, 2009
  2. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    It might be worth putzing with, but I think I would go with a different delay circuit entirely at this point, since there are so many other options out there.

    Ken
     
  3. duffy

    duffy New Member

    Joined:
    Dec 22, 2008
    Messages:
    2,618
    Likes:
    73
    Location:
    nortern 'sconsin
    Yeah, I mentioned the friendly TDR early on, but here we are.

    In the attachment is what I'm thinking. Question is: what would the values of C2 and R4 be to stop the chatter, yet still allow it to turn on? The caps will divide down the initial voltage for the base, but if c2 was, say, 47µf, that would still give us 8V to drive the resistor network to the base... relay kicks it, C2 discharges through R4, C1 discharges through R2 and C1. R4 needs to always discharge faster, so make R2 = 220k.

    Transistor sails on wobbly legs through the linear sea to the shore of can't-quite-manage-the-relay current. Relay cuts out, motor cuts out, C2 cuts in. The dischargesd C2 immediately subtracts a third of the charge from C1, and the circuit stays off in spite of the boost of 2V from Vcc without the motor load.

    Make sense?
     

    Attached Files:

  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. btcg

    btcg New Member

    Joined:
    Jan 31, 2009
    Messages:
    63
    Likes:
    1
    Location:
    Earth

    Here's a few links for the circuit "Duffy" drew:


    http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#delay.gif

    http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#relay_i.gif


    Bowden's Hobby Circuits

    Great pages!

    I'll look for it later, but somewhere I've got a few Popular Electronics from the 1960's that feature a few articles that are pretty much the same thing, written by Don Larsen.
     
  6. duffy

    duffy New Member

    Joined:
    Dec 22, 2008
    Messages:
    2,618
    Likes:
    73
    Location:
    nortern 'sconsin
    No, that first one is off, then turns on. It also has some funky reverse base-emitter thing I wouldn't trust - but a zener to boost the cut-off voltage higher is a good idea. Get it up more out of the flat region on C1's charge curve.

    The second one requires a contact to an ignition switch, no help there.
     
  7. jaganathan.k

    jaganathan.k New Member

    Joined:
    Feb 10, 2009
    Messages:
    1
    Likes:
    0
    please refer
    1.555 Ic datasheet and its application
    2.74hc4538 datasheet and its application
     
  8. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    I think I will try the dual power trick next, where the supply voltage is not the same as the load.
     
  9. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    I used both of those circuits in series, in my table-saw/shop-vacuum system. The delay-on-start circuit delays the start of the shop-vacuum, when the table saw starts, so I don't have two large motors starting simultaneously. The delay-on-break circuit keeps the vacuum running for a few seconds after the saw is shut off, and as the saw spins down, continuing dust collection. They have been working flawlessly for 5 years. In mine, the circuits drive small relays to assuring positive on/off switching of the LED in an SSR. Now, I would use an 8-pin microprocessor.

    Ken
     
    Last edited: Feb 11, 2009
  10. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    Guys, Thanks for all the help. However, I am going to have to go with a ready made product. I found a seconds timer custom made for this project.

    MistKing :: Misting Accessories :: Seconds Timer

    I thought I could get away cheaper by making my own, but the cost of all the parts I have gone trough I could have bought like 3 of these. Oh well. On to the next project.

    Thanks again for all your help.
     
  11. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    Looks like a solution! :)

    But, thanks for the problem/solution discussion opportunity. I hope you picked up some usable stuff, and not feel reluctant to dive in again. I always feel like I get more out of these than I put in. :D

    ken
     
    Last edited: Feb 11, 2009
  12. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    Well, I have one thing to try. Being as I have these parts... Is there a way to make a very simple circuit that when you apply power it has an output that generates a ground for a brief second then goes high and stays that way? (basically mimicking a momentary push button to ground.)
     
  13. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    zone,

    Yes. Are you think of a logic circuit or a power circuit? Voltage? Current? Time?

    Ken
     
  14. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    The circuit will have a 12v source @2amps, The time it needs to get to ground should be fast, the time it stays at ground should be short. The Diagram for the main device is Here (traced out the device, so it may not be 100% accurate) The trigger is what I need to get around. I paid like $25 for this crappy little thing I would like to make use of it.. :)
     
  15. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    I redrew your circuit...and it won't work the way it's drawn. Do you have a link to where you purchesed it? It looks like its supposed to be a time delay relay, triggered by a brief ground on the input. Is your input trigger supposed to be +5V>GND>+5V (your symbol) or just OPEN>GND>Open at power-up?

    Ken
     
  16. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    OPEN>GND>Open

    [​IMG]

    The Item came from canada, and was bought on ebay. I can take some Hi res photos from the bottom if that would help.

    Update: Left side is input from top down its -v trigger +v
     

    Attached Files:

    Last edited: Feb 12, 2009
  17. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    Can you add a component side shot? Did it come with any kind of documentation?
     
  18. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    Added to the underside post.
     
    Last edited: Feb 12, 2009
  19. KMoffett

    KMoffett Well-Known Member

    Joined:
    Oct 5, 2007
    Messages:
    2,497
    Likes:
    58
    Location:
    Minnesota, USA
    The circuit you drew would be OK if the transistor were an PNP instead of the 2N5088, a NPN. It's somewhat similar the circuit that duffy posted, early on.
    Because the trigger input needs to rapidly charge the capacitor C2 and then open, the easiest way would be another relay arranged as a monostable. The timing would depend on CX and the relay coil resistance.

    Ken
     

    Attached Files:

  20. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    The coil is 400Ω However I can not use a resister across +v and -v as the source is 2amps and would burn up anything I had, plus it will limit current to the motor. (it needs as much power as can be delivered.)
     
  21. zone97

    zone97 New Member

    Joined:
    Jan 28, 2009
    Messages:
    48
    Likes:
    0
    What I may do it get an automotive relay, and just hook it directly to power at startup and the trigger to nc just like above. It may do the same thing and not burn up.
     

Share This Page