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Delay "off" Timer

Discussion in 'General Electronics Discussion' started by mbost, Jan 28, 2016.

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  1. mbost

    mbost

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    Jan 28, 2016
    So, I've been searching this site (and the rest of google) for a couple days, and haven't really found anything that meets what I'm looking for. I'm a soldering tech and am good with electronics, but I don't know enough about whats out there to build the circuit diagram and parts list myself. So here's my problem.....
    I need a Timer delay circuit that can control a standard automotive relay for an adjustable amount of time ranging from 1-10 minutes (roughly). This unit will be activated by a momentary push button. The auto relay will be powering heated mirrors on my truck. So...in order of events...
    1) push momentary button
    2) timer circuit energizes, turns on a LED to show operation, and sends power to the auto relay, auto relay turns on mirror heat
    3) Timer circuit turns off and de-energizes auto relay after "X" minutes.

    Yes, I could buy a "defrost" switch from a parts store, but they're in the neighbor hood of 50-200 USD. Not worth it when I know its a simple enough circuit, and the parts are cheap. Plus it gives me something to keep my soldering skills up to date.
    Thank you all for any help.
     
  2. JMW

    JMW

    90
    3
    Jan 30, 2012
    Ebay offers dozens, various shapes sizes and capacities. Pick out several that seem to be good, you may have to contact the seller to verify what you're getting. Typically you'll buy several before you get exactly what you need. All the under $20 units come from our favorite far eastern supplier and there will be considerable language issues. But with a bit of patience you will eventually find what you need. As many of these are circuit boards, you will also need a suitable box to mount it.
    Regards, Let us Know
    JMW
     
  3. shrtrnd

    shrtrnd

    3,802
    507
    Jan 15, 2010
    You can Google circuits for what you want to do, but I'd go with JMW's solution.
    Unless you're a rabid do-it-yourselfer, why reinvent the wheel?
    There are plenty of TDR's (time delay relays) in normally open and normally closed configuration for your needs at reasonable cost.
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Me too because it's difficult to build it yourself cheaper than you can get a loaded board (nice too!) from Ebay's China stores.

    http://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=time+delay+relay+board&_sacat=0

    http://www.ebay.com/itm/DC-4-12V-Ti...213928?hash=item485ebee468:g:1EsAAOSw9N1VlYlc

    http://www.ebay.com/itm/12V-LED-Dig...128012?hash=item5b19dfe70c:g:id4AAOSwu4BVjrFF

    I chose the ones I listed because they actually included pertinent data!

    Chris
     
  5. mbost

    mbost

    9
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    Jan 28, 2016
    Because I'm nuts and enjoy headaches. :) What do you think of this circuit? How about if I ran pin 7 to pin 3? that should help it run more efficiently deliver more power. But would the circuit still work? And added a BD679 transistor from output in-between pins 3/7 to the relay?
     

    Attached Files:

  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    You can't use a single 555 to create a delay of 10 minutes and no,... connecting pin7 to pin3 isn't going to make it more efficient. It will disable it!

    Chris
     
  7. mbost

    mbost

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    Jan 28, 2016
    And that's why I'm here. I had found somewhere that stated connecting pin 3 to pin 7 did. That's why I check rather than be sorry later. Thank you CDrive. It wont run that long because of capacitor decay I'm guessing?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,480
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    Jan 21, 2010
    Check the resource on long duration timers. I think there may be some pointers to useful circuits, but I agree it will be cheaper to buy. But hey, if you want to build something it's not too hard.
     
  9. mbost

    mbost

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    Jan 28, 2016
    I enjoy building stupid things for no good reason, when I have time. Which doesn't happen very often. But its always fun to learn and experiment anyway. I have found several schematics that run in excess of 10 minutes, up to several hours. But, they are off before they turn on, and are operating buzzers and led's. Thank you steve. Ill take a look.
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    mbost, first off I forgot to welcome you to EP, so here it is...

    Welcome to Electronics Point!

    OK back to your project. The reason I said you can't milk 10 minutes out of a single 555 is because electrolytic caps leak. When using large values like your schematic has (1000uF) the timing will be very erratic and unreliable. Sometimes it may not time out at all or sometimes prematurely, especially in the harsh noisy environment of the automotive world, where it will be exposed to extreme temperatures, among other things.

    To extend a 555's limits you can use decade divider logic blocks or even a 4017 counter. A long time ago there was one manufacturer, I think it was Maxim, that offered a 555 + two decade counters on a single chip. They easily handled a 10 minute interval.

    In any event the timing cap should be ceramic disc types for short intervals and Tantalum caps for long periods.

    Chris
     
  11. mbost

    mbost

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    Jan 28, 2016
    Thank you Chris, that's the info I was looking for. As I mentioned I've found several 1-10 minute timers utilizing the 555. This particular one came form a book "50 circuits with the 555". I did find a different circuit with a 1M variable resister and a 220uF cap, but I keep thinking that large a resistor may not even charge the cap. I knew the Tantalum caps were better, (remembrance from A&P school, lol) so that's what I had spec'd out. I've been looking over these circuits for over a week, and it seems every single website/book has a different idea of what they are capable of doing and for how long. That's why I came here. I am by no means a electrical guru, I just solder really well and enjoy learning this stuff.
     
  12. mbost

    mbost

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    Jan 28, 2016
    Is this more like what you're talking about?
     

    Attached Files:

  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Yes, that's exactly what I'm talking about. I especially like the latch circuit. It prevents the circuit from drawing any current until S1 is depressed.

    Good job of searching!
    Chris
     
  14. mbost

    mbost

    9
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    Jan 28, 2016
    Cool. Had to modify my search to find it. Because I'm only going 1-10 minutes, I can eliminate C2 correct? Shouldn't pin 5 have a .01uF cap as well? Than you again for your help.
     
    Last edited: Jan 29, 2016
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
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    May 8, 2012
    Yes and yes. You will also need to add 1000pF and .01uF to .1uF caps between the V+ lines and GND (close to the supply pins) of both chips. This is because the automotive environment is like shoving a chip up your colon! It's a nasty, inhospitable place for electronics!! In fact you may have to add a small resistance like 10Ω between the chips V+ to the normally off node of S1. This will further help in keeping electrical noise out of your circuit.

    Chris
     
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  16. mbost

    mbost

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    Jan 28, 2016
    Thank you again. :) I'll update as I go.
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    If you have any questions don't hesitate to ask. We are very friendly here.

    BTW, what's your name? As you can see my Mom and Dad didn't name me CDRIVE. ;) Come to think of it no one has ever asked me where that handle came from.

    Chris
     
  18. mbost

    mbost

    9
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    Jan 28, 2016
    No problem. I just figured you were a microsoft programmer. LOL. My names Logan.
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Hi Logan. Just in case you need it. The 10Ω can be >=1/4W and the caps should be rated 25 to 50VDC.
    Chris
    upload_2016-1-29_20-37-3.png
     

    Attached Files:

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