Intermittent Relay...

Discussion in 'Homework Help' started by aq_rules, Feb 10, 2010.

  1. aq_rules

    aq_rules Thread Starter Member

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    Hey,
    These Days I was working on a home work project, its a team work,our task was to turn a simple car into a completely sensor loaded car...well our car is equipped with all the sensors which were required but now we want to place a wiper on the rear glass(windshield,i dun noe ny better word for this)....we are done with the fitting nd all other procedures but now what we want is an intermittent relay switch circuit which turns on the wiper for 2 seconds and stops for 5 seconds and repeat the cycle until the switch is turned off.....i hope u guyz getting this...

    It would be better if u guys would upload some schematics....i want a simple schematic which only have the electronical components and a relay,not the wiper motor nd all those things, because i'll simply connect the loose wires which i've left under the cars steering...so i'd like to see the basic circuit diagram....

    Plzz help..
  2. beenthere

    beenthere Retired Moderator

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    You can always use a 2N2646 UJT as a relaxation oscillator that trips the relay. Jameco still carries them.
  3. aq_rules

    aq_rules Thread Starter Member

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    plzz cn u give a lil more explaination
  4. beenthere

    beenthere Retired Moderator

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  5. aq_rules

    aq_rules Thread Starter Member

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    yea i noe that:p:p....found nothing there thts y m here...
  6. beenthere

    beenthere Retired Moderator

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    Okay - put base1 to ground and place the relay coil between +12 volts and base 2. When the UJT fires, the wiper will start a cycle.
  7. aq_rules

    aq_rules Thread Starter Member

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    one more question....how will i set the timer?? of 2 and 5 seconds...2seconds on and 5seconds off...
  8. Ron H

    Ron H E-book Developer

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    A 555 would be a lot simpler. This sound like a job for...

    Bill Marsden!

    Bill, where are you, boy?:D
  9. aq_rules

    aq_rules Thread Starter Member

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    yea bill, plz help, where r u???
  10. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    I just back from work (OT), when I get a chance I'll see what I can do. I've been catching up on the forum whilst eating my raisin bran.

    How long do you want it to stay off as a maximum duration?

    A suggestion, go through my various threads and blog, and see what comes closest to working for you. When I get back I'll help out, either tweaking your solution or suggesting something I think is better. This way you get some practice designing. It is more than half the fun I think, and if it works you get bragging rights (if it doesn't it's my fault :D).
  11. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    Quick question, did this start off as a working windshield wiper? In other words, does it finish a cycle if you turn the wiper off before it has finished moving?

    PM is the way to go contacting me. I don't handle technical questions via PM, but I usually honor requests to look at a thread and give feedback. I suspect most of the guy around here do that.

    It is now my bed time, I work vampire hours (go in to work at 10PM, get off at 7AM).
  12. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    OK, let me break this problem down, you need a waveform something like this...

    [​IMG]

    The fixed duration is around 1 second, the variable can be from ½ seconds to 10 seconds (or more).

    A standard 2 resistor 555 astable produces the inverted version of this waveform. This is not really a problem though.

    I do not know the circuit of the intermittent wiper motor. I can only assume it has power to allow it to finish a wipe, and a switch input to allow it to turn on. In other words, 3 wires. I would probably go this route...

    [​IMG]

    I pulled and modified the schematic from my cookbook sections in my blog...

    http://forum.allaboutcircuits.com/blog.php?b=381

    CR1 basically separates the time on from the time off, each resistor controls one or the other. It messes with the math a little, but overall the effect is worth it.

    Attached Files:

    Last edited: Feb 14, 2010
  13. Ron H

    Ron H E-book Developer

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    Bill, is CR1 backward? It shorts out R2 during discharge.
  14. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    Yes, it was. Fixed now. Thank you.
  15. Ron H

    Ron H E-book Developer

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    Bill, I'm not intending to nitpick here. I think your drawings would make a lot more sense if you made a few changes. As it was, your timing diagrams were confusing to me. Attached are my suggestions, with the changes circled (ovalled?) in red.

    Attached Files:

  16. Ron H

    Ron H E-book Developer

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    No comment? Am I FOS?
  17. retched

    retched AAC Fanatic!

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    Father Of Satan?
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    I haven't seen Bill around at all today...yet..
  18. Ron H

    Ron H E-book Developer

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  19. JoeJester

    JoeJester AAC Fanatic!

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    Ron,

    The changes you recommended are warranted.
  20. Ron H

    Ron H E-book Developer

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    Thanks for the feedback, Joe.
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