Simple Circuit to Reverse Pos Neg Leads from battery?

Discussion in 'The Projects Forum' started by Gamedojo, Mar 17, 2015.

  1. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    Hello everyone,

    I work for a Point of Sale display company and we have a need for a circuit that can control how a battery connects to a small motor. We need the motor to move right for a small time, then reverse direction.

    I have proposed we use a simple circuit to reverse the polarity of the power from the battery and then after a specific amount of time, reverse it back...and so on and so on forever.

    Can any of you guys point me in the right direction? Can this be done simply with diodes and capacitors, or will a programmed Op Amp be needed?

    I am a novice, so be kind.

    Thanks!

    Tyler
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    if its a small dc motor, you can use a 555 timer and relay.
     
  3. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    yes, very small motor.

    ... Is there any schematics you might be able to point to? Thank you SO much for the quick reply.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are a whole raft of previous posts here that do exactly this.
    Max.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
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    Dodgydave likes this.
  6. Dodgydave

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    Jun 22, 2012
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  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also do you need end stops, or does it matter if it over runs, i.e. no physical stop present??
    Max.
     
  8. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    Whats happening is a "head" is turning left and then right. there is no absolute location it must stop before reversing, but it would be a good idea to have it in the same place each time so the head doesn't go too far over time.

    (I have to thank all of you for such fast and informative responses! Quite an amazing forum!)
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You can put a 2 limit switches in series with the motor leads, one at each end of travel, a diode across each allows reverse without anymore switching.
    Max.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Or forget all that and just do it mechanically..
    Back and forth can easily be accomplished with the motor turning in one direction only..
     
  11. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    We are exploring the mechanical option as well, but it gets far more complicated and the more moving parts you have the greater the risk of failure. An electronic option would also be far cheaper.
     
  12. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    best solution is to use the timer for the motor as a flip flop, with a limit switch at each end of the turn, this would flip the direction of the motor

    555.png
     
  13. Evil Lurker

    Member

    Aug 25, 2011
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    Since you are running a POS you should already have an MCU running the thing and hopefully a couple free ports. I'd consider going with a small stepper motor maybe powered by an off the shelf $3 L293 or some other driver or if it is a regular brushed DC motor a dedicated driver IC similar to those used in cassette, CD-Rom, and VCRs where all you have to do is send a drive signal to the chip. I myself have an LB1943 from my junk pile that I have been playing with... shouldn't be too hard to get something similar.

    http://www.datasheetcatalog.com/datasheets_pdf/L/B/1/9/LB1943.shtml
     
  14. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    Circuit doesn't work... probably an error on my end, Here is the layout I created for my construction. When I hook it up, the motor runs, but doesn't switch... I also think I smelled some burning smell, so somethings not right:

    [​IMG]
     
  15. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    your motor is not on the wipers of the relay, looks like your supply shorts out, is pin 3 changing output going high and low, if so the 555 is working, if not oh dear.....
     
    Last edited: Mar 19, 2015
  16. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    Here is a pic of the relay. The wiper seems to be on the right side not the middle:

    [​IMG]
     
  17. Dodgydave

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    Jun 22, 2012
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    ok, get a voltmeter on pins 1& 2, is it rising and falling,and is pin 3 changing output. Also looks like the transistor is drawn wrong, C E reversed.
     
  18. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    voltmeter with neg on "1" and Pos on "2" reads a slow increase in voltage slowing down at around 4-5v. So its not rising and falling.

    As for the transistor, I'm not sure why you think its backwards. The Emmiter connects to the diode and the Collector goes straight to Positive battery terminal.
     
  19. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Your using the transistor as an Emitter follower, thats ok , pin 2 rises upto 2/3 supply then discharges to 1/3, what is the supply voltage and is it a power supply or battery.
     
  20. Gamedojo

    Thread Starter New Member

    Mar 17, 2015
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    As I said, pin 2 is not dropping...

    power supply is 8 D Batteries at 12v
     
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