DC motor reversing - N.O. momentaries

Discussion in 'The Projects Forum' started by PureWhiteWings, Jan 3, 2011.

  1. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    Well, I think I've used up my annual brain allowance on this one. =\

    I've got a 12v DC motor, two N.O. momentary switches, and a 12v power supply - pretty simple list of equipment. What I need to figure out (and get a parts list for) is how to get a circuit that will reverse the motor depending on which switch is pushed, with no power reaching the motor with both switches off.

    Bullet point version:
    • Button 1 = Forward
    • Button 2 = Backward
    • No button = Stop

    My only stipulation is that I'd like to keep H-bridges out of it due to the cost of obtaining them - I have relays piling up like mountains around here, so a solution using them would be best.

    Thanks in advance for the help!

    EDIT: Sorry, I forgot to mention that I've searched the forums, but haven't been able to get anything definitive working in my head.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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  3. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    Thanks for the link, but I've seen that one before, and I don't have a third switch to put in the circuit, nor is it desirable in this situation.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    You can use only two SPDT relays.

    Connect the motor on the Commons.
    Connect relay1 and relay2 NO to V+.
    Connect relay1 and relay2 NC to V-.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
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    What does your motor draw (I)?
     
  6. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    The problem with using two SPDT relays is - unless I'm totally missing something - when the switches are released, the motor will continue to spin, not the desired application.

    CDRIVE: If I recall correctly, 300ma.
     
    Last edited: Jan 3, 2011
  7. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    Anyone got any sort of idea?
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,649
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    Hello,

    Do you only need two pushbottons, one forward drive, one reverse drive?
    Do you also need endstops?

    Bertus
     
  9. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
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    Here is a relay H-Bridge.

    relay hbridge.jpg
     
  10. debe

    Well-Known Member

    Sep 21, 2010
    947
    184
    With only 300Ma current cant see why a H bridge IC is a cost factor as ive got probably 20 various types that handle 1 to 1.5A for free. They were obtained from older VCRs that were thrown out & there was usually 2 in each machine. All you need is the IC & your 2 switches.
     
  11. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    Haha, this is why I'm glad you guys are around, because you think of things I totally miss. :D

    I've got a couple old VCRs lying around, guess I just have a long way to go until I've got the right mindset to tackle harder stuff. I'll rip an H-bridge out of one of those and see what I can throw together with that. I'll report back on what I come up with.
     
  12. debe

    Well-Known Member

    Sep 21, 2010
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    184
    Some to start looking for BA6209. BA6418N. M54543L. TA7267. To go in one direction on IC in pic, pull P1 hi motor goes in one direction while button pressed, release stops. Pull P2 hi motor goes in other direction & stops when button released. Warning dont bush both buttons at the same time will blow the chip.
     
    Last edited: Jan 4, 2011
  13. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    By now I'm sure that you've seen the link to Sgt.Wookie's circuit (posted by BillB3857) which clearly disproves that assumption. Less the limit switches, it's exactly what you asked for. ;)
     
  14. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    I figure it'll be a learning experience to go the fun route and try to rip an H-bridge from this VCR. Problem being, there's a ton of chips on this board, and none of them match the ones listed up above. I mean, there's gotta be one in here somewhere, right?
     
  15. debe

    Well-Known Member

    Sep 21, 2010
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    The machines i wrecked were 1990s vintage mutch newer ones may have one mounted by the motor driving the cassete cariage mechanism. I had a shed full of 1980s to end of 1999 machines to throw out but i chose to dismantle them for lots of usefull parts.
     
  16. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
    12
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    I'll dig around more inside today and look up datasheets at the very least. The two I have are both 1989, but I dunno if that makes much of a difference.
     
  17. debe

    Well-Known Member

    Sep 21, 2010
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    Do you have manufacturer & model Number?
     
  18. PureWhiteWings

    Thread Starter New Member

    Jan 2, 2011
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    Okay, sorry it took so long, but life happened and I had no time to sit around and pull chips. The closest thing I've found so far is an AN3814K motor driver IC (datasheet attached as image). I don't know if this'll do it (I don't see how), but I tend to miss things when we start to delve into ICs. There's also more ICs whose function I haven't determined in the second one, but one VCR I know for a fact didn't have an H-bridge IC, or anything that turned up even as similar.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you happen across an L272, L2722, or KA334 - they are power opamps that could be used as an H-bridge for a low-power application like yours.

    You'll get some loss of power due to the saturation voltage of the opamps' output.

    ST Microelectronics' datasheet for the L2722 has a schematic for microcontroller control of a small DC motor:
    [​IMG]

    You could do something similar with switches instead of microcontroller inputs.
     
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