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Motor control via parallel port?

Discussion in 'Electronic Basics' started by mike, Dec 13, 2003.

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  1. mike

    mike Guest

    Hi,

    Trying to control a 12V 5A motor from the parallel port. I have to control
    ten of them, so I'm trying to get away without using expensive relays or
    optoisolators ($20-$30 each). I found a monolithic darlington transistor
    rated at 10 amps, already including reverse-current diodes and appropriate
    resistors, perfect for my application (so it seems).

    I'm planning on hooking up a low current cheap optoisolator/interrupter to
    drive this transistor from the parallel port (albeit high voltage isolation)
    so I have a good chance of not frying the computer if one of the motors
    overheat or blows. Would this work for my application?

    Any help would be appreciated.

    Please see:

    http://rocky.digikey.com/WebLib/Fairchild/Web Data/TIP140_141_142.pdf

    Thanks!
     
  2. Those darlingtons are marginal on their current capability. It is
    true that under some conditions, they can stand a 10 ampere current,
    but the gain curve that just makes it to 10 amperes specifies that
    there is 4 volts across the device. Are you willing to have your 12
    volt motor supply waste 4 volts across the transistor when the motor
    draws 10 amperes? A motor rated for 5 ampere drain will allow quite a
    bit more than 5 amperes pass during start up or stall. I would look
    into finding a big MOSFET to do the switching. One with an on
    resistance of less than (4 volts / 10 amperes)= 0.4 ohms would beat
    the darlington. For example, the NDP603AL has an on resistance of
    ..022 ohms which would waste only .022*10=.22 volts during a 10 amp
    surge. It is rated for 25 amps continuous duty, 100 amperes peak. It
    sells for $.087 each if you order 10 from Digikey.
    http://www.fairchildsemi.com/ds/ND/NDP603AL.pdf

    One other point... The diode that is internal to this device will not
    protect the device during turn off. This protects the device from
    applied reverse voltage. The motor produces a reverse voltage when it
    is switched off, but this reverse voltage effectively adds to the 12
    volt supply so as to increase the total voltage applied to the switch,
    not reverse it. You will need additional diodes, one across each
    motor, to clamp the reverse voltage they create. But the total energy
    is pretty small (if the motor doesn't get forced to turn backwards) so
    a 1 amp diode (1N4000) is probably plenty big.
     
  3. Si Ballenger

    Si Ballenger Guest

    You can get the transistor from radio shack and make a test rig
    using three 1.5v batteries in series (~4.5v) going through a 2.2k
    resistor (~2ma current) to simulate the parallel port control. If
    you need more current through the darlington base, you could use
    a common npn transistor controlled by the parallel port to put
    some higher current in fom the 12v supply instead of from the
    parallel port.
     
  4. Ian Stirling

    Ian Stirling Guest

    Another nice thing about MOSFETs is that if you don't care about speed
    (and with motors, you don't much) you can reduce or eliminate the
    need for a diode by picking the series resistor appropriately.
    This also reduces the likelyhood of damage to the driving gate if things
    go wrong.
    100K or so might be the right ballpark.
    (too slow, and the transistor spends too long in linear mode, and will
    heat up much. If you want to do PWM, this is a bad idea)
     
  5. the Wiz

    the Wiz Guest

    You might to get something like the 24 port controller card from
    http://www.boondog.com/

    More about me: http://www.jecarter.com/
    VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
    Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
    Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
    johnecarter [email protected] mindspring dot.dot com. Fix the obvious to reply by email.
     
  6. I would use the circuit of Fig C in the following URL.
    http://ourworld.compuserve.com/homepages/Bill_Bowden/r_ctrl.htm
    But with the motor in place of the relay. This is similar to a
    Darlingtom, but not the same, because the collectors are not tied
    together. This is important to minimize the power dissipation of the
    power transistor.

    Also, remember that a relay is good for an isolator to keep the
    voltages and currents on the contacts out of the PC. You can run
    240VAC thru the contacts and not have to worry about it getting to the
    PC side of the relay.



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  7. That's not what I see. The Digikey prices show $8.70 for ten.
    Even the mediocre IRF510 - which I believe is still avaiable at Radio
    Scrap - would do a halfway decent job. And you could parallel two of
    them. http://www.ee.nmt.edu/~wedeward/EE443L/FA99/IRF510.pdf
    A 1N4000 is a 7.5V zener diode, which would burn up as soon as the FET
    turned on and applied 12V across it.


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    ###Got a Question about ELECTRONICS? Check HERE First:###
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    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  8.  
  9. I have used the Darlington array IC on a projecct I just did controlling
    some 12V stepper motors with the Parallel Port. WOrked PERFECT!
    There's some info on myy site if you click "pan/tilt webcam". good luck with
    the project!

    Mike
    http://mikebeauchamp.com
     
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