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Motor control or relay? — Parallax Forums

Motor control or relay?

aabaab Posts: 8
edited 2004-12-01 18:06 in BASIC Stamp
I need to control two 5VDC motors, I must be able to make them go both directions and preferably would prefer to be able to also slow them down.

Are there any motor controllers that would allow me to control a motor's power (on/off), direction and speed?

Also, can a basic stamp trigger a relay directly connected to one of the output pins or can it not support the power reqired to flip a relay?

If the stamp can flip a relay, has anyone tried slowing down a motor with a delay by giving short bursts of power (like 0.1 second of power every 0.5 second)? I want to make an arm that can more fairly fast and then slow down as it approaches the destination for accurate positioning (I want it to accurately stop over the center hole of a CD, reach down into the CD hole and grab it).

Thanks
·

Comments

  • NewzedNewzed Posts: 2,503
    edited 2004-11-23 23:05
    First of all, you can not trigger a realy from a Stamp pin.· You need to use a Darlington array such as the ULN2803.· You can reverse the motor providing you use a DPDT relay and have it wired so that NC if forward and NO is reverse.· You will need a second relay to turn the motor on and off.

    By using PWM or PULSOUT you can control the speed of the motor but the speed control has to be programmed in.· It is not something you can change manually, unless you use serin commands to tell the Stamp to change the PWM.· Also, the Stamp can not PWM while it is translating a serin command.


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    ·
  • aabaab Posts: 8
    edited 2004-11-23 23:24
    Where can I find solid state relays? Would those be OK to give 0.1 pulses every 0.5 seconds for precision positioning?

    Thanks
  • agentileagentile Posts: 101
    edited 2004-11-28 20:30
    Solid state relays can be found at just about any electronics house.· I'd look at digkey and mouser.· Before that, maybe look at allelectronics.com -- they have surplus stuff (lots of relays) and so you'll pay a lot less there.· I've been using Hamlin and Omron reed relays and they work well for most of my applications.· I'm not sure they would be fast enough for what you are trying to do.· Have you considered just using a transistor to drive the motors?· If the motors don't draw too much current, you could use a BJT, which could be directly driven by a stamp I/O pin.



    agentile
  • aabaab Posts: 8
    edited 2004-11-28 20:49
    Is there any such thing as a DPDT solid state relay?

    Thanks
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2004-11-28 22:08
    aab -

    They may exist somewhere, but I've never found them. The best I've seen was DPST which I suppose you could use, Two of them back-to-back would create a two coil, solid state DPDT relay. A bit expensive though, I'd imagine.

    Regards,

    Bruce Bates
  • allanlane5allanlane5 Posts: 3,815
    edited 2004-11-29 21:40
    aab:
    What you are talking about is Pulse-Width-Modulation (PWM) control of DC motors. There are *lots* of resources that show you how to do this. Typically, this is done through an H-Bridge circuit (with transistors), which allows you to apply voltage in both directions, or turn it off.

    Go to AlWilliams.com, and look for some of his PWM co-processors. You really don't need to re-invent the wheel by trying to implement this with some mythical, poor response TTL mechanical relay.
  • Tom WalkerTom Walker Posts: 509
    edited 2004-12-01 18:06
    Google "H-Bridge"...

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