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12v from servo ports — Parallax Forums

12v from servo ports

neotericneoteric Posts: 144
edited 2006-01-09 22:03 in Robotics
OK, spent the morning reading about the servo ports.· On the BOE board, it appears you can set them to output raw power.· (Such as the 12v I have the board hooked to.)· However, I cannot seem to understand how this is done.· The center pin on the servo ports·appear to put out 12 volts nomatter how I set the pins in pbasic.· I have tried to research this question before I have posted....

All I am trying to do is get my standard 12V motor to go forward.

(You may have noticed I have a similar post here also.)· I am experimenting this week, because I have a little free time.· Sorry for all the questions.· I promise I have spent quite a bit of time answering many of these questions on my own before I ask....

[noparse]:)[/noparse]

Comments

  • Jon WilliamsJon Williams Posts: 6,491
    edited 2006-01-07 19:36
    If you look very closely at your BOE (assuming Rev C) you'll see a jumper between the P13 and P14 servo ports -- this jumper selects the center pin voltage.

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    Jon Williams
    Applications Engineer, Parallax
  • neotericneoteric Posts: 144
    edited 2006-01-07 19:56
    Thanks for helping.· However, I still don't understand.· How do I turn this voltage off, in order to turn off the device.·

    I am aware of the jumper.· One protects the servos with regulated output(5v), I beleive.· However, I am trying to put the 12v directly through.

    How do I switch the power off?· Setting pin·15 low, for example, does not seem to have an effect on it.

    Thanks.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-07 20:58
    I think you misunderstand how the servo ports (And possibly servos) work.· The pulse width on the Signal line controls the servos, not the voltage to the center pin.· If for some reason you wanted to disable it (Which I don't understand why), you could connect a relay between the center pin of that voltage jumper block and the Vin pin that you are jumpered to now.· But remember, if you kill the power to the servos that way they cannot maintain their position.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • dandreaedandreae Posts: 1,375
    edited 2006-01-09 20:15
    If you want to turn off just the servos you can switch the power switch to position one and it will disable the servo headers.

    Dave

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    Dave Andreae

    Tech Support
    dandreae@parallax.com
    Http://www.parallax.com



    Post Edited (Dave Andreae (Parallax)) : 1/9/2006 8:19:26 PM GMT
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-01-09 22:03
    Note that a "standard 12 volt motor" is NOT a 'servo'. A 'servo' is a small device used for controlling airplane control surfaces via radio control. It contains a comparator, a small motor connected to an output shaft and a variable resistor with some gears. The BS2 uses a control signal to that comparator to set the position of the servo.

    This is VERY different from "a standard 12 volt motor". Most servo's would be destroyed by 12 volts, for one thing.

    Usually, to control a 'real' motor, you need some Pulse-Width-Modulation (PWM) source to control speed, and several transistors to route power to the motor. The servo connection is NOT going to do it.

    Look up PWM and "H-Bridge". An "H-Bridge" is that set of transistors I was talking about.
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