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BOE bot I/O pins and current — Parallax Forums

BOE bot I/O pins and current

ArchiverArchiver Posts: 46,084
edited 2000-08-05 00:29 in General Discussion
Hi guys,
I recently got a boe bot, and now that I've zipped right through the
experiments, I've got lots of ideas to try out. First question: I've heard
that if there's too much current draw/sink/something like that, the I/O
pins (and therefore the stamp) can be damaged. Is this true? If so, how do
you prevent this?

Second question: What is current sink and draw? I'm confused. :-)

Lastly: I know that servos such as the ones in the boe bot are designed to
run off of 4-6 volts (at least that's what my r/c airplanes battery packs
feed them.) Is if OK to run them off the 9 volts that come from the VIN or
should I hook it up to the VDD (regulated to 5 volts) on the boe? The
reason I ask is because on the boe you have a choice between connecting a 9
volt battery or 4 AA cells, and I've got a lot of 9 volt batterys and very
few AAs.

Thanks for putting up with my newbie questions!
Mike Ball, AKA Flaming Headphones

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2000-08-04 03:45
    Mike,
    the bs2 I/O pins can 20mA and sink 25mA each. You will have to use NPN
    transistor switching if you require the use of a lot of output pins. Use
    the Vdd to source your servo(s) but you may want to make sure that your amp
    draw is in the exceptable range for the output of the Voltage Regulator that
    you are using.

    Original Message
    From: Flaming Headphones [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=iCQoxDDyYbPQ3HE4v8_-ypWKn37voR02z4FXcLyGZ6K-WcTNck1_K7GrrtVofoeZNJKZAlLTEb531MmMN96_qRg]headphones99@i...[/url
    Sent: Thursday, August 03, 2000 8:58 PM
    To: basicstamps@egroups.com
    Subject: [noparse][[/noparse]basicstamps] BOE bot I/O pins and current


    Hi guys,
    I recently got a boe bot, and now that I've zipped right through the
    experiments, I've got lots of ideas to try out. First question: I've heard
    that if there's too much current draw/sink/something like that, the I/O
    pins (and therefore the stamp) can be damaged. Is this true? If so, how do
    you prevent this?

    Second question: What is current sink and draw? I'm confused. :-)

    Lastly: I know that servos such as the ones in the boe bot are designed to
    run off of 4-6 volts (at least that's what my r/c airplanes battery packs
    feed them.) Is if OK to run them off the 9 volts that come from the VIN or
    should I hook it up to the VDD (regulated to 5 volts) on the boe? The
    reason I ask is because on the boe you have a choice between connecting a 9
    volt battery or 4 AA cells, and I've got a lot of 9 volt batterys and very
    few AAs.

    Thanks for putting up with my newbie questions!
    Mike Ball, AKA Flaming Headphones
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-04 23:55
    the terms source and sink are explained thus as fallows: any device is
    limited in the amout of current it can supply to an external circet or how
    much current it can source. also a device is limited in the amount of
    current it can pull out of a circet or how much it can sink . when a stamp
    is providing a positve voltage to some external componits the current flow
    is a source flow. and conversly when some external componits are providing
    voltage to the stamp io pins the stamp is sinking the current.

    i have not tried to run servos higher than 6 volts some options are:

    1. find the specs from a hobby store/ servo packaging/ off the web
    2. try and find out if it burns up (destructive testing)

    the higher the voltage that you run the servo at the more torque the servo
    will output so a third option if the servos won't react well to the 9vdc is
    to add a small 6vdc or what ever power supply being fed from the 9vdc

    lw


    >
    <
    Hi guys,
    I recently got a boe bot, and now that I've zipped right through the
    experiments, I've got lots of ideas to try out. First question: I've heard
    that if there's too much current draw/sink/something like that, the I/O
    pins (and therefore the stamp) can be damaged. Is this true? If so, how do
    you prevent this?

    Second question: What is current sink and draw? I'm confused. :-)

    Lastly: I know that servos such as the ones in the boe bot are designed to
    run off of 4-6 volts (at least that's what my r/c airplanes battery packs
    feed them.) Is if OK to run them off the 9 volts that come from the VIN or
    should I hook it up to the VDD (regulated to 5 volts) on the boe? The
    reason I ask is because on the boe you have a choice between connecting a 9
    volt battery or 4 AA cells, and I've got a lot of 9 volt batterys and very
    few AAs.

    Thanks for putting up with my newbie questions!
    Mike Ball, AKA Flaming Headphones

    Lincoln J. Worsham
    liworsha@g...
    Neuro Engineering Laboratory
    NASA Ames Research Center MS 269-1
    Moffett Field CA 94035-1000
    Phone 650-604-0461
    Fax 650-604-3594

    http://www.arc.nasa.gov/computing.html
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-05 00:29
    It's been my experience that servos don't hold up well at 9 volts,
    although they work well at 6 volts (and you get a bit more power than at
    4.8V). Can you just step the 9V down to six with a 6 volt regulator (7806)?

    Hope this helps, Duncan
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