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Activity Bot Encoder Question — Parallax Forums

Activity Bot Encoder Question

ajwardajward Posts: 1,129
edited 2015-03-07 02:30 in Robotics
Me again!

Activity Bob!

USPS delivered my encoders and wheels this afternoon. Yay! (Thanks again to Parallax for their fast order processing!!!!!!!)

Anywho, everything is connected 'n waiting for the first programming. I went back to the Activity Board because I couldn't see any easy way to connect the encoder pins I was using to 3.3 volts like in the assembly guide.
NOW my question... why do pins 14 and 15 have to be connected to 3.3 volts?

I'll probably have more questions as I go on.

Amanda

Comments

  • Hal AlbachHal Albach Posts: 747
    edited 2015-03-06 14:34
    The Electrical Connections page of the Activity Bot Web Tutorial indicates that the encoders are to be plugged into Servo positions 14 & 15 and the jumper be set to 5 Volts. 3.3 is not available at the servo connectors, just Vin or +5.
  • twm47099twm47099 Posts: 867
    edited 2015-03-06 14:50
    Amanda,
    The link below has the instructions for building the ActivityBot.

    learn.parallax.com/activitybot

    The section on electrical connections says to set the jumper for P14/P15 servo port headers to 5v. Note the connections for the 20kohm resistors between P14 and P15 at the back of the breadboard to the 3.3v bus at the left of the breadboard.

    Tom
  • ajwardajward Posts: 1,129
    edited 2015-03-06 21:02
    twm47099 wrote: »
    Amanda,
    The link below has the instructions for building the ActivityBot.

    learn.parallax.com/activitybot

    The section on electrical connections says to set the jumper for P14/P15 servo port headers to 5v. Note the connections for the 20kohm resistors between P14 and P15 at the back of the breadboard to the 3.3v bus at the left of the breadboard.

    Tom

    @ Hal & Tom: Yep... I got that. Read the instructions. Encoders connected to servo ports14 & 15, set to 5VDC and "breadboard pins" 14 & 15 connected to 3.3VDC through 20K resistors.Things mostly work. But, why the connection to 3.3 volts through the resistors? The instructions don't 'splain that. :-)

    Amanda
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2015-03-07 02:07
    The sensor used by the encoder has an open-collector output. So it needs to be pulled up to 3.3V to register a "high" when the output is not being pulled low.

    -Phil
  • ajwardajward Posts: 1,129
    edited 2015-03-07 02:30
    Phil Pilgrim (PhiPi) wrote: »
    The sensor used by the encoder has an open-collector output. So it needs to be pulled up to 3.3V to register a "high" when the output is not being pulled low.

    -Phil

    Ah... thanks Phil! While I don't completely understand the concept, I have a reason for it being done. It irks me when an odd instruction "do this" and there's no "because' following it. :-)

    Amanda
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