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Re: [SeattleRobotics] OOPic -- I2C -- PCF8574

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  • Steve Smith
    Charlie, Yeah, got that base covered. I am able to address each of the three....56, 57 and 58...that works fine. I talked about this enough that I got it
    Message 1 of 9 , Apr 30, 2002
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      Charlie,

      Yeah, got that base covered. I am able to address each of the
      three....56, 57 and 58...that works fine.

      I talked about this enough that I got it sorted out today.

      I now have common anode 7 seg displays instead of the common cathode
      type. I wired it up so that it goes +5 volts...through a resistor to
      the common of the 7 seg display. From there, each segment goes to one
      I/O line on the PCF8574. And from the I/O line to ground through the
      chip to complete the circuit.

      It's funny but the PCF8574 inverts the outputs....so I actually set the
      values to "0" to turn on a segment.

      But this worked perfectly. I've had this running over and hour --
      three digits -- no hangs.

      I mapped out the segments that need to be on for each digit....and so I
      can display whatever number I like very easily.

      I'm dense...it took me 2 weeks and a lot of conversations to get to
      this point. But it works quite well. Very quick. I have to put in
      an OOPic delay between lines or you can't see it count up....it's a
      blur. And that's exactly what I wanted. I'm going to set these
      values with an encoder....so it needs to be quick to avoid any lag from
      the user's inputs.

      Thanks for everyone's time and efforts.

      Steve

      > Steve,
      >
      > Have you set each PCF8574 to a different device address? You need to
      set
      > the A0, A1 and A2 pins to different values. There is a chart in the
      > datasheet. If the devices are at the same address then things could
      act
      > strangely.
      >
      > Charlie Heath
      > Ithaca, NY
      >
      > ----- Original Message -----
      > From: "Steve Smith" <steve@...>
      > To: <SeattleRobotics@yahoogroups.com>
      > Sent: Tuesday, April 30, 2002 10:14 AM
      > Subject: [SeattleRobotics] OOPic -- I2C -- PCF8574
      >
      >
      > >
      > > Hey guys.
      > >
      > > Anyone have any experience with the PCF8574 ?
      > >
      > > I'm trying to use this chip to communicate with the OOPic via I2C.
      I
      > > have no problems getting that to work. But I want to drive a 7
      segment
      > > display with the I/O lines of the PCF8574.
      > >
      > > If I just wire the LED's from I/O pin to ground, I only get like 1.5
      > > volts and so the display is very dim.
      > >
      > > So I tried to wire them with also a 220 ohm resistor from +5 volts
      to
      > > the I/O pins.....and then I/O pin through the 7 segment
      display....to
      > > ground.
      > >
      > > This works great....nice bright display....I can control it and
      with my
      > > code display any digit I want.
      > >
      > > The problem becomes when I try to run THREE of these chips at the
      same
      > > time with three 7 seg displays. I wrote code to make the first
      digit
      > > count from 0 to 9.....then the 2nd digit.....then the 3rd. With
      one
      > > digit wired up, it works 100% of the time. Very nice. With two
      > > digits / chips....it works like 70% of the time. But it will after
      > > some random amount of time hang up.....the OOPic operation will stop
      > > until I pull power to one chip....and then the other chip / display
      > > will go back to its counting. If I try with all three digits, it
      > > hangs immediately, rarely even getting through one cycle.
      > >
      > > Convulted problem I know. If anyone has any suggestions, I would
      love
      > > to hear them. I read in the datasheet about a pullup resistor so
      > > that's what I'm trying to do between +5 and the I/O line. But I'm
      not
      > > sure if that's the proper place in the circuit for that resistor or
      not.
      > >
      > > Any ideas??
      > >
      > > Thanks for listening.
      > >
      > > Steve S.
      > >
      > >
      > > Visit the SRS Website at http://www.seattlerobotics.org
      > >
      > > To unsubscribe from this group, send an email to:
      > > SeattleRobotics-unsubscribe@yahoogroups.com
      > >
      > >
      > > Your use of Yahoo! Groups is subject to
      http://docs.yahoo.com/info/terms/
      > >
      > >
      >
      >
      > Visit the SRS Website at http://www.seattlerobotics.org
      >
      > To unsubscribe from this group, send an email to:
      > SeattleRobotics-unsubscribe@yahoogroups.com
      >
      >
      > Your use of Yahoo! Groups is subject to
      http://docs.yahoo.com/info/terms/
      >
      >
      >
      >
    • Tom Theron
      I understand you have one limiting resistor feeding the common anode of the 7-seg. This will result in difference in brightness depending how many segments
      Message 2 of 9 , May 2, 2002
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        I understand you have one limiting resistor feeding the common anode of the
        7-seg. This will result in difference in brightness depending how many
        segments you light. Rather remove the single resistor to the CA, and place a
        separate 220R in series with each LED cathode and the PCF8574 pin. You then
        get the same amount of current sink through each LED regardless how many are
        lit the same time.

        Your previous problems getting the LED's to glow is because the PCF8574 can
        sink something like 25mA per IO pin, but only sources 1mA or so, thus you
        have to do a sink configuration to get enough current through the LED.

        Your confusion about the "0" switching on the LED segment is because of just
        this same thing. In order to sink current "into" the pin, you have to make
        it low, or "0".

        Cheers
        Tom Theron
      • David VanHorn
        I d like to know if anyone can help me with an evaluation on Protel 99 SE. I m a bit leery of just trusting the sales rep, and I have to make a snap decision
        Message 3 of 9 , May 2, 2002
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          I'd like to know if anyone can help me with an evaluation on Protel 99 SE.
          I'm a bit leery of just trusting the sales rep, and I have to make a snap
          decision on new schematic and PCB tools.

          Am I going to be able to run this on both my main system and my portable?

          My main system is an Athlon 2000 with a ton of ram, running XP pro.
          My portable is a Crusoe 700 with 128M, running ME. It would be difficult,
          but possible, to change the OS.
          I have not been able to run the protel demo on the portable.


          Also, I need to know how well it integrates to Pro-E in the sense that our
          mechanical and plastics guys have to give me oddly shaped boards, with
          physical restrictions, and I need Protel to express those limitations to me
          in some rational and easy to deal with manner.

          Finally, any comments on ease of use, problems, gotchas etc would be most
          helpful.
          What I'm using at the moment is Orcad 386 (The dos version)

          I'm in Vancouver at the moment, and will be coming through seattle on
          friday on my way home.
        • David VanHorn
          Well, requirements are clarifying, and it s looking like I m going to orcad 9.2. Has anyone used this with pro-engineer to pass mechanicals back and forth?
          Message 4 of 9 , May 3, 2002
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            Well, requirements are clarifying, and it's looking like I'm going to orcad
            9.2.
            Has anyone used this with pro-engineer to pass mechanicals back and forth?
          • Steve Greenfield
            You could ask this on the Homebrew_PCBs list. Despite the name, there are some professionals there. We ve got over 200 members.
            Message 5 of 9 , May 4, 2002
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              You could ask this on the Homebrew_PCBs list. Despite the name,
              there are some professionals there. We've got over 200 members.

              http://groups.yahoo.com/group/Homebrew_PCBs

              Steve Greenfield
              --- David VanHorn <dvanhorn@...> wrote:
              >
              > Well, requirements are clarifying, and it's looking like I'm
              > going to orcad
              > 9.2.
              > Has anyone used this with pro-engineer to pass mechanicals back
              > and forth?


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            • Mark Pepper
              Hey I am playing with the OOPIC and the PCF 8574 on the MarkIII sensor board and I need some seed code to help point me in the right direction Has anyone got
              Message 6 of 9 , Jul 5 12:58 PM
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                Hey

                I am playing with the OOPIC and the PCF 8574 on the MarkIII sensor
                board and I need some seed code to help point me in the right direction

                Has anyone got any code segments I could begin with please to help out.

                Regards

                Mark
              • benedict-list@hawaii.rr.com
                I finally cleaned up my motor test code. It s different from what I sent you on the OOPic list, but it s a lot easier to read now. I ve uploaded it to the
                Message 7 of 9 , Jul 7 7:31 PM
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                  I finally cleaned up my motor test code. It's different from what I sent
                  you on the OOPic list, but it's a lot easier to read now. I've uploaded
                  it to the Files area of the Mark III list in the OOPic example code area.
                  There's a folder in there now for sensor board code, and the motor code's
                  in there, too.

                  I'm going to go ahead and add digital I/O stuff for the Handyboard I/O
                  block and for the buzzer, but there's not really much to using them...
                  it's normal OOPic I/O port code.

                  Tom

                  On Wed, 5 Jul 2006, Mark Pepper wrote:

                  > Hey
                  >
                  > I am playing with the OOPIC and the PCF 8574 on the MarkIII sensor
                  > board and I need some seed code to help point me in the right direction
                  >
                  > Has anyone got any code segments I could begin with please to help out.
                  >
                  > Regards
                  >
                  > Mark
                  >
                  >
                  >
                  >
                  >
                  >
                  > Visit the SRS Website at http://www.seattlerobotics.org
                  > Yahoo! Groups Links
                  >
                  >
                  >
                  >
                  >
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