[dorkbotdc-blabber] Re: LED Cube Workshop - use an Arduino?

[adam koeppel]

I probably have time, but maybe not the skill.  Also, MAKE store is
currently out of Arduinos...  Damn holiday season...  I love the idea
of everyone having an Arduino for this and future projects.

On 12/6/07, Alberto Gaitán <alberto.gaitan at gmail.com> wrote:
> This is a  great idea. Especially because everk self-respecting maker
> needs an Arduino. I'm pretty sure I don't have the time for this
> conversion. If none of you do, either, perhaps we can recruit someone
> else from the greater list?
>
> The Arduino uses Processing as its language and it's pretty well
> documented. Haven't looked at the WinAVR C code and don't know how many
> lines o'code it has but someone with some chops could make short shrift
> of it. Can't be too long.
>
> Anyone else have the time to do this?
>
> Alberto
>
>
>
> On 12/6/07 4:07 PM, Tim Slagle wrote:
> > Thanks for the offer, but now that I think of it I have some AVR
> > prototyping boards that could be used instead of the MiniPOV kit
> > for my experimental purposes.
> >
> > This may complicate things even more, but instead of using
> > hacking the MiniPOV kit the LED cube could be driven from an
> > Arduino.  Someone would just have to convert the software from
> > WinAVR C to Arduino's Java-style code.  Then commercial Arduinos
> > could be bought, or kits could be made.    If people bought
> > assembled Arduinos they could focus on making the LED cube at
> > the meeting.  And their Arduino could be the basis of future
> > Make:DC projects as well.
> >
> > I would tentatively volunteer to do the software conversion but
> > if there is someone else with more confirmed free time it might
> > be better.  The Make: 3D cube C code could also just be burned
> > into the Arduino CPU (blowing away the bootloader etc) as a
> > backup plan.
> > --Tim
> >
> >
> >
> > --- adam koeppel <koeppel at gmail.com> wrote:
> >
> >> Hi Tim,
> >>
> >> I ordered a POV kit earlier to play around with.  I figured it
> >> would
> >> not supply enough currents for a massive array.  Your
> >> transistor
> >> solution should work fine.  If you want to play around with
> >> any of
> >> your ideas prior to the meeting, I will let you know when I
> >> have
> >> assembled the kit.  I would be happy to share it as a
> >> "testing" unit
> >> so we don't have to complicate the group order.
> >>
> >> Cheers,
> >>
> >> Adam
> >>
> >>
> >> On 12/6/07, Tim Slagle <tim at slagle.org> wrote:
> >>> Sign me up for a kit, but I would probably want it before
> >> the
> >>> meeting so I can put it together in advance.  If other
> >> people
> >>> want to do this it will complicate the logistics of a volume
> >>> order I'm afraid.
> >>>
> >>> Also, the circuit that drives the cube is a hack, and
> >> probably
> >>> wouldn't work too well to drive multiple cubes without
> >>> additional parts.  The cube is driven as three multiplexed
> >>> planes of 3x3=9 LEDs.  The LEDs in a plane are driven
> >> directly
> >>> from the AVR uC pins, which is okay, since they can drive
> >> about
> >>> 25mA.  But then the planes are addressed by pulling the
> >> current
> >>> from the whole 9 LEDs into a single AVR uC pin, which is a
> >> lot
> >>> more current than the AVR can sink.  So, the cubes will
> >> already
> >>> be operating at ~1/27th the brightness of a directly driven
> >> LED,
> >>> and adding more cubes in parallel would only make them
> >> dimmer.
> >>> One change that could be easily done to increase brightness
> >> is
> >>> use two AVR pins in parallel to sink current from the
> >> planes.  I
> >>> think there are enough extra I/O pins to do this for the
> >> 3x3x3
> >>> cube.  The firmware would then have to be changed to set two
> >>> bits instead of one to address the planes, but this should
> >> not
> >>> be a big deal.
> >>>
> >>> A better approach would be to drive the planes through a
> >>> transistor that could sink more current.  This would require
> >>> soldering three ~1Kohm resistors and 2N3904 or 2N2222 NPN
> >>> transistors to the plane drive I/O pins, and inverting the
> >> bit
> >>> values of the pins in the firmware.
> >>>
> >>> I would recommend making the LED cubes on a piece of perf
> >> board
> >>> if possible, so there would be room to wire up the drive
> >>> transistors on the board and you wouldn't have to solder
> >> them
> >>> directly to the POV kit.  But then, I think like an engineer
> >> :-)
> >>> Mark, if you make the LED grid assembly fixtures, space the
> >> LEDs
> >>> at some multiple of 0.1" so they will fit on a perfboard.
> >> They
> >>> need to be less than 1" apart so I'd say make them 0.7" or
> >> so.
> >>> One variation I've been thinking about that would be cool
> >> (but
> >>> require more firmware changes) would be to use bi-color
> >> LEDs.
> >>> As long as the drive voltage is kept around 3V and two-pin
> >>> reverse-connected LEDs are used, they could just be wired up
> >>> like the single-color cube.  Then in the software, the I/O
> >> pins
> >>> for inactive planes are set to be high-impedance inputs so
> >> no
> >>> current will flow, and the active plane is set high to
> >> address
> >>> one color and low to address the other color.  So the matrix
> >>> would be scanned like six planes of 3x3 with only one color
> >> on
> >>> at a time.  The plane bit values for the high-level
> >> addressed
> >>> color would have to be inverted since they are now active
> >> low.
> >>> I will try to buy some bipolar bi-color LEDs for my own use
> >> but
> >>> others may want them as well...
> >>> --Tim
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> --- adam koeppel <koeppel at gmail.com> wrote:
> >>>
> >>>> Yeah, if this works out well, it could be an installation
> >>>> worthy
> >>>> piece.  I definitely think the working towards a massive
> >>>> assembly
> >>>> approach is a good idea, and it will solve the shortage of
> >> POV
> >>>> kit
> >>>> problem.  We should probably do a little design work ahead
> >> of
> >>>> time to
> >>>> make sure a single POV kit can provide the power we need,
> >>>> although I
> >>>> don't imagine it will be a problem.  I'd just hate for it
> >> not
> >>>> to work
> >>>> because of a power shortage.  What do you guys think?
> >>>>
> >>>>
> >>>>
> >>>> On 12/6/07, Alberto Gaitán <alberto.gaitan at gmail.com>
> >> wrote:
> >>>>> Yes! I like the idea of divving up the work
> >> factory-style!
> >>>> ...some folks
> >>>>> building cubes, and others POV thingies. And the idea
> >> for a
> >>>>> mega-LED-cube is genius enough to stop traffic for hours
> >> in
> >>>> Boston!
> >>>>> A
> >>>>>
> >>>>>
> >>>>>
> >>>>> On 12/6/07 11:33 AM, R. Mark Adams, Ph.D. wrote:
> >>>>>> I think this sounds great- if we follow the 'sewing
> >>>> circle' approach,
> >>>>>> people are certain to feel like they had an enjoyable
> >>>> time, as well as
> >>>>>> (potentially) making something interesting.  I would
> >>>> suggest that we buy
> >>>>>> and build at least a couple of POV kits in advance, so
> >>>> people who finish
> >>>>>> their cubes could hook them up and get so see what
> >> they
> >>>> look like working.
> >>>>>>  in fact, if we encourage the group to work together
> >>>> collectively, we
> >>>>>> could set it up so that folks are each working on
> >> parts
> >>>> that can all come
> >>>>>> together in the end to have something working.
> >>>> mega-LED-cube, anyone? :-)
> >>>>>> I am happy to volunteer to buy a couple of kits/LEDs
> >> to do
> >>>> some
> >>>>>> pre-building if people would like.  I can also knock
> >> off
> >>>> some wooden jigs
> >>>>>> to aid in the LED cube construction. (I can use the
> >> robot
> >>>> I showed last
> >>>>>> time to make them- cool!)
> >>>>>>
> >>>>>> I also have some tool kits and soldering irons that
> >>>> tool-less folks can
> >>>>>> use at the meeting if they want.
> >>>>>>
> >>>>>> Thanks!
> >>>>>> Mark
> >>>>>>
> >>>>>> Gareth Branwyn wrote:
> >>>>>>> Hey Everybody,
> >>>>>>>
> >>>>>>> As I'm sure you all know, we need to step on it to
> >> get
> >>>> the LED Cube
> >>>>>>> workshop in gear.
> >>>>>>>
> >>>>>>> I talked to Dan Woods at the Maker Store and it's not
> >>>> firm yet, but
> >>>>>>> it sounds like they'lll sell us the MiniPOV kits for
> >> cost
> >>>> in exchange
> >>>>>>> for a "Sponsored by MAKE" and a link on their
> >> website, in
> >>>> the
> >>>>>>> announcements, etc. The problem is that, given the
> >>>> season, the kits
> >>>>>>> are in short supply. He said supply should free up
> >> after
> >>>> Xmas, so
> >>>>>>> hopefully they could have them to us in early
> >> January.
> >>>>>>> Tim Slagle said that he could get the LEDs
> >> themselves.
> >>>> Katie Bechtold
> >>>>>>> and Mark Adams have also volunteered to help. (all
> >> copied
> >>>> in here)
> >>>>>>> Alberto said that he'll draft the announcement that
> >>>> Koshland needs to
> >>>>>>> see, sooner than later. I'll also help in editing
> >> that.
> >>>>>>> So, we need to figure out ASAP how we're going to run
> >>>> this thing.
> >>>>>>> Personally, I'm not that concerned about whether the
> >>>> cubes are
> >>>>>>> finished by the end of the workshop or not. To me,
> >> these
> >>>> things are
> >>>>>>> more like a sewing circle than anything else, a
> >> chance to
> >>>> socialize,
> >>>>>>> geek out, learn a skill and a few tips from those
> >> more
> >>>> experienced,
> >>>>>>> etc. But others might have a different take.
> >>>>>>>
> >>>>>>> Given the "shortage" of POV kits, we may have trouble
> >>>> getting a lot,
> >>>>>>> if say, 25 or more people each wanted a kit. One
> >> thing we
> >>>> could do is
> >>>>>>> also approach Lady Ada, the maker, and see if she'd
> >> give
> >>>> us a
> >>>>>>> discount. Even if she didn't, we could buy them full
> >>>> price from her
> >>>>>>> (at $17.50 ea) and spread out the cost over all the
> >> kits
> >>>> we offered
> >>>>>>> to people.
> >>>>>>>
> >>>>>>> So, we need to get a show of hands ASAP for how many
> >>>> people plan to
> >>>>>>> purchase a kit. And for one thing, we should insist
> >> that
> >>>> you have to
> >>>>>>> be participating in the workshop to get the kit at
> >> the
> >>>> discounted price.
> >>>>>>> Gareth
> >>>>>>>
> >>>>>>>
> >>>>>>
> >>>
> >
> >
>