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

[Tim Slagle]

I know you would want to use Make: stuff when possible but there
are hundreds of Arduinos in stock at AdaFruit:
http://www.adafruit.com/index.php?main_page=index&cPath=17
SparcFun also has them:
http://www.sparkfun.com/commerce/product_info.php?products_id=666

I think the AdaFruit BoArduino would be the thing to use
however, then the transistor drive circuits and LED column
connections can just be plugged in to the protoboard without
soldering: 
http://www.adafruit.com/index.php?main_page=product_info&cPath=19&products_id=72
Lots of those in stock also, but they are sold as kits and would
need to be soldered up.  No harder than building a MiniPOV kit
and more useful in the future...
--Tim


--- adam koeppel <koeppel at gmail.com> wrote:

> 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
> > >>>>>>>
> > >>>>>>>
> > >>>>>>
> > >>>
> > >
> > >
> >
>