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

[R. Mark Adams, Ph.D.]

Fantastic idea!  Plus, the barebones Arduino kit costs about the same as
the POV kit, and is way more generally useful, IMHO.  I will take a look
at the WinAVR code and see what I can come up with.  besides, if we wanted
to do the "mega-cube" it would be way easier to do it with the code in
Processing...

-Mark


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


-- 
|                            |   "Information is light.      |
| R. Mark Adams, Ph.D.       |    Information in itself,     |
| Computational Biologist    |    about anything, is light." |
| rmadams at epotential.com     |       - Tom Stoppard          |