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

[Alberto Gaitán]

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