LED Cube

[Paul Beard]

Just in case anyone has never heard of these, an LED cube is a 3-dimensional grid of LEDs, which flash with animated sequences. They vary in size from 2x2x2 (8 LEDs) up to very large cubes indeed, but the practical limit for most home-build cubes is probably 8x8x8 (512 LEDs!!!!).

The LEDs can be single-colour or "RGB", which gives the possibility of at least 7 and potentially a huge range of colours with which to animate the cube.

I've build 2 LED cubes now, both single-colour, 4x4x4 (64 LEDs) using two different microcontrollers, but otherwise very similar design. My goal was to create a cube that was as simple as possible to construct, with the minimum of components, to make it easy for others to build too.

The first used a PicAxe microcontroller and has hand-wired on stripboard. The wiring was a bit of a nightmare, and Arduino is more popular than Picaxe, so I decided to have another go.

The "Mk 2" used a ATtiny85 and a custom PCB. a Tiny85 is the smaller brother of the chip used on most Arduinos, the Mega328. A regular Arduino can be used to test and then upload a sketch into the tiny85.

[m...@mattbrailsford.com]

Hey Paul,

Thanks for sharing. These look really cool. I've seen a few about, but never really looked into them fully.

Would love to see one in person if you fancy bringing one along one evening? Love the use of the ATIny85 too. I've been playing with these a bit lately myself and they are really cool for small projects that don't require too many inputs.

Nice work

Matt

[Chris Garrett]

On Wed, Oct 22, 2014 at 8:37 AM, Paul Beard <paul.r...@googlemail.com> wrote:

The "Mk 2" used a ATtiny85 and a custom PCB. a Tiny85 is the smaller brother of the chip used on most Arduinos, the Mega328. A regular Arduino can be used to test and then upload a sketch into the tiny85.

Is that a shift register or an LED driver next to the Tiny?

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[kal9001]

Looks good, I have 100 RGB LEDs on the way from god knows where and an LED cube is one of the many ideas I have had for a while to make. Probably starting off with a simple 3^3 or maybe a 4^3 to start with, I would love to be able to build one of the big 8^3  RGB ones, But thats over 1,500 leds. could be a challenge lol!

Very good use of the AT tiny, Its easy to forget they have the same CPU core and speed as their bigger brothers. Anything you can do with an Arduino Uno that only uses power + 5 pins can be done easily with an '85. You can even coax a 6th pin out if you like but its not recommended unless you have a proper programmer.

If you make a bigger cube you could look at the '84, Its got the same ram and flash as the '85 bit its a DIP14 so you have enough room to practically get a 20Mhz crystal on it and run the register bank plus have a serial input to upload the display. That way you don't have to try and squeeze all the animations into the small flash.

When I do mine I will probably use a 328P, I have a few on the way dont need to worry too much about program size or ram with them. If I can get it compact enough I would ideally get it onto an '85 or '84 for a sort of 'final' version.....Knowing my reputation of actually finishing anything we'll be lucky if its even started this time next year heh!

[Paul Beard]

On Wednesday, 22 October 2014 16:43:04 UTC+1, Chris Garrett wrote:

Is that a shift register or an LED driver next to the Tiny?

No, its a max7219. This chip is designed to drive LEDs and is quite a clever beast, which makes the whole project much simpler than shift registers. No series resistors are needed, plus the 7219 can handle much higher currents, removing the need for extra transistors and keeping the component count down. It also handles all the multiplexing, making the Arduino sketch much simpler too.

The chip was designed to run 7-segment displays originally (although it is often used for 8x8 matrix displays) and this leads to the slightly unusual design of the cube. When you see it up close, you realise that instead of a single block of 4x4x4 leds, the cube is actually two adjacent towers of 4x4x2.

I will aim to bring it along to the next meetup.

In the mean time, I wrote up full instructions for constructing it on the Arduino forum:

http://forum.arduino.cc/index.php?topic=226262.msg1636691#msg1636691

[Chris Garrett]

On Wed, Oct 22, 2014 at 10:29 AM, Paul Beard <paul.r...@googlemail.com> wrote:

No, its a max7219

Cool, will check out those bad boys

[Chris Garrett]

On Wed, Oct 22, 2014 at 10:40 AM, Chris Garrett <ch...@chrisg.com> wrote:

Cool, will check out those bad boys

Seems the dodgy ones work but are a risk

http://tronixstuff.com/2013/05/16/the-max7219-led-display-controller-real-or-fake/

I might try some ebay ones and see how badly they bork, plus a legit one from Adafruit or something

[kal9001 .]

Ive fond projects before that use different Maxim parts and they always seems very expensive. Id got for the cheapos, Especially if there like uber cheap so even if you blow up every other one they still cost less than the real stuff lol.

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[Chris Garrett]

On Wed, Oct 22, 2014 at 12:08 PM, kal9001 . <kal...@gmail.com> wrote:

Ive fond projects before that use different Maxim parts and they always seems very expensive. Id got for the cheapos, Especially if there like uber cheap so even if you blow up every other one they still cost less than the real stuff lol.

Just ordered one from Sparkfun for $5 and 5 from ebay for $2.56 ;)

[Paul Beard]

On Wednesday, 22 October 2014 19:18:39 UTC+1, Chris 

Just ordered one from Sparkfun for $5 and 5 from ebay for $2.56 ;)

They will both be fakes. Genuine Maxims are $10. You'll be fine.

[Chris Garrett]

On Wed, Oct 22, 2014 at 12:29 PM, Paul Beard <paul.r...@googlemail.com> wrote:

They will both be fakes. Genuine Maxims are $10

I thought the same but seems from the comments Sparkfun used to sell them at $10, so they seem to be discounting (5.95 versus adafruit $9.95). I am sure as you say will be fine either way. Good job I am not building for NASA space missions :D

[Paul Beard]

These cubes are delicate. I would like to design and build an acrylic box to protect it, possibly using the laser cutter we saw at Horizon col. I could do with some guidance on that if someone could help me? I suppose first step would be to find and learn to use a package to allow me to design the pieces. Ideally this would run on linux as I use Ubuntu not Windows.

Kevin, I plan to build an rgb cube some day too. Might stick to 4x4x4 for now. My idea is to use ws2812b leds, which would keep the hardware side simple. I just need to work out a good way to wire them up in a cube . Each led would need 3 connections: 5V, ground and data, the data lines must daisy-chain each led to the next. The cube structure needs wires running in 3 dimentions. So maybe 5V forms the vertical lines, ground lines run east-west and data north-south or... its an interesting puzzle...

[Chris Garrett]

On Wed, Oct 22, 2014 at 3:20 PM, Paul Beard <paul.r...@googlemail.com> wrote:

I suppose first step would be to find and learn to use a package to allow me to design the pieces

Usually a laser will import .dxf files, one of these might do http://www.techdrivein.com/2011/08/8-best-cad-apps-for-linux.html

[Paul Beard]

Thanks Chris. Too many choices! I need something basic, free and familliar to someone in the group so they can guide me.

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[kal9001 .]

Im a total noob when it comes to any kind of cat software, I would have thought it would be very simple to make a cube. You just need to make a square and four rectangles
Rectangles so that the long sides can slot down into the base to hide the mountings.

You can get special acrylic glue that effectively welds the seams together (Assuming they are cut very straight) so the visible corners wouldn't have screws or anything messing it up. Would defiantly make an RGB one, Maybe even a bigger one to make it worth the expense and effort to mount it really well.  

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[m...@mattbrailsford.com]

In terms of 3D modeling, I'd probably go with either Sketchup (does require a plugin to export DXF files though) or AutoDesk 123D Make (though not sure if it has a nix version). Both are free, and both are quite popular with makers. I use Sketchup myself so would be happy to show you how it works. It's really simple (hence why I use it :)).

For use with the laser cutter though, you are probably better off working in more of a flat way (think a box flattened out). I've attached an example of how I designed the box for my VoiceBox2000. For this I used Inkscape, which is a free vector based drawing application. Setting the rulers to mm though, and with the ability to export as DXF, it's also perfect for designing enclosures. Again, I'd be more than happy to demo this for you and help you get up to speed with it.

Another handy tool I used when designing my box was this website (http://www.makercase.com/). It helps you build the basic structure of your box, including laying out the finger joints for a similar box to what I created, or has a number of other joint types that might suite you better (I'd imagine plain old butt joints would be what you need).

Anyways, I'd recommend you take a look at the applications above and as I say, I'd be more than happy to show you more. Maybe we could use the projector at the college and have a bit of a session on it.

Matt

[Paul Beard]

On Thursday, 23 October 2014 08:45:13 UTC+1, m...@mattbrailsford.com wrote:

For use with the laser cutter though, you are probably better off working in more of a flat way (think a box flattened out). For this I used Inkscape, ... I'd be more than happy to demo this for you and help you get up to speed with it.

Thanks Matt, yes, I was thinking "flat". I knocked this up v. quickly to show my idea:

A demo at the next session would be spot on.

Paul

[Melvb]

Do you know Maxim give out samples FREE.  I got 3 off MAX7221CNG+ serial interface LED drivers for an Arduino project I was thinking about (not got any further than that yet) worth over £9 each.  The default seems to be 2 off, but as I was looking at RGB I asked for 3 and got them.  Just used my work email and postal address.

[m...@mattbrailsford.com]

Hey Paul,

That seems simple enough. Should definitely be able to get that designed up and maybe even cut at the next session if you wanna source some acrylic (3mm should be fine I would have thought).

Matt

[m...@mattbrailsford.com]

PS You could probably find perspex on ebay, but Hobarts seems a pretty reasonable place http://hobarts.com/

Matt

[kal9001 .]

You want flat edges on the mating surfaces as smooth as possible to. That way you can use an acrylic solvent which basically welds the plastic at the joint making an ideally transparent joint for your box.

https://www.youtube.com/watch?v=hT6Ow_cBTps 

[kal9001 .]

FYI the 'cement' they talk about is basically Acetone which is widely available and cheap. Some people have also used CLEAR nail varnish remover which has a high acetone content.

[chris stagg]

And theres me worrying about how much mirrored acrylic was gonna be... £4 ain't bad at all for 20×30cm.

On 23 Oct 2014 13:18, <m...@mattbrailsford.com> wrote:

PS You could probably find perspex on ebay, but Hobarts seems a pretty reasonable place http://hobarts.com/

Matt

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[Paul Beard]

On Thursday, 23 October 2014 13:18:35 UTC+1, m...@mattbrailsford.com wrote:

PS You could probably find perspex on ebay, but Hobarts seems a pretty reasonable place http://hobarts.com/

 

Thanks again Matt, your read my mind. So is "Perspex" just a brand name for acrylic, or is it somehow different/better than Hobart's own brand acrylic? 

[m...@mattbrailsford.com]

To be honest, I'm not entirely sure myself, hence why I looked for someone who stocked it specifically for laser cutting. I'm still yet to hear back from the college regarding suggested suppliers. I'm sure as long as it is acrylic, it should be fine.

Matt

[kal9001 .]

Perspex is a brand name for a kind of acrylic.

Acrylic is a generalisation and can mean any one of a hand full of different chemical compositions that all look and feel more or less the same but have varying properties.

I would imagine for an LED cube enclosure just your bog standard cheap 'acrylic' will do the job just fine. Unless perhaps you want to make it load bearing like if you wanted to build it all into a coffee table or something, Then because you need it to be scratch resistant and stronger you would perhaps look at one of the brands names like plexiglas or perspex that have a more rugged chemical composition.

Just bear in mind that ALL acrylic melts at fairly low temperatures and will mark and go translucent at even lower temperatures, It is also not chemical safe any solvents will also leave marks or worse. (this is why the acetone welding technique works well)

Or even ditch the acrylic and use polycarbonate , It melts much higher, Its much stronger and shatter proof, more chemical resistant but you pay for it.....(Lexan for example is polycarbonate and they advertise that as bullet resistant!)

[Paul Beard]

On Thursday, 23 October 2014 13:14:49 UTC+1, m...@mattbrailsford.com wrote:

Should definitely be able to get that designed up and maybe even cut at the next session if you wanna source some acrylic (3mm should be fine I would have thought).

It it possible/a good idea to "mock-up" first using some old corrugated cardboard that's approx 3mm thick? Get the laser to cut that, then if that fits together OK, you move on to the acrylic sheet. (Or would the cardboard just burst into flames...)

[Matt Brailsford]

You could probably just use a craft knife and cardboard to mock up no? I guess it depends what you wanna test by mocking it up? 

[kal9001 .]

Afaik you can cut cardboard in a laser cutter, That is if the laser cutter has cardboard as a supported material type. Otherwise turn the power down as low as it will go and hope it doesn't go through like a blow torch through butter and damage the machines base.

Mock ups could be useful if you're unsure of the dimensions or for complex parts, But as we are dealing with a five sided box that will only have one or two different measurements depending on how you go for it.
Unless of course you are going for a more complex design.

[Chris Garrett]

On Thu, Oct 23, 2014 at 10:26 AM, kal9001 . <kal...@gmail.com> wrote:

Otherwise turn the power down as low as it will go

You can also up the speed of the cut too - power/speed both impact if you are going to burn the place down :)

[kal9001 .]

Doing both may be over kill. I would imagine that it will have cardboard as a selectable material type. It may not have corrugated card and as its less dense than solid card would be for the same thickness so you would compensate by entering a thickness equal to its thickness if crushed flat.

Ether way as I say I doubt a test run would be needed if it is such a simple design. how wrong can you go really making an AxA square and four AxB rectangles :P 

[Matt Brailsford]

If you wanna learn 3D, maybe that can act as your mockup? That's what I do sometimes and just create blocks to represent maximum bounds of inner components to make sure stuff fits.  

[chris stagg]

With regards to getting clear acrylic plasticsheets.com seems to be the cheapest... under 12 for a 400x600 custom 3mm sheet including delivery and tax. Others were at least £3 more. The delivery is 5.95, whether thats for any size i dont know but thats still cheaper then anywhere else.

On 23 Oct 2014 17:51, "Matt Brailsford" <m...@mattbrailsford.com> wrote:

If you wanna learn 3D, maybe that can act as your mockup? That's what I do sometimes and just create blocks to represent maximum bounds of inner components to make sure stuff fits.  

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[kal9001 .]

All we need to do is go out on a night time and take those big plastic windows out of the back of bus stops >.<

I suspect they are probably polycarbonate and not acrylic. I've been put off trying to play with acrylic purely by the price, I mean sure its not deathly expensive but even at £12 a sheet you really want to know what you're doing with it instead of just to 'experiment'.

I'm sure in future we can all put our heads together and make larger orders for us all and save delivery, Maybe even get bulk discounts. Or as I said at the meetup perhaps in future we can tag out supplies onto the horizons orders and pay them instead of the supplier.

[chris stagg]

For the sheet i intend to use it all. As its a precision machine, it shouldn't make a hash of it if everything is setup right. If i had to test first i'd rummage around the scraps bin.

As a guide i found this...
http://wsa.wdfiles.com/local--files/laser-cutting-guide/cut%20diagramsmall.png
It may not be the same setup as horizons machine but if it can do all 4 cuts then making a test piece could be an idea.

Wheres the pdf for the laser cutter?
(A new thread may be better for that)

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