Introduction: Disco Drinks Coaster

Picture of Disco Drinks Coaster
Although we live just outside Cambridge in the UK, my wife is tragically addicted to all things Las Vegas. It's been nearly six months since our last visit, and she is pining for bright lights and cocktails. Few things make a drink nicer than some coloured lights in the vicinity.

Ever alert to the causes of my wife's grumpiness, I decided to cheer her up by making an animated, brightly lit drinks coaster.

Here it is under a gin and tonic:

And here it is, glass-free, displaying a spinning galactic ice-cube.

The coaster can be driven from any PC with a serial port and will display any 10 by 10-pixel video you wish.

Step 1: Buy Some Parts

You will need:

30 1K 0805 resistors (R1 - R30)
30 MBTA42 NPN transistors (Q1 - Q30)
10 100 Ohm 0805 resistors (R31 - R40)
10 FMMT717 PNP transistors (Q31 - Q40)
5 74HC594 SOIC shift registers (IC1 - IC5)
4 100nF 1206 capacitors (C1 - C4)

and finally:

100 TB5-V120-FLUX-RGB8000 RGB LEDs (LED00 - LED99)

The LEDs can be hard to get hold of at a decent price; eBay is once again the friend of the penurious electrical engineer.

Step 2: Make and Assemble the PCB

Picture of Make and Assemble the PCB

Manufacture one or more PCBs using the attached Gerber and drill files. A double-sided PTH process is required, so it is probably best to use one of the various small-volume professional PCB manufacturers; I have found PCB Train in the UK to be fairly reliable.

Assemble the board, taking great care when soldering the surface mount components. I found this one to be right at the limit of my dexterity. Note that there are two different types of SOT-23 transistor, and two types of 0805 resistor on the board. Look at the bottom silk layer to see the component names (R23 etc) and use this to match against the parts list in step 1.

Once you're done, your circuitboard should look like this.

Step 3: Drive the Board

This is the tricky bit. You need to use something (probably a microcontroller) to drive the board in a way which generates an image. Attach power and data cables to the connector in the bottom right of the board. Seen from above, we number the six pins:

1 2 3
4 5 6

The corresponding signals are:

1. XVOLTS - drive voltage for LEDs. Connect to 4V current limited supply.
2. SERIAL_CLOCK - shift data from SERIAL_DATA on positive-going edge.
3. SERIAL_LATCH - latch 40 bits from shift register to LED control on positive-going edge.
4. GROUND - common ground.
5. 5VOLTS - supply voltage for control circuitry. Connect to 5V supply.
6. SERIAL_DATA - input data for shift register.

To scan the display, clock 10 4-bit numbers into the shift register. To clock in a bit:

- bring SERIAL_CLOCK low
- modify SERIAL_DATA
- bring SERIAL_CLOCK high

Once 40 bits have been clocked in, the SERIAL_LATCH signal can be brought high to transfer them to the LED control circuitry. Each 4 bit number selectively enables the red, green and blue LEDs in one row, and selectively disables all LEDs in one column. So if we clock in a string:

0011 0100 0111 ...

This sets all the LEDs in row 0 to blue, all the LEDs in row 1 to green and all the LEDS in row 2 to cyan (green + blue). It disables all the LEDs in columns 0 and 2. By rapidly clocking in various combinations of values (typically with only 1 of the 10 column-disable bits low), we can scan the array to build up an image, and use pulse-width modulation to give a range of apparent intensities.

The attached firmware can be used with an Atmel ATmega644 to generate the required signals in response to serial input from a PC or Mac.

Step 4: A Warning and a Tip

A couple of words of warning. Modern LEDs can be very bright indeed. You could probably hurt yourself pretty badly by dialling them up to full intensity and ignoring your look-away reflex, so don't. Also, when debugging your firmware it is easy to stall the scanning process and burn out the precious LEDs. Use a decent current-limited bench power supply, with the current dialled back to a few tens of milliamps to avoid this happening.


Captain Pedantic (author)2007-09-22

I'd pay money for that (and I don't have much money to spare).

Well, the parts get cheaper all the time. There are Chinese guys on ebay selling factory-direct LEDs for a tenth what you'd pay from a western dealer. Not very well tested; if you look at the video you'll see I lost a few green dies and one blue die. LED projects are a lot of fun; just don't wear them to the airport :)

that's good im gonna try to cover the whole surface of a table with this. 

Tommyhzy (author)ebenupton2009-08-11

Why not the airport? (Oh and I agree with the Hong Kong dealers, they're so cheap it's not even funny. Compare 100x 12000mcd Leds at $6.99 including shipping... to $2 Radioshack for 1 measly LED) (:

Whoa. Didn't see THAT coming... I will defenitely not bring lit LEDs to airports anymore-- D:

Mr. Rig It (author)2008-05-19

This is still one of my all time favorites.

Illidan (author)2007-09-30

i'm in cambridge UK too! hi-five!

ruderobb (author)2007-09-23

How long would this run for before LEDs died? Also, how long you think it could run for on batteries (making it portable)?

ebenupton (author)ruderobb2007-09-23

Well, I had a few dies die (heh) during development. Out of 300 dies, I lost about 4 greens and 1 blue. Those look like early-life failures due to a lack of factory testing; when you buy from some guy in Hong Kong via eBay, you take what you get. The design at present drives the LEDs hard (up to 100mA @ 10% duty cycle), which is within spec but won't help lifespan. With the modifications I've discussed elsewhere (using the 74HC to pull down) this drops to more like 10mA @ 10% duty cycle. I'd figure on a few thousand hours of continuous use before significant numbers of failures. With the modifications, you could get a nice display at 100mA average with a 3.5V supply, so say 10 hours out of a 3VAh pack. It sucks that the raw material cost for this scuppers it as a commercial product :(

royalestel (author)ebenupton2007-09-29

So it costs what, around $30 to make? Have you seen those flat honeycomb LED arrays? I found the link, but apparently the product is no longer available through that retailer. . . Would such a thing be of use to you, though?

royalestel (author)royalestel2007-09-29

The one I was thinking of is at the very bottom of the list. Four screws and done!

eight (author)2007-09-28

RE: "we live just outside Cambridge in the UK, my wife is tragically addicted to all things Las Vegas" How about stringing Chrissy lights off ELY Cathedral instead? As in letting her do it :P You can grab a pint on Silver St in Cambridge. Everyone is happy !! OK, I know, not funny... Whadda I know... I'm just a dumb skppy convict... Nice project. Thanks for sharing it with us. Sorry about your wife, mate. (...addicted to all things Las Vegas...) : P

laernmoer (author)2007-09-27

Is condensation a problem? I'd imagine that you'd want to pot the whole thing - or at least a conformal coat.

ChrisGray (author)2007-09-27

Very nice indeed - I echo the comment that you should be selling these to Casinos for their bars. :) For people hopeless at electronic engineering, would you consider selling units of say 6 coasters?

Grady (author)2007-09-27

Maybe you oughta put tog kits & sell them, for noone would probably want to hunt down everything. It's too much work for me. I have 2 plastic glasses I got from our local flea mkt that does all this, with a push of the button on the bottom, which also stops it. I think yours would make nice Christmas gifts.

pimpin M (author)2007-09-25

this thing made me smile watching the video nice instructable

ebenupton (author)pimpin M 2007-09-26

Glad you like it. Seeing all the feeback, I think I'll try for a simplified, portable version.

Patrick Pending (author)2007-09-24

Great instructable and a great effect. Cheers, Pat. Pending

CreativeChick8 (author)2007-09-23

Veeerry Niiiice... I could never do that, though I would shell out some serious money (10 US dollars for 1 coaster) for battery operated ones!

Mr. Rig It (author)2007-09-22

You could sell that to Casino's in Vegas. Can you make it spell out Las Vegas and then make it flash?? Although if you did you might get attacked by your wife in a fit of gleeful love.

ebenupton (author)Mr. Rig It2007-09-23

Shamefully, I've not actually run a scrolling message across it. I should get it out today and do that as it's very straightforward.

Mr. Rig It (author)2007-09-22

That is down right cool!!!!!!!!! Or as you guys say in the UK, ACES!

royalestel (author)2007-09-22

I'd also pay money for that. In fact I've been mulling over this + appropriately sized LCD screen = High Dynamic Range display. (i.e. sunnybright technologies)

ebenupton (author)royalestel2007-09-22

Yeah. You don't want to look too closely at the board when it's drawing a couple of amps. 7 watts of electrical power at superbright LED conversion efficiencies can dazzle. Liz (my wife) could tell when I was working on it from the light overspill from my workshop. A matrix of fine-pitch white or RGB LEDs under a transmissive LCD panel would be sweet, but a bit beyond my time/money budget.

gmoon (author)2007-09-22

You could pre-program the AT644 with a set of patterns, and make this stand-alone, correct? I don't say this often about instructables, but all this project needs is to be encased (liquid-proofed) and you're ready for the marketing department!

gmoon (author)gmoon2007-09-22

Ah, but it's also powered externally... (maybe a flat pack battery?)

ebenupton (author)gmoon2007-09-22

Glad you liked it :) You could certainly bake some patterns into the 644; I just didn't have time to port my antialiased rasteriser to AVR, and it makes a nice demo to open up a terminal session to the board and start lighting up individual subpixels by typing. I think the biggest barrier to making a product out of this is the cost of the LEDs (40 cents each in 100 off, hard to see it going below 10 cents each anytime soon, even in ridiculous volumes). The drive electronics could be slimmed down by using the pulldown on the 74HC shift registers to do the column drive. There's a fair bit of kit off to one side (including my 200USD bench power supply) keeping it happy. At full brightness it can draw a couple of amps; you don't really need that much brightness though, and especially with the simplified drive electronics you could do something which looked good but could run for a few hours on some small batteries.

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