The Medea Vodka display is a really cool piece of technology. (Unfortunately its main purpose is advertising) If you haven’t seen it, it’s basically a 5 by 25 pixel LED display that you can program. Wrapped around a bottle of vodka.
I haven’t been able to find it for sale anywhere around Cambridge (supreme, libby’s), but for one glorious day a rep was selling it at the liquor store in Davis Sq., and I snagged a bottle. Apparently there are different colors, but blue was all that was available when I got mine.
The display itself is flexible pcb that fits into a specially formed channel in the side of the bottle and is held on by a translucent rubber band that covers it. There are little recesses in the bottle where the coin cell (cr2032) batteries fit.
The circuit itself is a really smart bit of engineering. The two CR2032 lithium batteries are connected in series to hit the necessary voltage for multiple blue LEDs. The PIC chip, which is always “on”, monitors the button states and drives the shift registers. The chip goes into a low power ‘sleep-mode’ when you press the off button. The 4 shift registers are cascaded together, so the PIC shifts in 4 bytes (32 bits), and then latches the shift registers simultaneously, which transfers the bytes from the storage buffer to the output side (LEDs).
The Atmel memory chip stores any saved messages (and possibly the font). I don’t have a PIC programmer, so I’m not sure if the PIC chip is locked or if you can program it still. The most interesting thing to me is the lack of current limiting resistors; they are not necessary because the batteries can’t source enough current to burn out any LEDs, but this also saves a ton of space! A side effect of saturating the battery’s capacity is that the voltage fluctuates massively; from about 4.4V to 5.5V as a message scrolls by with more or fewer ‘pixels’ lit. But the microcontroller does not brown out!
Using a multimeter and Eagle CAD I tried to sketch out the circuit a little bit to help myself with programming an AVR to drive the display. This is what I came up with:
It’s not perfect, but it should convey the basic idea.
Hopefully this helps you get started playing with this display, if you can find one. It’s especially cool to find that a display like this that isn’t tamper proofed with gobs of epoxy. Props to Medea for that!
In my next post I will show how I interfaced an atmega8 chip to this display and am controlling it wirelessly.
UPDATE: More here.