led belt buckle hack

Bought one of those LED belt buckles...not to wear! I want to hook it up to a serial line and control it from a pc. My hope was that there
were some dev points on the board that I could tap into. Looks like there's only 1 and it's got 5 solder points. I'm not sure if this was for power or control or both as I'm not an EE guy, just CS; but I do like to play around with electronics. Also, there's an atmel eprom 24C16AN (http://www.turbochip.dk/shop/produkt.asp?idH ) exposed. The largest chip has some black goop on it(epoxy?) for some reason. Maybe for "hack" protection like the xbox360 chips?
Last resort I guess I could desolder the 3 programming buttons and write something to use the button interface but that would be pretty ugly since programming this thing with the buttons is painful. You have to basically do it 1 char at a time by scrolling through the upper/lower alphabet.
I posted some pictures here of the back. The front is just a block of LEDs in a 7x21 row x column pattern. http://www.flickr.com/photos/thewilliamsfamily/sets/72157594480059341/detail /
Any help would be appreciated. -kevin
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NetKev wrote:

The EPROM is probably the character set - so that different variants for different languages can be produced by a single chip change.
The switches will be software de-bounced, so that will limit the "programming" speed that can be achieved.
There may be a test point that puts a test pattern on the LEDS (say, all on) but it almost certainly won't be of much use to you.
The LED column driver transistors are clearly visible and accessible on the left.
Your options are either to:
1) Isolate the LED row lines and the column transistor base lines and add your own PIC to drive those and interface to your serial line. Almost certainly not that difficult to do, if you use a re-programmable PIC to build things up "bit by bit".
or
2) As you suggest - but I would use three lines from a parallel port, rather than the serial port.
It wouldn't be that much a pain to program (2) - computers don't mind simple repetitive tasks!
--
Sue

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Are you sure those transistors are not for the rows? Looking closer at the board there are Q1-Q7 and R1-R7. There are exactly 7 rows and 21 columns. I'm wondering if it wouldn't be easier to just desolder the LEDs? I priced them online and they cost over $1 each. This device with 147 LEDs cost me $10.
-Kevin
Palindr☻me wrote:

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NetKev wrote:

Where did you get it? Ed

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ehsjr wrote:

I bought it when I saw the deal on dealspl.us and it was $9.99 + free shipping. It looks like they've since raised the price but it's still cheaper than buying wholesale smt leds. http://www.thinkgeek.com/gadgets/electronic/7c60 /
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NetKev wrote:

Thanks!
Ed
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NetKev wrote:

LOL, it was a guess as to what the front of the buckle looked like!

Well, there you go. The key thing is that it is a matrix, with X and Y lines.

At the moment you have the LEDs already soldered on to a board, with the driver transistors in place and (it looks like) all the X and Y lines accessible. Cutting those lines and taking 21+7 fine wire (I use Verowire - its insulation turns to flux as it is heated with an iron) to a piggyback board with a PIC or two on it and it's done. These are, presumably, SMT LEDs - unsoldering them is going to be easy (just put a hot air gun to the back and tap against the bench and they will all fall off). It's making a board and soldering them all back on, the right way around, that is going to take time...
--
Sue


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Palindr☻me wrote:

if i wanted to leave it in tact, what's the best way to interface with the printed lines? ...and figuring out how they are picking which leds turn on.
-Kevin
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NetKev wrote:

You're in luck.. The lines going to the base of the driver transistors will be easy to locate - just trace back from the base pins.
The 21 other lines all have to go through plated-through holes from the LED side to the "electronics" side - count the number of such holes and I wouldn't expect, for a simple circuit like this, to be more that the 21+7 needed for the LEDs - and those 7 extra are going to be very easy to identify.
Also, the holes are an ideal spot to /gently/ remove the coating and expose bare copper to solder to. I use a thing called a "fibre-glass pencil" to do this.
Then, as I have said, I would use Verowire to make the links.
Working out which is which - just do a continuity test (ohms on a multimeter) from the pins of an LED from each column and each row back to the wires coming off the board. Then label them.
--
Sue



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