Lo and Behold, 64 Pixels are Enough

I was enamoured with Alex Weber’s 64 Pixels project from the moment I saw it. When I happened across it (via Make:blog, I think), I was just starting the design process for my new satchel. I was thinking about making something similar, but no coherent vision had actually formed in my mind. Once I saw 64 Pixels, I knew it had, nay, must be affixed to my new bag.

Unfortunately, Futurlec jacked up my order, and recieved a trio of green led matrices. Not only do they require a higher voltage to drive them, they’re common cathode, as opposed to Alex’s common anode. That meant I had to do a little more legwork in order to make these buggers work. Fortunately, Alex was kind enough to preemptively include a section of code that handled a common cathode matrix. So that meant I all I had to do was hook up a bigger battery :)

Not so easy. If I added an extra battery (4.5V) or two (6V), random LEDs would flicker, making the entire thing a seizure-inducing mess. Alex was a great help in troubleshooting the problem, though we didn’t come up with a solution right away (I was busy, and I assume he was too; I don’t blame him for not flying across the Pond to solve my problem. (Though it would have been cool.)). Ultimately, I decided to actually READ the specs on the ATTiny, and found that it has a max voltage of 5.5V, and I was pushing 6V into it. The lowest resistor I had was 100 Ohms, and that wouldn’t even let the bugger turn on. So, thinking back to my friend Dan’s incessant reminders, I added a decoupling cap with an arbitrary value (read as: I grabbed whatever was handy), and lo and behold, it worked! So now, I have a wonderfully green and geeky Badge of Honor on my satchel, that (sort of) turns on when I throw the strap over my shoulders.

Proof that it works, on the breadboard. This is a sad image for two reasons. One, it’s upside down. Two, It’s a longer exposure due to crappy lighting, which made it capture the scrolling pixels. I promise it works just fine ;)

Proof that it works.
Here’s the matrix/chip unit ziptied to the shoulder strap. I personally like the red and black wires running back into the satchel. There’s a certain bomb-like *je nes se quois *to it. Up close, you can see the decoupling cap soldered on as an afterthought.

Attached to the strap
The switch is definitely a work in progress. I’ve got a long-levered momentary switch tied (by its own wires, no less) to the eyelet that the strap is attached to. On the lever is some glued-up paper with a zip-tie remnant stuck through it. The idea is that the lower portion of the zip-tie will get caught on the fabric and help push the button. The thickness of the paper helps make the button easier to push. I’m still trying to find a more reliable alternative…

The Switch
I don’t know why, but this stinking cat keeps showing up, and making me take pictures of him. At least he’s clean, this time. Also, I don’t know why I upload and include thes pics…

Cat Assistance