Christmas Ornament

This was supposed to be a really simple project. The idea was take an ATTiny85 chip, which costs all of $1.50, add in a shift register which costs maybe 50 cents a piece, and I've got a way to control a bunch of LED's. In this case, I did 16 LED's.. The first one I soldered up didn't work at all. Turns out I had soldered all of the connections wrong. The pinouts I used had been meant for viewing the chip from above. And I knew that. But when you're under the board and soldering the the bottom, it's pretty easy to get it backwards. I didn't use a socket on the shift register, so I just tossed that board and started over. Very frustrating. The next board I made, I used sockets, AND I made sure to be very sure I got everything in the right order. It still didn't work. Tried a different ATTiny, still no go. Lots of double checking and finally I decide to just breadboard the thing like I should have in the beginning.

Still no love on the breadboard, so I got out the scope. The CPU was working, it was sending data out to the shift register. I could see the data getting shifted out from time to time, but it just wouldn't change the LED's. I tried re-arranging the pinout, using different pins on the CPU. Nothing.Finally grabbed an LED and resistor and probed the "latch" pin at the CPU to see it pulsing. WTF, the whole thing started working! The lights were changing randomly like I had intended. 

I've done shift registers on ATTiny's plenty of times before without a problem. but that was with Arduino 022, not this new clusterfuck they call 1.0. So I ended up just soldering on a pull-up resistor between that output pin (pin2) and VCC.  I  don't really care, so long as it works.

The idea all along was that after I got this all soldered up, I was going to stuff it into an old lightbulb that I had hollowed out (snapped the end off of). Then I was going to fill it with clear polyurethane resin that hardens as had as plastic. The idea with the resin was to keep the wires from snapping off the bulbs (constant problem during assembly/troubleshoot/reassembly!), and to keep things from shorting out against each other, which was also a problem I was having.

There it is hanging on the tree. I used a very small 110v AC - 5v DC plug in adapter to power it. It's hanging from it's power wire, and i made a cap for the top f it that looks much like any of the other ornaments, out of aluminum foil. :)


© Una 2011