Every year we make a pumpkin to decorate the front porch for Halloween. My daughter, the artist in the family, traces the design on the pumpkin, I cut it out, we add a generic pumpkin light and wala! a pumpkin is ready.
This year I thought I would do something different. I had a few strips of red/blue/white 12v LEDs my Dad once gave me (and is impatiently waiting for me to do something with them!), and I decided to make a mood light based red/blue LED driver with the white LEDs flashing to create a sparking effect.
Rather than use a full Arduino for this project, I decided to try my hand at using the smaller format ATtiny84 on a custom board. I had recently bought some for tinkering and this seemed like the perfect first project. Much easier than I thought. Installed the AVRisp software on my Ruggeduino, connected the leads as required and added a few LEDs for testing. Works!
Why Ruggeduino, you ask? EZ. I have already
blown up used up all of my ATmega328 chips on other projects and I have yet to find a way to destroy the Ruggeduino. Wish I could say that about my UNO you see in the background of the pic above… but that is for another story.
With the ATtiny programming issues sorted out, time to figure out how to drive the 12v LED strips from the ATtiny. Despite using high gain A63 Darlington NPN transistors, I was not able to get the LEDs to full brightness with a single transistor. I found that if I use a 2n2222 to pull the base to ground, I could get the desired light output.
The software is a mashup of a moodlight sketch and a firelight sketch I had laying around. I added some potentiometer control to limit the brightness of the flashing white light. This would make the board more universal for other seasons. Once I was satisfied the design works, I put it all together on a piece of Radio Shack protoboard I had laying about. I wrapped short LED strips around a cardboard tube and dangled it from the top of the pumpkin.
A more visual representation of the project can be seen in a short video I uploaded to YouTube earlier today.
Oh… do you think any of the kids noticed the cool pumpkin by the door? sigh… damn candy…