This project started as simple projects do, but then kept growing with inevitable feature creep. The good news is that Candle+ meets all of the original needs with only minimal costs to really expand its usefulness tremendously.
I started with the need to make an electronic candle that is programmable so I can make it flicker and look like a regular flame from a candle. This will support a project my wife and I have been working on, which is a hanging glass lantern. We wanted to place two candles, one in the middle and another further down to make nice looking colored glass hanging ornament for your back porch in the evening. As we started working through the how-to mechanics, I was concerned that the lower candle was going to heat the upper candle just too much. So, why not do a faux candle out of some really bright LEDs and a tiny microprocessor? The concept was born.
So, in the span of about two evenings, I discovered that the ATtiny45/85 series of processors can be used with Arduino if you have an external programmer and it supports PWM, so I was on my way. After the first PCB design was complete, I noticed that I'd have to expose several pins for the ICSP programmer. Then the feature creep hit me like a wet fish: "hey, if I just expose a few more pins on here, I'll end up with a ATtiny break-out board". Then: "hey, since I have a micro-USB port here for recharging the battery, why not just add a couple of pull-up resistors to enable the virtual USB capability"? "Oh, and hey, it would be nice if this could be used on a breadboard? So, I'll need to line the pins up in a 0.1 pattern". "Doh, what if I don't want those LEDs or pull-ups on my circuit? Better put some solder jumpers in there to disconnect them if needed". And lastly, "hey, what if I want to have multiple blink patterns stored in flash? How 'bout a little momentary switch to change the flicker patterns or colors?" Thus, this is how the "plus" part of the candle project got there.
While it started as a utilitarian effort to provide a virtual candle for a lantern, it quickly grew into a prototyping platform for an ATtiny85 while still maintaining the original rechargeable candle idea I started with.
Specs:
The board is round (about 1.3 inches in diameter) with a flat spot on one side. The thought is that the whole board will sit on top of a lithium polymer battery down inside a frosted shot glass and the power cord can slip under the board where the flat spot is. I'll probably just use a piece of double sided sticky foam tape to attach the battery to the bottom of the board. That should keep from shorting out the vias with the foil shell of the battery and keep everything together in a nice neat package. Below is a picture of the design from Eagle. I'm currently waiting for the board to be fabricated and shipped to me from my favorite prototyping PCB shop OSHpark.
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