A POV Prototype
The best way to start a new project is to just jump into it. So for the heli lights, my first step was to prototype a POV display. I wanted to use an AVR microcontroller because I already had a programmer and some chips that I bought for other projects that I never got around to doing. The extent of my microcontroller knowledge didn’t go far beyond reading pushbuttons and lighting up LEDs, but I figured a POV display was pretty simple anyway, so this should be fairly easy to do. I looked to LadyAda’s SpokePOV for inspiration. She uses some 74HC595 shift registers with built-in latches to switch the LEDs on and off.
The 74HC595 is an 8-bit shift register. By daisy-chaining four of these chips together, I could address 32 LEDs individually and simultaneously using just a handful of output pins from the MCU. Unfortunately I did not have any 74HC595s on hand, but I did find some 74LS164s to use. These are also 8-bit shift registers but they lack the built-in latch of the 595s. To handle latching, I fed the output of the registers to some 74LS273 octal D flip-flops and used the flip-flop outputs to drive the LEDs. Within a couple of hours, I had my prototype built and spelling “LUKE” when I waved it through the air. (“LUKE” because that’s my roommate’s name, and I wanted him to be excited about what I just built.) Since it’s just for proof of concept, and since I was using a small breadboard, the prototype only used 16 LEDs. I knew that I wanted 32 LEDs for my blades, but I figured if I could daisy-chain two registers successfully, then doing the same to four of them should be no problem.