The original clock, meant as an engagement present for my sister and her fiance, Andria and I thought we could do it all in 6 days. A little too ambitious, but a great idea nevertheless.
After severely missing our deadline for the engagement party, we decided to start over. Taking a little more time and care we figured the clock would be better suited as a wedding gift. Since we now had 6 months instead of 6 days, we added a few more things, like the La Vie en Rose music box. I also decided that rather than use wired tubes, it would probably be better to allow for replacement of the tubes, so sockets would be necessary. To make the base, top level, and gear box for the stepper motor, I used multiple layers of ponoko cutouts:
The nixie tubes and music box (via stepper motor) are controlled from below through a standard nixie tube circuit. Two 74141 ICs are multiplexed to drive 4 tubes from one shift register. So 3 pins on the shift register can control 40 nixie tube pins! And since they’re multiplexed, the fading during transition effect is somewhat easier and tube life is increased. The tubes are powered using a switch mode power supply circuit based on the MAX1771 IC. Unfortunately, as often happens, I made a mistake in my circuit. I won’t go into details….because it’s embarassing. Luckily, there was an easy fix, as you can see from the image below, I had to add a small board below. Other than that, no problems….Eagle files are below if you’re interested.
The buttons shown there and the pcb below them come from sparkfun. Unfortunately, I had to buy three sets, and cut each one up to get the large buttons. I thought I was out of available pins for input on the microcontroller,(turned out I was wrong), but whatever works. The red LED switch is from radioshack, and the stepper motor is from here. Only a buck for a stepper motor! At first I was skeptical, then, after following the directions from the website, I was saddened to realize I might need a more powerful motor. However, then I stumbled across a datasheet for a different motor and decided to try their method. Turns out it worked great! So if you buy that motor, don’t follow their directions, my code is below for anyone that wants it.