Here’s my 555 Contest Entry!  A Nixie Tube Keychain!

Check out the schematics here:
555 Nixie Tube Keychain - Brett (FightCube.com) (1268)

Check out the video here (QUICK VERSION):

Here’s the super extended video (LONG VERSION):

I originally created the first video to get entered in the contest JUST BEFORE THE DEADLINE.  Had to cut out most of the details to get this cut and uploaded to the 555contest with 6 minutes to spare!!!

Picture gallery here:

As soon as I heard about the 555 timer contest, I knew I had to come up with something inspiring!  My buddy Jay recently introduced me to Nixie Tubes, and I thought… hmm, how can I use a tube and the 555 timer?  I noodled on it for a while, and ultimately came up with the notion of a KEYCHAIN!  Simple really, take the smallest Nixie Tube that displays digits, and make it display a ‘5’ in the smallest package possible and put it on a keychain.  That was the idea… and it took quite a journey to complete.

I started with LTSpiceIV, a circuit simulation software package.  I put together a few simple 555 configurations and shared them with the world for everyone to get cracking on 555 timer projects.  Little did I know then, but I was already way behind.  Once I got a 555 circuit driving a transformer, I played around with all kinds of feedback methods and transformer ratios.  I used voltage doubler circuits on the secondary of a smaller transformer, and also tried a simple boost converter topology.  The problem initially was that I was trying to step up a 3V battery to 140V+ with at least 1.5mA of current.  This is a tough feat with the 555.  Sure it will run down to 2V… ish, but you need to drive something with that 2-3V and multiply your voltage by at least 70X.  Also trying to get enough current from a super tiny battery is tough!  I researched just about every little coin cell and lithium camera battery out there, and almost at the last minute I went with the 12V A23 battery, which interestingly enough fits in a 1.5V N cell battery holder perfectly!

Once I got something up and running in LTspiceIV, I breadboarded the step-up part of the circuit.  At this point I really wasn’t considering anything else besides just displaying a ‘5’… but then that grew into a huge mess.  I thought, no… I need MOAR!!! so I decided to build a LOCK and KEY.  The keychain was going to be the Key obviously, and I was going to build a frequency decoder out of a crap load of 555’s.  I had schemed up a plan to build a Phase Locked Loop and Lock Detector out of 555’s, something that hasn’t been done as far as I could tell.  To make a long story WAY shorter.. I scrubbed the whole idea after I had it DONE.. really it wasn’t enough 555’s and was more transistor logic than anything.  It just wasn’t SHOWCASING the 555 for what it is.  A simple and really useful little timer chip… so I decided to keep things simple and just display the ‘5’.  My buddy Jay and I have coined this simplification process, “Get Dumb”.  When you just need to GET IT DONE… in the simplest and most effective way, stop thinking about it and Get Dumb.

Dumb I got, and the creative juices started flowing.  Before I knew it I was laying out the schematic in OrCad Capture, and doing a PCB layout in one night.  I had a single sided board that would power a digit, but that was too easy.  I needed a little bit more… So I added some solder jumpers to be able to easy “wick” off of solder from one jumper, and solder in a new digit.  This was good, real good.  It was clean, elegant, and … oh crap I need to mount this Nixie Tube some how… and what about an enclosure and push button???

Well I hadn’t gotten that far in my thought process… maybe I was dumbing it down too much?  Sitting up straight in my chair I decided… the PCB would BE the enclosure… because you can’t enclose ART.  And that’s what this IS, a work of art.  I quickly measured the IN-17’s lead spacing and found it would fit on a 0.1″ spaced SMT edge connector… custom of course… but fairly standard spacing.  Once I did this though, I had crept into the double sided realm!  Oh nos!  Thoughts of etching a double sided PCB and all of the alignment issues I was about to have scared me straight to bed.

I tossed and turned that night… gee this was like a week ago… and mulled it over as I tried to sleep.  I thought I could put a TQFP 32 pin microcontroller on the bottom and partially wire it up for a rainy day… but then, that would kill the simplicity of the 555.  Then a brilliant idea struck… what if I modulated the constant current driver that was originally just being pulled up to the supply rail?  I quickly concluded that it WOULD be done in the morning, as I drifted off to sleep.

The next morning it was back to LTSpiceIV, and I quickly whipped up two Astable oscillators and played with various resistor and capacitor values I had, and varied the power supply voltage to check if everything was working across the discharge range.  It was close enough, and a second page was born on my schematic.  Within a very short period of time I had added the components to the bottom of the layout (including a surface mount slide switch that I had to create a symbol and footprint for), routed everything and went back for my 3rd cup of coffee 😉

It was looking sweet, but I needed some components QUICKLY… and I ordered a bunch of stuff from Digikey.com on Thursday night, Feb 24th.  Naturally I HAD to make the shipment an OVERNIGHT delivery because well, I DIDN’T HAVE MUCH TIME LEFT!!!!!!!!!  Wouldn’t you know it though… they didn’t ship the parts out until Friday for Monday delivery.  A few curse words later and I decided I WOULD get this done… hell or high water.  I went down into my LAB and started working on the PCB.

It had been a little while since my last homemade PCB, but I remembered the steps… and found some new ones too.  I really like the PCB toner transfer method, and it’s super easy with the converted PCB Toner Laminator… which is way easier and more consistent than an iron.  The green foil is another step that adds a little more protection to the toner resist, and allows you to etch super fine tracks.  Most of the process went way better than expected, until I got to the silkscreen.  I was rushing towards the end, considering it was 2am on Sunday at this point… and added the Silkscreen via toner too hastily.  It mostly transferred though, so I can’t complain much.  The end result is rather bitchin’ if I do say so myself.

I hope this inspires some of you to play around with Nixie Tubes!  They are wonderful little devices, and I’ve tried to capture some of the awe and wonder of them in my pictures.