Last post about this was 8 months ago, works been busy so I haven't really thought about this, plus I was a bit low on my electronics piggy bank so had so rebuild that up. Lately I saw a Nixie Tube Watch that really caught my eye. Most I'd seen were two tubes like the famous Wozniak one from Cathode Corner I linked to last time but this one had 4 tubes which makes reading the time so much more practical. Its by a guy called "horizonte" and he's got a very skint instructable on it. So damn gorgeous, I figure I can do that, plus he's selling it on etsy for like $600! I'm still aiming to do inductive charging and haven't seen anyone in the community try that yet. So I'm back on the horse baby!
Inspiration
I went back and did a bunch of research on Nixies and other peoples' projects. At the end of this post is a small reading list I'd recommend, but the best way to start is just buy some stuff and try to build something, anything!
Power Supply
No matter what nixie tube you're doing you won't get anywhere if you can't make ~180vdc. Since I'm gonna have a single cell LiPo in my watch then I'll need to step up the 3.7v from the battery up to ~180v. Cathode Corner's design is a really cleaver one that wastes the least amount of power. Most Nixies have a series resistor to drop the initial 180v generated across the tube to about 120-160v since after the lighting the tube at 180v you can oporate the the tube from anything above ~120v. This 40 volt drop wastes a lot of power across that series resistor so what Cathode Corner did is to tune the boost converter circuit to have an open circuit output of 180v but once the 2mA starts flowing the feedback pin voltage raises 300mV to trick the regulator into regulating its voltage down to 140v, its truly genius. Some specific components he had in his original circuit were obselete now so I had to make due with what I could find. Remember that diode Vf is really important so schottkies really need to be schottkies. Also the transformer I ordered was way to big for a watch but I'll be changing that guy after this step once I light up some Nixies and have a stable circuit. See my digikey BOM for specific part numbers
To my surprise the circuit powred up at produced 170v! this was amazing, but the feeling was fleeting since after a power cycle it came back at like 50v. After a bunch of poking and proading I found out input capacitance is a big deal. See the screen grab of my scope below, you can see the damn power supply is trying to output 3.3v but the voltage at the chip's input goes all the way to 18v when the transformer kicks which was freaking out the converter. I soldered ~400nF cap at the input and I get out 180v clean! Also no more kickback from the transformer rippling back to my power supply.
One thing I've learned is input capacitance is really important. They tell you that in school but you never quite pay attention, definitely won't forget that. I've ordered an IN-17 Nixie tube from Sphere Research Corp in Canada. They're prices are a little higher than Russian sites but they are definitely reliable. Next step will be lighting that sample tube I bought and see its pretty numbers glow. After that the transformer has to change to something way smaller. Will need to look into digikey and mouser for parts. The design calls for 1:12 turn ratio but I don't know why a different ratio wouldn't work so we'll see. Hopefully I'll have another pretty picture for you guys in a few days!
Reading List: