Nixie clock demo

The latest project, a nixie clock, is almost done! Just needs a few more tweaks and a replacement driver chip for the left most digit.

Nixie test

Here is a short video of the nixie tube clock with the first nixie tube connected.  The controller board uses a PIC24FV32KA302 processor, a 74HC595 shift register, a 74LS374 octal latch and 74141 driver chip to control an IN-14 nixie tube.

Check back for more on the clock.

Nixie boards

So the nixie boards are in.  I used iTeadStudios from China to make a few daughter boards that hold 2 nixies, 2 74141 driver chips and a 74LS374 octal latch.  Using a 374 latch and the 74141 chips allow me to write an 8-bit value to the boards and latch it in.

The boards are 5cm by 5cm and cost <$2 each from iTead since I got 10. Shipping took about a month, so if you plan on using them, plan accordingly.

The daughter boards are attached to a controller board with a PIC24FV32KA302 micro and a 74LS595 shift register.  The controller was made by Advanced Circuits here in colorado and came in today after about ~5 business days. I have to say it is probally my best board ever, guess all this practice is paying off.  I did make a few mistakes, including routing the nixie board connector backwards, which means some hacked connector pins. Good decisions PCBs come from experience, experience come from making bad decisions PCBs.

Controller schematic

Daughter boards (I forgot to add 5V to the connector, so that is a blue wire)

Powering 170v tubes from the wall

So I’ve been working on how to power nixie tubes in the simplest way, getting 170v isn’t as easy as connecting a wall-wart and using an LDO.  There are lots of boost circuits to go from 5v or 12v up to ~170v, but there are tons of options, can be a little on the expensive and some include a bunch of extra components which I don’t really want to deal with.  I decided to investigate powering the tubes from the rectified 120vac mains.

US mains AC is 120v RMS, which means using a full-bridge rectifier would result in a peak voltage of 170vdc [RMS and and full bridge rectifier].  Adding a capacitor to the output would hold the voltage at the peak of 170vdc.  As power is used from the capacitor it is replenished to 170v at a rate of 120Hz, resulting a 120Hz ripple voltage.  The tubes only use 2.5 mA each, so with a total of  15mA of draw I figured a little DF04 bridge rectifier and a 200v 10uF cap should work just fine.  I made up a little test board last night and hooked up a scope today.

Looks like with a 20mA draw there is about 14v of ripple, the min voltage is 158v (above the cut off for the tubes) and the drain time once power is pulled is ~300ms, which means the cap won’t be charged to 170v for too long.

Now I just need to figure out a way to get down to 5v from the mains without a gigantic transformer

The start of the Nixie Clock

So I committed 100% to the Nixie Clock.  On September 29th I bought a lot of 6 IN-14 nixie tubes [datasheet pdf] off ebay from radiokomponent for about $9.50 each including shipping from the Ukraine.  I was a little worried about the shipping taking forever but they arrived in Colorado today, so not too bad. I also bought an IN-12B nixie [info] for about $6 to test with.

A word of warning on purchasing off ebay, the tube I purchased was an IN-12B, however the shipper sent an IN-12A.  The A part is without a comma, so be careful if you are expecting an exact part.

The tubes look in good shape, and look never used.  The IN-14s are about 2.25 inches tall including the plastic base, marked as “ИH-14” and have an awesome retro CCCP logo on the back, very cold war.

Tonight I made up a footprint in Eagle to mount the IN-12A and am routing it out on a little test PCB on my router (I know I need to post about that).  The IN-12A footprint isn’t too hard to make in eagle, everything is pretty much on the 0.5mm mark.  After two tries the PCB came out pretty good and mounts the IN-12B snug with 1.2mm (~48mil) holes.

Tonight after some research I bought six 74141 high voltage driver chips to interface the tubes.

That’s it for now, check back for more from the build

Next project

Super busy lately with work and taking an embedded design course for my masters.  In the embedded course we have to build a custom project by the end of the semester, I think I am going to build a Nixie clock that has a countdown and count up timer.

This video isn’t mine but it’s an idea on what I want to do.