Nixie Tube Clock

Note that this project is still being built. As of now only the power supply works

This is where I try to build a nixie tube clock. There end result should be a nice clock, but there really is no reason to make one. You could just go to a corner store and spend 20 bucks on a clock that will do more. They do look nice however, plus this thing will really be made from scratch. All the parts are individual parts, and will be installed on custom made boards.

First off nothing works without power, so lets begin with the power supply. The clock will have six nixie tubes of type IN-12A. IN-12B tubes are pretty much the same but they have a period next to them. These are Russian tubes, and are really quite difficult to find specs on. So courtesy of someone on Ebay here they are.

Before we begin let me just say if you don't know what you are doing do not try this, high voltages are dangerous and I am not responsible if anything bad happens even if it is because of an error in my design. As we can see from the tube specs in order to get the tube started we need a minimum of 170V DC and we want limit the supply to around 2.5ma of current, although I have found that 2ma of current is more than enough to light up a tube. To get 170+ volts I decided to design a little power supply. To supply 6 nixies plus a few 4 neon lights I will say it takes around 30 ma.

I used a Mouser part 546-187B120 transformer. This is a Hammond (Hammond part 187B120) 115VAC primary/120VCT secondary chassis mount transformer rated for 3VA. The transformer should produce wall voltage*1.0435. I measure the voltage by me to be 126VAC. This makes the transformer output 126*1.0435=131.4VAC. It is actually a bit higher than that, at 162.7VAC The DC rectified voltage should be around the peak to peak voltage of 162.7*sqrt(2)=230.1VDC. Due to losses and inperfections in the end I get 211VDC after it is rectified. This is good, plenty to fire up a tube.

This is the circuit from the LM317 data sheet. The 5V output circuit is based on this circuit. (T1, R2, R3, C2)

Next is the five volt portion of the supply. I had a 9VAC transformer hanging around so that is what I used. It is a Mouser part 673-030-7151-0, made by Pulse (part number 030-7151-0). It is a 115VAC/9VAC PCB mount 1.5VA transformer. It will fit right into the holes in the PCB I designed. This is rectified then fed into a linear voltage lm317 voltage controller, and dropped down to the required 5V.

All of the diodes are just your standard general purpose diodes. You can use anything you want provided they are rated for the correct voltage and current. So by no means does anyone need to use what I used.

Callout	Item	Value	Quantity
A1-9	Screw Terminal Blocks (I used PCBT2, and PCBT3 from futurlec.com)	2 or 3	As shown
None	Isolation Transformer	Mouser 546-187B120	1
None	9VAC Trnasformer	Mouser 673-030-7151-0	1
None	Diode	IN4004	9
R1	Resistor	1meg 1/2W (1/4W,1/8W ok)	1
R2	TrimPot	10K(Radiosmack 271-282 but can really be purchased anywhere)	1
R3	Resistor	290 (or similar)	1
T1	Voltage Regulator	LM317	1
C1	Electrolytic Cap	400V 47uf	1
C2	Electrolytic Cap	1f 5.5V	1

Note: The terminal blocks can be bought anywhere, futurlec is cheap and the service is good, but they are in Thailand and the stuff can take 2 weeks to get here. If you are in a rush they do carry them on mouser.

There are several notes that are imortant about this circuit board:
Be Very careful with R2 because it can easily be adjusted in such a way as to supply C2 with well above its rated voltage. Before plugging this circuitboard in make sure that R2 is turned ALL the way to one side. Counterclockwise, clockwise it doesn't matter, you just need the resistance to be low. After the unit is powered up plug a voltmeter into A7 and A8 and SLOWLY adjust. I say slowly because C2 is a 1 farad capacitor and can take minutes to charge. You may even want to substitue a smaller capacitor in its place, adjust R2, then install the 1f cap. This method gives the added safety (If you use a 50V cap or so) of not exploding if you over adjust R2. Depending on your requirements you may not even want to use such a large capacitor. The purpose of such a large cap is to keep the timekeeping part of the clock powered for a few hours when unplugged or if the power goes out If you don't need or care about that you can use something to smaller just to smooth out the DC.
R1 is not required but is recommended for safety. During operation it serves no purpose, once the supply looses power the resistor leaks the capicitor voltage away. The board should be safe to touch within 5 minutes or so.
On T1, a is Vin b is Vout, and c is adj.

A1	Connect to pin 5 (or 8) of Hammond transformer
A2	Connect to pin 8 (or 5) of Hammond transformer
A3	Connect to ground pin in receptacle
A4	Connect to hot (or nuetral) from receptacle
A5	Connect to pin nuetral (or hot) from receptacle
A6	Ground
A7	Nixie tube Voltage (210VDC)
A8	Low Voltage 5VDC
A9	Ground

The hot wire from the wall should be fused before going to the Hammond or being attached to the circuit board. I prefer to use plugs that have a fuse box built into it. Like mouser's 161-PF0030/28. Don't forget to get a cord.

Click on this picture to download a pdf of the board that will print to scale(provided you don't scale it when you print it).

To the right is the actual circuit board art that can be printed and used to create a working power supply. Use your own method, or use my method. Following this paragraph are actual pictures of my board. Note that there are corrections because the original one I made I screwed up. Rather than remaking it for myself I just fixed it and then corrected the drawings available on the site.