IN-12 Nixie Clock




About: I love electronics and all about DIY.

Ever since i discovered nixies i wanted to make a clock with them, but all the designs i found were for 4 or more nixies, required a custom power supply and a complicated driving system.

As the cheap guy i am, i didn't want to buy lots of nixies or components to make such complicated circuits. And after ages looking for a simple clock design i came up with this page.

This clock uses a single chip which i've already used before, the PIC16F84A. The circuit is also pretty simple since it uses a single nixie, driven by discrete transistors and doesn't need a powerful HV supply.

In the page only the schematic and code are provided because this guy builds his circuits on veroboard, But i wanted to make a good-looking clock so i decided to design and make a PCB.

The tube i've used is an IN-12A, but a B variant can be used as well (or any other nixie tube with the proper circuit modifications). The high voltage supply uses components from a disposable camera, so it also costs almost nothing.

The clock displays the time periodically flashing the digits from tens of hours to minutes.

To set the time you have to push the button when the digit you want to change is being displayed, it will increase each time you push and cycle from 0-9.

If you hold down the button during power on, the clock will rapidly cycle trough the digits. It is useful to kill off some "cathode poisoning" on nixies that have not been used in a while.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: The Main Board

The main board contains all the components except the high voltage power supply, so anyone can build a different HV circuit without changing this board.

The .brd and .sch files are available so you can modify the circuit as you please

The PDF file is linked down so you can make your own PCB.

The components needed for this board are:

-The IN-12 tube (4$ on ebay)

-A PIC16F84A

-10x high voltage SMD transistors (I've used the MMBTA42)

-13x 0805 resistors

-A 4MHz crystal

-2x 22pF capacitors

-A push button

-2x 2pin female headers + 1x 2pin 90º male header

-Fine soldering skills

Step 2: High Voltage Supply

This high voltage supply uses components salvaged from a disposable camera (only the transformer, the diode and the output capacitor). T reverse-engineered the camera circuit and made this one with the same design.

I've changed the original trough-hole transistor for a SI2302 mosfet and reversed the diode for a positive voltage output.

The LM317 lowers the 5v imput to the 1.5v the circuit needs. The copper fins keep it cool during operation.

To use this same circuit, you should check if the transformer you use is connected in the same way to the rest of the components (has the same pinout).

If you use a different mosfet, make sure it has a low on-resistance so it doesn't dissipate much heat.

Step 3: Program the PIC

To program the code into the PIC, you'll need a programmer circuit and software for it. I used a chinese k150 programmer with the software it came with. You need to load the .hex file into the program, and burn the chip with it.

Some of the program features are:

It keeps time very accurately.

Works in 24h format.

If you set a wrong time (like 26:72) it will eventually autoreset.

There is a chime logic pulse output on pin 2 (RA3). The logic output will give a number of pulses in accord to the hour when the minutes turn to zeros. For instance, there are 8 logic pulses from pin 2 when the time turns to 8:00. The output is not an audio frequency, it is a simple logic pulse, so one would need an tone or chime generator for the audio.

Holding down the time set switch while the clock is first powered up will set it in a test mode that cycles through all the digits. It is useful to kill off some "cathode poisoning" on nixies that have not been used in a while.

If you programmed it correctly, the first time you power it up it should start at 10:00 (unless you hold down the button)

Step 4: Ready to Work

The finished clock could fit in a 35mm (1.38 inch) sided cube. It can be powered with a li-ion battery or an usb cable (3-5.5v) and consumes about 150mA

I would have made a case for it but i didn't find any suitable material, i hope i could 3D print an enclosure.

If you decide to build this clock, remember that it uses high voltage (up to 400v). The HV supply i used isn't capable of killing anyone, but that doesn't mean it can't shock the hell out of you.

If you have any doubt about the instructable or need any help, fell free to ask it in the comments.

Also, you can vote me for the Make it glow contest.

Make it Glow!

Participated in the
Make it Glow!

2 People Made This Project!


  • Indoor Lighting Contest

    Indoor Lighting Contest
  • Make It Fly Challenge

    Make It Fly Challenge
  • Growing Beyond Earth Maker Contest

    Growing Beyond Earth Maker Contest

49 Discussions


7 months ago

from which camera is the transformer used? model?


Question 9 months ago

Hi, I just build this project but doesn't work.
it shows nothing when I power on.
but when I push the button while power on, it shows "1", push agin shows digit "2" etc, sometimes does not shows.
at least the psu is correct, i use different board for psu.

I use Pickit3 to program the hex to PIC chips, I try burn 2 PIC chips but the result is the same.

I can't fine what's wrong, I tought the programming, but I burn different chip and still the same.
I verify after burn shows no error.

help.... appriciate your help

andrea biffi

1 year ago

I love this clock! Awesome project I will try to make one for sure! Thanks!


1 year ago

Will the circuits and high voltage supply work with an IN-17 nixie?


2 years ago

Hey! I made the circuit on a breadboard with a 555 based power supply. When testing, the PIC runs about 10 times faster than it should. I checked every connection, every part (including the crystal). Any ideas what might be the cause of such issues?


4 years ago

Did you use a IN-12 a or b ? Is there a difference

2 replies

Reply 3 years ago

The only difference is that the IN-12B has a decimal point in the lower right corner. That's all!


3 years ago

I have no experience in these stuff, planning to build one. I have question that confused me a bit.

I've noticed copper fin is gone in the final product. Was it useless?

I see on step 2 picture +5v, GND ,GND, HV+ have male pin. is it pulled from male header?

What are those files brd,sch,hex,asm files are used for?

I Hope I don't get answer after a year ha ha

5 replies

Reply 3 years ago

Additional question, on step 1 is the red line on purple pcb board wire?


Reply 3 years ago

More questions, what part do I need to connect batttery and this invention, how to recharge the battery

Dashing Rainbow Dashp8662

Reply 3 years ago

If you look online, you can find Li-ion chargers that you can connect the battery to. The one I had (before I fried it accidentally) could be plugged into with a mini usb cable.


Reply 3 years ago

The red lines are jumper wires if you're making a single layer PCB.


Reply 3 years ago

thanks I'll look forward your answers


4 years ago on Introduction

Really cool project, I've never programmed a PIC before how did you work out the program. Do I need to use the .hex and .asm files to write to the PIC? What can I use to do that? Sorry I as I've said I'm a newbie. Thanks.

1 reply

4 years ago on Introduction

It's such a cool thing. I really want to repeat it. But I have a problem with the power board, I do not know what a transformer, a diode and a capacitor you have used and from which it took the camera. Tell please for more details about these and write their characteristics. I need your help, please help me.