Introduction: IN-12 Nixie Clock
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.
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)
-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.
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