Numitrons are neat display devices similar to nixie tubes but designed for much lower voltages. Numitrons are basically incandescent displays in which filaments create the segments.

They have a retro look that i liked so much. I bought 6x IV-9 russian numitrons in ebay, they were about 3$ each, they're pretty cheap!
At that time i didn't know what to do with them, but then i thought about a clock. Using software from a single LED display clock i made this impressive numitron clock.

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Step 1: Program the PIC

The original purpose of the software was to drive a single common-anode LED display rather than a numitron, but either way works.
The software was modified to flash the digits so the HHMM LEDs wouldn't be necessary. Also the software was modified so if the tens of hours is 0 then it is not displayed.
Moreover, the software does not check the input values so entering the wrong time such as 67:85 would be accepted, but eventually the clock will start resetting the digits correctly.

The clock operates off a PIC 16F84A using a program written by David Tait (software is further down this page). The crystal oscillator for the clock is a 4MHz crystal.

I think another microcontroller such as PIC16F628A could also work fine.

Step 2: The circuit

After testing on the breadboard,  the clock works fine, with the current crystal the clock comes forward a minute each 3 days, with a precision one it can be solved, but it's good enough for me; because setting time is easy.
You can see the test video below and download the eagle schematic to modify it.

Since numitron displays are just complex bulbs, it could be a problem to drive them from the processor, but in this case, it's not a problem:
The PIC16F84A can source or sink 25mA per I/O pin.

But each port has a limit:

Maximum current sunk by PORTA-80 mA
Maximum current sourced by PORTA-50 mA

Maximum current sunk by PORTB-150 mA
Maximum current sourced by PORTB-100 mA

With IV-9/IV-16 each segment draws 20mA, but be careful if you choose another numitron!
edb19848 months ago

Hey there, nice guide -did you got the idea from Jon Stanley's website Electronixandmore? - on there if you read a few of his posts the accuracy of the crystal is addressed with two 24pf capacitors to ground.

if you want to make a watch why not try my design? its made from the same schematic you are using but forgeting the idea of a PCB. runs from one 18350 with a boost circuit to bring it up to 5v. it has the option to turn the LED's on and or off. with LED' on the battery will last about 20 hours, with them off it lasts about a day and a half. please note its not finished yet, and if your wondering the case is 3D printed.

pinomelean (author)  edb19848 months ago

Yes, the software and schematic came from there, i also forgot to use capacitors, but in the secod version (a pocket watch) i've added them an it keeps time a lot better.

You can comment using the "i made it" button, Nice watch though.

My new one is smaller, only 2x3.5x4.5cm with battery and case :)

Cool, did you get anywhere with trying to program it to show the time at the press of a button?

pinomelean (author)  edb19848 months ago

I need to learn a bit more about programming, i'm new in this.

The nerdling9 months ago

i slightly modded the board so now it is a proper watch :) i added a different button and capacitors to the crystal as mentioned in a comment below

here is a link to a 3d model of the board

pinomelean (author)  The nerdling9 months ago

I'm planning to make a second version, a pocket watch with a battery and so, i'm editing the software so it only shows the time when you push a button, to save energy. It will also use tiny incandescent bulbs instead of LEDs.

Maybe i'll post an instructable about it, but i need time.

Meanwhile you can take a look to the files below, they could be usefull for you!

mikoto093127 days ago

Thanks for detailed instruction. And I wonder if I can get .hex file that allows to display time when only a switch pressed, not periodcally.

pinomelean (author)  mikoto093127 days ago
I'm currently working ond that and many other upgrades to make a numitron watch.
I will probably publish an instructable when i finish it.
Ploopy5 months ago


florinc made it!6 months ago

I made a similar one, using Arduino Pro Mini:

Suraj Grewal8 months ago
ihart9 months ago

Awesome project!

pewtu9 months ago
In reply to g4ipz in UK you can get a free non restricted schematic and pcb drafting software Designspark given away by RS components. Are the files available for the redesign which includes the 2 extra capacitors and new layout?
pinomelean (author)  pewtu9 months ago

The .SCH and .BRD files are available in ''The circuit'' and ''PCB design'' steps, you can edit them and modify all you want, but that, without comercial purposes :)

g4ipz9 months ago

Hi Pinomelean. A nice little instructable.

Out of interest which schematic diagram and PCB drafting software do you use for your designs please as I like the end results better than what I use at the moment.

pinomelean (author)  g4ipz9 months ago

I use cadsoft eagle, with this softare you can open and edite the schematic and board files.

g4ipz pinomelean9 months ago

Thanks for that but I just checked the price and even the hobbyist version is well out of my price range. Thanks anyway.

pinomelean (author)  g4ipz9 months ago

If you mean the hobbist version of eagle, it's free!

That's why i use it.

Culito pinomelean9 months ago

This page shows $169 bucks, $69 for the "light" version...

pinomelean (author)  Culito9 months ago

Enter in the ''download'' tab and click on download eagle, choose your os and when you've intalled, choose the free version, it has limitations, but for hobbists is enough.

shizumadrive9 months ago

Id say it more retro than steampunk but its a very cool project. Id like to to see make a case and turn it into a watch

pinomelean (author)  shizumadrive9 months ago

Yeah, a case would make it look better, as i said to the nerdling (comments) i'm designing a pocket clock, just like this but with mini incandescent bulbs, portable with battery and much more features.

zaphodd429 months ago

Had to vote! Had to print it and put it in my "to-do" folder! Great 'ible! Thanx for the work!

When you say single digit, does that mean it gives the time serially? Flashing min, then tens of min, then hours, then tens of hours?

pinomelean (author)  luckylulujoe139 months ago

I flashes tens of hour, then hours, then tens of min, then min. Just like reading the time from left to right.

The LEDs indicate the digit being displayed.

uhclem9 months ago

I am surprised the micro is able to sink/source enough current to light the filaments.

pinomelean (author)  uhclem9 months ago

The PIC16F84A can source or sink 25mA per I/O pin.

But each port has a limit:

Maximum current sunk by PORTA-80 mA

Maximum current sourced by PORTA-50 mA

Maximum current sunk by PORTB-150 mA

Maximum current sourced by PORTB-100 mA

With this clock it isn't a problem since each segment draws 20mA.

andrea biffi9 months ago

I LOVE this watch!

pewtu9 months ago
Gaining 3 minutes a day seems quite a bit. How about putting a couple of 22pf capacitors, one from pin 15 to ground and the other from pin 16 to ground to load the crystal an see if it helps. Like the neat layout.

Says one minute every three days, not three every day; though the latter is still more accurate than the average non-professionally-adjusted mechanical clock mechanism.

pinomelean (author)  pewtu9 months ago

Thanks, i will try it in future projects.

Hardwired229 months ago
I like it!!


pinomelean (author)  kyle brinkerhoff9 months ago

Thanks, when i discovered them (and nixies) i couldn't think in LEDs anymore, retro displays rule!