Hex Display Module

Hex character module made from 3mm USSR 7-segment displays

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A simple binary to hex display module with tiny 7-segment LEDs and MC14495 hex drivers.

I ran across some tiny green 7-segment displays for sale, advertised as NOS parts from the USSR. The seller said they were L104V, but I couldn't find any information with that part number. It was also stated they were identical to Sanken Electric SEL620, but that would require a very loose interpretation of the word "identical".  The seller provided a partial, modern looking datasheet and a few specs for the part, which was helpful. But, I kept looking and found a writeup from Industrial Alchemy about the AL304V with some excellent photos that are actually identical looking to the L104V parts. Armed with a new part number I was able to find a Russian language datasheet. After a bit of research, I decided to pair the displays with MC14495 decoder/drivers. I purchased both at the same time, the LEDs from Ukraine and the drivers from China. The LEDs took 17 days to arrive to me on the West coast of the US, and the driver chips took 21 days.

My goal is to use these parts to create both 2 and 4 character hex display modules. The aesthetics of the finished project is important, I want something that looks different and shows off these cool looking 7-segment displays. I don't have a project to use the finished display module in yet, but I have a few ideas.


Datasheet for MC14495

Adobe Portable Document Format - 124.75 kB - 09/23/2023 at 14:33



Datasheet for AL304V (Russian language)

Adobe Portable Document Format - 160.45 kB - 09/23/2023 at 14:32


  • Design Ideas

    Robert10/01/2023 at 22:50 0 comments

    The look of these vintage displays are what drew me to them, and the gold pins are an important part of that visual appeal. I'd like to be able to keep the pins straight and visible, and preferable gold. Unfortunately, solder will cover some of the gold finish, that is unless gold solder is an option (doubtful). I haven't made any decisions yet, but soldering them down to a PCB is the backup plan. My primary plan is to use a socket of some kind.

    To help consider ideas, I made a model of the displays in Tinkercad. I'm rather new to 3d modeling, so it was good practice. It's not perfect, but it should work.

    I also mocked up some PCB mounting patterns.

  • Exp 1 Update

    Robert09/29/2023 at 00:30 0 comments

    While I wait for parts to use the 7-segment Soviet displays, I picked up a few HP units that will fit on a breadboard. I already verified the driver chips are functional, so I didn't really need these new displays, but I got them anyway. They seem to work fine and I really like their all-red look. The part number is 5082-7653. I've also worked on a rough draft of the circuit board, once the new parts arrive I'll verify some measurements and get the boards ordered. 

  • First Experiment

    Robert09/26/2023 at 01:08 0 comments

    I put together a quick breadboard circuit to test the functionality of the MC14495 driver chips I purchased. I don't have a breadboard friendly common-cathode 7-segment display at the moment, so I used one column of a 8x8 matrix and a single LED to test all 9 outputs. I also added a dip switch to test the 5 inputs. Thankfully, all the chips seem to be fully functional.

    The lit column is (from top to bottom) a, b, c, d, e, f, g and h+i. The currently displayed character is 'A', so all segments except d are lit. Additionally, h+i is lit because the character is a letter and j is not lit (green LED) because the data inputs are not all 1's.

  • LED Driver

    Robert09/24/2023 at 01:52 0 comments

    For a 4 character module I'll need to drive up to 32 LEDs with a common cathode configuration. Each character in the display will be a hexadecimal character of a 4-bit binary number. Additionally, the module must have a have a single latch line to latch data from a bus.

    The MC14495 "Hexadecimal-to-Seven Segment Latch/Decoder LED Driver" is a common suggestion. It is designed for common cathode, it has a character ROM for 7-segment hexadecimal characters, it has built-in 290Ω current-limiting resistors and it has a latch. Unfortunately, to keep it simple, it requires 1 chip per character. And, they are not as common and cheap as they used to be.

    For I/O, the MC14495 has a 4-bit data input (A, B, C, D) along with a latch enable (LE) input. For outputs, it has one for each segment in a 7-segment display (a, b, c, d, e, f, g), and a line that is low for characters 0 thru 9 and goes high when the character is A thru F (h + i). Finally, it has a line that is normally high-impedance but goes low when the character is F (j). I don't have a use for the (h+i) and (j) outputs, so I'll tie them to ground. 

    The MC14495 is larger than the L104V, which  presents a challenge in keeping the finished project small enough and nice to look at.

  • The 7-Segment Displays Arrive

    Robert09/23/2023 at 14:59 0 comments

    From the photos and datasheet I knew exactly how big these parts were, but there is something different about holding them in your hand. These things are small, very small. I don't know how I'm going to breadboard the circuit with something so small. I don't want to solder the pins yet so I'm currently coming up with a solution. For now, I'll post photos and specs of the LEDs.

    I'll be conservative the first time I light up these LEDs. Both sources of information agree on 3v, which sounds about right for a green LED. But they disagree on maximum current per segment, one says 7mA, the other says 11mA. 

    Here is the partial datasheet provided by the seller:

    And here are the specifications listed in the description:

    Important part in the AL304V datasheet, auto-translated from Russian:

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Lee Hart wrote 10/02/2023 at 14:47 point

This is a great project idea. I have some ancient red MAN-1 7-seg LEDs in this same package. You may have inspired me to use them.

A thought for a project: How about an 1802 ELF computer? (Popular Electronics August 1976) It used two (now rare) H-P hex displays, but many people have used the MC14495 with two 7-seg LEDs to replace it.

  Are you sure? yes | no

Robert wrote 10/02/2023 at 16:49 point

What a coincidence, an original ELF is on my project list. I've been researching and collecting parts to build several of them for a while. If it works out, I'll keep two and sell the extra parts on Tindie. In fact, I recognize your name from the COSMAC ELF Group, I've been browsing the message archives regularly.

I want to complete an easy project or two as a warm-up before I start the ELF. I've never been good at documenting my projects, so I'm trying to change that. I plan to have one ELF as original as possible, but the second one I want to look unique, so I'll use these Soviet 7-segment displays.

The MAN1 is a great looking display, Industrial Alchemy has a short writeup and some nice photos of it, I'd love to pick up a pair one day. 

  Are you sure? yes | no

jdFin wrote 09/30/2023 at 02:42 point

New follower can't wait to see what you do with these things. Pressure's on! :)

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allexoK wrote 09/24/2023 at 15:07 point

Cool project!

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Robert wrote 09/25/2023 at 01:53 point

Thanks! I loved the look of the 7-segment displays and figured I could use them for an easy project.

  Are you sure? yes | no

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