Make my own 7 Segment Display

[PixieDust]

Hi,

I want to make a custom 7 segment display because I can't find one for sale that suits my needs. I spent a few hours scouring the net and came up with no results in terms of how to make one. Well there's people making massive ones, but I need to make a tiny one, the whole unit needs to be no more than 10mm in height. Any tips, suggestions, ideas?

[phil from seattle]

I don't think you've looked hard enough.  I went on mouser and found several that were 10mm high or less.

[PixieDust]

It's not the size that I can't find, it's the way the characters are displayed.

[Ian.M]

If you really had to, you could mount a series chain of 0402 or even 0201 SMD LEDs for each segment on a custom double sided FR4 PCB to make the desired segment pattern for the required number of digits, then either laser cut or 3D print the face of the display from black ABS, with each segment as a void, and attach it to the PCB with translucent resin to fill each segment and diffuse the dots from the individual LEDs.   

It would be rather expensive and a total PITA to assemble . . . . .

[Leo Bodnar]

It does not specify it should be LED so my solution would be to make custom LCD panel.  If you want it glow, use LED backlight.
I have made custom LCD panels (coincidentally, 7-segment displays in the shape and digit distance I wanted) in China and it is really easy.  Send them a drawing or sketch, approve their drawing, pay, then get half a dozen samples and go for production if OK.

Leo

P.S. I have been told there was a custom LCD video recently on eevblog

[PixieDust]

That's the same train of thought as I had. Only I got stuck on how to fill the cutout for the LED 'lenses'. I couldn't think of anything better than injecting plastic of some sort. Resin sounds like a much more workable solution although I'm sure finding it in small quantities will be a massive PITA. Might need a syringe for this and will have to research appropriate resins for the job. Thankfully, I don't need to make too many of these, so I think the PITA factor is minimal.

Leo, it has to be LED.

If anyone has any other suggestions, I'm all ears.

[Ian.M]

Resin is a *massive* PITA factor for assembly.  You basically need to pot the assembled PCB in the resin without getting any on the pins (or back side and edges if you are building a module for SMD mounting),  hold the display face plastic in position against the PCB until it cures, and get a good finish on the segment faces.   This will probably require tape to retain the resin, that is peeled off the display face after the resin has cured followed by polishing it.    Many clear Epoxies would be suitable, probably with some white or coloured pigment added to obtain the desired degree of translucency

Another option would be graphic OLED displays.   30mm x 11.5mm displays are readily available and each could show three 10mm high digits with similar spacing to discrete 10mm 7 segment LED displays, or four digits if you use tighter spacing and narrower digits.    If you need to emulate a multiplexed 7 segment LED, you'll also need a MCU that can read the segment and digit lines fast enough to keep up with the multiplexing and send appropriate graphics to the OLED whenever a segment changes.

[GeorgeOfTheJungle]

You don't even need resin, any diffuser will do for example paper:

[Buriedcode]

I believe most diffusing plastic is epoxy with glass powder added, at a pinch standard hot-glue seems to work reasonably well, but given its thickness can be very hard to fill the gaps evenly.

So what kind of digits are we talking about here? how many segments?

[PixieDust]

You basically need to pot the assembled PCB in the resin without getting any on the pins

Is resin conductive?

I don't think resin is a problem. I can assemble it in layers. Have a top layer with the resin injected and then another layer separating the top layer from the PCB. That way the resin won't even be touching the LEDs. It'll be like a cake.

Another option would be graphic OLED displays.   30mm x 11.5mm displays are readily available and each could show three 10mm high digits with similar spacing to discrete 10mm 7 segment LED displays, or four digits if you use tighter spacing and narrower digits.    If you need to emulate a multiplexed 7 segment LED, you'll also need a MCU that can read the segment and digit lines fast enough to keep up with the multiplexing and send appropriate graphics to the OLED whenever a segment changes.

I'll have a look into OLEDs but I don't think they'll suit. Displays are really not ideal in terms of shape. I need other things in the vicinity of the digits and the displays will be in the way.

You don't even need resin, any diffuser will do for example paper:

Didn't know this. But I think it looks a bit too dull/washed out with paper.

I believe most diffusing plastic is epoxy with glass powder added, at a pinch standard hot-glue seems to work reasonably well, but given its thickness can be very hard to fill the gaps evenly.

So what kind of digits are we talking about here? how many segments?

Thanks! Will look into this.

[CatalinaWOW]

You don't mention quantity.  Will this be produced or is it a one off?  In the latter case a couple more options come up.  From thinking of the three separate functions you are trying to achieve.

1.  Diffusion/blending of LED light.
2.  Elimination of crosstalk/bleeding between segments.
3.  Segment definition.

The first can be achieved with sheet diffusers as mentioned above.  Paper is not the only option.

The second could in a pinch be done by gluing up walls of paper.  More practical would be stacking layers of paper cut with a stencil cutter.  And finally this could be achieved using a sheet of honeycomb material.  The honeycomb material doesn't have to match the segment shape, just have to have cells smaller than the spacing between segments.  This approach eliminates alignment issues, but it will be tough to source honeycomb of that small cell size.  0.69 mm is smallest I have seen advertised, and I haven't actually seen that.

Finally, the segment definition can be printed on a top layer. 

Some implementations of this approach would even be suitable for a production approach.

[james_s]

I have some 4" high 7 segment LED displays, they were not terribly expensive.

Lots of options for making your own though. Cut a mask out of black plastic sheet and then glue a sheet of frosted plastic over it, illuminate the segments with LEDs. Another option is route the segments into a sheet of plywood with a CNC router and cover with frosted plastic. If you don't care about the diffused segment look, you can make them out of rows or outlines of individual LEDs, or on a PCB using SMT LEDs. I saw a project years ago of a 7 segment LED clock made with EL strips forming the segments. If I had space I always thought it would be cool to make a large clock using 4' fluorescent tubes as the segments. Your imagination is the limit.

[tooki]

It's not the size that I can't find, it's the way the characters are displayed.

Meaning what?

[DaJMasta]

Have you looked around at old school LED matrix single character displays?  There are some 5x7 matrix single character displays in DIP packages that are not nearly as thick as most regular LED modules that could fit the bill if you don't mind the retro look.


If you really need ultra thin and you're doing DIY... you could probably use side firing SMD LEDs and then use a 3d printed gasket to basically form the segments adjacent to the arranged LEDs (so it's shifted up, for example, from the pattern of LEDs on the PCB) but fits over the LEDs to reduce thickness.  Then you fill the segment wells the LEDs are aiming into with your diffuser.  Complicated and probably a horrible idea for a production run, but probably something you could get right in a couple attempts for a one-off.


I think the blurred look you're seeing on the paper diffuser is something that could be worked around by sort of adjusting the focus of the LED.  Using one with a different illumination angle, or playing with the depth of the black plastic piece may give you much better results.  Using a potting compound to fill in the wells would probably alleviated this, though.  It also could be that the paper wasn't totally level in the shot and you're seeing some variation from that.

[GeorgeOfTheJungle]

I think the blurred look you're seeing on the paper diffuser is something that could be worked around by sort of adjusting the focus of the LED.  Using one with a different illumination angle, or playing with the depth of the black plastic piece may give you much better results.  Using a potting compound to fill in the wells would probably alleviated this, though.  It also could be that the paper wasn't totally level in the shot and you're seeing some variation from that.

Yep, I had the camera in one hand and was trying to hold it with the other, so the paper was a bit oblique and separated, not sticking perfectly to the leds. Also a plastic diffuser can have much better optical qualities than a paper.

[tooki]

Try a piece of frosted scotch tape (tesa film), pressed down firmly. I’ve used it before to diffuse non-diffused LEDs, simply by drilling a hole in my project box and sticking the tape to the inside. Gives a really nice look to me. I’d love to see what that looks like on your 3D-printed display!

[ebastler]

It's not the size that I can't find, it's the way the characters are displayed.

Meaning what?

+1. This thread feels a bit pointless unless you tell us what you are after.

[tooki]

Yeah, PixieDust, you need to cut out this secrecy bullshit and just explain what you're trying to build. We've all pieced together that it's a replacement for some vintage LED matrix module or something, it's not as though you're inventing something revolutionary. But your secrecy is really frustrating to others because it means that a) we waste time proposing things that we'd know are pointless if we knew what the project was, and b) it means it's a one-way flow of information — we contribute because we learn from others, and you are withholding your side of this bargain.

[PixieDust]

There's really no secrecy. What I'm trying to make is pretty much exactly what George of the Jungle posted. Just smaller. I was just trying to figure out the ins and outs of 7 segment displays. I think I have it now, should be able to get something together. Will post results when I get around to finishing it. I was just trying to figure out how to fill my tiny cutouts for the segments, you guys provided some good ideas. Hopefully the minimum size of resins isn't 60L, because I'll be needing a tiny amount.

[DaJMasta]

You could likely use almost any nonconductive clear epoxy resin and just mix in a little pigment.  You may have to test to get the opacity and coloring you want, but you can get it just a couple ounces at a time from a hardware store.

[tooki]

There's really no secrecy. What I'm trying to make is pretty much exactly what George of the Jungle posted. Just smaller. I was just trying to figure out the ins and outs of 7 segment displays. I think I have it now, should be able to get something together. Will post results when I get around to finishing it. I was just trying to figure out how to fill my tiny cutouts for the segments, you guys provided some good ideas. Hopefully the minimum size of resins isn't 60L, because I'll be needing a tiny amount.

You were asked repeatedly to elaborate on the requirements, and to elaborate on the “deficiencies” you mentioned, but you’ve given literally zero reply to that. My comment stands.

[PixieDust]

Sweet thanks, will look into it.

[floobydust]

Remake of the TIL311 dot-matrix LED display, there's a PIC16 on the underside. PC boards available from OSH Park.

For frosted epoxy, I've used dental cement. It's a two part, and fast cure.

[james_s]

Hey that's cool, I have a few of those TIL311 displays around somewhere, always thought they were neat.

[ratatax]

Yet another dude who thinks he have THE idea and post for help without answering half of the questions. I bet he did nothing with that "secret idea"