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Fun With General Radio Edge-Lit Displays
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TOPIC: Fun With General Radio Edge-Lit Displays

Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #1

  • Ty_Eeberfest
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A few weeks ago I bought those General Radio "Numerik" edge lit displays that Stuckey was selling. The good news is that they're nice displays in good condition. The bad news is that they're missing the clip-on "back piece thingies" that hold the light bulbs firmly in place and provide the center contact for each bulb. (Stuckey was honest about this - I bought them knowing they were missing these parts).

So finally I've decided that rather than get into a complicated machine shop project to try to re-create the missing pieces I'll scrap the light bulbs and use LEDs on a PCB instead.

So far I have drawn up this design but haven't had it fabricated:

pcbart.jpg


The board fits onto the back of one display unit - 6 boards needed for a 6 digit clock. The blue circles are LEDs on the "back" side of the board, positioned to poke into the holes where the light bulbs used to go. 12 LEDs for 12 holes: 0 - 9, Left and Right decimals. The DIPs are on the "front" of the board. One is just an array of 12 resistors for the LEDs. The other is a HEF-4894B, which is a 12-bit shift register with output latching. It's made for driving LEDs (kinda like a low voltage high current version of the Supertex HV5530 that's sometimes used for driving Nixies).

The connectors at the bottom are for daisy chaining 6 units together to form what amounts to one big 72 bit shift register (12 bits X 6 digits). Like so:

chained.jpg


Here's the "proof of concept" setup:

concept.jpg


The green board is a leftover "main board" from my Panaplex clock project. It was made to put out Serial Data, Strobe, Latch and Blanking signals to drive HV5530s. With a few little mods it's now putting out those same signals at the right level to drive the HEF-4894Bs. Depending on the program it either puts out 7 segment (Panaplex) or 1-of-10 (most Nixies and these edge-lits) formatted serial data.

I thought I could use the green LEDs in the picture but they're nowhere near bright enough to make the displays look good. Seriously bright Cree LEDs are now on order.

Schematic of display boards attached.
Attachments:
Look into it later when the dust is clearing off the crater.
Last Edit: 1 year, 6 months ago by Ty_Eeberfest.
The following user(s) said Thank You: Stuckey

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #2

  • Dekatron42
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Nice!

When will you go one step further and use the LTC5940 to drive RGB-LEDs so that you can do colour shifting of the LEDs?

I've been tinkering with this and edge-lit displays of another make and model but I just don't have the time to finish it.

I was thinking along the lines of having different colors for different alarms, flshing the digits when the alarm goes off, and time zones in different colours plus the nice colour changing scheme when it gets dark so you won't be disturbed by them during the night when you are sleeping.

The variations with RGB-LEDs are endless, almost so that you will have to stop yourself so you get something done.

/Martin

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #3

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Thanks for the response Martin. The main reason I posted my unfinished project is to see what feedback I'd get.

I did briefly consider using RGB LEDs. I approached the project with the preconceived notion that the display drivers needed to go on the same boards as the LEDs. The idea was to do this on the cheap, i.e. make use of leftovers and keep the amount of new PCB fab (by far the most costly part of a project since I don't etch my own boards) to a minimum. So when I started to work out what parts could fit on a board the size of the back of the displays I quickly realized RGB wasn't gonna happen.

But the cool thing is that my boards will be able to be removed from the displays by removing 2 screws. I can have my monochrome clock now, and if I feel like spending more time and money later I can develop a from-scratch set of boards for RGB off to the side, and then screw them onto the displays when ready.

You gave me a few new ideas for possible uses for RGB capabilities. I grabbed a TLC5940 data sheet - interface is kinda complicated, but manageable with some effort. This could definitely be fun to work on in the future.

Regarding the current monochrome version...

I can probably control brightness by doing software based PWM of the OE (blanking) line. It works with Nixies, should work with LEDs with some tweaking of the timing. If so, then writing code to dim it during certain hours is almost trivial.

It occurred to me today that the 12 resistor network is not strictly necessary. 3 resistors would do - one for each decimal and one for all the digits - since only one digit, and maybe one or both decimals, will be lit at any time. Can't think of any reason to light up multiple digits at once.
Look into it later when the dust is clearing off the crater.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #4

  • Dekatron42
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You are correct that RGB needs some more PCB space, unless you go to surface mounting of the leds and IC. I have a another type of edgelit display that has one PCB on each end with six lamps on each end so that one is a little bit more complicated since it will need at least 20 wires (or a contact) on each PCB.

There are loads of arduino projects with the LTC5940 ao there is much to borrow from if you go that way in the future.

There is one reason for having each resistor there and that is if you want to cross-fade (blend) digits when they count.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #5

  • Ty_Eeberfest
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Yeah, it would appear that with something like TLC5940s three ICs are needed per display. No way can that fit on the back of my displays. Would definitely need to put the drivers on a separate board and deal with 12 * 3 + 1 = 37 leads per display harness. I could do it but not this time. As for using SMT, well, it's wonderful for automated assembly but for hobby / hand work I try to avoid it.

Good point about the cross-fading. I have nothing better to do right now than play around with this so I "forked off" a version with 3 discrete resistors to see if I could see any benefit. Not much to be gained really, since I already have DIP resistor networks on hand.
Look into it later when the dust is clearing off the crater.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #6

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You can always make one large PCB with all leds for all displays and then use PCB contacts like those on an arduino board to connect to a second PCB with all the drivers on.

I wish every day had at least 48 hours, then it would probably not be any problem to make all projects I have in line.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #7

  • Zedsquared
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Have you thought of using some of the RGB LEDs with built in controllers you can get these days? You buy them in strings and they act like a big shift register so you only need one or two control lines for the lot.
I've used WS2812 strings bought from aliexpress with the arduino fastSPI library sucessfully (needs an ATmega328 @ 16MHz to drive ) Once you get the library going it's just a case of filling an array with 8 bit RGB values and calling the send routine when you want the colour ro change.
The WS2812 does require rather tight timing in the driver routines whereas the WS2801 uses a seperate data and strobe line and is much more forgiving.

Here's a vid I made of a couple of 5m reels (300 LEDs on each) all being driven by one I/O pin:
[video]https://www.youtube.com/watch?v=d-JOyAO6o_U[/video]

Cheers,
Robin.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #8

  • Ty_Eeberfest
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Dekatron42 wrote:
You can always make one large PCB with all leds for all displays and then use PCB contacts like those on an arduino board to connect to a second PCB with all the drivers on.

I wish every day had at least 48 hours, then it would probably not be any problem to make all projects I have in line.


Agreed about wanting some 48 hour days. Wish I knew where to order some from

A single large PCB is certainly an option. If you look close at the photo in my OP you'll see that each display has black "side fins" protruding above the bare aluminum "lamp deck" on each side. So to use a single board it would be necessary to A - mill the "fins" of the displays (since they do nothing useful), or B - mill some slots into the PCB, or C - build the board with the LEDs standing tall on their leads so that the board can lay on top of the fins and the LEDs will still stick well into the lamp holes.

In the current monochrome version the individual PCBs will sit below the top of the fins, about 3mm abvove the lamp deck. It just so happens that using by LEDs with self-standoffs (warts) on their leads they'll end up at just the right depth into the holes.

I fine tuned the monochrome board layout over the weekend and placed the fab order this morning, so the monochrome version is definitely getting built.
Look into it later when the dust is clearing off the crater.
Last Edit: 1 year, 6 months ago by Ty_Eeberfest.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #9

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Zedsquared wrote:
Have you thought of using some of the RGB LEDs with built in controllers you can get these days? You buy them in strings and they act like a big shift register so you only need one or two control lines for the lot.
I've used WS2812 strings bought from aliexpress with the arduino fastSPI library sucessfully (needs an ATmega328 @ 16MHz to drive ) Once you get the library going it's just a case of filling an array with 8 bit RGB values and calling the send routine when you want the colour ro change.
The WS2812 does require rather tight timing in the driver routines whereas the WS2801 uses a seperate data and strobe line and is much more forgiving.

Here's a vid I made of a couple of 5m reels (300 LEDs on each) all being driven by one I/O pin:
[video]https://www.youtube.com/watch?v=d-JOyAO6o_U[/video]

Cheers,
Robin.


I've heard of these smart LEDs but never looked into them (aside from reading some guy's blog post about hacking a string of Christmas lights that used a similar scheme). I'll definitely look into this further. Also, I'm not a fan of Arduino but I'm not too proud to take a peek at how their library works!

The LED reel vid is pretty cool. Then I looked at your channel and started watching your fireworks vids. I take it you're a licensed pyro man? Cool... get paid to make things 'splode! I subscribed.
Look into it later when the dust is clearing off the crater.

Re: Fun With General Radio Edge-Lit Displays 1 year, 6 months ago #10

  • Zedsquared
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Yep, I get to play pyro some weekends (and weekdays during peak season around Nov 5th) Good fun Thanks for the subscribe, nothing new likely to turn up till August though when the summer events season gets underway I'm afraid. The vids marked GZ or Ground zero are from cameras left on the firing site for upclose and personal 'splosions This one is my favorite, we were competing in a big competition and threw up a *lot* of material


Thinking further on the LEDs they may not be bright enough to use with your edge lit displays, however they are a little painful to look at on full brightness so you never know. It seems to be easier and cheaper to buy them on flexi PCB strips rather than seperate!
Cheers,
Robin.
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