LED Matrix

[PixieDust]

Hi,

I'm looking to make a matrix from some LEDs per attachment.

The LEDs need to be just 0.1125mm from each other. So given the pads for these things are on the edges, how would you go about making a PCB for this? Not much room for traces!

I'm trying to make a standard matrix like this:

https://www.circuitspecialists.com/blog/getting-started-with-an-led-matrix-tutorial/

EDIT: I'm starting to think that black cross is meant to represent traces.

EDIT 2: Maybe not, the 4 pads are R G B and earth.

[ebastler]

I'm trying to make a standard matrix like this:
https://www.circuitspecialists.com/blog/getting-started-with-an-led-matrix-tutorial/

The trick is that you don't make these, you buy them! 

Seriously though -- you have opened or posted in multiple threads regarding various ideas to build you own LED displays. All of your proposals have rather demanding manufacturing requirements; but in no case have you explained what drives the need for a custom display. What do you need that can't be served by an off-the shelf LED matrix, OLED display, or 7-segment--display (over in the other thread)? Could you provide more specific background?

[PixieDust]

I'm trying to recreate a device which you can't buy anywhere anymore, hasn't been made in decades. At the moment I'm just doing research.

In this thread:

https://www.eevblog.com/forum/profile/?area=showposts;u=166412

I'm asking about something that I know now is possible. Making custom 7 segment displays is definitely possible. What I'm trying to make is small, but not unreasonable. Just clarifying details.

In this thread:

https://www.eevblog.com/forum/beginners/soldered-0805-vs-0603-vs-0402-vs-0201-vs-01005-vs-008004-today-)/msg1423403/#msg1423403

This is the tough one (unrelated to the 7 segment display problem) and I'm just doing researching trying to figure out if it's at all possible. I have easier means of recreating it, but I want to see if I can make it (my device that I'm trying to recreate) authentic.

[John Heath]

You can cheat buy using virtual LEDs. This reduces the number of LEDs needed to 1/3 which will buy you some more room on the PC board. An example is a column of red then green then blue LEDs. When a white image is panning from right to left the R G and B LEDS will all appear to be white LEDs. The reason is the mind does not have a projector to know what the eye sees so it reconstructs it in a logical way into meaning. It is not logical for the LED to be red for a white image so it changes the red to white in the mind. The buzz word for this is virtual LED display. 

[ebastler]

OK, so it's a secret what device you actually want to build. 

Fair enough, but that makes it difficult to give advice. You seem to have a very specific solution path in mind, and are only asking questions about that -- but there might be much better solutions to meet your actual requirements.

An OLED or TFT matrix seems like the way to go...And if you are after a close-to-original recreation of a historical device: If your model is multiple decades old, are you sure that it used thousands of 0201 SMD LEDs?

[PixieDust]

You can cheat buy using virtual LEDs. This reduces the number of LEDs needed to 1/3 which will buy you some more room on the PC board. An example is a column of red then green then blue LEDs. When a white image is panning from right to left the R G and B LEDS will all appear to be white LEDs. The reason is the mind does not have a projector to know what the eye sees so it reconstructs it in a logical way into meaning. It is not logical for the LED to be red for a white image so it changes the red to white in the mind. The buzz word for this is virtual LED display.

Unfortunately, all the LEDs are the same colour. It's a monochrome display. The LED that I showed just happens to be have R G B in it, I just need to use one colour. It's the only one I've managed to have found in the right size.

OK, so it's a secret what device you actually want to build. 

Fair enough, but that makes it difficult to give advice. You seem to have a very specific solution path in mind, and are only asking questions about that -- but there might be much better solutions to meet your actual requirements.

An OLED or TFT matrix seems like the way to go...And if you are after a close-to-original recreation of a historical device: If your model is multiple decades old, are you sure that it used thousands of 0201 SMD LEDs?

If I make it, I'll definitely show it, but I don't like showing goals until they are made.

I'm only fumbling from one idea to the next. But fair point, I may be going down the wrong path. Haven't thought about it this way.

According to the images that I've dug up, it's made of tiny LEDs, but not as small as a TFT display. They are definitely rather large even if 0201 can't be classified as large.

[John Heath]

I have an idea that has not been tried yet. You can see some fan LED displays that use just a row of LEDs then spin the fan and time the LED on / off timing for a display. They work rather well and have very few parts. My idea was to use dollar store red laser pointers. 7 of them all pointing from left to right for seven horizontal lines. Now turn the fan on. The lasers reflect off the fan blade showing 7 parallel lines. Now it is just a matter of timing with a PIC to put a message on the box fan laser LED sign. Best I can tell there is no practical application for such a sign which makes it the ideal hobby project as it will be one of a kind.

[mikeselectricstuff]

What size matrix ?

With that LED size you're probably going to need at least 4 layers and via sizes smaller than most pooling services. And I don't think that spacing will be viable - you're going to need to increase the pitch - 1mm or so is probably doable.

You'll need to have vias in the pads, so they need to be small enough not to cause any wicking issues.

Smallest I've done is 0402s on a 1.25mm pitch and this used 0.2mm hole and 0.15mm track/space on 4 layers, and that was just monochrome.

[ebastler]

it's made of tiny LEDs, but not as small as a TFT display. They are definitely rather large even if 0201 can't be classified as large.

Well, those cheap little monochrome OLED displays have pixel sizes between 0.2 and 0.27 mm. Not that different from an 0201 LED. You can get them in various sizes; 0.96", 1.3" and 1.54" diagonals with 64*128 pixel displays seem to be common. They come with white, blue or yellow emission. No red or green, I'm afraid; but if that's what you need you could use an overlay film with a white display.

Available with breakout boards in many variations on ebay, or just the naked display with a fine-pitch flex connector. They do not waste a lot of real estate around the display. Definitely worth a look if you can make the form factor work for you. The ones I have tried have very nice contrast and viewing angle, fast response times, and a fast interface if you get the SPI variant (not I²C). They do not make the internal frame sync signal accessible, however -- so driving them via PWM application to obtain gray scale pixels won't work, but will cause flicker/tearing.

[mikeselectricstuff]

it's made of tiny LEDs, but not as small as a TFT display. They are definitely rather large even if 0201 can't be classified as large.

Well, those cheap little monochrome OLED displays have pixel sizes between 0.2 and 0.27 mm. Not that different from an 0201 LED. You can get them in various sizes; 0.96", 1.3" and 1.54" diagonals with 64*128 pixel displays seem to be common. They come with white, blue or yellow emission. No red or green, I'm afraid; but if that's what you need you could use an overlay film with a white display.

Available with breakout boards in many variations on ebay, or just the naked display with a fine-pitch flex connector. They do not waste a lot of real estate around the display. Definitely worth a look if you can make the form factor work for you. The ones I have tried have very nice contrast and viewing angle, fast response times, and a fast interface if you get the SPI variant (not I²C). They do not make the internal frame sync signal accessible, however -- so driving them via PWM application to obtain gray scale pixels won't work, but will cause flicker/tearing.

There are some small RGB OLEDs - these would be the cheapest option if there is a size that suits.

[ebastler]

There are some small RGB OLEDs - these would be the cheapest option if there is a size that suits.

I think Pixiedust mentioned somewhere that he only needs a monochrome display, which got me thinking of the monochrome OLEDs. But agreed -- if you need a color which the monochrome displays don't offer, you could simply feed monochrome data to an RGB display. The small monochrome displays are probably still cheaper though; on the order of $4 at single quantities.

[mikeselectricstuff]

OK so 0201 is probably the smallest you can get - for best packing in a square martix, you want to have them at 45 degree angles relative to the grid. You need one via per LED, so design rules will dictate the highest density - doubt it will be much below 1mm

[PixieDust]

I have an idea that has not been tried yet. You can see some fan LED displays that use just a row of LEDs then spin the fan and time the LED on / off timing for a display. They work rather well and have very few parts. My idea was to use dollar store red laser pointers. 7 of them all pointing from left to right for seven horizontal lines. Now turn the fan on. The lasers reflect off the fan blade showing 7 parallel lines. Now it is just a matter of timing with a PIC to put a message on the box fan laser LED sign. Best I can tell there is no practical application for such a sign which makes it the ideal hobby project as it will be one of a kind.

The idea I get form this is to use fiber optics and connect them up to LEDs, but this will be one heck of a project to do for around 4000 LEDs!

What size matrix ?

With that LED size you're probably going to need at least 4 layers and via sizes smaller than most pooling services. And I don't think that spacing will be viable - you're going to need to increase the pitch - 1mm or so is probably doable.

You'll need to have vias in the pads, so they need to be small enough not to cause any wicking issues.

Smallest I've done is 0402s on a 1.25mm pitch and this used 0.2mm hole and 0.15mm track/space on 4 layers, and that was just monochrome.

Start with a 10 x 10 matrix.

hmm, sounds like it's not going to work. I've also been asking around and haven't been able to find places that do traces fine enough for the job.

Well, those cheap little monochrome OLED displays have pixel sizes between 0.2 and 0.27 mm. Not that different from an 0201 LED. You can get them in various sizes; 0.96", 1.3" and 1.54" diagonals with 64*128 pixel displays seem to be common. They come with white, blue or yellow emission. No red or green, I'm afraid; but if that's what you need you could use an overlay film with a white display.

Available with breakout boards in many variations on ebay, or just the naked display with a fine-pitch flex connector. They do not waste a lot of real estate around the display. Definitely worth a look if you can make the form factor work for you. The ones I have tried have very nice contrast and viewing angle, fast response times, and a fast interface if you get the SPI variant (not I²C). They do not make the internal frame sync signal accessible, however -- so driving them via PWM application to obtain gray scale pixels won't work, but will cause flicker/tearing

Had a look at all the offerings of OLEDs, no luck unfortunately.

[ebastler]

Had a look at all the offerings of OLEDs, no luck unfortunately.

I find it a bit frustrating to provide suggestions in some detail, and then just get a curt "won't work" answer, without further details which requirements are not met and what you need. I guess the secrecy around this earth-shaking development leaves you no choice...

I'm out of here for now. Will have another look if and when you have something you can actually talk about.

[mikeselectricstuff]

Had a look at all the offerings of OLEDs, no luck unfortunately.

I find it a bit frustrating to provide suggestions in some detail, and then just get a curt "won't work" answer, without further details which requirements are not met and what you need. I guess the secrecy around this earth-shaking development leaves you no choice...

+1


If you give us the actual constraints - max size, minmum resolution, production volume, which things are flexible, you will get more useful answers, and maybe find a solution you'd not thought of.
 

[obiwanjacobi]

My guess he is making TILL311's...   

[tooki]

I'm trying to recreate a device which you can't buy anywhere anymore, hasn't been made in decades. At the moment I'm just doing research.

In this thread:

https://www.eevblog.com/forum/profile/?area=showposts;u=166412

I'm asking about something that I know now is possible. Making custom 7 segment displays is definitely possible. What I'm trying to make is small, but not unreasonable. Just clarifying details.

In this thread:

https://www.eevblog.com/forum/beginners/soldered-0805-vs-0603-vs-0402-vs-0201-vs-01005-vs-008004-today-)/msg1423403/#msg1423403

This is the tough one (unrelated to the 7 segment display problem) and I'm just doing researching trying to figure out if it's at all possible. I have easier means of recreating it, but I want to see if I can make it (my device that I'm trying to recreate) authentic.

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]

Alright guys, here it is:

The size of the overall unit is roughly 120mm x 210mm

there are:

rectangular LED matrices for digits, each of those matrices looks to be 5 x 10 LEDs (3 of them) and is 6.5mm x 3.2mm, the larger one is 5 x 20 LEDs. And there's x 8 of these arrangements for the whole unit. I'm estimating that each LED needs to be 0.5mm x 0.5mm in size and positioned as I mentioned very closely together.

These digit matrices are surrounded by a ring of LEDs. For the top two indicators, there's 2 rings of 2 different coloured LEDs (green and orange), for the bottom 6, there's just 1 ring.

The ring of green LED's is composed of most likely 3 LEDs which are connected in series, because all three on each radial are lit at the same time. The outer ring has 4 orange LEDs lit at the same time which straddle the inner ring. As the digits change, the radial that is lit up changes also, CW for increasing values, CCW for decreasing values.

I'm estimating that these LEDs can be 0.6mm x 0.3mm.

The segment displays have 2 LEDs per segment and I'm estimating that these are the same size LEDs as those on the rings.

These segment displays are different to the ones I'm trying to make in this thread:

https://www.eevblog.com/forum/projects/make-my-own-7-segment-display/msg1423366/#msg1423366

That thread is for another project.

So to summarise, there are 3 types of LEDs necessary for this project:

0.5mm x 0.5mm green LEDs, 0.6mm x 0.3mm green and 0.6mm x 0.3mm orange LEDs.

Here are the problems:

1.) Down the bottom, there are buttons and knobs. If I use a TFT or OLED display, I'm not sure how I'll be able to mount buttons and a pot in a slim enough fashion over the the screen.

2.) If I use a TFT/OLED display (I already have a TFT display that I can use to display all these things and in fact after doing the search, I even found a better one), HOWEVER, the problem is that although it's possible to find a screen with an appropriate active area, the problem then becomes - the instruments that straddle my gadget. The metal casing will protrude out and overlap with the adjacent instruments, which is not ideal. Workable, but not ideal.

So ideally, it would be nice to actually make my highly complex LED matrix and have the unit totally fit within it's footprint. This is the main reason why I'm trying to do it the hard way because having a TFT display stuff up all the adjacent unit positioning.

EDIT & P.S.: I looked over the available OLED/TFT displays on digikey and none of them were of the right size. I need square ones, but they are all rectangular. So if you put them side by side, then they overlap in inappropriate places.

[ebastler]

Thanks for sharing! That is a neat display indeed.

Is your replica intended to go on an actual aircraft, or is this for use in a simulator? For the latter (and maybe for the former as well?), I would think that using one portrait-format display for the whole thing would be your best bet. Larger smartphone/phablet screens, or maybe one from a small tablet, should be the right size. Then put a physical overlay with the cut-outs and lettering over it to make it more "real".

Yes, it would feel slightly "fake"... But hey, they were faking mechanical displays and dials in the original LED display! 

[Ian.M]

Another possibility for a simulator would be rear projection onto a ground glass screen overlaid by a filter to get enough contrast.   Start with a portable HDMI projector . . . ..

[PixieDust]

Thanks for sharing! That is a neat display indeed.

Is your replica intended to go on an actual aircraft, or is this for use in a simulator? For the latter (and maybe for the former as well?), I would think that using one portrait-format display for the whole thing would be your best bet. Larger smartphone/phablet screens, or maybe one from a small tablet, should be the right size. Then put a physical overlay with the cut-outs and lettering over it to make it more "real".

Yes, it would feel slightly "fake"... But hey, they were faking mechanical displays and dials in the original LED display! 

Just for a simulator.

That's the way I was going to make it, even already bought the screen. But then found the image of the matrix and thought maybe it's possible to do it properly.

Hmm, rear projection is an interesting idea. Is there going to be enough contrast on one of those I wonder?

[voltsandjolts]

That is a very nice display. I bet it works great with a wide range of ambient lighting, has a great viewing angle, wide operating temperature range, high noise immunity and laughs off any vibration you throw at it. For those reasons I can understand your desire to use an LED matrix - because LEDs just work. Reliably. Always. **

Mechanically more complicated but: maybe you could consider some type of lens to reduce the apparent size of a larger LED matrix, like the stackable Liteon arrays https://www.digikey.co.uk/products/en/optoelectronics/display-modules-led-dot-matrix-and-cluster/96

_{** OK, some of that depends on driver circuitry too but when using an off the shelf OLED you lose control over that to a large extent.}

Edit: Ahh, this is for a simulator, so you have more options.

[mikeselectricstuff]

EDIT & P.S.: I looked over the available OLED/TFT displays on digikey and none of them were of the right size

There are a lot more display types out there than are stocked by Digikey, so worth looking at other sources in case there is something that may fit.

[capt bullshot]

This is a great display unit. Want one.
These LED matrices are made of naked LED chips placed on horizontal traces and vertically connected by bond wires (like in this 4 digit alphanumeric display). You can still buy these as standard modules (4 or 8 characters 7x5 matrix), but yours is for sure custom made from pure unobtainium.

I've got another idea: in modern car dash boards, they use TFT LCDs masked by "instrument dummys" (so they get round shapes and whatever). If you place a large and brilliant enough TFT screen behind that mask, it'll at least look alike this original display.

[chris_leyson]

Hi PixieDust, just read your post about the simulator display and remember this https://www.4dsystems.com.au/product/uLCD_220RD/. I think maybe the YouTube video https://youtu.be/fRhZx4gfyCI has had a bit of post processing though.
Anyway, you said you were looking for square displays and something like the 4D systems uOLED-128-G2 1.5 inch display might come close to your requirements. From a practical point of view however, the display and driver PCB are stuck to the plastic carrier with double sided tape and I never had much luck getting them apart. Display is SSD1351U3, Phoenix Display DLC0150BNOF, and Mouser even have a breakout board 763-NHD1.5128128UGC3.