# Display with LEDs - What technique to use?

Status
Not open for further replies.

#### atferrari

##### Well-Known Member
I am planing to create kind of a display with LEDs. Round or square, the board's expected size could be around 30 x 30 cm. LEDs' position is not expected to change; just the programing of the driver. Number of LEDs expected to be, most probably, around 64, laid in straight lines. Accuracy of the LEDs' location IS important.

At least for the first attempt (not sure if there would be a second) what is the best advisable technique? a cardboard piece, soldering wires to connect them to drivers and micro in charge, a PCB ( have to order it custom made and locally, it is expensive), or...?

Used to use veroboard in the last years, I realized that here it would be unusable because of the exact location of each LED they cannot provide. Discarded it already.

I am open to suggestions. The size of this and long runs of traces/wires, is of concern.

Help / suggestions, appreciated.

#### atferrari

##### Well-Known Member
Problem is Ian, that my LEDs in each line, would be not equidistant at all.

And lines are not going to be parallel to each other either.

#### Externet

##### Active Member
Hi Agustín.
Next time you visit U.S., let me know where to ship for you a few of these I have behind spider webs, about that size or larger...

----> http://g02.s.alicdn.com/kf/HTB14xtl...electronic-signs-led-gasoline-price-board.jpg

I noticed their supply is 24VDC, LEDs grouped/seried in disarray, not as digit 'segments'; and could check the ICs they use if convenient to know. They are controlled via radio to change display numbers.

#### Superdat

##### Member
I am planing to create kind of a display with LEDs. Round or square, the board's expected size could be around 30 x 30 cm. LEDs' position is not expected to change; just the programing of the driver. Number of LEDs expected to be, most probably, around 64, laid in straight lines. Accuracy of the LEDs' location IS important.

Used to use veroboard in the last years, I realized that here it would be unusable because of the exact location of each LED they cannot provide. Discarded it already.

Help / suggestions, appreciated.
Hi
1W LEDs can be stuck individually, but 64W!
If you want to use regular 5mm pcb LEDs or even 10mm, maybe time to think about making your own pcb.
5mm LEDS would look a bit lost on 30cm Sq, there are only 8 in 30cm, approx 1 per 40mm sq.
Even 10mm would have alot of space around it.
Regardless of whoch you use there will be alot of wire/traces. If you use something like a Max7219, Cathodes for each column of 8 LEDS are common, then 8 wires from each of these to the Max7219. Next each Anode in a row connected to the next, 8 rows then another 8 wires back to the Max7219. Five wires from Max7219 to the micro.
If you use high power LEDs and Max7219 you'll need a driver transistor for each LED.
You'll need 8 of these for the common cathode switching too.

Last edited:

#### atferrari

##### Well-Known Member
Hi
This is a bit contradictary, LEDs in Straight lines but veroboard isn't accurate enough! Veroboard has a 2.54mm matrix, how accurate do you want?
The effects I want to achieve include "perfect" circles so I want to work free of any fixed grid as a veroboard would provide.

Last edited:

#### Superdat

##### Member
Hi
I've just edited my post, you did say the LEDs weren't parallel. Warning: Always read the posts before answering! ;-)

#### Superdat

##### Member
You might get closer to a circle than you think. Do you have LibreOffice? If yes, Use Draw and set a 0.1 inch (I don'd think you can set 2.54mm) grid.
Draw a circle of the correct size, then see how the LEDs will fit, you can change the LED alignment to get it as close to the circle as possible.

Just thought, quick look at the datasheet one driver transistor for each LED isn't correct.
Most likely one for each row i.e. 8. If you want the high power LEDs I'll have another look.

Last edited:

#### atferrari

##### Well-Known Member
My OP is about implementing the board, Superdat. Just that.

#### JonSea

You can have ten 100mm x 100mm boards made in China for about $10 (a buck a piece). If you could get by with a 20cm x 20cm display and can make the boards symmetrical, 4 boards could provide what you want at the great price. You could design the boards with extra LED locations to make each corner unique. You haven't said how you're going to control the LEDs. I agree with the MAX7219 choice with the LEDs arranged in an 8 x 8 matrix, which would make the layout pretty simple. Alternatively, each board could be designed to be stand-alone, with a MAX7219 amd hp to 64 LEDs on each corner. #### atferrari ##### Well-Known Member You can have ten 100mm x 100mm boards made in China for about$10 (a buck a piece). If you could get by with a 20cm x 20cm display and can make the boards symmetrical, 4 boards could provide what you want at the great price. You could design the boards with extra LED locations to make each corner unique.
I got a similar suggestion in another forum. Several small boards to assemble the big one. In the drawing board now. Thanks.

#### Superdat

##### Member
My OP is about implementing the board, Superdat. Just that.
OK so are you saying you know how to do the technical stuff?
You haven't mentioned the type of LED you plan to use? 1W LEDs can be individually placed and a pcb isn't needed but it will need a lot of power.
You could design and make your own pcb, it's not all that difficult. You would need to learn how to use a PCB layout SW, I use a free version of Diptrace.
You are limited to 300 pins but the max size is about a page. If you want to try this method let me know and I'll check the exact size it can make.
30cm is big though, if you used toner transfer you might need 2xA4 or whatever size paper you have in Argentina.
Don't try to make your traces too small 1.5mm max. Alignment of double sided is quite difficult, I didn't find it as easy as is suggested on Utube.
If you do try double sided, make your Vias big so that a little misalignment is OK, otherwise use wire instead.
I did find a method but only after about 4-6 failures.
30cm Sq would be expensive if made commercially.
Do you have a suitable laser printer?
Light sensitive copper clad is supposed to be better but more expensive (I've not used it). You still need a printer but an ink jet is OK.
If it's a one off as in I'm never going to make another pcb, you could buy a small amount or copper dissolving chemical and sponge the copper until it's gone. No tank.
I don't like ferric cloride, it's a bit too agressive for my liking. I use ammonium persulphate which is a little slower but doesn't try to attack every bit of iron in the room!

#### Pommie

##### Well-Known Member
At Dirtypcbs you can get 100 1" square pcbs for $20. You could put a solder pad on top for the row connection and one on the bottom for the column. Glue them to a 30cm square piece of cardboard and your all set to go. You could also buy 100 RGB LEDs for about$20 and have them all addressable. Search WS2812B LED RGB 5050.

Mike.

#### Superdat

##### Member
At the minute we are all gusessing, the OP hasn't given enough information about what he is trying to do.

#### AnalogKid

##### Well-Known Member
With LEDs with 1" leads, couldn't you use vero board, put them in the holes nearest their "true" location, and bend them around? That should be good enough for a prototype. For production, a pc board is mandatory for this kind of placement.

ak

#### AnalogKid

##### Well-Known Member
Hi Agustín.
Next time you visit U.S., let me know where to ship for you a few of these I have behind spider webs, about that size or larger...
Hey, I'm in the US. Just sayin' ...

ak

Status
Not open for further replies.