PCB Suggestions?

[Peepsalot]

I would like to make a fairly large (~1sqft) LED display consisting of 16x16(256 total) LEDs. Every cathode in a row would be connected, as would every anode in a column. I would like to do this as cost effectively as possible. Since they are laid out in a grid like this, there is the big problem of intersecting rows/columns of wires. Right now I think my best option is a single sided PCB that I would etch myself, but I'd also have to wire up 256 jumper wires. I've never etched a board before, but I think I can handle the job. It seems doing a double sided board would make for much less soldering, and I wouldn't have to cut and strip 256 tiny wires, and i'd "only":roll: have to drill 512 holes instead of 1024, but I don't think I could handle the etching like that. The companies I have seen that do this sort of thing for you charge outrageous prices for a board that size.

Does anyone know a source of cheap, precut jumper wires? Or some better suggestions?

Also, what software do you guys use for board design? I tried this eagle free version, but when I try to move the components around, it says this feature not supported in this version.

 

[DirtyLude]

I would think it would be easier for something of this size and relative simplistic wiring to just get a sheet of aluminum or steel and drill all the LED holes into it. Mount them in and free wire the rows and columns

 

[Peepsalot]

I'm not sure I follow you. Aluminum or steel would just conduct, electrically connecting every pin of every component I put on it.

 

[DirtyLude]

The sheet is only there to hold the led's, it's not used as a pcb. Just use regular wire and solder to wire all the leds together. It's pretty simple wiring, since everything goes in direct rows and columns. A homemade PCB for this seems like overkill.

This assumes you aren't using SMD LEDs.

 

[Peepsalot]

OK, that make sense, I kinda figured what you meant right after I posted that. I think this is a good idea that will make things a whole lot easier. The silver reflective backing might even help the aesthetics of the project. And I can just use some steel rods or something to connect the leds together. At different heights for cathode and anode so the rows/columns don't touch. That would be pretty simple to do I think. This hadn't occured to me, although I knew there had to be a simpler way. Thanks.

 

[DirtyLude]

If you use unshielded wiring (basicly rods) to connect your LED's together, it would be a good idea to spray the back down with some conformal coating after it all together and working.

Obviously a nice drill press would be pretty helpful here, getting all the LED holes drilled out nicely.

 

[Peepsalot]

What kind of conformal coating would you recommend? I've never even heard of it until now.

I'm looking into maybe getting a little benchtop drill press. Can't decide on a model though.

 

[DirtyLude]

I can't really suggest anything. I just got a can from my local electronics store. The choices were expensive silicon, and less expensive acrylic, so I bought the acrylic. Seems to work well for me, but I don't have any experience with anything else.

I know some people were talking about verithane or something similar as a cheap coating.

 

[k7elp60]

I have built a number of large LED displays. Most of the LED's were mounted in holes on the plastic panel. I have been able to wire the LED's with wire wrap wire and and a hand wrapping tool.

 

[Russlk]

I have used urethane floor varnish as a coating, it works well and doesn't get too hard.

The free version of Eagle will allow you to move parts onto the board but you cannot move the parts off the board. If you delete the board outline, parts cannot be moved.

 

[Peepsalot]

I have built a number of large LED displays. Most of the LED's were mounted in holes on the plastic panel. I have been able to wire the LED's with wire wrap wire and and a hand wrapping tool.

Do you use bare wire wrap? Like the tool on pg 14 of this:
https://www.electro-tech-online.com/custompdfs/2006/03/WireWrap-3.pdf
It looks handy to be able to do it with one coninuous wire. Or do you do an individual wire for each connection?

Why are the prices of these tools so insanely inflated? I see some cheap ones on ebay, but none of the "strapping" type. From what I can tell, the other tools don't do a continuous wire feed like that, but maybe I misunderstand how they work.

 

[Russlk]

I bought my hand wire wrap tool from OK industries 30 years ago, it still is working. It is designed for #30 krynar wire and is still available: http://www.trynci.net/productdetails.aspx?productid=19423.
Don't remember what I paid, but it was a lot less than $24.

For twisting two LED wires together, you could drill two holes in the end of a small rod (1/4 inch pot shaft).

 

[k7elp60]

I use the exact tool the Russlk's link showed. I too have had my tool for well over 20 years and it still works fine. I also use the #30 wire. At one time you could buy the wire in all the standard colors and in different lengths. The different lengths were prestripped. For example if you bought 1", the individual wires are really 3" long but have 1" of insulation in the middle and 1" of bare wire on each end. If you bought 3" the insulation was 3" and 1" of bare wire on each end.
When mounting the LED's I make sure all the anodes are facing the same way, then I cut the leads to a little over a 1/2". I used short lengths of the wire wrap wire and daisy chained the connections. If for some reason I used shorter LED leads I would cut about 1/4" off each bare lead of the wire wrap wire.
I have 1000's of various lenghts, and chances of me using it all is rather remote so if peepsalot would like some I give it to him just for the shipping charges.

 

[Peepsalot]

I use the exact tool the Russlk's link showed. I too have had my tool for well over 20 years and it still works fine. I also use the #30 wire. At one time you could buy the wire in all the standard colors and in different lengths. The different lengths were prestripped. For example if you bought 1", the individual wires are really 3" long but have 1" of insulation in the middle and 1" of bare wire on each end. If you bought 3" the insulation was 3" and 1" of bare wire on each end.
When mounting the LED's I make sure all the anodes are facing the same way, then I cut the leads to a little over a 1/2". I used short lengths of the wire wrap wire and daisy chained the connections. If for some reason I used shorter LED leads I would cut about 1/4" off each bare lead of the wire wrap wire.
I have 1000's of various lenghts, and chances of me using it all is rather remote so if peepsalot would like some I give it to him just for the shipping charges.

That would be awesome if you could do send me some. You've made them before, so if you could send however much you think it would take to complete such a project(12"x12", 16LEDx16LED), I would really appreciate it. Just let me know your paypal address and shipping cost to 78759 or whatever other payment method you want.

I sent you my full address in a private message. Thanks for the tips and help everyone.

 

[Peepsalot]

k7elp60, since you say you have made displays a few times before, could you also give me any tips on powering the LEDs?

Mainly just what sort of power pulses they are able to withstand. I was told they could handle maybe 100ma pulsed at a low duty cycle, so I was going to see if I could give each column 100ma, at 6.25% (100% / 16 columns) duty cycle. And the screen would be refreshed probably at 60hz, so each pulse would only last about 1 millisecond. Does this sound reasonable? I haven't powered LEDs with pulses like this before. I guess it depends a lot on the LED being used, I am looking for something pretty cheap, since there will be so many of them, and simple red color is fine. Probably a kinda wide angle LED would be used.

 

[Nigel Goodwin]

k7elp60, since you say you have made displays a few times before, could you also give me any tips on powering the LEDs?

Mainly just what sort of power pulses they are able to withstand. I was told they could handle maybe 100ma pulsed at a low duty cycle, so I was going to see if I could give each column 100ma, at 6.25% (100% / 16 columns) duty cycle. And the screen would be refreshed probably at 60hz, so each pulse would only last about 1 millisecond. Does this sound reasonable? I haven't powered LEDs with pulses like this before. I guess it depends a lot on the LED being used, I am looking for something pretty cheap, since there will be so many of them, and simple red color is fine. Probably a kinda wide angle LED would be used.

You can pulse them at as high a current as their maximum rating multiplied by the number of multiplexed digits. So for 16 digits, and if you wanted 10mA brightness, them you run them at 160mA - their average current will be 10mA.

Apparently this DOESN'T apply to the massively bright Luxeon type LED's, but you won't be using those!.

 

[Russlk]

I have driven cheap LEDs at 100 mA and they survived. 1 mS pulses refreshed at 60 Hz should work.

 

[philba]

many LED datasheets spec both a max continuous If and a max pulsed If. It's not unusual to see 100 mA max pulsed. I'm not sure of the duty cycle though I'm pretty sure 1% will be ok.

If you are multiplexing the LEDs, you will want to pulse at higher current.