Suggestions required for mounting 192 LEDs

Imagine a tightly-packed rectangular grid of 192 individual discrete 5mm LEDs, in a 24x8 formation...









I intend to use them for POV display purposes and I have all the circuitry finished already (phew!).

My problem is that I need some physical means of mounting them all neatly and in a manner that allows any individual LED to be simply pulled out and replaced (eg. with a different colour one, or a replacement for a blown LED, yada yada).

I've searched very hard for things like "LED Mount", "LED holder", "LED PCB connector" and all combinations of those, but to no avail. The only item I did find was about 65 cents for a single LED holder of appropriate manufacture - that is WAAAAY too expensive for my budget. (It was the "VCCLite PCV 220", which is pretty close but it's not stackable and it's overengineered for my needs).

I'm willing to make something that would let me do this but I an mot sure how I would even attempt that.

All my LEDs will share common anodes (per column) and common cathodes (per row), so they will be addressed as row/column pairs.

I'm completely stumped on this one. Do you guys have any crazy suggestions I could try, or know of any existing solution?

Bearing in mind that I already have the 192 LEDs sitting on my bench and waiting to be plugged into the project as soon as I find a way around this technical obstacle.

A simple female header? http://www.pololu.com/catalog/product/1012

Thanks for the reply :). That was my first thought, but I discounted it because of the difficulty in routing the copper tracks for common anodes and cathodes.

Good idea but for my needs it’s still too tricky because I don’t have access to accurate manufacturing processes (in my tiny budget anyway). I’m just a noob in my bedroom soldering bits together :slight_smile:

I would say if your packing them tightly together then you going to have that problem no matter what mounting solution you find. Good luck with it though and dont forget the pics for us when its done.

Oh, sorry then. But I don't find too many differences between the VCCLite PCV 220 and the female header.

Why do you say it is difficult the routing? You must it do anyways, no? And what do you mean with accurate manufacturing processes? It is just a 1 or 2 copper layers with trough-hole components.

And I also solder in my bedroom ;D, don't have an "electronics space"

Get a small piece of plywood or MDF, use a trysquare to rule on a grid, drill holes where the lines cross then push the LEDs through the holes. You can then solder all the leads together on the underside, lead to lead rather than through wires. That should work, although it may be different to what you want. /me

Chiva: "differences between the VCCLite PCV 220 and the female header" Indeed, but look closer at the pinout view. It would suggest that rotating the right-hand pin by 180 degrees is possible (thus giving a diagonal layout).

You can't cram a .100 pinout into a diagonal arrangement. Which is the routing problem I'm having with the female header idea.

Are you using a veroboard or something like that?

How about something like this? Cut them off 2 at a time, trim your LED legs to the same length, stuff them in the sockets. http://www.marcospecialties.com/product.asp?ic=SIP20L

Just solder them in place. If you're doing POV, you don't want the LEDs working loose from friction fit connectors and pelting spectators at 60mph.

What is POV?

What is POV?

POV is persistance of vision, which uses the fact that your eye retains the light image for a short period of time. Like when you twirl a light at night - it makes a circle.

This is used to make pictures in the air by moving it - hence the need for them to be soldered of otherwise fastened in a really good way.

Thanks. Aren't POV devices usually 1 LED in width? 24x8 seems kinda big for that.

Ah - that was a leading question .. was wondering how a god didn't know that one.

Now that you mention it .. yea ... normally 1 width. I too am interested in now 8 pixels wide will be used in a POV.

Well, if 24x8 is really desired, this might be a good time to learn about PCB services. For example, expresspcb.com will make you three 2.5" x 3.8" double sided boards with really fast turnaround for $51. I spent just a few minutes drawing up a bunch of 5mm LEDa on a board - 24 wide won't fit on a board, but 16 will. Stopping at 12 x 8, adding some via & mounting holes, you could mount 2 side by side by trimming the 2nd one (and I even added a couple of lines for a hacksaw guide), putting in 8 jumpers to connect the two and bring all your lines out to 2 connectors to go to your transistor drivers.

Desoldering 2 leads to remove an LED is pretty simple, I've had to do to it a couple of times for bad LEDs, the boards have held up well to reworking with no lifted traces.

Could even move the 8 pin connector over add your current limit resisters there too.

My device will be non-kinetic (it's going to be screwed to my office wall :)) the "POV" comes into it when you consider that only 1 led will be lit at any given moment. It will be like a very small, low-res TV set in essence.

I can hear you all thinking "What is this idiot talking about and why is he doing this stupid project?", Yeah I know. I'm only doing this as a means to an end... to teach myself about the various aspects of electronics design and manufacture - I'm a hobbyist and nothing more.

This thing will simply be a one-off, just to see if I can see a project from end to end.

Thanks for the hints about veroboard and the turned pins idea. I think that's the only way I can realistically do this.

I've been measuring things up and I can arrange the LEDS on a 7.62mm (full metal jacket anyone? :)) square grid if I skip 2 rows between leds horizontally and 1 row vertically. I think the skipped rows will allow me to trace the anode/cathodes without too much trouble, but it will be a HUGE amount of soldering.

With that in mind I think I'll try to get hold of some 8"x4", double-sided copper clad perfboard, at least that will make the traces easier to route, plus i won't have to drill it myself.

Well thanks for your help guys, I appreciate your valuable time and knowledge! :)

Cheers.

You have checked out the peggy2 kit, right? 625 LEDs...

I've decided to go with the perfboard and turned pins idea...

Many thanks everyone. :)

Looks like a good start - what's the interconnect plan?

Well, I originally wanted to use solder bridges between the pads to make nice clean lines along the board, but for some reason I couldn't get the solder to bridge easily, I was making too much of a mess that way. Good job I tried it out on a bit of scrap perf first!

In the end I decided to connect all the cathodes in each horizontal row of LED sockets together using a single strand of stripped bell wire to give the solder something to adhere to. That's worked well enough, even if it's a bit ugly. But it's not as if that side will be visible in the final build anyway.

I've just finished that a few minutes ago. Now I've got to make lots of small bits of wire and thread them through at 90 degrees to the first set of wires and then make connections to all the anodes in each column of LEDs.

That's going to keep me busy for another day or three!

I'll upload more pics when it's done.