Graphic panel overlays and light pipes

I assume the prospect of having something *molded* isn't appropriate? E.g., a single piece that implements *all* of the pipes? (see below)

Make sure the overlay is "flexible enough" in that 0.52" span to deflect enough to actuate the switches. And, not *too* flexible (nor too

As with the light pipe, you could consider a molded piece that presents *all* of these "plungers" so that the piece can be fitted to the PCB (!) -- ensuring perfect alignment with the switches (and LEDs, if you combine them all into one part).

Consider what will happen *when* one of those INDIVIDUAL actuator snaps/falls off (rattling around inside the case AND making that button inoperable)

Also consider (evaluate) the visual effect that mounting the displays behind the panel will have. E.g., will you end up with "internal reflections" when yiewing the displays off-axis?

And, of course, how all of these little "bits" will affect servicing (if it is tedious to reassemble -- holding every little piece in JUST the right spot as you cram it into its enclosure -- then your warranty and service costs will have to reflect that)

If you make the LED windows clear, that will work fine. You can even stand up the LED with spacers if required. If your SMT, then there are short light pipes that could be used. I would not worry about how close the pipe end is, just get one long enough before going custom. Since you are using tactile keys on the PCB, make sure they are as large as the buttons otherwise the membrane overlay will wear in the area of a smaller key. We use a membrane with keys designed into it, clear/red windows for 7-segment displays and clear LED ports. THe membrane lays on top of the 7-segment displays, and the LED ports are not a problem for the T-1 3/4 led's we use.

Front panel express is fine for one-offs. They do come out neat. But if you did the entire front in a membrane it would look spiffy. Have a local sheet metal house cut a bare panel, clear alodine, and stick on the membrane.

Another option is to just inlay the membrane in the small area you have shown that has the keys and LED's. Either way the cost of the membrane is going to run $2k or so for tooling.

Cheers

Hi Paul,

You know you can get tactile switches in various heights? You can normally make everything line up without little extension pieces.

Any you can definitely get PCB mounted light guides that can go behind a panel, not used any that short though, can't you just use LEDs directly?

The switches I am using also come with an extension that is made to have =

snap-on caps, but I want the keypad to be sealed with no holes. I made a =

small panel to try various ways to mount the PCB and switches. What I = did=20 was make a 1/8" thick aluminum sub-panel with 0.257" holes that I filled =

with 0.25" nylon spacers that I already had. Then in the main panel I=20 drilled 0.50" diameter holes. When I mounted the PC board so the spacers =

extended past the surface, the laminated overlay actuated the switches=20 without pressing them, and when I aligned them a little below the = surface,=20 the overlay seemed to be too stiff to work well.

So, I used foam double-stick tape to mount the overlay above the = extended=20 spacers, and the foam was soft enough to allow the switches to operate, = but=20 the action is still stiffer than I would like. It's good enough for the = demo=20 unit for now, but I'll need to look more closely at the overlay material =

that will be supplied by the manufacturer. It's probably more flexible, = and=20 thinner (6 to 10 mils), than the laminated overlay I made, which is 14 = mils.=20 I think I need to get samples of the material to see if it's flexible=20 enough. They are proposing PET or polycarbonate (Lexan), but maybe I = should=20 consider silicone.

directly?

There are three T-1 LEDs that are thru-hole, and the others (for the=20 switches) are 1206 SMD. For the production unit, I could use T-1s and=20 extensions to mount them high enough to fit into holes in the panel, but =

still below the overlay. If I use SMD, I'll need the light pipes. If I = use=20 the sub-panel, the light pipes could be mounted through that, and the = hole=20 in the panel could be larger to accommodate the diameter of the lenses. = Or I=20 could use a thicker panel and have the holes counterbored, but that = would=20 probably be more expensive than making the sub-panel.

Another possibility is to use a relatively thick foam adhesive backing = that=20 will give flexibility to the keys and a soft feel to the panel, almost = like=20 a floating floor system with a thin foam underlayment. Maybe I should = allow=20 the overlay manufacturer to select the PCB components and determine the = best=20 way to make the panel. I'm locked in to the present basic design only = for=20 the initial prototype to be used as a demo. I will be redoing the board, = and=20 I need to align the LEDs a little better, so the production unit will be = a=20 bit different. Hopefully I can just get this unit working reasonably = well=20 and in a presentable form so we can get input from potential customers = at=20 the show, and maybe there will be even more changes.

Thanks to all,

Paul=20

Yes getting enough flexibility is a problem. We usually use the thinner overlay material and the spacing needs to be quite closely controlled. There is usually some item in the stackup that can be fine tuned like the PCB spacers or the panel thickness. I never thought of the foam tape idea; that might work. By the way the $2000 someone mentioned sounds high for a plain flat overlay. We pay more like $400 for a self-adhesive overlay with a few spot colours. (Even that always seems high to me, why is it a thin piece of printed plastic sheet costs more than a PTH PCB?)

I would expect $2000 to get me the keyswitches integrated too, which is probably the way to go for production. (But we have made 1kpcs of a

You can also get the keys 'domed' or with a domed boarder. Might make flexibility a little better. I used this approach with the standard 5mm round push button thru round holes under square domed keys.

Cheers