I am designing a portable instrument which will have a 12.6" x 8.6" x =
1/8"=20 thick panel. It will have two four-digit seven-segment red LED displays = and=20 a 5x2 tactile keypad with a small red LED for each switch. The PC board = with=20 the switches and LEDs will be mounted about 0.38" behind the panel.The overall layout can be seen here:
After talking to several companies about making the graphic overlay, I = have=20 some questions, and since I have not designed a panel like this, I was=20 hoping someone may have experience or insight to offer.
I plan to use light pipes to transfer light from the LEDs to the surface = of=20 the panel. But the ones I have found seem to have a lens that extends = above=20 the panel, which requires the overlay to have holes for them. But it may = be=20 preferable to have clear windows in the overlay, and light pipes which = are=20 flush with the surface of the panel. I have not found any light pipes = that=20 are designed this way, but perhaps I can use acrylic (Lucite) rods cut = to=20 length, and then finish the ends properly for best light transmission.=20 Plastic rods are much cheaper than the light pipes, but if I need to = polish=20 the ends it will drive the cost up. The light pipes I am considering = are:
The other question is how to construct the keypad. I am using tactile=20 switches which are mounted to the PCB and have a firm actuation force. = But=20 the PC board will be mounted such that there is a gap of about 0.32" = from=20 the surface of the panel to the surface of the switch. I plan to have = holes=20
0.52" dia in the panel, and then glue a 0.50" dia x 0.31" long nylon = spacer=20 to the overlay so that pushing the surface will transfer to the switch. = I=20 may need to adjust the mounting so that there is either a slight preload = or=20 a slight gap. The switches I am using are:I made a rough prototype overlay by laminating a printed copy of the = panel,=20 and it will probably be good enough to make a working prototype of the=20 instrument, but I am looking for the best way to design this for = production=20 (20-100/year). BTW, I am getting the panels made by an on-line service = that=20 has excellent quality, fast delivery, and very low cost. My panel will = be=20 about $65 with 5 day turn.
Thanks!
Paul=20