Further investigation of the counter looks like it will be very difficult to provide some lighting to the screen, especially using LED tape as you did. I tried it last night by laying a stretch of the tape across the top of the gap between the front plate and the pcb and the LCD screen is very close to this edge, effect on the screen, nil but plenty of light spill to edges of the bezel.
Unlike your RC module, the counter does not have a secondary window, the LCD is stepped so it fits into the bezel and finishes almost flush with the front panel. This leaves the thinnest of open glass edges to capture the light and channel it through the LCD panel itself. Also when I presented the section of LEDs to the screen in the region of the counting section of the PCB, the counter sprung into life and started counting. This shows that area is very sensitive to spurious signals but that might have been because the LEDs were powered from a wall wart, maybe better smoothing would prevent it. Total gap between front plate and the PCB is 4mm so there is not a lot of space to play with either.
Hmmm... if you were powering the light from an RGB controller, multiple PWM channels would certainly generate some noise the counter could pick up.
It sucks that this display is flush/recessed mount; sounds like your only other option would be to make a diffuser from scratch to go behind the LCD, and this would only work if is is NOT one of those with an opaque reflector. Most are at least somewhat translucent, though.
What are the dimensions of the LCD, and how much gap is there between it and the PCB behind it? I may know of something ready-made that could be cut to fit.
mnem
I'm all out of "pithy" right now.
The size of the LCD is about 103.5mm by 30mm and the space between it and the pcb is 3mm. There are a couple of holes in the pcb directly behind the display and I have shone a light through and it does light up part of the display very dimly and looks milky.
Dang... There were a couple vendors on Aliex with letter-sized sheets of perspex that had been etched as a backlight/diffuser some while back; guess this wasn't a popular product.
I'd suggest one of the
LED backlight kits made for the Turnigy 9X RC transmitter; but the active portion of that is 80mm x 40mm. They ARE 3mm thick though, and pretty cheap. You MIGHT be able to butt 2 of them against each other to get the length you need; I've never tried.
You CAN make your own diffuser; all you need to do is cut a piece of clear acrylic to size, then circularly wet buff one side with 1200 grit emery paper until the surface is uniformly hazy. Wrap the back and edges with film cut from a silver mylar balloon and Bob's your Auntie. To get even dispersal of the LED light with end-lighting, make one end about 4-6mm extra-long, then use the round edge of a soldering iron tip to make a roughly hemispherical proportioned D-shaped indentation(s) in that edge for the LED(s) to set into. Pick the flash off that you create with the iron and then proceed to buff, wrap with mylar, etc.
Good luck!
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mnem
"It's okay sweetie... we'll name the children after all the dead stars."