I made this bad pun prototype at the space for Red Nose Day 5/23/19.
The front was one coat of cheap black spray paint (two would have been better) on some 2mm clear acrylic, with the letters laser raster etched to ablate the paint. 100% speed and 30% power worked well. Resolution was fine for the task at hand. Some onionskin paper behind the plastic provided a diffuser.
Scott proposed a two layer diffuser – adding one close to the LEDs. My impression was that the illumination that gave was a little less uniform than the roughly collimated beam straight from the LED. But the illumination across the word due to short throw was much worse than the double diffuser would have provided.
The biggest disappointment was that the letters were so visible from outside light reflected from the onionskin when the LEDs were off. For a next version, a translucent black diffuser would be much better, using more LEDs if needed to get appropriate brightness. With 6 PWM pins, more Nos could be included.
Here’s a clip of it at the space. Sorry about the focus. I tried to reduce the typical LED white-out by running the LEDs much dimmer for the clip by reducing the max PWM value from 255 to 40. But that ran into integer division digitization issues with fade-in/-out. Using full 255 PWM max and actual resistors would have provided much better video results. Or take a minute and redo the fade in/out math. Hmm – I tried to improve video quality by changing brightness on the camera to darker overall. But I think that’s going the wrong direction. Oops.