And being portable, it would also have to be a low current drain operation.
The main inspiration for this design was one of those miniature pocket LCD televisions, produced in the 1980's, where sunlight passed through a milky-white translucent screen, and then through a transparent LCD video display, and then reflected off an angled mirror to the viewer. And it was obvious that a full size screen version would work just as well. So, in a way, this project is really not an invention of mine.
Using plywood, the base was constructed to mount solidly on top of a sturdy camera tripod.
An angled box was then constructed, to hold a mirror, at exactly 45 degrees to the video screen (as well as the viewer).
The inside of the finished box was then painted flat black, and a standard mirror mounded on the internal 45-degree angle surface.
A video monitor for this device could be made from a used video monitor, by removing the backlight, and mounting it, horizontally, over the angled mirror.
But since I was rushing to throw this thing together for an upcoming Earth Day Festival, I decided, instead, to simply purchase a used ($ 45.00) Panasonic PT-L104P LCD Overhead Projection Panel. Although it only had a 10.4-inch diagonal maximum display area, it would be a good start. Operating on 12VDC, 10 Watts, and with RCA video, S-video, and RGB video inputs, the monitor was well-suited for the task. And, designed to function on top of a hot overhead projector, the unit also had three internal cooling fans.
To provide symmetrical light distribution to the back (top) of the LCD monitor, a translucent, milky-white, plastic cover from a square, fluorescent ceiling light fixture, was inverted and used as a skylight.
A used portable 12VDC stereo boom-box was then mounted to the lower-front, so that the entire unit is in perfect balance on top of the camera tripod.
I was planning to add an extended, lightweight sun visor to the front, but decided not to, after determining that it was not needed.
Using a cheap Micca Mplay device (5VDC), multiple avi video clips can be stored and played from a SD card.
To moderate the sound, of multiple, dissimilar video clips, the audio from the Micca Mplay is ported through a Sima SVS-1 Volume Stabilizer (12VDC).
The brightness, and contrast, of the monitor was turned up to maximum, and the entire device was rotated until the viewing angle was at 90 degrees to the sun's rays. I will later design a solar tracker to maintain this required 90-degree positioning.
A final note:
It was a hot day in the park, at the Berkeley Earth Day Festival 2012, and most of the public did their best to find and sit under shade trees. Only a small percentage of the crowd was lured in by the video showings -and most of them were more intrigued by the device, instead of the content of the video message. Sunny, cooler days may be the most favorable conditions to set up in.