I have my motion sensor project working! I used a PIR motion sensor, a Teensy USB development board, and an arduino relay module.
This is my PIR motion sensor:
for now I just set it on top of the poster display, but eventually I'll make a nice housing for it and either wall or ceiling mount it.
It has a 3 pin connector, with +5v, ground, and +3.3v signal output. the signal output goes high when motion is detected and low when there is no motion.
the +5v and ground are supplied by the usb connection to the Teensy board. the 3.3v trigger is connected back to one of the digital inputs on the Teensy.
Also connected to the Teensy Board, is a 5v arduino relay module. the relay is triggered by one of the Teensy digital IO pins and is wired to the TV's button panel to simulate a button push on the power button. You could also send a power code over IR if you wanted to.
I also have a signal wire running from the IR/LED module to one of the analog inputs on the Teensy. This is used to determine the power state of the TV. when its on, approx 3v is sent to an analog input on the teensy. I chose to use the analog input simply to avoid connecting any extra circuitry to make it work on the digital inputs. (need at least 3.3v to signal HIGH input). this way we only simulate a power button push to turn the tv on if its in the off state, if its already on, the relay doesnt need to be triggered because it would turn the screen off instead.
Once motion is detected, the relay is triggered to turn the screen on. after a set amount of time (i figured 20 minutes was good), the relay is triggered again to turn the screen off. every time motion is detected the timeout is reset, so the screen will stay on as long as there is movement before the 20 min timeout expires. The code i wrote for the Teensy also watches for Strings to be sent over USB-Serial so I can send a command from the MoviePoster software to turn the screen on. For example, I always want the poster display on when a movie is playing, regardless of if motion is detected. this could also be used to turn the display on and off at certain times of day.