I have customers with Sennheiser wireless headphones in their
theaters.  The transmitter is installed in the equipment rack.
Usually this is a long way from where they sit, in some cases in a
different room.  When the transmitter has been in "standby" mode for
about 3 minutes it shuts off - the only way to wake it up again is to
push a button on the transmitter.  Also, a single transmitter can pair
with multiple headphone receivers, but only if the transmitter is in
the right mode.
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<img src="wireless_headphone_antisleep.orig.jpg">
<p>
I embedded a Teensy.  It monitors the status light on the transmitter
(analog input).  It measures the interval between blinks.  When the
transmitter goes to sleep, it "pushes" the button to wake it back up
again.  The program can tell what mode the transmitter is in by the
interval between flashes - if the transmitter is in the wrong mode, it
will push the button to change it!
<p>
Now my customers are very happy!
<p>
William Phelps<br>
Meier-Phelps Consulting, Mountain View, CA<br>
"Optimized by William Phelps" (tm)<br>