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Infrared
switch
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2007-03-10
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using the same technic like a remote control we built an
infrared contactless switch for our robot mullrats
(object detection in the
front part)
there should be very less influence from daylight and el.
lights
therefore we used infrared LED's and phototransistors with an small
bandwith and a TINY26 microcontroller
4 pins are connencted to LL-Fet's
which are for pulsing four IR-Led's with higher current than the tiny could
deliver
four IR-transistors are connected to the ADC channels 
the LED's have a 30cm distance to the transistors
first the analog-digital
conversation values are read for a few times
then the according LED is
switched on and the ADC-value is read for the next few times
if there is an
object in between, the "on"-values should be much higher than the
"off-values"
our board is dimensioned that there is a plus of 16 bits in
"on"-status
this plus is linear, independent from the background light, the
gain is constant
a 60W standardlamp 30cm away from the phototransistors
produces a background of 120 bit (led-off=120bit, led-on=136bit)
->there
should be no problems with extreme background light and the multiple AD-values
(in 0,6ms) makes a good average 
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