The IR proximity the I have built is simply 16 IR sensors
connected to a multiplexor so that each sensor is checked about three
times a second.  555 timer #1 provides the 32kHz square wave for the
output LED's.  I chose this frequence based on the input
characteristics of the receivers.  Other receivers are designed to
respond to 38kHz light so the values of the 555 will have to adjusted.
To keep noise to a minimum it is necessary to place a 0.1 uF capacitor
across the power leads of each 555.  555 timer #2 is the rate at which
the sensors are switched between.  The values are roughly set up to
operate at 60Hz although I think that I may have made a mistake in the
values.  I have never tried to run this circuit faster than 50Hz but
there is no reason that it shouldn't operate moderately faster.  The
output of the second 555 is connected to the clock input of 74163 4
bit counter.  The output of the first 555 is connected to the G1 input
of the 74154.  By doing this, the '154 is constantly being disabled
and enabled so the output pins are also modulated at this rate.  It
may sound confusing but it's simple and it works well.  Each one of
the outputs on the '154 is connected to a variable 1k resistor and
then to an IR LED.  The resistor is there so that later the sensing
distance can be adjusted.
	
	The receiver is basically the same concept as the transmitter
circuit.  A Sharp IR sensor is the receiver of our 32kHz signal.  The
output of the Sharp sensor is connected to a 4.7uF capacitor that is
connected to Vcc.  This is done to filter some noise out of the
signal.  The value of this capacitor was chosen by experimentation and
should work for you.  It is imperative that a 10k pull-up resistor is
connected from each input of the 74150 to Vcc!  The resistors are
needed because the inputs cannot be left floating as this would cause
false detection data.  The output of the 74150 goes high when one of
the 16 sensors returns a signal.  A total of five inputs must be run
to the handyboard for the circuit to work properly.  They are:

1) The output from the 74150 (goes high when receiver receives a signal).
2) The four address lines from the 74163 circuit(shows which sensor
detected the signal).

	The circuit will work fine if you have less than 16 sensors
connected at a time (I myself only use 14 of them).  If you choose to
do though there you must have the pull-up resistors installed on the
74150.  The computer that receives the signal will have to monitor the
output signal from the 74150 constantly as it can change rapidly.
When it sees a signal it should then record the four bit address of
the signal and go about its business.  As of the writing of this I
have not written any software drivers yet so if anyone wants to give
it a try let me know.  If you have any questions please E-mail me at
kas219@email.psu.edu.  Good luck!

		Keith Soldavin