Ultrasonic waves are gathered by transducers on each of the receivers. Each
transducer has a 'cone' of usable operation of approximately 40 degrees. The
output of the transducer is fed to a single stage, common collector amplifier
using a 2N2222 transistor. This amplifier provides impedance matching for the
transducer and a gain of five volts/volt to the signal. The amplified signal
is fed into the non-inverting input of a 741 operational amplifier, where it
is again amplified by a factor of twenty volts/volt. Feedback components of
the operational amplifier circuit detect out-of-phase signals arriving at the
input of the operational amplifier. These signals cancel to produce a smaller
output. Likewise, in-phase signals produce a larger output from the operational
amplifier. A DC detector is employed at the output of the operational amplifier
to strip the AC component of the signal and send a proportional DC voltage to
the microprocessor controller. Two receivers are used on the front of the
puppy to produce a differential-steering signal. A rear receiver is installed
to recognize signals coming from behind the puppy.
Ultrasonic Transmitter
Microprocessor Controller
Infrared Proximity Detector
