The LM1812 is a complete ultrasonic transceiver on a chip designed
for use in a variety of pulse-echo ranging applications. The chip
operates by transmitting a burst of oscillations with a transducer, then
using the same transducer to listen for a return echo. Ifan echo of
sufficient amplitude is received, the LM1812 detector puts out a pulse
of approximately the same width as the original burst. The closer the
reflecting object, the earlier the return echo.
Ultrasonic-Transceiver Circuit Diagram
Echos
could be received immediately after the initial burst was transmitted,
except for the fact that the transducer rings. When transmitting, the
transducer is excited with several hundred volts peak to peak, and it
operates in a loudspeaker mode. Then, when the LM1812 stops transmitting
and begins to receive, the transducer continues to vibrate or ring,
even though excitation has stopped. The transducer acts as a microphone
and produces an ac signal initially the same amplitude as the transmit
pulse. This signal dies away as is governed by the transducer"s damping
factor, but as long as detectable ringing remains, the LM1812"s detector
will be held on, masking any return echos.Link
