The “Smart Rock”: A Micropower Transponder
Design Note 161 Dale Eager
INTRODUCTION
A “smart rock” is a locating device that is buried at a specific
site. It is interrogated by a portable source and responds
with information about its position, identification number
or any data that it has collected since its last interrogation.
Ideally, a smart rock, once placed, will wait, listening for
its interrogator, for many years, or even for decades. A
smart rock buried on a nature trail might send its identification number to a traveler’s handheld transponder, which
would decode the identification number and play a message
describing the surrounding sights. It could also be used
to direct the traveler which way to turn at a trail junction.
Smart rocks are sometimes placed along the edges of
cliffs so that interrogators built into vehicles, such as
bulldozers, will cause them to stop before they get too
close to the edge.
THE MICROPOWER SUBCIRCUITS
The Oscillator
Figure 1 shows the LTC В® 1440 implementing a micropower
oscillator. This circuit provides the references for both
voltage and frequency needed in our rock; it draws only
a few microamps of battery current. …