Selective proximity detector

Claim 1

Apparatus for detecting the approach toward a reference point on the ground of a heavy vehicle traveling on the ground, said apparatus comprising in combination: (a) single geophone means mounted and adapted to respond to vibrations in the ground and to provide an output indicative of vibrations sensed thereby; (b) first means including high-pass means connected to receive the output of said geophone means, said first means further including means for providing an output when the long-term average of high frequency vibrations reaches a predetermined relation to the short-term average thereof; (c) second means including low pass means connected to receive the output of said geophone means, said second means further including means for providing an output when the long-term average of low-frequency vibrations reaches a predetermined relation to the short-term average thereof; (d) an oscillator means having an output for providing pulses; (e) OR circuit means having three inputs and an output means; (f) counter means having an input and an output; (g) AND circuit means having a pair of inputs and an output; (h) latch means having an input and an output; (i) means including inverter means for connecting the output of said first means to one of said inputs of said OR circuit means, said other inputs of said OR circuit means being connected to receive: (1) the output of said oscillator means, and (2) an output from said counter means, and said OR circuit output means being connected to the input of said counter means; (j) means including inverter means for connecting the output of said counter means to one of the input means of said AND circuit means; (k) means connecting the output of said second means to the other of the input means of said AND circuit means; and (l) means connecting the output of said AND circuit means to the input of said latch means; whereby said apparatus functions as follows: (1) in the absence of any vehicle signals (i) said OR circuit means is inhibited by said first means, thus preventing pulses from said oscillator means from being applied to said counter means so that the output of said counter means is low, and (ii) the outputs of said second means, said AND circuit means and said latch means are low, and (2) upon the approach of a heavy vehicle (i) said first means (in response to high frequency vibrations) enables said OR circuit means to pass said pulses to said counter means to thereby, after a predetermined time interval, cause a high output from said counter means and (ii) said second means (in response to low frequency vibrations) operates as aforesaid to provide an output and thereby enable said AND circuit means to thereby actuate said latch means to thereby have a high signal at the output thereof so as to signal the presence of a heavy vehicle, provided, however, that if said high output from said counter means occurs prior to the production of the output signal from said second means, then a subsequent output signal from said second means will be ineffective to actuate said latch means.