Personal aid signalling system

A personal-aid call system for activating a remote alarm signal, comprising in combination:

• a. a self-contained portable transmitter adapted to be carried by a person, said transmitter generating a composite output signal characterized by a carrier frequency and a modulating frequency,
• b. manual control means for enabling actuation of said transmitter, at will, by said person,
• c. a receiver tuned to receive said composite signal, said receiver having a detector for demodulating the composite signal to yield a demodulated signal having a frequency characterized by a fixed relationship to that of the modulating frequency,
• d. decoder means including a gated, resettable counter device of the frequency divider type,
• e. means for generating a control signal which is independent of the composite output signal, to gate said frequency-divider type counter device thereby enabling the counter device over a predetermined counting interval of time,
• f. said counter device being connected to the detector output of said receiver for measuring the frequency of the demodulated signal by counting consecutive, uniformly spaced cycles thereof over said predetermined counting interval of time,
• g. means connected with said control signal generating means for periodically resetting the counter device to zero,
• h. said counter device having a plurality of parallel, digital output terminals,
• i. said decoder means including a plurality of manually selectable switches respectively connected to at least some of the digital output terminals of the frequency-divider type counter device,
• j. said decoder means further including a plurality of digital inverters connected respectively in line with at least some of said counter device output terminals and connected respectively with said switches,
• k. a gate having multiple inputs connected with said switches, respectively, for sensing a condition wherein there is a uniform digital voltage level on all of said gate inputs,
• l. indicating means connected with said decoder means for providing an alarm when a particular modulating frequency is detected by the counter device whereby the user, when needing assistance, actuates the transmitter which in turn triggers the alarm for the purpose of alerting others to the existence of such a need, and
• m. means associated with said control signal generating means for momentarily disabling the alarm during said predetermined counting interval of time, thereby preventing inadvertent actuation of the alarm while the counter device is tallying a count.