Security and alarm system employing a particular pulse width

Abstract

A security and alarm apparatus has a pulse width discriminator circuit which includes: a monostable multivibrator having a trigger input connected to a data input of a flip-flop, a data output connected to a clock input of the flip-flop, and a pulse width control input; and a pulse width control circuit connected to the pulse width control input which causes a pulse produced by the monostable multivibrator to have one width when the flip-flop is in a first state and a larger width when the flip-flop is in a second state, the flip-flop producing at its data output a signal which is a logic high voltage when the frequency of an input signal at the trigger input has exceeded a first predetermined frequency and until it thereafter falls below a second predetermined frequency less than said first predetermined frequency, and which is a logic low voltage when the input signal has fallen below the second predetermined frequency until the input signal again exceeds the first predetermined frequency. The apparatus includes a plurality of sensors which can each detect an alarm condition, a radio transmitter which transmits a detected alarm condition to a radio receiver having an output connected to the trigger input, and an arrangement producing a display in response to the output of the flip-flop.