T.V. motion detector with false alarm immunity

Claim 1

In a motion detector for a television viewing field of the type in which a television camera's output signal is processed in series by a low pass filter, a differentiator, a zero crossing detector and digital pulse generator so that digital signals related to edges visible in the viewing field are furnished to a following storage memory and to a comparison circuit which receives the real-time signals from the digital pulse generator and also the stored signals of a previous field from the storage memory and compares them and produces an alarm output signal if a difference between them indicates edge movement, the improvement wherein the comparison circuit comprises a phase detector circuit comprising an XOR gate receiving the real-time and stored signals with the XOR gate output connected to a first monostable multivibrator whose output is connected to a first input of a second monostable multivibrator and with the XOR gate output also connected to a second trigger input of the second monostable multivibrator, the output of which produces a motion indicating signal only when the difference in real-time and stored signals surpasses the output pulse length of the first monostable multivibrator.