The absence of a pulse in the pulse train applied to the input of this circuit causes a high level to be generated at the output. The RC circuit must be calculated so that its time constant is less than that of the interval between three pulses, and greater than after consecutive pulses. This allows to detect the absence of the intermediate pulse. The circuit works with voltages from 5 to 15 V and is compatible with TTL and CMOS logic. Among the applications for it are data communication systems, security, and alarms.
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