Datasheet NE555, SA555, NA555 (Diodes) - 9

NE555/SA555/NA555 PRECISION TIMERS Typical Applications Characteristics (cont.) Missing Pulse Detector
The circuit shown in Figure 7 can be used to detect a missing pulse or abnormally long spacing between consecutive pulses in a train of pulses. The timing interval of the monostable circuit is retriggered continuously by the input pulse train as long as the pulse spacing is less than the timing interval. A longer pulse spacing, missing pulse, or terminated pulse train permits the timing interval to be completed, thereby generating an output pulse as shown in Figure 8.  
T UC NEW PROD Fig. 7 Circuit for Missing Pulse Dectector Fig. 8 Timing Waveforms for Missing Pulse Dectector Frequency Divider
By adjusting the length of the timing cycle, the basic circuit of Figure 1 can be made to operate as a frequency divider. Figure 9 shows a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle.
Fig. 9 Divide by Three Circuit Waveforms
NE555/SA555/NA555 9 of 14 February 2012 Document number: DS35112 Rev. 4 - 2
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