Missing Pulse Detector based on NOR gate

The circuit shown in Fig.8.9 employs four 2-input NOR gates as a missing pulse detector. The pin numbers are for a CMOS 4001B, and the circuit can be powered from a 5V to 12V supply. Gates from the CMOS 74HC series (i.e. 74HC02) will also work, but note that the pin numbers are different, and the supply must be between 4V and 6V. At the heart of the circuit is a monostable, comprised of gates IC1a and IC1b.  The timing period is set by the values of capacitor C1 and resistor R2, according to the formula:

Time in seconds = 0·7 × R × C

Figure 1. Missing Pulse circuit using NOR gate