Pushbutton interface - combined debounce and latch fuction

The circuit here extends the effec- tiveness of the simple push-to-make switch by enabling it to be used as either a "one-shot", with clean, de- bounced edges, or as a push-on/push- off latch. These functions remove I 5...15v 0 J. Ritchie the problems associated with any switch, that of electronic "noise". Resistor R1 and capacitor C1 "de- bounce" the switch and provide a positive edge to trigger the monostable FF1. This generates pulses (in anti- phase) at its Q and Q outputs. The pulse width is determined by R1, R3 and C2. The positive pulse (Q) is fed to an "OR" gate consisting of D2, D3 and R5. The trailing edge of the negative pulse is used to trigger flip- flop FF2. The normal (or stable) state of FF1 is with its Q output low and (logically enough) its Q output high. In this condition, if the switch is closed briefly and then released, the J and K inputs will be low when the triggering edge arrives. In this case FF1 will ignore it and stay reset. If, however, the switch is h...