switch indicator - one pulse per switch position

one pulse per switch position It is sometimes necessary to generate a pulse as soon as a mechanical switch is operated. The circuit proposed here does just that and only needs a small number of components. Furthermore it can easily be expanded for more con- tacts. The circuit diagram shows the layout for a six-way switch. An im- portant feature of the circuit is that it works with both make-before-break and break-before-make switches. A couple of EXOR gates (N1 and N2) are used to detect when switch- ing takes place; N1 handles positions 1 . . . 4 and N2 takes care of pos- itions5and6.AnumberofLEDs 730n (D1 . . . D6) indicate the switch position selected. Every time the position is switched the level at the output of N2 changes, thereby trig- gering the monostable multivibrator consisting of N3, R1 and C1. With the values stated, this causes a 200 ps pulse to be output at pin 8 of N3. When building this circuit it must be remembered that the inputs of N1 and N2 have pull-up resist...