A circuit has been designed to debounce a mechanical switch, which is used to activate a digital circuit. Contacts tend to make and break connections several times until the switch contacts settle out. The repetitive activity plays havoc with digital circuits because more than one state condition could be activated by the switch as it bounces around between state conditions.

A circuit has been designed to debounce a mechanical switch, which is used to activate a digital circuit. Contacts tend to make and break connections several times until the switch contacts settle out. The repetitive activity plays havoc with digital circuits because more than one state condition could be activated by the switch as it bounces around between state conditions.

A Monostable Multivibrator generates a single pulse output when activated by a trigger command.

The switch debouncer circuit will recognize the first state condition activated by the switch and latch the circuit into this condition for a predetermined period of time until the switch bouncing settles down. In this way, the circuit will respond to only one pulse generation performed by the depressing of the switch and not several state transitions caused by contact bouncing.

This circuit can also be used for a monostable multivibrator or one-shot multivibrator. A monostable multivibrator generates a single pulse output when activated by a trigger command. The pulse width or pulse duration in this circuit is defined by selecting the proper values of a resistor and capacitor arrangement.

This work was done by Randal S. McNichol of the Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com under the Electronic Components & Circuits category, or circle no. 111 on the TSP Order Card in this issue to receive a copy by mail ($5 charge). MFS-31141