Elimination of False Data Caused by Switch Bounce of a Switch-Contact Keyboard
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
When a key of a switch-contact keyboard is depressed, a software program determines whether the switch is open or closed by sampling it a multiple number of times during a fixed period of time and counts the number of times the switch is sensed as being closed during this fixed time period. If this count exceeds a threshold value, the switch is deemed to be closed. This requires only one byte of storage regardless of the number of keys on the switch-contact keyboard. The opening and closing of a switch by depression of a key and by bounce is shown in Fig. 1, with the multiple samples during a fixed time period being indicated within the test interval. When a key is sensed as being depressed by the switch being closed, the frequency at which the state of the switch is sampled is much higher than the normal scan rate.