The keyboard is used to enter data, and other values to the system microcontroller. Keyboard normally available in three configurations, namely: linear keyboard, matrix keyboard and the keyboard is encoded. Linear keyboard is used when the number of inputs to be given a little. The keyboard is generally used is a matrix keyboard. When the keyboard is connected to the microcontroller, the following factors should be considered,
1. Contact Bounce (bounce)
Contact bounce refers to the oscillation of the contact when the button is pressed (Fig. 1.23). quality keyboard has a bounce period 1-5 mdetik.Jjika bounce ignored microcontroller responds to the button is pressed and released beberapakali when in fact only pressed once. Contact dbouncing through hardware or software made for meghindari effect several times kontakyang undesirable when the contact closes, thus we will get only a single operating ON and OFF.
Hardware debouncing is done using the RC circuit (Figure 1:24 (a) or a Schmitt trigger circuit (Figure 1:24 (b), if debouncing done using software, the delay time given is 20 -50 ms fter button is pressed sebeum executable program.
Figure 24 Bounce contact
Figure 25 Hardware debouncing by using the RC circuit
Figure 26 Hardware debouncing by using a Schmitt trigger
2. Multiple key.
If more than one button is pressed, then only the keys are valid only be executed.
3. Key hold.
There are two types of keyboard actuation, namely: two-key lock-out and the N-key rollover. Two-key lockout takes into account only one button is pressed. While the N key rollover will ignore all buttons pressed until only one who suppressed. 1:25 Picture shows the relationship matrix keypad with mikrokontroler.Di-16 here, each column and row are connected to the microcontroller pins.
The column is usually at the level HIGH. Lane configured as an output and the column is used as a line scan. Button actuation censored by sending a LOW signal to every lane and every moment only one lane censored.
Figure 27 Relationship matrix 16-button keypad with microcontroller