We've already seen how pressing multiple keys in the same row may disturb the readings, but that problem can already be considered solved. Now let's see what happens if multiple keys are pressed both in the same row and in the same column.
In the picture on the right three switches were pressed simultaneously. Two of them share column 2 and two row m. That means one of those three pressed switches shares both its row and its column with some other pressed switch. This situation is commonly referred to as ghosting. Suppose we're currently reading column 1 (so it's output pin at the bottom is pulled down to ground - "0" state). Because of this characteristic setting of pressed switches, even though the remaining switch (top-left in the picture) is not pressed, the state of the R2 line is "0", because it is pulled down by C1 (currently at "0") through all the 3 pressed switches. This causes the keyboard controller to read the state of that key as "pressed" no matter if it's actually pressed or not. The word ghosting comes from the fact that some key combinations pressed together cause such "ghost" keypresses to appear, even though the keys are not physically pressed.
e sad, navodno sa mnogo dioda ovo bi trebalo da bude reseno
ali ja sam sad nesto skeptican i razmisljam se da li da idem na ovu varijantu, sa matricom i mnogo dioda, ili da uzmem lepo mcu sa 100 io pinova i citam taster po taster i a u pm .. pcb mora pravim pa mora pravim (ili vucem zice videcemo), mcu dal ce kosta 3$ ili 5$ ne pravi nikakvu razliku (dadoh vec 300+eur samo za tastere) ... pa reko da pitam kolege sta misle o celoj prici ? dal neko ima bolju ideju?
fora je sto bih ja zeleo NKRO (dakle bilo koju kolicinu tastera pritisnutih u isto vreme da mogu da budu detektovani).