Does anybody know how this works [see atached link] ? It's a 12 keys keyboard which use only 4 wires. I need a clue about how the software it's made, and, generaly how this thing works :)
Thank you
mdavid escreveu:
ya, i know how that works, where u wante conmect that?
It's nice... what he's doing is energizing one column of keys at a time (1/4/7/*, 2/5/8/0, or 3/6/9/#), and then using the four pins to read back which (if any) button is pressed. But... since he uses one of those same four pins to energize a column, he needs two ways to energize each column: When the leftmost diode is driven, the 3/6/9/# column is energized, but he can't read back "#" since it's already high. Hence, he'll next drive the 2nd to leftmost diode, which still powers up the 3/6/9/# column, and now he can read # (but not 6 -- but he already checked that last time).
The pin driving the LED is an input while he's "scanning" the keys, although it'll light up if 1, 2, or 3 are pressed. If the duty cycle of scanning is low, this probably won't be visible. (He could add a largish resistor between the top row and the input pin to reduce this effect, if it is noticed.) When he's not scanning he can use it to flash the LED or whatever.
---Joel
Thanks, Joel. I took another look to that schematic. Your explanations it's ok, but i think he does the "scanning" on rows (Make one row "0" logic), and then use the other 3 (connected to columns now through corresponding diodes) to see what key was pressed.
Marius.
you mean the 3x4 matrix is controlled by 4 IO pins,
I expect what they do is turn on the pullups on those pins and then take them low one at a time and see which others follow,
Bye. Jasen
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