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uC economic keyboard

J

Joel Kolstad

Jan 1, 1970
0
mdavid said:
http://www.josepino.com/pic_projects/security_keypad/JP6296.gif
Does anybody know how this works [see atached link] ? It's a 12 keys
keyboard which use only 4 wires.

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
 
M

mdavid

Jan 1, 1970
0
http://www.josepino.com/pic_projects/security_keypad/JP6296.gif
Does anybody know how this works [see atached link] ? It's a 12 keys
keyboard which use only 4 wires.

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.
 
J

jasen

Jan 1, 1970
0
http://www.josepino.com/pic_projects/security_keypad/JP6296.gif

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 :)

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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