hippy
Ex-Staff (retired)
Here's a novel way of interfacing a 4x4 keypad using just 4 I/O lines.
It requires being able to make all the I/O lines input or output and won't work with a pre-assembled 4x4 keypad with just row and column lines coming out from it. With an 18X using the Shadow TRISB register to turn the Outputs into Inputs, a few current limiting R's and using SERTXD for comms a 64-key to serial keypad could be created.
I cannot take credit - That belongs to Elektor ...
http://books.google.com/books?hl=en&id=rZDbnQ0siCYC&dq=308+circuits&printsec=frontcover&source=web&ots=sKIHHZvieV&sig=GRV3t4ORjfAhY23E-J06wytFwmE&sa=X&oi=book_result&resnum=3&ct=result#PPA61,M1
And credit for the online link goes to Nick McClick on another forum ...
http://forums.parallax.com/forums/default.aspx?f=25&m=282160
It would probably make sense to add some pull-downs or pull-ups on the I/O lines or use internal weak-pull-ups if available ( which I think this circuit may rely on ).
It requires being able to make all the I/O lines input or output and won't work with a pre-assembled 4x4 keypad with just row and column lines coming out from it. With an 18X using the Shadow TRISB register to turn the Outputs into Inputs, a few current limiting R's and using SERTXD for comms a 64-key to serial keypad could be created.
I cannot take credit - That belongs to Elektor ...
http://books.google.com/books?hl=en&id=rZDbnQ0siCYC&dq=308+circuits&printsec=frontcover&source=web&ots=sKIHHZvieV&sig=GRV3t4ORjfAhY23E-J06wytFwmE&sa=X&oi=book_result&resnum=3&ct=result#PPA61,M1
And credit for the online link goes to Nick McClick on another forum ...
http://forums.parallax.com/forums/default.aspx?f=25&m=282160
It would probably make sense to add some pull-downs or pull-ups on the I/O lines or use internal weak-pull-ups if available ( which I think this circuit may rely on ).
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