I know this has been discussed before but the solutions provided are
not what is needed for this project, so here it is.
What I have is a matrix keypad (3x4).
What I need is when a key is pressed _one pin_ of the decoder is
connected to ground. The ideal solution would be a series of logic
gates or similar basic circuitry.
Thanks for your time,
Lewis
So you have that 3x4 matrix (7 wires) and that decoder (12 wires + GND). A
solution for a conversion is not half as easy as it looks like, especially
when using basic building blocks like gates. Problem is the matrix keypad
which cannot be read out using combinatorial logic only. You will need some
clock and a shift register or similar to put signals on the rows (or
columns). When correctly designed, the signals on all seven lines determine
which key was pressed (if any). This code is not continuously available
however as other keys also needs to be scanned. So you will need to build in
some timing for validation of the key pressed. Another method is to stop
scanning as long as a key is presed. Conversion from the 7 bits code to the
12 bits one is straightforward using combinatorial logic, although you will
need a lot of gates.
This type of circuits has been build and I still can build them if I really
need to. Otherwise I won't. Using a simple, cheap, 28 pins micro or similar,
will be far easier and faster to design and requires much less components
and so board space.
petrus bitbyter