Hold button until the decimal point flashes. Sometimes it's immediate.
Buttons:
C D E F
8 9 A B
4 5 6 7
0 1 2 3
~ Design
~~~~~~~~~~~~~~~
Latch input:
* Row address is taken straight from the counter, which is decoded to drive the rows
* Column address is taken from an encoder just like in the simple button encoder
Latch load signal is taken from the columns. Propagation delay matters here: it must be slower than the encoder.
Simple button encoder:
http://everycircuit.com/circuit/4986331016200192
