10x4 matrix keyboard using only portB

[aratti]

Thank you Darel to have pointed out the problem, which I did noticed! I will modify the software to have only one output pin at the time on portB. The updated version will be posted tomorrow.

Thank againg for your promp notification.

Kind regards

Al.

[aratti]

Here the updated version of software and hardware.

It was necessary to pulldown the rows as well (4x5K resistors) in order to avoid floating inputs. It has been tested and it works.

If you have downloaded the file from the previuos post please discard them and download the updated file from this post.

Thank you again to Darel, and sorry for the inconvenience to all the members of the forum that have visited my post.

Al.

[mister_e]

I like the concept, good job!

[Darrel Taylor]

Awwwwww! No RBC Interrupts. :(

Such a nice little keypad scheme.
If only it would ....
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[aratti]

Darel be patient next release will be with "PORTB change interrupts". For that I need to build a new hardware prototype and it will take few days.
I had to fix the bug you pointed out quickly, otherwise I could not sleep!

Regards

Al.

[falingtrea]

If I am looking at this correctly, the one drawback to this design is that you can't detect multiple keypresses in the sam row, right? In fact, holding two keys down in the same row could cause the wrong character code to be generated. Like holding down 1,1,and 1,8 gives you the code for 1,9, right? Not trying to nitpick. Just wanted to make sure I understood the advantages and disadvantages to the design.

[aratti]

Yes Tim, this is the price you have to pay for the extra keys!

If the spacing of the keypad is done properly than chances to press two contiguous keys at the same time are really rare, but since number of keys available is no more an issue, you can dedicate one key to delate the possible unwanted input.

Al.

[T.Jackson]

I believe that a protocol is possible to detect simultaneous key presses, BUT it would fail if both keys were pressed at exactly the same time (incredibly unlikely though). However, if it did occur -- the procedure would return the key that equated to the binary sum of the two keys held down.

You would only need microseconds of a difference between the keys being pressed to come up with something that works.

Trent Jackson

[Ioannis]

Since we are talking about mechanical switch, that micro seconds might be to short time in my opinion. Debouncing is needed to read the switch correctly.

Ioannis

[T.Jackson]

Moreover ...

I think if the columns were each given a unique, physical delay, say using an RC circuit -- you'd eliminate the possibility of two keys ever being processed as one.