10x4 matrix keyboard using only portB

[aratti]

During the weekend I came to the conclusion that the project should be for 60 keys.
The reason is that it is simpler to workout a smaller keypad from a larger one. (at least in this case)

Just remove the unnecessary switches and diodes and you have the keypad already designed.

The software has also been changed a bit in order to work around the fact that 16F84A could not accomodate an array of 61 bytes.
So with this new solution I had it at work reducing also the code work space.

Now the software works with all combination of keypad from 4x1 to 4x15 (Rows x Columns)

I am attaching the file with the new version (Hardware & Software) sure that this will make life easier.
Al.

[Darrel Taylor]

Hi Aratti,

You're doing a good job here, but there are a couple issues I'd like to bring up.
Don't shoot me.

While scanning the first row, you set PortB =16 which puts RB4 high and RB5-7 low.

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3010" /><!-- -->

If someone accidentally presses keys 1.1 and 2.1 at the same time, you have a dead short across RB4 and RB5. If you have a small power supply it won't last long because the PIC will reset as soon as the voltage drops low enough. But if you have a strong power supply, somethings likely to smoke.

The problem can be overcome a couple ways, either by adding ~100 ohm resistors in series with each Row's pin. Or you can manipulate the TRIS register in your program instead of PORTB, and only allow 1 Row at a time to be in OUTPUT mode.

And, it would be allot nicer to have the Outputs on the lower bits of PORTB, and the Inputs on RB4-7.

Then you would be able to use the PortB Change interrupts to monitor the keypad, and you wouldn't have to keep scanning it all the time. You would then place all outputs to HIGH and when you get an interrupt, scan the rows 1 by 1 like normal.

HTH,

[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 ....
<br>

[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.