■ FIGURE 9.
PCB
implementation
of a paired
sensor
touchpad.
case, however, I made up my own symbols for the Back
and Enter keys. Also, you can clearly see the paired sensor
elements that I used for the 10 digit keys and the single
sensor elements that I used for the six remaining keys. Of
18
February 2011
course, we now know that I could have included five
more sensors for my six-pin interface, but I wanted to keep
it simple for my first attempt.
Fortunately, there was absolutely no frustration
involved in testing this version of a touch-sensitive keypad.
It consistently functions well, and can reliably detect and
discriminate which key has been pressed — probably
because all the sensor areas are on the top of the board.
Also, because it only uses six touch inputs, it’s faster than
the stripboard version, so reasonably quick key-presses are
always detected. However, I still want to modify the PCB
slightly, and have another prototype produced for testing.
As you can see, the PCB covers the power rails on the
bottom edge of the breadboard which turns out to be
more inconvenient than I thought it would. Also, the
keypad wobbles a little when pressed vigorously. For both
those reasons, I plan to redesign the way the keypad
connects to the breadboard.
When I have tested the modified prototype board, I’ll
have the keypad produced in quantity and add it to the
PCBs that are currently listed on my website. I hope to
have the final PCBs available shortly after this issue is
published. (However, I have never been known for the
accuracy of my time predictions, so check my site
periodically if you are interested in the touch-sensitive
keypad.) I will also include the program that I used to
decode the keypad, but in case you’re interested in seeing
what’s involved in the decoding process, the software that
I used ( TouchPairedDecode.bas) is also available for
downloading at the N&V website.
MORE TO COME ...
As I mentioned last time, we aren’t finished with the
18M2’s touch inputs yet. In the next installment, we’ll
experiment with the possibility of using touch sensors to
detect the presence of water or other liquids, and/or to
measure the level of a fluid in a non-metallic tank. As you
already know, I would like to develop a simple means of
measuring the level of water in the tank of my espresso
machine. In addition, I’m sure you can come up with
useful applications of your own for a simple and reliable
water-sensing device.
When we have finished our exploration of the touch
inputs on PICAXE processors, we’ll move on to some of
the other new 18M2 features. I especially want to take a
look at the 18M2’s “multi-tasking” capabilities. See you
next time … NV
