For the following questions refer to figure 1.1 of the attached doc.
I'd like to use a ring electrode with a back-firing smt led centered in the ring. Drawing the schematic for the qtouch sensor, should I omit the electrodes leaving the resistors hanging and add the smt pad in PCB? Otherwise, I'm wondering how to represent the electrode symbol for the schematic. Would it have a pin to connect a trace to? I guess the footprint would have a smt pad with the diameter I want and then an inner diameter big enough to accommodate the led. Then place the back-firing footprint inside the ring electrode. My hurdle now is representing the electrode in the schematic.
On Sat, Jul 19, 2008 at 1:34 AM, DJ Delorie <
dj@xxxxxxxxxxx> wrote:
For plain circles, smt pads are easier and better.
If you wanted to do a resistive touch sensor with a circle with a ring
around it, you'd do the circle as a pad and a smaller circle (radius
== ring width) beside it. Then, when you lay out the board, add an
arc centered on the big pad, intersecting the small pad. Adjust the
angles with a text editor to come close to but not touch any traces
leading away from the center pad (or connect the center pad with a
via, and make the arc full circle. Make the solder mask for the
center pad big enough to expose the ring too.