Detect where touch happened on a big capacitive electrode

Question

I have a big-ish electrode (10cm x 10cm) that works fine for detecting touch over the whole electrode (as a boolean - simple touch vs. release) but I was wondering if there was a way to detect where on the electrode there was a touch, using filtered data or something? I saw this link where the person made a capacitive touch grid. All their copper tape rows/columns are touching. When I try to connect multiple clips to a single electrode though (more-or-less what they did) my MPR121 becomes unresponsive.

I'm using an Arduino Uno, a Sparkfun MPR121 capsense breakout, and this library for interacting with the MPR121.

Here's a basic program I have running at the moment just to check out an average of filtered data readings to see if there's a pattern. There isn't. The readings are anywhere between 250 and 580 no matter where the electrode is touched.

#include <MPR121.h>
#include "Wire.h"

int readingSum = 0;

void setup() {
  Serial.begin(9600);
  Wire.begin();
  MPR121.begin(0x5A);
  MPR121.setInterruptPin(2);

  MPR121.setTouchThreshold(50);
  MPR121.setReleaseThreshold(40);

  delay(1000);
}

void loop() {
  if (MPR121.touchStatusChanged()) {
    MPR121.updateAll();
    if (MPR121.isNewTouch(0)) {
      for (uint8_t i = 0; i < 8; i++) {
          readingSum += MPR121.getFilteredData(0);
      }
      Serial.println(readingSum / 8);
    }
    readingSum = 0;
  }
}

Answer 1

As @jsotola mentioned in the comments, no I don’t think there is a way to take a single electrode and turn it into a touchpad. Touchpads rely on a grid of addressable capacitance points to resolve a location.

I didn’t spend a lot of time investigating the link you referenced. However I wonder if you allowed for the adhesive backing on the copper tape when you attempted to replicate the example. It looks to me to be rows and columns of copper conductor separated by a thin layer of adhesive. Not the same thing as one big conductor.