Problem with readings of capacitive sensors (copper foil)

Other Hardware Sensors
1

Hi everyone :slight_smile:

I'm working on a project where I cast a plaster bust (I have a silicone mold) which gets equipped with capacitive sensors (copper foil) at some spots to make it interactive.

Here's how I do it:

  • I brush a thin layer of plaster inside of the silicone mold and let it dry
  • Then I glue some round pieces of copper foil (diameter approx. 2.5 cm) onto it and solder a cable to each one
  • Then I apply a layer of hot glue
  • Then another layer of copper foil (over the whole whole surface of the sensors/hot glue). I then solder a cable onto it (for grounding)
  • Then the rest of the plaster, I let it dry, remove the bust, done :slight_smile:

So far, so good. What's problematic now is that one of the sensors isn't working.

I did a test with 3 sensors and one doesn't really work. I made 2 videos showing the readings:

  • This shows sensors 1 + 2 --> Working well
  • This shows sensors 1 + 3 --> It's like slow mo, as if something was stuck. By the way, the code is the same, I just switched cables on a breadboard.

Here's the code:

#include <CapacitiveSensor.h>

//CapacitiveSensor cs_4_2 = CapacitiveSensor(4,2);
CapacitiveSensor cs_4_6 = CapacitiveSensor(4,6);
CapacitiveSensor cs_4_8 = CapacitiveSensor(4,8);

void setup() {
  //cs_4_2.set_CS_AutocaL_Millis(0xFFFFFFFF);
  cs_4_6.set_CS_AutocaL_Millis(0xFFFFFFFF);
  cs_4_8.set_CS_AutocaL_Millis(0xFFFFFFFF);
  Serial.begin(9600);
}

void loop() {
  long start = millis();
  //long total1 =  cs_4_2.capacitiveSensor(30);
  long total2 =  cs_4_6.capacitiveSensor(30);
  long total3 =  cs_4_8.capacitiveSensor(30);

  //Serial.println(total1);
  //Serial.print("\t");
  Serial.print(total2);
  Serial.print("\t");
  Serial.println(total3);

  delay(10);
}

It would be so awesome if someone has an idea what could be causing this. Is there a short circuit going on or was there a soldering problem?

Thanks and best wishes