Simply add a 1M Ohm resistor between the touch sensor pad (which can be anything!) and the ground. Connect the touch sensor pad to a GPIO pin on the Raspberry Pi Pico. The GPIO pin should be configured as an input pin with a pull-up resistor. The touch sensor pad will act as a capacitive touch sensor.
graph TD
A[Raspberry Pi Pico] --> B[Touch Sensor pad];
B --> C[1M Ohm Resistor];
C --> GND[Ground];
B --> D[GPIO Pin e.g., GP15];
D --> A;
Capacitive touch sensors work by detecting the change in capacitance when a conductive object (such as a human finger) comes in contact with the sensor. The human body acts as a capacitor, and when it comes in contact with the sensor, the capacitance of the sensor changes. This change in capacitance is detected by the sensor, and the touch is registered.
We can detect the touch by measuring the time it takes for the GPIO pin to discharge. When the touch sensor pad is not touched, the GPIO pin will discharge slowly. When the touch sensor pad is touched, the GPIO pin will discharge quickly. By measuring the time it takes for the GPIO pin to discharge, we can detect the touch.