Chapter 10 Touch Sensor

ESP32 offers up to 10 capacitive touch GPIO, and as you can see from the previous section, mechanical switches are prone to jitter that must be eliminated when used, which is not the case with ESP32’s built-in touch sensor. In addition, on the service life, the touch switch also has advantages that mechanical switch is completely incomparable.

Project 10.1 Read Touch Sensor

This project reads the value of the touch sensor and prints it out.

Component List

ESP32-WROVER x1	GPIO Extension Board x1
Breadboard x1
Jumper M/M x2

Related knowledge

Touch sensor

ESP32’s touch sensor supports up to 7 GPIO channels as capacitive touch pins. Each pin can be used separately as an independent touch switch or be combined to produce multiple touch points. The following table is a list of available touch pins on ESP32.

Functions of pins	ESP32 GPIO number
GPIO4	GPIO4
MTDO	GPIO15
MTCK	GPIO13
MTDI	GPIO12
MTMS	GPIO14
32K_XN	GPIO33
32K_XP	GPIO32

The pin numbers are shown in the figure above. When you need to use the TouchPad, you only need to call the TouchPad function to initialize the corresponding pins.

The electronic signals generated with the touch are analog, which are converted by the internal ADC. You may have found that all touch pins have featured with ADC.

The way to connect the hardware is as follows:

Circuit

Schematic diagram

Hardware connection If you need any support, please contact us via: support@freenove.com

Code

Move the program folder “Freenove_Ultimate_Starter_Kit_for_ESP32/Python/Python_Codes” to disk(D) in advance with the path of “D:/Micropython_Codes”.

Open “Thonny”, click “This computer” -> “D:” -> “Micropython_Codes” -> “10.1_Read_Touch_Sensor” and double click “Read_Touch_Sensor.py”.

10.1_Read_Touch_Sensor

Click “Run current script”, touch the jumper wire with your finger and observe the messages printed in “Shell”.

Messages printed at “Shell”:

Reference

Class TouchPad

Before each use of TouchPad module, please add the statement “ from machine import TouchPad “to the top of the python file.

TouchPad(pin): Initialize the TouchPad object and associate it with ESP32 pins.

pin: Pin(4)、Pin(15)、Pin(13)、Pin(12)、Pin(14)、Pin(32)、Pin(33)

TouchPad.read(): Read the capacitance of touchpad. If your fingers touch TouchPad pins, the capacitance decreases; Otherwise, it will not change.

Project 10.2 Touch Lamp

In this project, we will use ESP32’s touch sensor to create a touch switch lamp.

Component List

ESP32-WROVER x1		GPIO Extension Board x1
Breadboard x1
LED x1	Resistor 220Ω x1	Jumper M/M x3

Circuit

Schematic diagram

Hardware connection

If you need any support, please contact us via: support@freenove.com

Code

Move the program folder “Freenove_Ultimate_Starter_Kit_for_ESP32/Python/Python_Codes” to disk(D) in advance with the path of “D:/Micropython_Codes”.

Open “Thonny, click “This computer” -> “D:” -> “Micropython_Codes” -> “10.2_TouchLamp”and double click “TouchLamp.py”.

10.2_TouchLamp

Click “Run current script” and then touch the jumper wire with your finger. The state of LED will change with each touch and the detection state of the touch sensor will be printed in the “Shell”

LED displays as follows:

The following is the program code:

from machine import TouchPad, Pin
import time

PRESS_VAL=70    #Set a threshold to judge touch
RELEASE_VAL=200 #Set a threshold to judge release

led=Pin(2,Pin.OUT)
tp = TouchPad(Pin(4,Pin.IN,Pin.PULL_UP))
isPressed = 0

def reverseGPIO():
    if led.value():
        led.value(1)
        print("Turn off led")
    else:
        led.value(0)
        print("Turn on led")

while True:
    if tp.read() < PRESS_VAL:
        if not isPressed:
            isPressed = 1
            reverseGPIO()
            print("Touch detected!")
            time.sleep_ms(100)
    if tp.read() > RELEASE_VAL:
        if isPressed:
            isPressed = 0
            print("Touch released!")
            time.sleep_ms(100)

Import Pin and TouchPad modules.

from machine import TouchPad, Pin
import time

The closer the return value of the function read() is to 0, the more obviously the touch action is detected. As this is not a fixed value, a threshold value needs to be defined. When the value of the sensor is less than the threshold, it is considered a valid touch action. Similarly, define a threshold value for the released state, and the value between the sensor value and the threshold is regarded as an invalid interference value.

PRESS_VAL=70    #Set a threshold to judge touch
RELEASE_VAL=200 #Set a threshold to judge release

First, decide whether the touch is detected. If yes, print some messages, reverse the state of LED and set the flag bit isProcessed to 1 to avoid repeatedly executing the program after a touch is detected.

if tp.read() < PRESS_VAL:
    if not isPressed:
        isPressed = 1
        reverseGPIO()
        print("Touch detected!")
        time.sleep_ms(100)

And then decide whether the touch key is released. If yes, print some messages, and set isProcessed to 0 to avoid repeatedly executing the program after a touch is released and to prepare for the next touch detector.

if tp.read() > RELEASE_VAL:
    if isPressed:
        isPressed = 0
        print("Touch released!")
        time.sleep_ms(100)

Customize a function that reverses the output level of the LED each time it is called.

def reverseGPIO():
    if led.value():
        led.value(1)
        print("Turn off led")
    else:
        led.value(0)
        print("Turn on led")