Espressif ESP32 Technical Reference Manual page 638

29 On-Chip Sensors and Analog Signal Processing
– CPU waiting in deep sleep and saving power until touch detection and subsequent wake up
– Touch detection managed by the ULP coprocessor
The user program in ULP coprocessor can trigger a scanning process by checking and writing into
specific registers, in order to verify whether the touch threshold is reached.
Note:
ESP32 Touch Sensor has not passed the Conducted Susceptibility (CS) test for now, and thus has limited application
scenarios.
29.2.3 Available GPIOs
All 10 available sensing GPIOs (pads) are listed in Table 29-1.
Touch Sensing Signal Name
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
29.2.4 Functional Description
The internal structure of the touch sensor is shown in Figure 29-2. The operating flow is shown in Figure
29-3.
The capacitance of a touch pad is periodically charged and discharged. The chart "Pad Voltage" shows the
charge/discharge voltage that swings from DREFH (reference voltage high) to DREFL (reference voltage low).
Espressif Systems
Table 29-1. ESP32 Capacitive Sensing Touch Pads
Figure 29-2. Touch Sensor Structure
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Pin Name
GPIO4
GPIO0
GPIO2
MTDO
MTCK
MTDI
MTMS
GPIO27
32K_XN
32K_XP
ESP32 TRM (Version 5.2)