Espressif ESP32 Technical Reference Manual page 639

29 On-Chip Sensors and Analog Signal Processing
During each swing, the touch sensor generates an output pulse, shown in the chart as "OUT". The swing slope
is different when the pad is touched (high capacitance) and when it is not (low capacitance). By comparing the
difference between the output pulse counts during the same time interval, we can conclude whether the touch
pad has been touched.
cycle.
29.2.5 Touch FSM
The Touch FSM performs a measurement sequence described in section 29.2.4. Software can operate the
Touch FSM through dedicated registers. The internal structure of a touch FSM is shown in Figure 29-4.
The functions of Touch FSM include:
• Receipt of a start signal, either from software or a timer
– when SENS_SAR_TOUCH_START_FORCE=1,
measurement
– when SENS_SAR_TOUCH_START_FORCE=0, measurement is triggered periodically with a timer.
The Touch FSM can be active in sleep mode. The
used to set the cycles. The sensor is operated by RTC_FAST_CLK, which normally runs at 8 MHz. More
information on that can be found in chapter
• Generation of XPD_TOUCH_BIAS / TOUCH_XPD / TOUCH_START with adjustable timing sequence
To select enabled pads, TOUCH_XPD / TOUCH_START is masked by the 10-bit register
_PAD_WORKEN.
• Counting of pulses on TOUCH0_OUT ~ TOUCH9_OUT
The result can be read from SENS_SAR_TOUCH_MEAS_OUTn. All ten touch sensors can work simultane-
ously.
• Generation of a wakeup interrupt
The FSM regards the touch pads as "touched", if the number of counted pulses is below the threshold.
The 10-bit registers
pads, i.e. SET1 & SET2. If at least one of the pads in SET1 is "touched", the wakeup interrupt will be
generated by default. It is also possible to configure the wakeup interrupt to be generated only when
pads from both sets are "touched".
Espressif Systems
TIE_OPT is used to establish the initial voltage level that starts the charge/discharge
Figure 29-3. Touch Sensor Operating Flow
SENS_TOUCH_PAD_OUTEN1
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SENS_SAR_TOUCH_START_EN
SENS_SAR_TOUCH_SLEEP_CYCLES
Reset and Clock.
& SENS_TOUCH_PAD_OUTEN2
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is used to initiate a single
register can be
SENS_SAR_TOUCH
define two sets of touch
ESP32 TRM (Version 5.2)