Touch Sensor

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Introduction

A touch sensor system is built on a substrate which carries electrodes and relevant connections under a protective flat surface. When a user touches the surface, the capacitance variation is used to evaluate if the touch was valid.

Touch sensor on ESP32-S2 can support up to 14 capacitive touch pads / GPIOs.

The sensing pads can be arranged in different combinations (e.g., matrix, slider), so that a larger area or more points can be detected. The touch pad sensing process is under the control of a hardware-implemented finite-state machine (FSM) which is initiated by software or a dedicated hardware timer.

For design, operation, and control registers of a touch sensor, see ESP32-S2 Technical Reference Manual > On-Chip Sensors and Analog Signal Processing [PDF].

In-depth design details of touch sensors and firmware development guidelines for ESP32-S2 are available in Touch Sensor Application Note.

Functionality Overview

Description of API is broken down into groups of functions to provide a quick overview of the following features:

  • Initialization of touch pad driver

  • Configuration of touch pad GPIO pins

  • Taking measurements

  • Adjusting parameters of measurements

  • Filtering measurements

  • Touch detection methods

  • Setting up interrupts to report touch detection

  • Waking up from Sleep mode on interrupt

For detailed description of a particular function, please go to Section API Reference. Practical implementation of this API is covered in Section Application Examples.

Initialization

Before using a touch pad, you need to initialize the touch pad driver by calling the function touch_pad_init(). This function sets several .._DEFAULT driver parameters listed in API Reference under Macros. It also removes the information about which pads have been touched before, if any, and disables interrupts.

If the driver is not required anymore, deinitialize it by calling touch_pad_deinit().

Configuration

Enabling the touch sensor functionality for a particular GPIO is done with touch_pad_config().

Use the function touch_pad_set_fsm_mode() to select if touch pad measurement (operated by FSM) should be started automatically by a hardware timer, or by software. If software mode is selected, use touch_pad_sw_start() to start the FSM.

Touch State Measurements

The following function come in handy to read raw measurements from the sensor:

It can also be used, for example, to evaluate a particular touch pad design by checking the range of sensor readings when a pad is touched or released. This information can be then used to establish a touch threshold.

For the demonstration of how to read the touch pad data, check the application example peripherals/touch_sensor/touch_sensor_v2/touch_pad_read.

Optimization of Measurements

A touch sensor has several configurable parameters to match the characteristics of a particular touch pad design. For instance, to sense smaller capacity changes, it is possible to narrow down the reference voltage range within which the touch pads are charged / discharged. The high and low reference voltages are set using the function touch_pad_set_voltage().

Besides the ability to discern smaller capacity changes, a positive side effect is reduction of power consumption for low power applications. A likely negative effect is an increase in measurement noise. If the dynamic range of obtained readings is still satisfactory, then further reduction of power consumption might be done by reducing the measurement time with touch_pad_set_meas_time().

The following list summarizes available measurement parameters and corresponding ‘set’ functions:

Relationship between the voltage range (high / low reference voltages), speed (slope), and measurement time is shown in the figure below.

Touch Pad - relationship between measurement parameters

Touch pad - relationship between measurement parameters

The last chart Output represents the touch sensor reading, i.e., the count of pulses collected within the measurement time.

All functions are provided in pairs to set a specific parameter and to get the current parameter’s value, e.g., touch_pad_set_voltage() and touch_pad_get_voltage().

Filtering of Measurements

If measurements are noisy, you can filter them with provided API functions. The ESP32-S2’s touch functionality provide two sets of APIs for doing this.

There is an internal touch channel that is not connected to any external GPIO. The measurements from this denoise pad can be used to filters out interference introduced on all channels, such as noise introduced by the power supply and external EMI. The denoise paramaters are set with the function touch_pad_denoise_set_config() and started by with touch_pad_denoise_enable()

There is also a configurable hardware implemented IIR-filter (infinite impulse response). This IIR-filter is configured with the function touch_pad_filter_set_config() and enabled by calling touch_pad_filter_enable()

Touch Detection

Touch detection is implemented in ESP32’s hardware based on the user-configured threshold and raw measurements executed by FSM. Use the functions touch_pad_get_status() to check which pads have been touched and touch_pad_clear_status() to clear the touch status information.

Hardware touch detection can also be wired to interrupts. This is described in the next section.

If measurements are noisy and capacity changes are small, hardware touch detection might be unreliable. To resolve this issue, instead of using hardware detection / provided interrupts, implement measurement filtering and perform touch detection in your own application. For sample implementation of both methods of touch detection, see peripherals/touch_sensor/touch_sensor_v2/touch_pad_interrupt.

Touch Triggered Interrupts

Before enabling an interrupt on a touch detection, you should establish a touch detection threshold. Use the functions described in Touch State Measurements to read and display sensor measurements when a pad is touched and released. Apply a filter if measurements are noisy and relative capacity changes are small. Depending on your application and environment conditions, test the influence of temperature and power supply voltage changes on measured values.

Once a detection threshold is established, it can be set during initialization with touch_pad_config() or at the runtime with touch_pad_set_thresh().

Finally, configure and manage interrupt calls using the following functions:

When interrupts are operational, you can obtain the information from which particular pad an interrupt came by invoking touch_pad_get_status() and clear the pad status with touch_pad_clear_status().

Application Examples

API Reference

Functions

esp_err_t touch_pad_fsm_start(void)

Set touch sensor FSM start.

Note

Start FSM after the touch sensor FSM mode is set.

Note

Call this function will reset benchmark of all touch channels.

Returns

  • ESP_OK on success

esp_err_t touch_pad_fsm_stop(void)

Stop touch sensor FSM.

Returns

  • ESP_OK on success

esp_err_t touch_pad_sw_start(void)

Trigger a touch sensor measurement, only support in SW mode of FSM.

Returns

  • ESP_OK on success

esp_err_t touch_pad_set_meas_time(uint16_t sleep_cycle, uint16_t meas_times)

Set touch sensor times of charge and discharge and sleep time. Excessive total time will slow down the touch response. Too small measurement time will not be sampled enough, resulting in inaccurate measurements.

Note

Though this API name is same as ESP32, it has opposite logic of capacity. The touch sensor on ESP32-S2 will fix the count of charge and discharge cycles (specified by the second parameter) and then record the count of the clock cycles(which is 8 MHz) during the sensing period as the raw value. That means the raw value will increase as the capacity of the touch pad increasing.

Note

The greater the duty cycle of the measurement time, the more system power is consumed.

Parameters

  • sleep_cycle – The touch sensor will sleep after each measurement. sleep_cycle decide the interval between each measurement. t_sleep = sleep_cycle / (RTC_SLOW_CLK frequency). The approximate frequency value of RTC_SLOW_CLK can be obtained using rtc_clk_slow_freq_get_hz function.

  • meas_times – The times of charge and discharge in each measurement of touch channels. Range: 0 ~ 0xffff. Recommended typical value: Modify this value to make the measurement time around 1 ms. The clock frequency is 8 MHz, so the raw value will be about 8000 if the measurement time is 1 ms

Returns

  • ESP_OK on success

esp_err_t touch_pad_get_meas_time(uint16_t *sleep_cycle, uint16_t *meas_times)

Get touch sensor times of charge and discharge and sleep time.

Parameters

  • sleep_cycle – Pointer to accept sleep cycle number

  • meas_times – Pointer to accept measurement times count.

Returns

  • ESP_OK on success

esp_err_t touch_pad_set_idle_channel_connect(touch_pad_conn_type_t type)

Set connection type of touch channel in idle status. When a channel is in measurement mode, other initialized channels are in idle mode. The touch channel is generally adjacent to the trace, so the connection state of the idle channel affects the stability and sensitivity of the test channel. The CONN_HIGHZ(high resistance) setting increases the sensitivity of touch channels. The CONN_GND(grounding) setting increases the stability of touch channels.

Parameters

type – Select idle channel connect to high resistance state or ground.

Returns

  • ESP_OK on success

esp_err_t touch_pad_get_idle_channel_connect(touch_pad_conn_type_t *type)

Set connection type of touch channel in idle status. When a channel is in measurement mode, other initialized channels are in idle mode. The touch channel is generally adjacent to the trace, so the connection state of the idle channel affects the stability and sensitivity of the test channel. The CONN_HIGHZ(high resistance) setting increases the sensitivity of touch channels. The CONN_GND(grounding) setting increases the stability of touch channels.

Parameters

type – Pointer to connection type.

Returns

  • ESP_OK on success

esp_err_t touch_pad_set_thresh(touch_pad_t touch_num, uint32_t threshold)

Set the trigger threshold of touch sensor. The threshold determines the sensitivity of the touch sensor. The threshold is the original value of the trigger state minus the benchmark value.

Note

If set “TOUCH_PAD_THRESHOLD_MAX”, the touch is never be triggered.

Parameters

  • touch_num – touch pad index

  • threshold – threshold of touch sensor. Should be less than the max change value of touch.

Returns

  • ESP_OK on success

esp_err_t touch_pad_get_thresh(touch_pad_t touch_num, uint32_t *threshold)

Get touch sensor trigger threshold.

Parameters

  • touch_num – touch pad index

  • threshold – pointer to accept threshold

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if argument is wrong

esp_err_t touch_pad_set_channel_mask(uint16_t enable_mask)

Register touch channel into touch sensor scan group. The working mode of the touch sensor is cyclically scanned. This function will set the scan bits according to the given bitmask.

Note

If set this mask, the FSM timer should be stop firsty.

Note

The touch sensor that in scan map, should be deinit GPIO function firstly by touch_pad_io_init.

Parameters

enable_mask – bitmask of touch sensor scan group. e.g. TOUCH_PAD_NUM14 -> BIT(14)

Returns

  • ESP_OK on success

esp_err_t touch_pad_get_channel_mask(uint16_t *enable_mask)

Get the touch sensor scan group bit mask.

Parameters

enable_mask – Pointer to bitmask of touch sensor scan group. e.g. TOUCH_PAD_NUM14 -> BIT(14)

Returns

  • ESP_OK on success

esp_err_t touch_pad_clear_channel_mask(uint16_t enable_mask)

Clear touch channel from touch sensor scan group. The working mode of the touch sensor is cyclically scanned. This function will clear the scan bits according to the given bitmask.

Note

If clear all mask, the FSM timer should be stop firsty.

Parameters

enable_mask – bitmask of touch sensor scan group. e.g. TOUCH_PAD_NUM14 -> BIT(14)

Returns

  • ESP_OK on success

esp_err_t touch_pad_config(touch_pad_t touch_num)

Configure parameter for each touch channel.

Note

Touch num 0 is denoise channel, please use touch_pad_denoise_enable to set denoise function

Parameters

touch_num – touch pad index

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG if argument wrong

  • ESP_FAIL if touch pad not initialized

esp_err_t touch_pad_reset(void)

Reset the FSM of touch module.

Note

Call this function after touch_pad_fsm_stop.

Returns

  • ESP_OK Success

touch_pad_t touch_pad_get_current_meas_channel(void)

Get the current measure channel.

Note

Should be called when touch sensor measurement is in cyclic scan mode.

Returns

  • touch channel number

uint32_t touch_pad_read_intr_status_mask(void)

Get the touch sensor interrupt status mask.

Returns

  • touch interrupt bit

esp_err_t touch_pad_intr_enable(touch_pad_intr_mask_t int_mask)

Enable touch sensor interrupt by bitmask.

Note

This API can be called in ISR handler.

Parameters

int_mask – Pad mask to enable interrupts

Returns

  • ESP_OK on success

esp_err_t touch_pad_intr_disable(touch_pad_intr_mask_t int_mask)

Disable touch sensor interrupt by bitmask.

Note

This API can be called in ISR handler.

Parameters

int_mask – Pad mask to disable interrupts

Returns

  • ESP_OK on success

esp_err_t touch_pad_intr_clear(touch_pad_intr_mask_t int_mask)

Clear touch sensor interrupt by bitmask.

Parameters

int_mask – Pad mask to clear interrupts

Returns

  • ESP_OK on success

esp_err_t touch_pad_isr_register(intr_handler_t fn, void *arg, touch_pad_intr_mask_t intr_mask)

Register touch-pad ISR. The handler will be attached to the same CPU core that this function is running on.

Parameters

  • fn – Pointer to ISR handler

  • arg – Parameter for ISR

  • intr_mask – Enable touch sensor interrupt handler by bitmask.

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Arguments error

  • ESP_ERR_NO_MEM No memory

esp_err_t touch_pad_timeout_set(bool enable, uint32_t threshold)

Enable/disable the timeout check and set timeout threshold for all touch sensor channels measurements. If enable: When the touch reading of a touch channel exceeds the measurement threshold, a timeout interrupt will be generated. If disable: the FSM does not check if the channel under measurement times out.

Note

The threshold compared with touch readings.

Note

In order to avoid abnormal short circuit of some touch channels. This function should be turned on. Ensure the normal operation of other touch channels.

Parameters

  • enable – true(default): Enable the timeout check; false: Disable the timeout check.

  • threshold – For all channels, the maximum value that will not be exceeded during normal operation.

Returns

  • ESP_OK Success

esp_err_t touch_pad_timeout_resume(void)

Call this interface after timeout to make the touch channel resume normal work. Point on the next channel to measure. If this API is not called, the touch FSM will stop the measurement after timeout interrupt.

Note

Call this API after finishes the exception handling by user.

Returns

  • ESP_OK Success

esp_err_t touch_pad_read_raw_data(touch_pad_t touch_num, uint32_t *raw_data)

get raw data of touch sensor.

Note

After the initialization is complete, the “raw_data” is max value. You need to wait for a measurement cycle before you can read the correct touch value.

Parameters

  • touch_num – touch pad index

  • raw_data – pointer to accept touch sensor value

Returns

  • ESP_OK Success

  • ESP_FAIL Touch channel 0 haven’t this parameter.

esp_err_t touch_pad_read_benchmark(touch_pad_t touch_num, uint32_t *benchmark)

get benchmark of touch sensor.

Note

After initialization, the benchmark value is the maximum during the first measurement period.

Parameters

  • touch_num – touch pad index

  • benchmark – pointer to accept touch sensor benchmark value

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Touch channel 0 haven’t this parameter.

esp_err_t touch_pad_filter_read_smooth(touch_pad_t touch_num, uint32_t *smooth)

Get smoothed data that obtained by filtering the raw data.

Parameters

  • touch_num – touch pad index

  • smooth – pointer to smoothed data

esp_err_t touch_pad_reset_benchmark(touch_pad_t touch_num)

Force reset benchmark to raw data of touch sensor.

Parameters

touch_num – touch pad index

  • TOUCH_PAD_MAX Reset basaline of all channels

Returns

  • ESP_OK Success

esp_err_t touch_pad_filter_set_config(const touch_filter_config_t *filter_info)

set parameter of touch sensor filter and detection algorithm. For more details on the detection algorithm, please refer to the application documentation.

Parameters

filter_info – select filter type and threshold of detection algorithm

Returns

  • ESP_OK Success

esp_err_t touch_pad_filter_get_config(touch_filter_config_t *filter_info)

get parameter of touch sensor filter and detection algorithm. For more details on the detection algorithm, please refer to the application documentation.

Parameters

filter_info – select filter type and threshold of detection algorithm

Returns

  • ESP_OK Success

esp_err_t touch_pad_filter_enable(void)

enable touch sensor filter for detection algorithm. For more details on the detection algorithm, please refer to the application documentation.

Returns

  • ESP_OK Success

esp_err_t touch_pad_filter_disable(void)

disable touch sensor filter for detection algorithm. For more details on the detection algorithm, please refer to the application documentation.

Returns

  • ESP_OK Success

esp_err_t touch_pad_denoise_set_config(const touch_pad_denoise_t *denoise)

set parameter of denoise pad (TOUCH_PAD_NUM0). T0 is an internal channel that does not have a corresponding external GPIO. T0 will work simultaneously with the measured channel Tn. Finally, the actual measured value of Tn is the value after subtracting lower bits of T0. The noise reduction function filters out interference introduced simultaneously on all channels, such as noise introduced by power supplies and external EMI.

Parameters

denoise – parameter of denoise

Returns

  • ESP_OK Success

esp_err_t touch_pad_denoise_get_config(touch_pad_denoise_t *denoise)

get parameter of denoise pad (TOUCH_PAD_NUM0).

Parameters

denoise – Pointer to parameter of denoise

Returns

  • ESP_OK Success

esp_err_t touch_pad_denoise_enable(void)

enable denoise function. T0 is an internal channel that does not have a corresponding external GPIO. T0 will work simultaneously with the measured channel Tn. Finally, the actual measured value of Tn is the value after subtracting lower bits of T0. The noise reduction function filters out interference introduced simultaneously on all channels, such as noise introduced by power supplies and external EMI.

Returns

  • ESP_OK Success

esp_err_t touch_pad_denoise_disable(void)

disable denoise function.

Returns

  • ESP_OK Success

esp_err_t touch_pad_denoise_read_data(uint32_t *data)

Get denoise measure value (TOUCH_PAD_NUM0).

Parameters

data – Pointer to receive denoise value

Returns

  • ESP_OK Success

esp_err_t touch_pad_waterproof_set_config(const touch_pad_waterproof_t *waterproof)

set parameter of waterproof function.

The waterproof function includes a shielded channel (TOUCH_PAD_NUM14) and a guard channel. Guard pad is used to detect the large area of water covering the touch panel. Shield pad is used to shield the influence of water droplets covering the touch panel. It is generally designed as a grid and is placed around the touch buttons.

Parameters

waterproof – parameter of waterproof

Returns

  • ESP_OK Success

esp_err_t touch_pad_waterproof_get_config(touch_pad_waterproof_t *waterproof)

get parameter of waterproof function.

Parameters

waterproof – parameter of waterproof

Returns

  • ESP_OK Success

esp_err_t touch_pad_waterproof_enable(void)

Enable parameter of waterproof function. Should be called after function touch_pad_waterproof_set_config.

Returns

  • ESP_OK Success

esp_err_t touch_pad_waterproof_disable(void)

Disable parameter of waterproof function.

Returns

  • ESP_OK Success

esp_err_t touch_pad_proximity_enable(touch_pad_t touch_num, bool enabled)

Enable/disable proximity function of touch channels. The proximity sensor measurement is the accumulation of touch channel measurements.

Note

Supports up to three touch channels configured as proximity sensors.

Parameters

  • touch_num – touch pad index

  • enabled – true: enable the proximity function; false: disable the proximity function

Returns

  • ESP_OK: Configured correctly.

  • ESP_ERR_INVALID_ARG: Touch channel number error.

  • ESP_ERR_NOT_SUPPORTED: Don’t support configured.

esp_err_t touch_pad_proximity_set_count(touch_pad_t touch_num, uint32_t count)

Set measure count of proximity channel. The proximity sensor measurement is the accumulation of touch channel measurements.

Note

All proximity channels use the same count value. So please pass the parameter TOUCH_PAD_MAX.

Parameters

  • touch_num – Touch pad index. In this version, pass the parameter TOUCH_PAD_MAX.

  • count – The cumulative times of measurements for proximity pad. Range: 0 ~ 255.

Returns

  • ESP_OK: Configured correctly.

  • ESP_ERR_INVALID_ARG: Touch channel number error.

esp_err_t touch_pad_proximity_get_count(touch_pad_t touch_num, uint32_t *count)

Get measure count of proximity channel. The proximity sensor measurement is the accumulation of touch channel measurements.

Note

All proximity channels use the same count value. So please pass the parameter TOUCH_PAD_MAX.

Parameters

  • touch_num – Touch pad index. In this version, pass the parameter TOUCH_PAD_MAX.

  • count – The cumulative times of measurements for proximity pad. Range: 0 ~ 255.

Returns

  • ESP_OK: Configured correctly.

  • ESP_ERR_INVALID_ARG: Touch channel number error.

esp_err_t touch_pad_proximity_get_data(touch_pad_t touch_num, uint32_t *measure_out)

Get the accumulated measurement of the proximity sensor. The proximity sensor measurement is the accumulation of touch channel measurements.

Parameters

  • touch_num – touch pad index

  • measure_out – If the accumulation process does not end, the measure_out is the process value.

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Touch num is not proximity

esp_err_t touch_pad_sleep_channel_get_info(touch_pad_sleep_channel_t *slp_config)

Get parameter of touch sensor sleep channel. The touch sensor can works in sleep mode to wake up sleep.

Note

After the sleep channel is configured, Please use special functions for sleep channel. e.g. The user should uses touch_pad_sleep_channel_read_data instead of touch_pad_read_raw_data to obtain the sleep channel reading.

Parameters

slp_config – touch sleep pad config.

Returns

  • ESP_OK Success

esp_err_t touch_pad_sleep_channel_enable(touch_pad_t pad_num, bool enable)

Enable/Disable sleep channel function for touch sensor. The touch sensor can works in sleep mode to wake up sleep.

Note

ESP32S2 only support one sleep channel.

Note

After the sleep channel is configured, Please use special functions for sleep channel. e.g. The user should uses touch_pad_sleep_channel_read_data instead of touch_pad_read_raw_data to obtain the sleep channel reading.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • enable – true: enable sleep pad for touch sensor; false: disable sleep pad for touch sensor;

Returns

  • ESP_OK Success

esp_err_t touch_pad_sleep_channel_enable_proximity(touch_pad_t pad_num, bool enable)

Enable/Disable proximity function for sleep channel. The touch sensor can works in sleep mode to wake up sleep.

Note

ESP32S2 only support one sleep channel.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • enable – true: enable proximity for sleep channel; false: disable proximity for sleep channel;

Returns

  • ESP_OK Success

esp_err_t touch_pad_sleep_set_threshold(touch_pad_t pad_num, uint32_t touch_thres)

Set the trigger threshold of touch sensor in deep sleep. The threshold determines the sensitivity of the touch sensor.

Note

In general, the touch threshold during sleep can use the threshold parameter parameters before sleep.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • touch_thres – touch sleep pad threshold

Returns

  • ESP_OK Success

esp_err_t touch_pad_sleep_get_threshold(touch_pad_t pad_num, uint32_t *touch_thres)

Get the trigger threshold of touch sensor in deep sleep. The threshold determines the sensitivity of the touch sensor.

Note

In general, the touch threshold during sleep can use the threshold parameter parameters before sleep.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • touch_thres – touch sleep pad threshold

Returns

  • ESP_OK Success

esp_err_t touch_pad_sleep_channel_read_benchmark(touch_pad_t pad_num, uint32_t *benchmark)

Read benchmark of touch sensor sleep channel.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • benchmark – pointer to accept touch sensor benchmark value

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG parameter is NULL

esp_err_t touch_pad_sleep_channel_read_smooth(touch_pad_t pad_num, uint32_t *smooth_data)

Read smoothed data of touch sensor sleep channel. Smoothed data is filtered from the raw data.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • smooth_data – pointer to accept touch sensor smoothed data

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG parameter is NULL

esp_err_t touch_pad_sleep_channel_read_data(touch_pad_t pad_num, uint32_t *raw_data)

Read raw data of touch sensor sleep channel.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • raw_data – pointer to accept touch sensor raw data

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG parameter is NULL

esp_err_t touch_pad_sleep_channel_reset_benchmark(void)

Reset benchmark of touch sensor sleep channel.

Returns

  • ESP_OK Success

esp_err_t touch_pad_sleep_channel_read_proximity_cnt(touch_pad_t pad_num, uint32_t *proximity_cnt)

Read proximity count of touch sensor sleep channel.

Parameters

  • pad_num – Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode.

  • proximity_cnt – pointer to accept touch sensor proximity count value

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG parameter is NULL

esp_err_t touch_pad_sleep_channel_set_work_time(uint16_t sleep_cycle, uint16_t meas_times)

Change the operating frequency of touch pad in deep sleep state. Reducing the operating frequency can effectively reduce power consumption. If this function is not called, the working frequency of touch in the deep sleep state is the same as that in the wake-up state.

Parameters

  • sleep_cycle – The touch sensor will sleep after each measurement. sleep_cycle decide the interval between each measurement. t_sleep = sleep_cycle / (RTC_SLOW_CLK frequency). The approximate frequency value of RTC_SLOW_CLK can be obtained using rtc_clk_slow_freq_get_hz function.

  • meas_times – The times of charge and discharge in each measure process of touch channels. The timer frequency is 8Mhz. Range: 0 ~ 0xffff. Recommended typical value: Modify this value to make the measurement time around 1ms.

Returns

  • ESP_OK Success

Functions

esp_err_t touch_pad_init(void)

Initialize touch module.

Note

If default parameter don’t match the usage scenario, it can be changed after this function.

Returns

  • ESP_OK Success

  • ESP_ERR_NO_MEM Touch pad init error

  • ESP_ERR_NOT_SUPPORTED Touch pad is providing current to external XTAL

esp_err_t touch_pad_deinit(void)

Un-install touch pad driver.

Note

After this function is called, other touch functions are prohibited from being called.

Returns

  • ESP_OK Success

  • ESP_FAIL Touch pad driver not initialized

esp_err_t touch_pad_io_init(touch_pad_t touch_num)

Initialize touch pad GPIO.

Parameters

touch_num – touch pad index

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if argument is wrong

esp_err_t touch_pad_set_voltage(touch_high_volt_t refh, touch_low_volt_t refl, touch_volt_atten_t atten)

Set touch sensor high voltage threshold of chanrge. The touch sensor measures the channel capacitance value by charging and discharging the channel. So the high threshold should be less than the supply voltage.

Parameters

  • refh – the value of DREFH

  • refl – the value of DREFL

  • atten – the attenuation on DREFH

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if argument is wrong

esp_err_t touch_pad_get_voltage(touch_high_volt_t *refh, touch_low_volt_t *refl, touch_volt_atten_t *atten)

Get touch sensor reference voltage,.

Parameters

  • refh – pointer to accept DREFH value

  • refl – pointer to accept DREFL value

  • atten – pointer to accept the attenuation on DREFH

Returns

  • ESP_OK on success

esp_err_t touch_pad_set_cnt_mode(touch_pad_t touch_num, touch_cnt_slope_t slope, touch_tie_opt_t opt)

Set touch sensor charge/discharge speed for each pad. If the slope is 0, the counter would always be zero. If the slope is 1, the charging and discharging would be slow, accordingly. If the slope is set 7, which is the maximum value, the charging and discharging would be fast.

Note

The higher the charge and discharge current, the greater the immunity of the touch channel, but it will increase the system power consumption.

Parameters

  • touch_num – touch pad index

  • slope – touch pad charge/discharge speed

  • opt – the initial voltage

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if argument is wrong

esp_err_t touch_pad_get_cnt_mode(touch_pad_t touch_num, touch_cnt_slope_t *slope, touch_tie_opt_t *opt)

Get touch sensor charge/discharge speed for each pad.

Parameters

  • touch_num – touch pad index

  • slope – pointer to accept touch pad charge/discharge slope

  • opt – pointer to accept the initial voltage

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if argument is wrong

esp_err_t touch_pad_isr_deregister(void (*fn)(void*), void *arg)

Deregister the handler previously registered using touch_pad_isr_handler_register.

Parameters

  • fn – handler function to call (as passed to touch_pad_isr_handler_register)

  • arg – argument of the handler (as passed to touch_pad_isr_handler_register)

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_STATE if a handler matching both fn and arg isn’t registered

esp_err_t touch_pad_get_wakeup_status(touch_pad_t *pad_num)

Get the touch pad which caused wakeup from deep sleep.

Parameters

pad_num – pointer to touch pad which caused wakeup

Returns

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG parameter is NULL

esp_err_t touch_pad_set_fsm_mode(touch_fsm_mode_t mode)

Set touch sensor FSM mode, the test action can be triggered by the timer, as well as by the software.

Parameters

mode – FSM mode

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if argument is wrong

esp_err_t touch_pad_get_fsm_mode(touch_fsm_mode_t *mode)

Get touch sensor FSM mode.

Parameters

mode – pointer to accept FSM mode

Returns

  • ESP_OK on success

esp_err_t touch_pad_clear_status(void)

To clear the touch sensor channel active status.

Note

The FSM automatically updates the touch sensor status. It is generally not necessary to call this API to clear the status.

Returns

  • ESP_OK on success

uint32_t touch_pad_get_status(void)

Get the touch sensor channel active status mask. The bit position represents the channel number. The 0/1 status of the bit represents the trigger status.

Returns

  • The touch sensor status. e.g. Touch1 trigger status is status_mask & (BIT1).

bool touch_pad_meas_is_done(void)

Check touch sensor measurement status.

Returns

  • True measurement is under way

  • False measurement done

GPIO Lookup Macros

Some useful macros can be used to specified the GPIO number of a touch pad channel, or vice versa. e.g.

  1. TOUCH_PAD_NUM5_GPIO_NUM is the GPIO number of channel 5 (12);

  2. TOUCH_PAD_GPIO4_CHANNEL is the channel number of GPIO 4 (channel 0).

Macros

TOUCH_PAD_GPIO1_CHANNEL
TOUCH_PAD_NUM1_GPIO_NUM
TOUCH_PAD_GPIO2_CHANNEL
TOUCH_PAD_NUM2_GPIO_NUM
TOUCH_PAD_GPIO3_CHANNEL
TOUCH_PAD_NUM3_GPIO_NUM
TOUCH_PAD_GPIO4_CHANNEL
TOUCH_PAD_NUM4_GPIO_NUM
TOUCH_PAD_GPIO5_CHANNEL
TOUCH_PAD_NUM5_GPIO_NUM
TOUCH_PAD_GPIO6_CHANNEL
TOUCH_PAD_NUM6_GPIO_NUM
TOUCH_PAD_GPIO7_CHANNEL
TOUCH_PAD_NUM7_GPIO_NUM
TOUCH_PAD_GPIO8_CHANNEL
TOUCH_PAD_NUM8_GPIO_NUM
TOUCH_PAD_GPIO9_CHANNEL
TOUCH_PAD_NUM9_GPIO_NUM
TOUCH_PAD_GPIO10_CHANNEL
TOUCH_PAD_NUM10_GPIO_NUM
TOUCH_PAD_GPIO11_CHANNEL
TOUCH_PAD_NUM11_GPIO_NUM
TOUCH_PAD_GPIO12_CHANNEL
TOUCH_PAD_NUM12_GPIO_NUM
TOUCH_PAD_GPIO13_CHANNEL
TOUCH_PAD_NUM13_GPIO_NUM
TOUCH_PAD_GPIO14_CHANNEL
TOUCH_PAD_NUM14_GPIO_NUM

Structures

struct touch_pad_denoise

Touch sensor denoise configuration

Public Members

touch_pad_denoise_grade_t grade

Select denoise range of denoise channel. Determined by measuring the noise amplitude of the denoise channel.

touch_pad_denoise_cap_t cap_level

Select internal reference capacitance of denoise channel. Ensure that the denoise readings are closest to the readings of the channel being measured. Use touch_pad_denoise_read_data to get the reading of denoise channel. The equivalent capacitance of the shielded channel can be calculated from the reading of denoise channel.

struct touch_pad_waterproof

Touch sensor waterproof configuration

Public Members

touch_pad_t guard_ring_pad

Waterproof. Select touch channel use for guard pad. Guard pad is used to detect the large area of water covering the touch panel.

touch_pad_shield_driver_t shield_driver

Waterproof. Shield channel drive capability configuration. Shield pad is used to shield the influence of water droplets covering the touch panel. When the waterproof function is enabled, Touch14 is set as shield channel by default. The larger the parasitic capacitance on the shielding channel, the higher the drive capability needs to be set. The equivalent capacitance of the shield channel can be estimated through the reading value of the denoise channel(Touch0).

struct touch_filter_config

Touch sensor filter configuration

Public Members

touch_filter_mode_t mode

Set filter mode. The input of the filter is the raw value of touch reading, and the output of the filter is involved in the judgment of the touch state.

uint32_t debounce_cnt

Set debounce count, such as n. If the measured values continue to exceed the threshold for n+1 times, the touch sensor state changes. Range: 0 ~ 7

uint32_t noise_thr

Noise threshold coefficient. Higher = More noise resistance. The actual noise should be less than (noise coefficient * touch threshold). Range: 0 ~ 3. The coefficient is 0: 4/8; 1: 3/8; 2: 2/8; 3: 1;

uint32_t jitter_step

Set jitter filter step size. Range: 0 ~ 15

touch_smooth_mode_t smh_lvl

Level of filter applied on the original data against large noise interference.

struct touch_pad_sleep_channel_t

Touch sensor channel sleep configuration

Public Members

touch_pad_t touch_num

Set touch channel number for sleep pad. Only one touch sensor channel is supported in deep sleep mode. If clear the sleep channel, point this pad to TOUCH_PAD_NUM0

bool en_proximity

enable proximity function for sleep pad

Macros

TOUCH_PAD_BIT_MASK_ALL
TOUCH_PAD_SLOPE_DEFAULT
TOUCH_PAD_TIE_OPT_DEFAULT
TOUCH_PAD_BIT_MASK_MAX
TOUCH_PAD_HIGH_VOLTAGE_THRESHOLD
TOUCH_PAD_LOW_VOLTAGE_THRESHOLD
TOUCH_PAD_ATTEN_VOLTAGE_THRESHOLD
TOUCH_PAD_IDLE_CH_CONNECT_DEFAULT
TOUCH_PAD_THRESHOLD_MAX

If set touch threshold max value, The touch sensor can’t be in touched status

TOUCH_PAD_SLEEP_CYCLE_DEFAULT

Excessive total time will slow down the touch response. Too small measurement time will not be sampled enough, resulting in inaccurate measurements.

Note

The greater the duty cycle of the measurement time, the more system power is consumed.The number of sleep cycle in each measure process of touch channels. The timer frequency is RTC_SLOW_CLK (can be 150k or 32k depending on the options). Range: 0 ~ 0xffff

TOUCH_PAD_MEASURE_CYCLE_DEFAULT

The times of charge and discharge in each measure process of touch channels. The timer frequency is 8Mhz. Recommended typical value: Modify this value to make the measurement time around 1ms. Range: 0 ~ 0xffff

TOUCH_PAD_INTR_MASK_ALL

All touch interrupt type enable.

TOUCH_PROXIMITY_MEAS_NUM_MAX

Touch sensor proximity detection configuration

TOUCH_DEBOUNCE_CNT_MAX
TOUCH_NOISE_THR_MAX
TOUCH_JITTER_STEP_MAX

Type Definitions

typedef struct touch_pad_denoise touch_pad_denoise_t

Touch sensor denoise configuration

typedef struct touch_pad_waterproof touch_pad_waterproof_t

Touch sensor waterproof configuration

typedef struct touch_filter_config touch_filter_config_t

Touch sensor filter configuration

Enumerations

enum touch_pad_t

Touch pad channel

Values:

enumerator TOUCH_PAD_NUM0

Touch pad channel 0 is GPIO4(ESP32)

enumerator TOUCH_PAD_NUM1

Touch pad channel 1 is GPIO0(ESP32) / GPIO1(ESP32-S2)

enumerator TOUCH_PAD_NUM2

Touch pad channel 2 is GPIO2(ESP32) / GPIO2(ESP32-S2)

enumerator TOUCH_PAD_NUM3

Touch pad channel 3 is GPIO15(ESP32) / GPIO3(ESP32-S2)

enumerator TOUCH_PAD_NUM4

Touch pad channel 4 is GPIO13(ESP32) / GPIO4(ESP32-S2)

enumerator TOUCH_PAD_NUM5

Touch pad channel 5 is GPIO12(ESP32) / GPIO5(ESP32-S2)

enumerator TOUCH_PAD_NUM6

Touch pad channel 6 is GPIO14(ESP32) / GPIO6(ESP32-S2)

enumerator TOUCH_PAD_NUM7

Touch pad channel 7 is GPIO27(ESP32) / GPIO7(ESP32-S2)

enumerator TOUCH_PAD_NUM8

Touch pad channel 8 is GPIO33(ESP32) / GPIO8(ESP32-S2)

enumerator TOUCH_PAD_NUM9

Touch pad channel 9 is GPIO32(ESP32) / GPIO9(ESP32-S2)

enumerator TOUCH_PAD_NUM10

Touch channel 10 is GPIO10(ESP32-S2)

enumerator TOUCH_PAD_NUM11

Touch channel 11 is GPIO11(ESP32-S2)

enumerator TOUCH_PAD_NUM12

Touch channel 12 is GPIO12(ESP32-S2)

enumerator TOUCH_PAD_NUM13

Touch channel 13 is GPIO13(ESP32-S2)

enumerator TOUCH_PAD_NUM14

Touch channel 14 is GPIO14(ESP32-S2)

enumerator TOUCH_PAD_MAX
enum touch_high_volt_t

Touch sensor high reference voltage

Values:

enumerator TOUCH_HVOLT_KEEP

Touch sensor high reference voltage, no change

enumerator TOUCH_HVOLT_2V4

Touch sensor high reference voltage, 2.4V

enumerator TOUCH_HVOLT_2V5

Touch sensor high reference voltage, 2.5V

enumerator TOUCH_HVOLT_2V6

Touch sensor high reference voltage, 2.6V

enumerator TOUCH_HVOLT_2V7

Touch sensor high reference voltage, 2.7V

enumerator TOUCH_HVOLT_MAX
enum touch_low_volt_t

Touch sensor low reference voltage

Values:

enumerator TOUCH_LVOLT_KEEP

Touch sensor low reference voltage, no change

enumerator TOUCH_LVOLT_0V5

Touch sensor low reference voltage, 0.5V

enumerator TOUCH_LVOLT_0V6

Touch sensor low reference voltage, 0.6V

enumerator TOUCH_LVOLT_0V7

Touch sensor low reference voltage, 0.7V

enumerator TOUCH_LVOLT_0V8

Touch sensor low reference voltage, 0.8V

enumerator TOUCH_LVOLT_MAX
enum touch_volt_atten_t

Touch sensor high reference voltage attenuation

Values:

enumerator TOUCH_HVOLT_ATTEN_KEEP

Touch sensor high reference voltage attenuation, no change

enumerator TOUCH_HVOLT_ATTEN_1V5

Touch sensor high reference voltage attenuation, 1.5V attenuation

enumerator TOUCH_HVOLT_ATTEN_1V

Touch sensor high reference voltage attenuation, 1.0V attenuation

enumerator TOUCH_HVOLT_ATTEN_0V5

Touch sensor high reference voltage attenuation, 0.5V attenuation

enumerator TOUCH_HVOLT_ATTEN_0V

Touch sensor high reference voltage attenuation, 0V attenuation

enumerator TOUCH_HVOLT_ATTEN_MAX
enum touch_cnt_slope_t

Touch sensor charge/discharge speed

Values:

enumerator TOUCH_PAD_SLOPE_0

Touch sensor charge / discharge speed, always zero

enumerator TOUCH_PAD_SLOPE_1

Touch sensor charge / discharge speed, slowest

enumerator TOUCH_PAD_SLOPE_2

Touch sensor charge / discharge speed

enumerator TOUCH_PAD_SLOPE_3

Touch sensor charge / discharge speed

enumerator TOUCH_PAD_SLOPE_4

Touch sensor charge / discharge speed

enumerator TOUCH_PAD_SLOPE_5

Touch sensor charge / discharge speed

enumerator TOUCH_PAD_SLOPE_6

Touch sensor charge / discharge speed

enumerator TOUCH_PAD_SLOPE_7

Touch sensor charge / discharge speed, fast

enumerator TOUCH_PAD_SLOPE_MAX
enum touch_tie_opt_t

Touch sensor initial charge level

Values:

enumerator TOUCH_PAD_TIE_OPT_LOW

Initial level of charging voltage, low level

enumerator TOUCH_PAD_TIE_OPT_HIGH

Initial level of charging voltage, high level

enumerator TOUCH_PAD_TIE_OPT_MAX
enum touch_fsm_mode_t

Touch sensor FSM mode

Values:

enumerator TOUCH_FSM_MODE_TIMER

To start touch FSM by timer

enumerator TOUCH_FSM_MODE_SW

To start touch FSM by software trigger

enumerator TOUCH_FSM_MODE_MAX
enum touch_trigger_mode_t

Values:

enumerator TOUCH_TRIGGER_BELOW

Touch interrupt will happen if counter value is less than threshold.

enumerator TOUCH_TRIGGER_ABOVE

Touch interrupt will happen if counter value is larger than threshold.

enumerator TOUCH_TRIGGER_MAX
enum touch_trigger_src_t

Values:

enumerator TOUCH_TRIGGER_SOURCE_BOTH

wakeup interrupt is generated if both SET1 and SET2 are “touched”

enumerator TOUCH_TRIGGER_SOURCE_SET1

wakeup interrupt is generated if SET1 is “touched”

enumerator TOUCH_TRIGGER_SOURCE_MAX
enum touch_pad_intr_mask_t

Values:

enumerator TOUCH_PAD_INTR_MASK_DONE

Measurement done for one of the enabled channels.

enumerator TOUCH_PAD_INTR_MASK_ACTIVE

Active for one of the enabled channels.

enumerator TOUCH_PAD_INTR_MASK_INACTIVE

Inactive for one of the enabled channels.

enumerator TOUCH_PAD_INTR_MASK_SCAN_DONE

Measurement done for all the enabled channels.

enumerator TOUCH_PAD_INTR_MASK_TIMEOUT

Timeout for one of the enabled channels.

enum touch_pad_denoise_grade_t

Values:

enumerator TOUCH_PAD_DENOISE_BIT12

Denoise range is 12bit

enumerator TOUCH_PAD_DENOISE_BIT10

Denoise range is 10bit

enumerator TOUCH_PAD_DENOISE_BIT8

Denoise range is 8bit

enumerator TOUCH_PAD_DENOISE_BIT4

Denoise range is 4bit

enumerator TOUCH_PAD_DENOISE_MAX
enum touch_pad_denoise_cap_t

Values:

enumerator TOUCH_PAD_DENOISE_CAP_L0

Denoise channel internal reference capacitance is 5pf

enumerator TOUCH_PAD_DENOISE_CAP_L1

Denoise channel internal reference capacitance is 6.4pf

enumerator TOUCH_PAD_DENOISE_CAP_L2

Denoise channel internal reference capacitance is 7.8pf

enumerator TOUCH_PAD_DENOISE_CAP_L3

Denoise channel internal reference capacitance is 9.2pf

enumerator TOUCH_PAD_DENOISE_CAP_L4

Denoise channel internal reference capacitance is 10.6pf

enumerator TOUCH_PAD_DENOISE_CAP_L5

Denoise channel internal reference capacitance is 12.0pf

enumerator TOUCH_PAD_DENOISE_CAP_L6

Denoise channel internal reference capacitance is 13.4pf

enumerator TOUCH_PAD_DENOISE_CAP_L7

Denoise channel internal reference capacitance is 14.8pf

enumerator TOUCH_PAD_DENOISE_CAP_MAX
enum touch_pad_shield_driver_t

Touch sensor shield channel drive capability level

Values:

enumerator TOUCH_PAD_SHIELD_DRV_L0

The max equivalent capacitance in shield channel is 40pf

enumerator TOUCH_PAD_SHIELD_DRV_L1

The max equivalent capacitance in shield channel is 80pf

enumerator TOUCH_PAD_SHIELD_DRV_L2

The max equivalent capacitance in shield channel is 120pf

enumerator TOUCH_PAD_SHIELD_DRV_L3

The max equivalent capacitance in shield channel is 160pf

enumerator TOUCH_PAD_SHIELD_DRV_L4

The max equivalent capacitance in shield channel is 200pf

enumerator TOUCH_PAD_SHIELD_DRV_L5

The max equivalent capacitance in shield channel is 240pf

enumerator TOUCH_PAD_SHIELD_DRV_L6

The max equivalent capacitance in shield channel is 280pf

enumerator TOUCH_PAD_SHIELD_DRV_L7

The max equivalent capacitance in shield channel is 320pf

enumerator TOUCH_PAD_SHIELD_DRV_MAX
enum touch_pad_conn_type_t

Touch channel idle state configuration

Values:

enumerator TOUCH_PAD_CONN_HIGHZ

Idle status of touch channel is high resistance state

enumerator TOUCH_PAD_CONN_GND

Idle status of touch channel is ground connection

enumerator TOUCH_PAD_CONN_MAX
enum touch_filter_mode_t

Touch channel IIR filter coefficient configuration.

Note

On ESP32S2. There is an error in the IIR calculation. The magnitude of the error is twice the filter coefficient. So please select a smaller filter coefficient on the basis of meeting the filtering requirements. Recommended filter coefficient selection IIR_16.

Values:

enumerator TOUCH_PAD_FILTER_IIR_4

The filter mode is first-order IIR filter. The coefficient is 4.

enumerator TOUCH_PAD_FILTER_IIR_8

The filter mode is first-order IIR filter. The coefficient is 8.

enumerator TOUCH_PAD_FILTER_IIR_16

The filter mode is first-order IIR filter. The coefficient is 16 (Typical value).

enumerator TOUCH_PAD_FILTER_IIR_32

The filter mode is first-order IIR filter. The coefficient is 32.

enumerator TOUCH_PAD_FILTER_IIR_64

The filter mode is first-order IIR filter. The coefficient is 64.

enumerator TOUCH_PAD_FILTER_IIR_128

The filter mode is first-order IIR filter. The coefficient is 128.

enumerator TOUCH_PAD_FILTER_IIR_256

The filter mode is first-order IIR filter. The coefficient is 256.

enumerator TOUCH_PAD_FILTER_JITTER

The filter mode is jitter filter

enumerator TOUCH_PAD_FILTER_MAX
enum touch_smooth_mode_t

Level of filter applied on the original data against large noise interference.

Note

On ESP32S2. There is an error in the IIR calculation. The magnitude of the error is twice the filter coefficient. So please select a smaller filter coefficient on the basis of meeting the filtering requirements. Recommended filter coefficient selection IIR_2.

Values:

enumerator TOUCH_PAD_SMOOTH_OFF

No filtering of raw data.

enumerator TOUCH_PAD_SMOOTH_IIR_2

Filter the raw data. The coefficient is 2 (Typical value).

enumerator TOUCH_PAD_SMOOTH_IIR_4

Filter the raw data. The coefficient is 4.

enumerator TOUCH_PAD_SMOOTH_IIR_8

Filter the raw data. The coefficient is 8.

enumerator TOUCH_PAD_SMOOTH_MAX

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