Capacitive Touch Sensor

[中文]

Introduction

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

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 the ESP32-S2 are available in Touch Sensor Application Note.

Overview of Capacitive Touch Sensor Versions

Hardware Version

Chip

Main Features

V1

ESP32

Version 1, the channel value decreases when it is touched

V2

ESP32-S2

Version 2, the channel value increases when it is touched Supports waterproof, proximity sensing and sleep wake-up

ESP32-S3

Version 2, support proximity measurement done interrupt

V3

ESP32-P4

Version 3, support frequency hopping

Overview of Touch Sensor Channels

Channel

GPIO

CH0

Internal

CH1

IO1

CH2

IO2

CH3

IO3

CH4

IO4

CH5

IO5

CH6

IO6

CH7

IO7

CH8

IO8

CH9

IO9

CH10

IO10

CH11

IO11

CH12

IO12

CH13

IO13

CH14

IO14

Terminology in the Driver

  • Touch Sensor Controller: The controller of the touch sensor, responsible for configuring and managing the touch sensor.

  • Touch Sensor Channel: A specific touch sensor sampling channel. A touch sensor module has multiple touch channels, which are usually connected to the touch pad for measuring the capacitance change. In the driver, sampling of one channel is called one measurement and the scanning of all registered channels is called one scan.

  • Touch Sensor Sampling Configuration: Touch sensor sampling configuration refers to all the hardware configurations that related to the sampling. It can determine how the touch channels sample by setting the number of charging times, charging frequency, measurement interval, etc. The ESP32-S2 only support one set of sample configuration, so it doesn't support frequency hopping.

File Structure

File Structure of Touch Sensor Driver

File Structure of Touch Sensor Driver

Finite-state Machine

The following diagram shows the state machine of the touch sensor driver, which describes the driver state after calling a function, and the constraint of the state transition.

Finite-state Machine of Touch Sensor Driver

Finite-state Machine of Touch Sensor Driver

The diagram above is the finite-state machine of the touch sensor driver, which describes how the state transferred by invoking different APIs. <other_configurations> in the diagram stands for the other optional configurations, like reconfigurations to the touch sensor controller or channels, callback registration, filter, and so on.

Note

touch_channel_read_data() can be called at any time after the channel is registered (i.e., since INIT state), but please take care of the validation of the data.

Functionality Introduction

Categorized by functionality, the APIs of Capacitive Touch Sensor mainly include:

Touch Sensor Controller Management

Touch Sensor is controlled by controller handle touch_sensor_handle_t, it can be initialized and allocated by touch_sensor_new_controller().

// Some target has multiple sets of sample configuration can be set, here take one for example
#define SAMPLE_NUM 1
touch_sensor_handle_t sens_handle = NULL;
// sample configuration
touch_sensor_sample_config_t sample_cfg[SAMPLE_NUM] = {
    // Specify sample configuration or apply the default sample configuration via `TOUCH_SENSOR_Vn_DEFAULT_SAMPLE_CONFIG`
    // ...
};
// Use the default touch controller configuration
touch_sensor_config_t touch_cfg = TOUCH_SENSOR_DEFAULT_BASIC_CONFIG(SAMPLE_NUM, sample_cfg);
// Allocate a new touch sensor controller handle
ESP_ERROR_CHECK(touch_sensor_new_controller(&touch_cfg, &sens_handle));

To delete the controller handle and free the software and hardware resources, please call touch_sensor_del_controller(). But note that you need to delete the other resources that based on the controller first, like the registered touch channels, otherwise it can't be deleted directly.

ESP_ERROR_CHECK(touch_sensor_del_controller(sens_handle));

You can also update the configurations via touch_sensor_reconfig_controller() before the controller is enabled.

touch_sensor_config_t touch_cfg = {
    // New controller configurations
    // ...
};
ESP_ERROR_CHECK(touch_sensor_reconfig_controller(sens_handle, &touch_cfg));

Touch Sensor Channel Management

There are multiple touch channels in the touch sensor module, the touch sensor channel is controlled by the channel handle touch_channel_handle_t. It can be initialized and allocated by touch_sensor_new_channel().

// ...
touch_channel_config_t chan_cfg = {
    // Touch channel configurations
    // ...
};
touch_channel_handle_t chan_handle = NULL;
int chan_id = 0;
// Allocate a new touch sensor controller handle
ESP_ERROR_CHECK(touch_sensor_new_channel(sens_handle, chan_id, &chan_cfg, &chan_handle));

To delete the touch channel handle and free the software and hardware resources, please call touch_sensor_del_channel().

ESP_ERROR_CHECK(touch_sensor_del_channel(chan_handle));

You can also update the configurations via touch_sensor_reconfig_channel() before the controller is enabled.

touch_channel_config_t chan_cfg = {
    // New touch channel configurations
    // ...
};
ESP_ERROR_CHECK(touch_sensor_reconfig_channel(chan_handle, &chan_cfg));

Filter Configuration

The filter can help to increase the stability in different use cases. The filter can be registered by calling touch_sensor_config_filter() and specify the configurations touch_sensor_filter_config_t. These configurations mainly determine how to filter and update the benchmark and read data. Please note that all touch channels will share this filter.

To deregister the filter, you can call touch_sensor_config_filter() again, and set the second parameter (i.e. touch_sensor_filter_config_t pointer) to NULL.

// ...
touch_sensor_filter_config_t filter_config = {
    // Filter configurations
    // ...
};
// Register the filter
ESP_ERROR_CHECK(touch_sensor_config_filter(sens_handle, &filter_config));
// ...
// Deregister the filter
ESP_ERROR_CHECK(touch_sensor_config_filter(sens_handle, NULL));

Callback

Calling touch_sensor_register_callbacks() to register the touch sensor event callbacks. Once the touch sensor events (like on_active, on_inactive) trigger, the corresponding callbacks will be invoked, so that to deal with the event in the upper application.

For the general example, when the measured data of the current touch channel exceed the benchmark + active_threshold, this channel is activated, and the driver will call on_active callback to inform the application layer. Similar, when the active channel measured a lower data than benchmark + active_threshold, then this channel will be inactivated, and on_inactive will be called to inform this channel is released.

Note

To ensure the stability of the triggering and releasing, active_hysteresis and debounce_cnt can be configured to avoid the frequent triggering that caused by jitter and noise.

Please refer to touch_event_callbacks_t for the details about the supported callbacks.

touch_event_callbacks_t callbacks = {
    .on_active = example_touch_on_active_cb,
    // Other callbacks
    // ...
};
// Register callbacks
ESP_ERROR_CHECK(touch_sensor_register_callbacks(sens_handle, &callbacks, NULL));

// To deregister callbacks, set the corresponding callback to NULL
callbacks.on_active = NULL;
// Other callbacks to deregister
// ...
ESP_ERROR_CHECK(touch_sensor_register_callbacks(sens_handle, &callbacks, NULL));

Enable and Disable

After finished the configuration of the touch controller and touch channels, touch_sensor_enable() can be called to enable the touch sensor controller. It will enter READY status and power on the registered channels, then you can start scanning and sampling the touch data. Note that you can only do scanning and reading operation once the controller is enabled. If you want to update the controller or channel configurations, you need to call touch_sensor_disable() first.

// Enable touch sensor
ESP_ERROR_CHECK(touch_sensor_enable(sens_handle));
// ...
// Disable touch sensor
ESP_ERROR_CHECK(touch_sensor_disable(sens_handle));

Continuous Scan

With the touch controller enabled, touch_sensor_start_continuous_scanning() can be called to start the continuous scanning to all the registered touch channels. The read data of these touch channels will be updated automatically in each scan. Calling touch_sensor_stop_continuous_scanning() can stop the continuous scan.

// Start continuous scan
ESP_ERROR_CHECK(touch_sensor_start_continuous_scanning(sens_handle));
// ...
// Stop continuous scan
ESP_ERROR_CHECK(touch_sensor_stop_continuous_scanning(sens_handle));

Oneshot Scan

With the touch controller enabled, touch_sensor_trigger_oneshot_scanning() can be called to trigger an one-time scan to all the registered touch channels. Note that oneshot scan is a blocking function, it will keep blocking and only return when the scan is finished. Moreover, you can't trigger an oneshot scan after the continuous scan has started.

// Trigger an oneshot scan with timeout 1000 ms
ESP_ERROR_CHECK(touch_sensor_trigger_oneshot_scanning(sens_handle, 1000));

Benchmark Configuration

Normally, you don't have to set the benchmark manually, but you can force reset the benchmark to the current smooth value by calling touch_channel_config_benchmark() when necessary.

touch_chan_benchmark_config_t benchmark_cfg = {
    // Benchmark operations
    // ...
};
ESP_ERROR_CHECK(touch_channel_config_benchmark(chan_handle, &benchmark_cfg));

Read Measurement Data

Call touch_channel_read_data() to read the data with different types. Like, benchmark, smooth data, etc. You can refer to touch_chan_data_type_t for the supported data types.

#define SAMPLE_NUM  1  // Take one sample configuration set for example
uint32_t smooth_data[SAMPLE_NUM] = {};
// Read the smooth data
ESP_ERROR_CHECK(touch_channel_read_data(chan_handle, TOUCH_CHAN_DATA_TYPE_SMOOTH, smooth_data));

Waterproof Configuration

The ESP32-S2 supports waterproof. Waterproof can be registered by calling touch_sensor_config_waterproof() and specify the configurations touch_waterproof_config_t. There are two parts of the waterproof function:

  • Immersion (in-water) proof: touch_waterproof_config_t::guard_chan can be specified for detecting immersion. It is usually designed as a ring on the PCB, which surrounds all the other touch pads. When this guard ring channel is triggered, that means the touch panel is immersed by water, all the touch channels will stop measuring to avoid falsely triggering.

  • Moisture (water-drop) proof: touch_waterproof_config_t::shield_chan can be specified for detecting moisture. It usually uses the grid layout on the PCB, which covers the whole touch panel. The shield channel will charge and discharge synchronously with the current touch channel, when there is a water droplet covers both shield channel and normal touch channel, touch_waterproof_config_t::shield_drv can strengthen the electrical coupling caused by the water droplets, and then reconfigure the active threshold based on the disturbance to eliminate the influence that introduced by the water droplet.

To deregister the waterproof function, you can call touch_sensor_config_waterproof() again, and set the second parameter (i.e. touch_waterproof_config_t pointer) to NULL.

touch_waterproof_config_t waterproof_cfg = {
    // Waterproof configurations
    // ...
};
// Register waterproof function
ESP_ERROR_CHECK(touch_sensor_config_waterproof(sens_handle, &waterproof_cfg));
// ...
// Deregister waterproof function
ESP_ERROR_CHECK(touch_sensor_config_waterproof(sens_handle, NULL));

Proximity Sensing Configuration

The ESP32-S2 supports proximity sensing. Proximity sensing can be registered by calling touch_sensor_config_proximity_sensing() and specify the configurations touch_proximity_config_t.

Since the capacitance change caused by proximity sensing is far less than that caused by physical touch, large area of copper foil is often used on PCB to increase the sensing area. In addition, multiple rounds of scans are needed and the result of each scan will be accumulated in the driver to improve the measurement sensitivity. The scan times (rounds) can be determined by touch_proximity_config_t::scan_times. Generally, the larger the scan times and charging times is, the higher the sensitivity will be, however, the read data will be unstable if the sensitivity is too high. Proper parameters should be determined regarding the application.

The accumulated proximity data can be read by touch_channel_read_data() with the data type TOUCH_CHAN_DATA_TYPE_PROXIMITY

To deregister the proximity sensing, you can call touch_sensor_config_proximity_sensing() again, and set the second parameter (i.e. touch_proximity_config_t pointer) to NULL.

touch_proximity_config_t prox_cfg = {
    // Proximity sensing configuration
    // ...
};
// Register the proximity sensing
ESP_ERROR_CHECK(touch_sensor_config_proximity_sensing(sens_handle, &prox_cfg));
// ...
// Deregister the proximity sensing
ESP_ERROR_CHECK(touch_sensor_config_proximity_sensing(sens_handle, NULL));

Sleep Wake-up Configuration

The ESP32-S2 supports waking-up the chip from light sleep or deep sleep with the touch sensor as a wake-up source. The wake-up functionality can be registered by calling touch_sensor_config_sleep_wakeup() and specifying the configurations touch_sleep_config_t.

After registering the touch sensor sleep wake-up, the chip will continue to sample the touch channels after sleep, which will increase the power consumption during the sleep. To reduce the sleep power consumption, you can reduce the number of charging and discharging times, increase the sampling interval, etc.

Moreover, please note that the operations like sampling, wake-up are all done by hardware when the main core is sleeping. Since this driver runs on the main core, it cannot provide functions such as reading or configuring during the sleep.

If you want to read or configure the touch sensor during the sleep, you can turn to the driver components/ulp/ulp_riscv/ulp_core/include/ulp_riscv_touch_ulp_core.h which based on the Ultra Low Power (ULP) Coprocessor.

  • Light sleep wake-up: you need to set slp_wakeup_lvl to TOUCH_LIGHT_SLEEP_WAKEUP to enable the light sleep wake-up by touch sensor. Note that any registered touch channel can wake-up the chip from light sleep.

  • Deep sleep wake-up: beside setting slp_wakeup_lvl to TOUCH_DEEP_SLEEP_WAKEUP, you need to specify deep_slp_chan additionally. In order to reduce the power consumption, only the specified channel can wake-up the chip from the deep sleep when RTC_PREI power domain off. And also, the driver supports to store another set of configurations for the deep sleep via deep_slp_sens_cfg, this set of configurations only takes effect during the deep sleep, you can customize the configurations to save more power. The configurations will be reset to the previous set after waking-up from the deep sleep. Please be aware that, not only deep sleep wake-up, but also light sleep wake-up will be enabled when the slp_wakeup_lvl is TOUCH_DEEP_SLEEP_WAKEUP.

To deregister the sleep wake-up function, you can call touch_sensor_config_sleep_wakeup() again, and set the second parameter (i.e. touch_sleep_config_t pointer) to NULL.

touch_sleep_config_t light_slp_cfg = {
    .slp_wakeup_lvl = TOUCH_LIGHT_SLEEP_WAKEUP,
};
// Register the light sleep wake-up
ESP_ERROR_CHECK(touch_sensor_config_sleep_wakeup(sens_handle, &light_slp_cfg));
// ...
// Deregister the light sleep wake-up
ESP_ERROR_CHECK(touch_sensor_config_sleep_wakeup(sens_handle, NULL));
touch_sleep_config_t deep_slp_cfg = {
    .slp_wakeup_lvl = TOUCH_DEEP_SLEEP_WAKEUP,
    .deep_slp_chan = dslp_chan_handle,
    // Other deep sleep configurations
    // ...
};
// Register the deep sleep wake-up
ESP_ERROR_CHECK(touch_sensor_config_sleep_wakeup(sens_handle, &deep_slp_cfg));

Denoise Channel Configuration

The ESP32-S2 supports the internal background noise suppression by the denoise channel. Denoise channel can be registered by calling touch_sensor_config_denoise_channel() and specify the configurations touch_denoise_chan_config_t.

Denoise channel is an internal channel that not fanned out. After the denoise channel is enabled, the sampled data of the other touch channels will minus the data of the denoise channel automatically, so the final measurement result of the touch channels will be attenuated compare to the original data.

Aside of the common touch channel configuration, the reference capacitance that attached to the denoise channel can be set by touch_denoise_chan_config_t::ref_cap. And the noise suppression resolution can be set by touch_denoise_chan_config_t::resolution. The higher the resolution, the greater and more accuracy the denoise channel sample data will be, and the better suppression effect it takes. But at the same time, the attenuation of other touch channel sampling values also increases.

For example, the denoise channel resolution is touch_denoise_chan_resolution_t::TOUCH_DENOISE_CHAN_RESOLUTION_BIT8, i.e., maximum sample data is 255. Assuming the actual sample data of a normal touch channel is 10000, and the denoise channel sample data is 100, then the final measurement result of the touch channel will be 10000 - 100 = 9900; If we increase the resolution to touch_denoise_chan_resolution_t::TOUCH_DENOISE_CHAN_RESOLUTION_BIT12, i.e., maximum sample data is 4095, the resolution is 16 times greater. So the denoise channel sample data will be about 100 * 16 = 1600, then the final measurement result of this touch channel will be 10000 - 1600 = 8400.

To deregister the denoise channel, you can call touch_sensor_config_denoise_channel() again, and set the second parameter (i.e. touch_denoise_chan_config_t pointer) to NULL.

touch_denoise_chan_config_t denoise_cfg = {
    // Denoise channel configurations
    // ...
}
// Register the denoise channel
ESP_ERROR_CHECK(touch_sensor_config_denoise_channel(sens_handle, &denoise_cfg));
// ...
// Deregister the denoise channel
ESP_ERROR_CHECK(touch_sensor_config_denoise_channel(sens_handle, NULL));

Application Examples

API Reference

Header File

  • components/esp_driver_touch_sens/include/driver/touch_sens.h

  • This header file can be included with:

    #include "driver/touch_sens.h"

  • This header file is a part of the API provided by the esp_driver_touch_sens component. To declare that your component depends on esp_driver_touch_sens, add the following to your CMakeLists.txt:

    REQUIRES esp_driver_touch_sens

    or

    PRIV_REQUIRES esp_driver_touch_sens

Functions

esp_err_t touch_sensor_new_controller(const touch_sensor_config_t *sens_cfg, touch_sensor_handle_t *ret_sens_handle)

Allocate a new touch sensor controller.

Note

The touch sensor driver will be in INIT state after this function is called successfully.

Parameters

  • sens_cfg -- [in] Touch sensor controller configurations

  • ret_sens_handle -- [out] The return handle of the touch controller instance

Returns

  • ESP_OK On success

  • ESP_ERR_NO_MEM No memory for the touch sensor controller

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller is already allocated

esp_err_t touch_sensor_del_controller(touch_sensor_handle_t sens_handle)

Delete the touch sensor controller.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state).

Parameters

sens_handle -- [in] Touch sensor controller handle

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE Controller not disabled or still some touch channels not deleted

esp_err_t touch_sensor_new_channel(touch_sensor_handle_t sens_handle, int chan_id, const touch_channel_config_t *chan_cfg, touch_channel_handle_t *ret_chan_handle)

Allocate a new touch channel from the touch sensor controller.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state).

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • chan_id -- [in] Touch channel index

  • chan_cfg -- [in] Touch channel configurations

  • ret_chan_handle -- [out] The return handle of the touch channel instance

Returns

  • ESP_OK On success

  • ESP_ERR_NO_MEM No memory for the touch sensor channel

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller has not disabled or this channel has been allocated

esp_err_t touch_sensor_del_channel(touch_channel_handle_t chan_handle)

Delete the touch channel.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state).

Note

If the channel has been enabled other sub-features like proximity sensing, sleep wakeup, waterproof, denoise. The attached sub-features will be disabled while deleting the channel.

Parameters

chan_handle -- [in] Touch channel handle

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller has not disabled

esp_err_t touch_sensor_reconfig_controller(touch_sensor_handle_t sens_handle, const touch_sensor_config_t *sens_cfg)

Re-configure the touch sensor controller.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state).

Note

The re-configuration only applies to the touch controller, so it requires the controller handle that allocated from touch_sensor_new_controller, meanwhile, it won't affect the touch channels, no matter the channels are allocated or not.

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • sens_cfg -- [in] Touch sensor controller configurations

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller has not disabled

esp_err_t touch_sensor_reconfig_channel(touch_channel_handle_t chan_handle, const touch_channel_config_t *chan_cfg)

Re-configure the touch channel.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state).

Note

The re-configuration only applies to a particular touch channel, so it requires the channel handle that allocated from touch_sensor_new_channel

Parameters

  • chan_handle -- [in] Touch channel handle

  • chan_cfg -- [in] Touch channel configurations

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller has not disabled

esp_err_t touch_sensor_config_filter(touch_sensor_handle_t sens_handle, const touch_sensor_filter_config_t *filter_cfg)

Configure the touch sensor filter.

Note

This function is allowed to be called after the touch sensor is enabled

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • filter_cfg -- [in] Filter configurations, set NULL to disable the filter

Returns

  • ESP_OK: Configure the filter success

  • ESP_ERR_INVALID_ARG: The sensor handle is NULL

esp_err_t touch_sensor_enable(touch_sensor_handle_t sens_handle)

Enable the touch sensor controller.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state). And the touch sensor driver will be in ENABLED state after this function is called successfully.

Note

Enable the touch sensor will power on the registered touch channels

Parameters

sens_handle -- [in] Touch sensor controller handle

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller has already enabled

esp_err_t touch_sensor_disable(touch_sensor_handle_t sens_handle)

Disable the touch sensor controller.

Note

This function can only be called after the touch sensor controller is enabled (i.e. ENABLED state). And the touch sensor driver will be in INIT state after this function is called successfully.

Note

Disable the touch sensor will power off the registered touch channels

Parameters

sens_handle -- [in] Touch sensor controller handle

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller has already disabled

esp_err_t touch_sensor_start_continuous_scanning(touch_sensor_handle_t sens_handle)

Start the scanning of the registered touch channels continuously.

Note

This function can only be called after the touch sensor controller is enabled (i.e. ENABLED state). And the touch sensor driver will be in SCANNING state after this function is called successfully. And it can also be called in ISR/callback context.

Note

The hardware FSM (Finite-State Machine) of touch sensor will be driven by its hardware timer continuously and repeatedly. i.e., the registered channels will be scanned one by one repeatedly.

Parameters

sens_handle -- [in] Touch sensor controller handle

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The touch sensor controller is not enabled or the continuous scanning has started

esp_err_t touch_sensor_stop_continuous_scanning(touch_sensor_handle_t sens_handle)

Stop the continuous scanning of the registered touch channels immediately.

Note

This function can only be called after the continuous scanning started (i.e. SCANNING state). And the touch sensor driver will be in ENABLED state after this function is called successfully. And it can also be called in ISR/callback context.

Note

Stop the hardware timer and reset the FSM (Finite-State Machine) of the touch sensor controller

Parameters

sens_handle -- [in] Touch sensor controller handle

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

  • ESP_ERR_INVALID_STATE The continuous scanning has stopped

esp_err_t touch_sensor_trigger_oneshot_scanning(touch_sensor_handle_t sens_handle, int timeout_ms)

Trigger an oneshot scanning for all the registered channels.

Note

This function can only be called after the touch sensor controller is enabled (i.e. ENABLED state). And the touch sensor driver will be in SCANNING state after this function is called successfully, and then switch back to ENABLED state after the scanning is done or timeout.

Note

The block time of this function depends on various factors, In common practice, recommend to set the timeout to several seconds or wait forever, because oneshot scanning can't last for so long.

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • timeout_ms -- [in] Set a positive value or zero means scan timeout in milliseconds Set a negative value means wait forever until finished scanning

Returns

  • ESP_OK On success

  • ESP_ERR_TIMEOUT Timeout to finish the oneshot scanning

  • ESP_ERR_INVALID_ARG Invalid argument

  • ESP_ERR_INVALID_STATE The touch sensor controller is not enabled or the continuous scanning has started

esp_err_t touch_sensor_register_callbacks(touch_sensor_handle_t sens_handle, const touch_event_callbacks_t *callbacks, void *user_ctx)

Register the touch sensor callbacks.

Note

This function can be called when the touch sensor controller is NOT enabled (i.e. INIT state).

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • callbacks -- [in] Callback functions

  • user_ctx -- [in] User context that will be passed to the callback functions

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG NULL pointer

  • ESP_ERR_INVALID_STATE Touch sensor controller has not disabled

esp_err_t touch_channel_config_benchmark(touch_channel_handle_t chan_handle, const touch_chan_benchmark_config_t *benchmark_cfg)

Confiture the touch sensor benchmark for all the registered channels.

Note

This function can be called no matter the touch sensor controller is enabled or not (i.e. ENABLED or SCANNING state). And it can also be called in ISR/callback context.

Parameters

  • chan_handle -- [in] Touch channel handle

  • benchmark_cfg -- [in] The benchmark configurations

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG NULL pointer

esp_err_t touch_channel_read_data(touch_channel_handle_t chan_handle, touch_chan_data_type_t type, uint32_t *data)

Read the touch channel data according to the types.

Note

This function can be called no matter the touch sensor controller is enabled or not (i.e. ENABLED or SCANNING state). And it can also be called in ISR/callback context.

Note

Specially, TOUCH_CHAN_DATA_TYPE_PROXIMITY data type will be read from the cached data in the driver, because the proximity data need to be accumulated in several scan times that specified by touch_proximity_config_t::scan_times. For other data types, the data are read from the hardware registers directly (not cached in the driver). The channel data in the register will be updated once the measurement of this channels is done, And keep locked until the next measurement is done.

Parameters

  • chan_handle -- [in] Touch channel handle

  • type -- [in] Specify the data type to read

  • data -- [out] The data array pointer. If the target supports multiple sample configurations (SOC_TOUCH_SAMPLE_CFG_NUM), the array length should be equal to the frequency hopping number that specified in touch_sensor_config_t::sample_cfg_num, otherwise the array length should be 1.

Returns

  • ESP_OK On success

  • ESP_ERR_INVALID_ARG Invalid argument or NULL pointer

esp_err_t touch_sensor_config_waterproof(touch_sensor_handle_t sens_handle, const touch_waterproof_config_t *wp_cfg)

Configure the touch sensor water proof channels.

Note

Once waterproof is enabled, the other touch channels won't be updated unless the shield channels is activated.

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • wp_cfg -- [in] Water proof channel configurations, set NULL to disable the water proof function

Returns

  • ESP_OK: Configure the water proof success

  • ESP_ERR_INVALID_ARG: The sensor handle is NULL

  • ESP_ERR_INVALID_STATE: The touch sensor is enabled

esp_err_t touch_sensor_config_proximity_sensing(touch_sensor_handle_t sens_handle, const touch_proximity_config_t *prox_cfg)

Configure the touch sensor proximity sensing channels.

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • prox_cfg -- [in] Proximity channels configurations, set NULL to disable the proximity sensing

Returns

  • ESP_OK: Configure the proximity channel success

  • ESP_ERR_INVALID_ARG: The sensor handle is NULL

  • ESP_ERR_INVALID_STATE: The touch sensor is enabled

esp_err_t touch_sensor_config_sleep_wakeup(touch_sensor_handle_t sens_handle, const touch_sleep_config_t *sleep_cfg)

Configure the touch sensor to wake-up the chip from sleep.

Note

Call this function to enable/disable the touch sensor wake-up the chip from deep/light sleep To only enable the touch sensor wake-up the chip from light sleep, set the touch_sleep_config_t::deep_slp_chan to NULL. During the light sleep, all enabled touch channels will keep working, and any one of them can wake-up the chip from light sleep. To enable the touch sensor wake-up the chip from both light and deep sleep, set the touch_sleep_config_t::deep_slp_chan to an enabled channel. During the deep sleep, only this specified channels can work and wake-up the chip from the deep sleep, and other enabled channels can only wake-up the chip from light sleep.

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • sleep_cfg -- [in] Sleep wake-up configurations, set NULL to disable the touch sensor wake-up the chip from sleep

Returns

  • ESP_OK: Configure the sleep channel success

  • ESP_ERR_INVALID_ARG: The sensor handle is NULL

  • ESP_ERR_INVALID_STATE: The touch sensor is enabled

esp_err_t touch_sensor_config_denoise_channel(touch_sensor_handle_t sens_handle, const touch_denoise_chan_config_t *denoise_cfg)

Configure the touch denoise channel.

Note

The denoise channel is used to suppress the internal background noise. Once the denoise channel enabled, the measured data of the other touch channels will minus the data of the denoise channel automatically. So the channel data will be attenuated after enabling the denoise channel.

Parameters

  • sens_handle -- [in] Touch sensor controller handle

  • denoise_cfg -- [in] Denoise channel configurations, set NULL to disable the touch channel

Returns

  • ESP_OK: Configure the denoise channel success

  • ESP_ERR_INVALID_ARG: The sensor handle is NULL or invalid denoise configuration

  • ESP_ERR_INVALID_STATE: The touch sensor is enabled

Header File

  • components/esp_driver_touch_sens/include/driver/touch_sens_types.h

  • This header file can be included with:

    #include "driver/touch_sens_types.h"

  • This header file is a part of the API provided by the esp_driver_touch_sens component. To declare that your component depends on esp_driver_touch_sens, add the following to your CMakeLists.txt:

    REQUIRES esp_driver_touch_sens

    or

    PRIV_REQUIRES esp_driver_touch_sens

Macros

TOUCH_TOTAL_CHAN_NUM

The total channel number of the touch sensor

TOUCH_SAMPLE_CFG_NUM

The supported max sample configuration number

TOUCH_PROXIMITY_CHAN_NUM

The supported proximity channel number in proximity sensing mode

Type Definitions

typedef struct touch_sensor_s *touch_sensor_handle_t

The handle of touch sensor controller

typedef struct touch_channel_s *touch_channel_handle_t

The handle of touch channel

Enumerations

enum touch_sleep_wakeup_level_t

The chip sleep level that allows the touch sensor to wake-up.

Values:

enumerator TOUCH_LIGHT_SLEEP_WAKEUP

Only enable the touch sensor to wake up the chip from light sleep

enumerator TOUCH_DEEP_SLEEP_WAKEUP

Enable the touch sensor to wake up the chip from deep sleep or light sleep

Header File

  • components/esp_driver_touch_sens/hw_ver2/include/driver/touch_version_types.h

  • This header file can be included with:

    #include "driver/touch_version_types.h"

  • This header file is a part of the API provided by the esp_driver_touch_sens component. To declare that your component depends on esp_driver_touch_sens, add the following to your CMakeLists.txt:

    REQUIRES esp_driver_touch_sens

    or

    PRIV_REQUIRES esp_driver_touch_sens

Structures

struct touch_sensor_sample_config_t

Sample configurations of the touch sensor.

Public Members

uint32_t charge_times

The charge and discharge times of this sample configuration, the read data are positive correlation to the charge_times

touch_volt_lim_h_t charge_volt_lim_h

The upper voltage limit while charging a touch pad. i.e., the touch controller won't charge the touch pad higher than this high voltage limitation.

touch_volt_lim_l_t charge_volt_lim_l

The lower voltage limit while discharging a touch pad. i.e., the touch controller won't discharge the touch pad lower than this low voltage limitation.

touch_idle_conn_t idle_conn

The connection of the idle touch channels. The idle touch channel is a channel which is enabled and power-on but not under measuring.

touch_bias_type_t bias_type

The type of the touch sensor bias. Which affects the charge/discharge stability and power consumption

struct touch_sensor_config_t

Configurations of the touch sensor controller.

Public Members

uint32_t power_on_wait_us

The waiting time between the channels power on and able to measure, to ensure the data stability

float meas_interval_us

Measurement interval of each channels

uint32_t max_meas_time_us

The maximum time of measuring one channel, if the time exceeds this value, the timeout interrupt will be triggered. Set to '0' to ignore the measurement time limitation, otherwise please set a proper time considering the configurations of this sample configurations below.

uint32_t sample_cfg_num

The sample configuration number that used for sampling, CANNOT exceed TOUCH_SAMPLE_CFG_NUM

touch_sensor_sample_config_t *sample_cfg

The array of this sample configuration configurations, the length should be specified in touch_sensor_config_t::sample_cfg_num

struct touch_channel_config_t

Configurations of the touch sensor channel.

Public Members

uint32_t active_thresh[TOUCH_SAMPLE_CFG_NUM]

The active threshold of each sample configuration, while the touch channel smooth value minus benchmark value exceed this threshold, will be regarded as activated

touch_charge_speed_t charge_speed

The speed of charging and discharging the touch pad, the higher the speed, the faster charging and discharging

touch_init_charge_volt_t init_charge_volt

The initial voltage before charging/discharging a touch pad

struct touch_sensor_filter_config_t

Configurations of the touch sensor filter.

Public Members

touch_benchmark_filter_mode_t filter_mode

Benchmark filter mode. IIR filter and Jitter filter can be selected, TOUCH_BM_IIR_FILTER_16 is recommended

uint32_t jitter_step

Jitter filter step size, only takes effect when the filter_mode is TOUCH_BM_JITTER_FILTER. Range: [0 ~ 15]

int denoise_lvl

The denoise level, which determines the noise bouncing range that won't trigger benchmark update. Range: [0 ~ 4]. The greater the denoise_lvl is, more noise resistance will be. Specially, 0 stands for no denoise Typically, recommend to set this field to 1.

struct touch_sensor_filter_config_t::[anonymous] benchmark

Benchmark configuration.

Benchmark filter

touch_smooth_filter_mode_t smooth_filter

Smooth data IIR filter mode

uint32_t active_hysteresis

The hysteresis threshold to judge whether the touch channel is active If the channel data exceed the 'touch_channel_config_t::active_thresh + active_hysteresis' The channel will be activated. If the channel data is below to 'touch_channel_config_t::active_thresh - active_hysteresis' the channel will be inactivated.

uint32_t debounce_cnt

The debounce count of the touch channel. Only when the channel data exceed the touch_channel_config_t::active_thresh + active_hysteresis for debounce_cnt times The channel will be activated. And only if the channel data is below to the touch_channel_config_t::active_thresh - active_hysteresis for debounce_cnt times, the channel will be inactivated. (The unit of debounce_cnt is the tick of the slow clock source)

struct touch_sensor_filter_config_t::[anonymous] data

Data configuration.

Channel data filter

struct touch_sleep_config_t

Configuration of the touch sensor sleep function.

Public Members

touch_sleep_wakeup_level_t slp_wakeup_lvl

The sleep level that can be woke up by touch sensor.

touch_channel_handle_t deep_slp_chan

The touch channel handle that supposed to work in the deep sleep. It can wake up the chip from deep sleep when this channel is activated. Only effective when the touch_sleep_config_t::slp_wakeup_lvl is TOUCH_DEEP_SLEEP_WAKEUP

uint32_t deep_slp_thresh[TOUCH_SAMPLE_CFG_NUM]

The active threshold of the deep sleep channel during deep sleep, while the sleep channel exceed this threshold, it will be regarded as activated Only effective when the touch_sleep_config_t::slp_wakeup_lvl is TOUCH_DEEP_SLEEP_WAKEUP

touch_sensor_config_dslp_t *deep_slp_sens_cfg

Specify the touch sensor configuration during the deep sleep. Note that these configurations will no take effect immediately, they will be set automatically while the chip prepare to enter sleep. Set NULL to not change the configurations before entering sleep. The sleep configuration mainly aims at lower down the charging and measuring times, so that to save power consumption during the sleep. Only effective when the touch_sleep_config_t::slp_wakeup_lvl is TOUCH_DEEP_SLEEP_WAKEUP

struct touch_waterproof_config_t

Configuration of the touch sensor waterproof function.

Public Members

touch_channel_handle_t guard_chan

The guard channel of that used for immersion detect. Set NULL if you don't need the guard channel. Typically, the guard channel is a ring that surrounds the touch panels, it is used to detect the large area that covered by water. While large area of water covers the touch panel, the guard channel will be activated.

touch_channel_handle_t shield_chan

The shield channel that used for water droplets shield, can't be NULL. The shield channel can only be the No.14 channel on touch version 2. Typically, the shield channel uses grid layout which covers the touch area, it is used to shield the influence of water droplets covering both the touch panel and the shield channel. The shield channel will be paralleled to the current measuring channel (except the guard channel) to reduce the influence of water droplets.

uint32_t shield_drv

The shield channel driver, which controls the drive capability of shield channel, range: 0 ~ 7 The larger the parasitic capacitance on the shielding channel, the higher the drive capability needs to be set.

uint32_t immersion_proof

Enable to protect the touch sensor pad when immersion detected. It will temporary disable the touch scanning if the guard channel triggered, and enable again if guard channel released. So that to avoid the fake touch when the touch panel is immersed in water.

struct touch_waterproof_config_t::[anonymous] flags

Flags of the water proof function

struct touch_proximity_config_t

Configuration of the touch sensor proximity function.

Public Members

touch_channel_handle_t proximity_chan[TOUCH_PROXIMITY_CHAN_NUM]

The touch channel handles that will be configured as proximity sensing channels

uint32_t scan_times

The total scan times of EACH sample configuration, all sample configurations share a same scan_times. The measurement result of each scanning will be accumulated together to get the final result.

struct touch_denoise_chan_config_t

Configuration of denoise channel.

Public Members

touch_charge_speed_t charge_speed

The speed of charging and discharging the denoise touch channel, the higher the speed, the faster charging and discharging

touch_init_charge_volt_t init_charge_volt

The initial voltage before starting charging/discharging the denoise channel

touch_denoise_chan_cap_t ref_cap

The reference capacitance of the denoise channel.

touch_denoise_chan_resolution_t resolution

The noise suppression resolution of the denoise channel. The higher the resolution, the better the suppression effect, but at the same time, the attenuation of other touch channel sampling values also increases.

struct touch_base_event_data_t

Base event structure used in touch event queue.

Public Members

touch_channel_handle_t chan

the current triggered touch channel handle

int chan_id

the current triggered touch channel number

uint32_t status_mask

the current channel triggered status. For the bits in the status mask, if the bit is set, the corresponding channel is active if the bit is cleared, the corresponding channel is inactive

struct touch_event_callbacks_t

Touch sensor callbacks.

Note

Set NULL for the used callbacks.

Public Members

bool (*on_active)(touch_sensor_handle_t sens_handle, const touch_active_event_data_t *event, void *user_ctx)

Touch sensor on active event callback. Callback when any touch channel is activated.

Param sens_handle

[in] Touch sensor controller handle, created from touch_sensor_new_controller()

Param event

[in] Touch sensor active event data

Param user_ctx

[in] User registered context, passed from touch_sensor_register_callbacks()

Return

Whether a high priority task has been waken up by this callback function

bool (*on_inactive)(touch_sensor_handle_t sens_handle, const touch_inactive_event_data_t *event, void *user_ctx)

Touch sensor on inactive event callback. Callback when any touch channel is inactivated.

Param sens_handle

[in] Touch sensor controller handle, created from touch_sensor_new_controller()

Param event

[in] Touch sensor inactive event data

Param user_ctx

[in] User registered context, passed from touch_sensor_register_callbacks()

Return

Whether a high priority task has been waken up by this callback function

bool (*on_measure_done)(touch_sensor_handle_t sens_handle, const touch_meas_done_event_data_t *event, void *user_ctx)

Touch sensor on measure done event callback. Callback when the measurement of all the sample configurations on the current touch channel is done.

Param sens_handle

[in] Touch sensor controller handle, created from touch_sensor_new_controller()

Param event

[in] Touch sensor measure done event data

Param user_ctx

[in] User registered context, passed from touch_sensor_register_callbacks()

Return

Whether a high priority task has been waken up by this callback function

bool (*on_scan_done)(touch_sensor_handle_t sens_handle, const touch_scan_done_event_data_t *event, void *user_ctx)

Touch sensor on scan done event callback. Callback when finished scanning all the registered touch channels.

Param sens_handle

[in] Touch sensor controller handle, created from touch_sensor_new_controller()

Param event

[in] Touch sensor scan done event data

Param user_ctx

[in] User registered context, passed from touch_sensor_register_callbacks()

Return

Whether a high priority task has been waken up by this callback function

bool (*on_timeout)(touch_sensor_handle_t sens_handle, const touch_timeout_event_data_t *event, void *user_ctx)

Touch sensor on measurement timeout event callback. Callback when measure the current touch channel timeout.

Param sens_handle

[in] Touch sensor controller handle, created from touch_sensor_new_controller()

Param event

[in] Touch sensor timeout event data

Param user_ctx

[in] User registered context, passed from touch_sensor_register_callbacks()

Return

Whether a high priority task has been waken up by this callback function

bool (*on_proximity_meas_done)(touch_sensor_handle_t sens_handle, const touch_prox_done_event_data_t *event, void *user_ctx)

Touch sensor on proximity sensing measurement done event callback. Callback when proximity sensing measurement of the current channel is done.

Param sens_handle

[in] Touch sensor controller handle, created from touch_sensor_new_controller()

Param event

[in] Touch sensor proximity sensing measure done event data

Param user_ctx

[in] User registered context, passed from touch_sensor_register_callbacks()

Return

Whether a high priority task has been waken up by this callback function

struct touch_chan_benchmark_config_t

Touch sensor benchmark configurations, to set or reset the benchmark of the channel.

Public Members

bool do_reset

Whether to reset the benchmark to the channel's latest smooth data

Macros

TOUCH_MIN_CHAN_ID

This file is only applicable to the touch hardware version2 Version 2 includes ESP32-S2 and ESP32-S3.

The minimum available channel id of the touch pad

TOUCH_MAX_CHAN_ID

The maximum available channel id of the touch pad

TOUCH_SHIELD_CHAN_ID

The touch channel that can be used as the shield channel

TOUCH_SENSOR_DEFAULT_BASIC_CONFIG(sample_cfg_number, sample_cfg_ptr)

Helper macro to the default configurations of the touch sensor controller.

Parameters

  • sample_cfg_number -- [in] The number of the sample configurations, which can only be 1 here because there is only one sample configuration

  • sample_cfg_ptr -- [in] The pointer to the sample configurations

TOUCH_SENSOR_V2_DEFAULT_SAMPLE_CONFIG(chg_times, volt_low, volt_high)

Helper macro to the default sample configurations.

Note

This default configuration uses sample frequency = clock frequency / 1

Parameters

  • chg_times -- [in] The charge times of the touch channel

  • volt_low -- [in] The low voltage limit of the touch channel

  • volt_high -- [in] The high voltage limit of the touch channel

TOUCH_SENSOR_DEFAULT_FILTER_CONFIG()

Helper macro to the default filter configurations.

Type Definitions

typedef touch_sensor_config_t touch_sensor_config_dslp_t

Touch sensor configuration during the deep sleep.

Note

Currently it is the same as the normal controller configuration. The deep sleep configuration only takes effect when the chip entered sleep, so that to update a more power efficient configuration.

typedef touch_base_event_data_t touch_meas_done_event_data_t

Measure done event data.

Note

Currently same as base event data

typedef touch_base_event_data_t touch_scan_done_event_data_t

Scan done event data.

Note

Currently same as base event data

typedef touch_base_event_data_t touch_active_event_data_t

Active event data.

Note

Currently same as base event data

typedef touch_base_event_data_t touch_inactive_event_data_t

Inactive event data.

Note

Currently same as base event data

typedef touch_base_event_data_t touch_prox_done_event_data_t

Proximity sensing measure done event data.

Note

Currently same as base event data

typedef touch_base_event_data_t touch_timeout_event_data_t

Timeout event data.

Note

Currently same as base event data

Enumerations

enum touch_chan_data_type_t

The data type of the touch channel.

Values:

enumerator TOUCH_CHAN_DATA_TYPE_RAW

The raw data of the touch channel

enumerator TOUCH_CHAN_DATA_TYPE_SMOOTH

The smooth data of the touch channel

enumerator TOUCH_CHAN_DATA_TYPE_BENCHMARK

The benchmark of the touch channel

enumerator TOUCH_CHAN_DATA_TYPE_PROXIMITY

The proximity data of the proximity channel

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