Temperature Sensor

Introduction

The ESP32-S2 has a built-in sensor used to measure the chip’s internal temperature. The temperature sensor module contains an 8-bit Sigma-Delta ADC and a DAC to compensate for the temperature offset.

Due to restrictions of hardware, the sensor has predefined measurement ranges with specific measurement errors. See the table below for details.

predefined range (°C)	error (°C)
50 ~ 125	< 3
20 ~ 100	< 2
-10 ~ 80	< 1
-30 ~ 50	< 2
-40 ~ 20	< 3

备注

The temperature sensor is designed primarily to measure the temperature changes inside the chip. The temperature value depends on factors like microcontroller clock frequency or I/O load. Generally, the chip’s internal temperature might be higher than the ambient temperature.

Functional Overview

Resource Allocation - covers which parameters should be set up to get a temperature sensor handle and how to recycle the resources when temperature sensor finishes working.
Enable and Disable Temperature Sensor - covers how to enable and disable the temperature sensor.
Get Temperature Value - covers how to get the real-time temperature value.
Power Management - covers how temperature sensor is affected when changing power mode (i.e. light sleep).
Thread Safety - covers how to make the driver to be thread safe.

Resource Allocation

The ESP32-S2 has just one built-in temperature sensor hardware. The temperature sensor instance is represented by temperature_sensor_handle_t, which is also the bond of the context. It would always be the parameter of the temperature APIs with the information of hardware and configurations, so user can just create a pointer of type temperature_sensor_handle_t and passing to APIs as needed.

In order to install a built-in temperature sensor instance, the first thing is to evaluate the temperature range in your detection environment (For example: if the testing environment is in a room, the range you evaluate might be 10 °C ~ 30 °C; if the testing in a lamp bulb, the range you evaluate might be 60 °C ~ 110 °C). Based on that, the following configuration structure should be defined in advance: temperature_sensor_config_t:

range_min. The minimum value of testing range you have evaluated.
range_max. The maximum value of testing range you have evaluated.

After the ranges are set, the structure could be passed to temperature_sensor_install(), which will instantiate the temperature sensor instance and return a handle.

As mentioned above, different measure ranges have different measurement errors. The user doesn’t need to care about the measurement error because we have an internal mechanism to choose the minimum error according to the given range.

If the temperature sensor is no longer needed, you need to call temperature_sensor_uninstall() to free the temperature sensor resource.

Creating a Temperature Sensor Handle

Step1: Evaluate the testing range. In this example, the range is 20 °C ~ 50 °C.
Step2: Configure the range and obtain a handle

temperature_sensor_handle_t temp_handle = NULL;
temperature_sensor_config_t temp_sensor = {
    .range_min = 20,
    .range_max = 50,
};
ESP_ERROR_CHECK(temperature_sensor_install(&temp_sensor, &temp_handle));

Enable and Disable Temperature Sensor

Enable the temperature sensor by calling temperature_sensor_enable(). The internal temperature sensor circuit will start to work. The driver state will transit from init to enable.
To Disable the temperature sensor, please call temperature_sensor_disable().

Get Temperature Value

After the temperature sensor is enabled by temperature_sensor_enable(), user can get the current temperature by calling temperature_sensor_get_celsius().

// Enable temperature sensor
ESP_ERROR_CHECK(temperature_sensor_enable(temp_handle));
// Get converted sensor data
float tsens_out;
ESP_ERROR_CHECK(temperature_sensor_get_celsius(temp_handle, &tsens_out));
printf("Temperature in %f °C\n", tsens_out);
// Disable the temperature sensor if it's not needed and save the power
ESP_ERROR_CHECK(temperature_sensor_disable(temp_handle));

Power Management

When power management is enabled (i.e. CONFIG_PM_ENABLE is on), temperature sensor will still keep working because it uses XTAL clock (on ESP32-C3) or RTC clock (on ESP32-S2/S3).

Thread Safety

In temperature sensor we don’t add any protection to keep the thread safe. Because from the common usage, temperature sensor should only be called in one task. If you must use this driver in different tasks, please add extra locks to protect it.

Unexpected Behaviors

The value user gets from the chip is usually different from the ambient temperature. It is because the temperature sensor is built inside the chip. To some extent, it measures the temperature of the chip.
When installing the temperature sensor, the driver gives a ‘the boundary you gave cannot meet the range of internal temperature sensor’ error feedback. It is because the built-in temperature sensor has testing limit. The error due to setting temperature_sensor_config_t:
1. Totally out of range, like 200 °C ~ 300 °C.
2. Cross the boundary of each predefined measurement. like 40 °C ~ 110 °C.

Application Example

Temperature sensor reading example: peripherals/temp_sensor.

API Reference

Header File

components/driver/include/driver/temperature_sensor.h

Functions

esp_err_t temperature_sensor_install(const temperature_sensor_config_t *tsens_config, temperature_sensor_handle_t *ret_tsens)

Install temperature sensor driver.

参数

tsens_config – Pointer to config structure.
ret_tsens – Return the pointer of temperature sensor handle.

返回

ESP_OK if succeed

esp_err_t temperature_sensor_uninstall(temperature_sensor_handle_t tsens)

Uninstall the temperature sensor driver.

参数

tsens – The handle created by temperature_sensor_install().

返回

ESP_OK if succeed.

esp_err_t temperature_sensor_enable(temperature_sensor_handle_t tsens)

Enable the temperature sensor.

参数

tsens – The handle created by temperature_sensor_install().

返回

ESP_OK Success
ESP_ERR_INVALID_STATE if temperature sensor is enabled already.

esp_err_t temperature_sensor_disable(temperature_sensor_handle_t tsens)

Disable temperature sensor.

参数

tsens – The handle created by temperature_sensor_install().

返回

ESP_OK Success
ESP_ERR_INVALID_STATE if temperature sensor is not enabled yet.

esp_err_t temperature_sensor_get_celsius(temperature_sensor_handle_t tsens, float *out_celsius)

Read temperature sensor data that is converted to degrees Celsius.

备注

Should not be called from interrupt.

参数

tsens – The handle created by temperature_sensor_install().
out_celsius – The measure output value.

返回

ESP_OK Success
ESP_ERR_INVALID_ARG invalid arguments
ESP_ERR_INVALID_STATE Temperature sensor is not enabled yet.
ESP_FAIL Parse the sensor data into ambient temperature failed (e.g. out of the range).

Structures

struct temperature_sensor_config_t

Configuration of measurement range for the temperature sensor.

备注

If you see the log the boundary you gave cannot meet the range of internal temperature sensor. You may need to refer to predefined range listed doc api-reference/peripherals/Temperature sensor.

Public Members

int range_min: the minimum value of the temperature you want to test

int range_max: the maximum value of the temperature you want to test

temperature_sensor_clk_src_t clk_src: the clock source of the temperature sensor.

Macros

TEMPERATURE_SENSOR_CONFIG_DEFAULT(min, max): temperature_sensor_config_t default constructure

Type Definitions

typedef struct temperature_sensor_obj_t *temperature_sensor_handle_t: Type of temperature sensor driver handle.

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