esp-idf/examples/peripherals/timer_group/gptimer_capture_hc_sr04/README.md

Supported Targets	ESP32-C6	ESP32-H2	ESP32-P4

HC-SR04 Example based on GPTimer Capture and ETM

(See the README.md file in the upper level 'examples' directory for more information about examples.)

The general purpose timer can capture internal timer count value into dedicated registers. This feature can be used to measure the time between two events. With the help of ETM (Event Task Matrix) peripheral, we can route different events to trigger the GPTimer's capture task. In this example, we configure one GPIO to detect any edge signals and then notify the GPTimer to capture the timestamp at once, all done by hardware.

This example also shows how to decode the pulse width signals generated from a common HC-SR04 sonar sensor -- HC-SR04.

The signal that HC-SR04 produces (and what can be handled by this example) is a simple pulse whose width indicates the measured distance. An excitation pulse is required to send to HC-SR04 on Trig pin to begin a new measurement. Then the pulse described above will appear on the Echo pin after a while.

Typical signals:

Trig       +-----+
           |     |
           |     |
      -----+     +-----------------------
Echo                   +-----+
                       |     |
                       |     |
      -----------------+     +-----------

 +--------------------------------------->
                Timeline

How to Use Example

Hardware Required

• A development board with ESP SOC chip that supports ETM peripheral
• An HC-SR04 sensor module

Connection :

        +------+              +--------------------------------------+
+-------+      |              |                                      |
|       |  VCC +--------------+ 5V                                   |
+-------+      |              |                                      |
        + Echo +----=====>----+ HC_SR04_ECHO_GPIO (internal pull up) |
        |      |              |                                      |
        + Trig +----<=====----+ HC_SR04_TRIG_GPIO                    |
+-------|      |              |                                      |
|       |  GND +--------------+ GND                                  |
+-------|      |              |                                      |
        +------+              +--------------------------------------+

You can change the GPIO number according to your board, by HC_SR04_TRIG_GPIO and HC_SR04_ECHO_GPIO in the source code.

Build and Flash

Run idf.py -p PORT flash monitor to build, flash and monitor the project.

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

I (339) cpu_start: Starting scheduler.
I (344) example: Configure trig gpio
I (344) gpio: GPIO[0]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 0| Pulldown: 0| Intr:0
I (354) example: Configure echo gpio
I (354) gpio: GPIO[1]| InputEn: 1| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:3
I (364) example: Create etm event handle for echo gpio
I (374) example: Create gptimer handle
I (384) example: Get gptimer etm task handle (capture)
I (384) example: Create ETM channel then connect gpio event and gptimer task
I (394) example: Install GPIO edge interrupt
I (404) example: Enable etm channel and gptimer
I (404) example: Start gptimer
I (424) example: Measured distance: 93.40cm
I (934) example: Measured distance: 103.93cm
I (1444) example: Measured distance: 102.09cm
I (1954) example: Measured distance: 122.47cm

Troubleshooting

For any technical queries, please open an issue on GitHub. We will get back to you soon.