HC-SR04 ultrasonic ranging sensor~

#ifndef USE_SR04
#define USE_SR04                            // Add support for HC-SR04 ultrasonic devices (+1k code)
    #define SR04_MAX_SENSOR_DISTANCE  500   // Set sensor max detection distance    #endif

HC-SR04 (HC-SR04P and JSN-SR04T) is an ultrasonic ranging sensor. Provides 2cm to 300cm of non-contact measurement functionality with a ranging accuracy that can reach up to 3mm. Each HC-SR04 module includes an ultrasonic transmitter, a receiver and a control circuit. See HC-SR04 Ultrasonic Sensor for more information.

Buy example: - AliExpress - Sparkfun

The US-100 can also be use as a HC-SR04 if you remove the jumper at the back (check Adafruit documentation).

Configuration~

Wiring~

The HC-SR04 operates at 5V and therefore the echo signal will be 5V as well. Connecting the echo pin via a voltage divider (see schematic) will divide the 5V to 3.3V, which is the operating voltage of an ESP8266.

There is a variant of the HC-SR04, called HC-SR04P. It mainly operates at 3.3V and then it doesn't need the voltage divider but you will notice a range drop of about 1 meter.

Tasmota Settings~

In the Configuration -> Configure Module page assign:

1. GPIOx to SR04 Tri (69)
2. GPIOy to SR04 Ech (70)

Tasmota Main~

After a reboot webUI displays the HC-SR04 distance.

Sensor sends a tele/%topic%/SENSOR JSON response:

{"Time":"2019-01-01T22:42:35","SR04":{"Distance":16.754}}

ESP32 Example with MQTT~

The HC-SR04 can be used with ESP32 devices running Tasmota.

Example Wiring~

Standard HC-SR04 modules output a 5V Echo signal. ESP32 GPIO pins are 3.3V only, so the Echo pin must be connected through a voltage divider or level shifter.

Tasmota Configuration~

Assign:

• GPIO5 → SR04 Tri
• GPIO18 → SR04 Ech

Then save and restart the device.

MQTT Telemetry~

Distance measurements are published to:

tele/%topic%/SENSOR

Example payload:

{"Time":"2026-06-16T12:00:00","SR04":{"Distance":42.6}}

Troubleshooting~