ESPHome Ultrasonic sensor SR04T via UART

I received the same sensor (AJ-SR04M) and I can’t get it to work. It shows no distance readings. I have been following this thread but to no avail. Can someone enlighten me where to put the AJ_SR04M_Sensor.h file. I was hoping to use it withou any resistor (to work just like the HC-SR04). Are there any changes to the code?

Hello - I found this post interesting - I’m starting to connect AJ-SR04M to my HA via esphome board : esp32 or wemos D1 mini

Have You considered voltages ?

I assume that You get 5v for AJ-SR04M from the board (esp32 or D1mini) but as far as I know TX/RX pins on these boards are working with 3.3v.
So If You connect TX/RX from SR04M You get 5v signal … and connecting it to 3.3v pins can cause damage or malfunction.
There is an instruction how to connect and there is a film presenting it is working but this example is based on Arduino UNO - there are 5v pin !
film - arduino UNO working with AJ-SR04M

So … did You noticed this “voltage question” ?

Hello everyone,
I am trying to reproduce this configuration on my Home Assistant via ESPHOME.
However, I have errors, and I’m more than new to Arduino.

My setup is a “Wemos D1 mini” with “JSN-SR04T” (AJ-SR04M) and 47KΩ residence on R19

In /homeassistant/esphome/
Here is my file AJ_SR04M_Sensor.h

#include "esphome.h"
class AJ_SR04M_Sensor : public PollingComponent, public UARTDevice, public Sensor {

  AJ_SR04M_Sensor(UARTComponent *parent) : PollingComponent(5000), UARTDevice(parent) {}

// AJ_SR04M_Sensor format:
// Trigger: 0x00
// Response: Byte1          Byte2  Byte3  Byte4               Byte5
//           Start Byte=FF  MSB    LSB    Checksum (LSB+MSB)  00

  void update() override {
    char frame[5];
    int pos = 0;

    float value = 0.0;

    while (available()) {

      frame[pos] = read();
      if(pos==5) {
        if ((frame[0] == 0xFF) && (frame[4] == 0x00) && ((frame[1]+frame[2])==frame[3])) {
          value = ((frame[1]<<8) + frame[2]) / 10.0;

and my esp-cuve.yaml file

  name: esp-cuve
  friendly_name: esp-cuve
    - AJ_SR04M_Sensor.h

  id: uart_bus
  tx_pin: D1
  rx_pin: D2
  baud_rate: 9600
  stop_bits: 1
  rx_buffer_size: 4

  board: d1_mini

# Enable logging
  baud_rate: 0

  ssid: !secret wifi_ssid
  password: !secret wifi_password


  port: 80

# Time:
  - platform: homeassistant
    timezone: "Europe/Paris"
    id: homeassistant_time

# Status Binary Sensor:
  - platform: status
    name: "Status"

# Restart Button:
  - platform: restart
    name: "Restart"


  - platform: custom
    lambda: |-
      auto my_sensor = new AJ_SR04M_Sensor(id(uart_bus));
      return {my_sensor};
     unit_of_measurement: cm
     accuracy_decimals: 1
     name: "Distance"

No error on compilation but here are the logs

[20:21:22][D][uart_debug:114]: >>> 01
[20:21:27][D][uart_debug:114]: >>> 01
[20:21:32][D][uart_debug:114]: >>> 01
[20:21:37][D][uart_debug:114]: >>> 01
[20:21:42][D][uart_debug:114]: >>> 01

Do you have any idea where the problem could come from?
Thank you again for your help

Just curious, did you get it working? I’m in the same situation.

Did you figure this one out? I’m very new to esphome so I’m really just trying anything an everything, but I’ve just got it working by removing the checksum comparison.

Wish I could say why that would be causing errors for me, but its the only way I’m getting any readings, and have been consistent and very accurate.

I’m having issues getting this working - see

on a D1 mini is an 8266 so there are only 2 UARTs and the second is transmit-only. You have to use the default hardware UART0 on GPIO01 and GPIO03 per the UART Bus documentation UART Bus — ESPHome

Using the debug example to see whether there’s data going back and forth is also super useful.

Additionally, I had to take out the frame[4] == 0x00 check, because for some reason that byte always has a value on mine even though the uart debug log only shows 4 bytes being received. Now it works fine.

Edit: ended up tweaking it a bit so that it’s a little more flexible, and doesn’t block while waiting for a response.

  # AJ_SR04M custom component
  - platform: custom
    lambda: |-
      auto my_sensor = new AJ_SR04M_Sensor2(id(uart_bus),60000,0x01);
      return {my_sensor};
      name: "Distance"
      icon: mdi:arrow-expand-vertical
      unit_of_measurement: cm 
      accuracy_decimals: 1
      state_class: measurement
#pragma once

#include <vector>

#include "esphome/core/component.h"
#include "esphome/components/sensor/sensor.h"
#include "esphome/components/uart/uart.h"

#include "esphome/core/helpers.h"
#include "esphome/core/log.h"

#include "esphome.h"

//namespace esphome {
//namespace aj_sr04m {

static const char *const TAG = "aj_sr04m.sensor";
class AJ_SR04M_Sensor2 : public sensor::Sensor, public PollingComponent, public uart::UARTDevice {
    AJ_SR04M_Sensor2(UARTComponent *parent, uint32_t polling_period, uint8_t read_trigger) : PollingComponent(polling_period), UARTDevice(parent) {
        read_trigger_ = read_trigger;
    //void setup() override {
    //  ESP_LOGCONFIG(TAG,"Setup of Custom AJ_SR04M_Sensor Finished.");
    void update() override {
        //this->write_byte(0x00); // Try this
        //this->write_byte(0x55); // Try this
        //this->write_byte(0x01); // Try this
        //ESP_LOGV(TAG,"Sent read request to sensor");
        ESP_LOGV(TAG,"Sent read request to sensor using %02x", read_trigger_);

    void loop() override {
        while (this->available() > 0) {
            uint8_t data;
            ESP_LOGV(TAG, "Read byte from sensor: %x", data);
            if (this->buffer_.empty() && data != 0xFF)
            if (this->buffer_.size() == 4)
    void dump_config() override {
      LOG_SENSOR("","AJ_SR04M Sensor",this);
    std::uint8_t read_trigger_;
    std::vector<uint8_t> buffer_;
    void check_buffer_() {
        // AJ_SR04M_Sensor format:
        // Trigger: 0x01 (some use 0x00 or 0x55)
        // Response: Byte0          Byte1  Byte2  Byte3               Byte4
        //           Start Byte=FF  MSB    LSB    Checksum (LSB+MSB)  00 (not always?)
        //The Byte4 description might be a lie 2024.06.09 ejb
        uint8_t checksum = this->buffer_[0] + this->buffer_[1] + this->buffer_[2];
        if (this->buffer_[3] == checksum) {
            uint16_t distance = encode_uint16(this->buffer_[1], this->buffer_[2]);
            if (distance > 200) {
                float scaled_distance = distance / 10.0f;
                ESP_LOGV(TAG, "Distance from sensor: %umm, %.1fcm", distance, scaled_distance);
            } else {
                ESP_LOGW(TAG, "Invalid data read from sensor: %s", format_hex_pretty(this->buffer_).c_str());
        } else {
            ESP_LOGW(TAG, "Checksum failed: %02x != %02x", checksum, this->buffer_[3]);
};//class AJ_SR04M_Sensor2

//}//namespace aj_sr04m
//}//namespace esphome