Talking to the Bojke Modbus laser distance sensor over RS485

Thought I'd give Claude Code a go. This costs a reasonably modest $20 / £18 per month, cancellable at any time, so not a bit extravagance if it actually provides some benefit to me.

I told it about my Bojke laser sensor and it went off to find the technical data, then created some code for use in the Arduino IDE targeting the Waveshare ESP32-S3 used in the ESP32-S3-POE-ETH-8DI-8DO board. It came up trumps with this one after I provided some more details. Pretty smart - and the code looks pretty well formatted etc!

/**

 * ============================================================

 *  BOJKE BL-30NZ-485 Laser Displacement Sensor

 *  Waveshare ESP32-S3-POE-ETH-8DI-8DO board

 * ============================================================

 */

#include <Arduino.h>

#include <Wire.h>

// ── I2C pins (from I2C_Driver.h) ─────────────────────────────

#define I2C_SCL_PIN   41

#define I2C_SDA_PIN   42

// ── TCA9554 I2C expander (from WS_TCA9554PWR.h) ──────────────

#define TCA9554_ADDRESS     0x20

#define TCA9554_INPUT_REG   0x00

#define TCA9554_OUTPUT_REG  0x01

#define TCA9554_CONFIG_REG  0x03

// ── RS485 pins (from WS_GPIO.h) ──────────────────────────────

#define TXD1     17

#define RXD1     18

#define TXD1EN   21

// ── RS485 serial port ─────────────────────────────────────────

HardwareSerial rs485Serial(1);

// ── Modbus settings ───────────────────────────────────────────

#define MODBUS_BAUD                115200

#define MODBUS_SLAVE_ID            0x01

#define SENSOR_REG_ADDR            0x0000

#define SENSOR_REG_COUNT           0x0002

#define MODBUS_RESPONSE_TIMEOUT_MS 500

#define EXPECTED_RESPONSE_LEN      9

#define POLL_INTERVAL_MS           1000

// ─────────────────────────────────────────────────────────────

//  TCA9554 helpers

// ─────────────────────────────────────────────────────────────

void TCA9554_WriteReg(uint8_t reg, uint8_t data) {

    Wire.beginTransmission(TCA9554_ADDRESS);

    Wire.write(reg);

    Wire.write(data);

    Wire.endTransmission();

}

void TCA9554_Init(uint8_t pinMode, uint8_t pinState) {

    TCA9554_WriteReg(TCA9554_OUTPUT_REG, pinState);

    TCA9554_WriteReg(TCA9554_CONFIG_REG, pinMode);

}

// ─────────────────────────────────────────────────────────────

//  CRC-16/IBM

// ─────────────────────────────────────────────────────────────

uint16_t modbusCRC(const uint8_t *buf, uint8_t len) {

    uint16_t crc = 0xFFFF;

    for (uint8_t i = 0; i < len; i++) {

        crc ^= (uint16_t)buf[i];

        for (uint8_t j = 0; j < 8; j++)

            crc = (crc & 1) ? (crc >> 1) ^ 0xA001 : crc >> 1;

    }

    return crc;

}

// ─────────────────────────────────────────────────────────────

//  Build FC04 request

// ─────────────────────────────────────────────────────────────

void buildFC04Request(uint8_t *frame, uint8_t slaveId,

                      uint16_t regAddr, uint16_t regCount) {

    frame[0] = slaveId;

    frame[1] = 0x04;

    frame[2] = regAddr >> 8;

    frame[3] = regAddr & 0xFF;

    frame[4] = regCount >> 8;

    frame[5] = regCount & 0xFF;

    uint16_t crc = modbusCRC(frame, 6);

    frame[6] = crc & 0xFF;

    frame[7] = crc >> 8;

}

// ─────────────────────────────────────────────────────────────

//  Read sensor distance

// ─────────────────────────────────────────────────────────────

float readDistanceMM() {

    while (rs485Serial.available()) rs485Serial.read();

    uint8_t request[8];

    buildFC04Request(request, MODBUS_SLAVE_ID,

                     SENSOR_REG_ADDR, SENSOR_REG_COUNT);

    Serial.print("[TX] ");

    for (int i = 0; i < 8; i++) {

        if (request[i] < 0x10) Serial.print('0');

        Serial.print(request[i], HEX);

        Serial.print(' ');

    }

    Serial.println();

    rs485Serial.write(request, sizeof(request));

    rs485Serial.flush();

    uint8_t response[EXPECTED_RESPONSE_LEN];

    uint8_t bytesReceived = 0;

    uint32_t deadline = millis() + MODBUS_RESPONSE_TIMEOUT_MS;

    while (millis() < deadline && bytesReceived < EXPECTED_RESPONSE_LEN) {

        if (rs485Serial.available())

            response[bytesReceived++] = rs485Serial.read();

    }

    Serial.print("[RX] ");

    for (int i = 0; i < bytesReceived; i++) {

        if (response[i] < 0x10) Serial.print('0');

        Serial.print(response[i], HEX);

        Serial.print(' ');

    }

    Serial.println();

    if (bytesReceived < EXPECTED_RESPONSE_LEN) {

        Serial.println("[ERR] Timeout / incomplete response");

        return NAN;

    }

    if (response[0] != MODBUS_SLAVE_ID) { Serial.println("[ERR] Wrong slave ID"); return NAN; }

    if (response[1] == 0x84) { Serial.println("[ERR] Modbus exception"); return NAN; }

    if (response[1] != 0x04) { Serial.println("[ERR] Wrong function code"); return NAN; }

    uint16_t rxCRC   = (uint16_t)response[7] | ((uint16_t)response[8] << 8);

    uint16_t calcCRC = modbusCRC(response, 7);

    if (rxCRC != calcCRC) { Serial.println("[ERR] CRC mismatch"); return NAN; }

    uint16_t raw = ((uint16_t)response[5] << 8) | response[6];

    return raw * 0.001f;

}

// ─────────────────────────────────────────────────────────────

//  setup()

// ─────────────────────────────────────────────────────────────

void setup() {

    Serial.begin(115200);

    delay(2000);

    Serial.println("\n=== BOJKE BL-30NZ-485 on Waveshare ESP32-S3-POE-ETH-8DI-8DO ===");

    // I2C init

    Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);

    Serial.println("I2C initialised");

    // TCA9554 init — all outputs, all HIGH (matches Waveshare Dout_Init)

    TCA9554_Init(0x00, 0xFF);

    Serial.println("TCA9554 initialised");

    // RS485 init — exactly as Waveshare demo

    rs485Serial.begin(MODBUS_BAUD, SERIAL_8N1, RXD1, TXD1);

    if (!rs485Serial.setPins(-1, -1, -1, TXD1EN))

        Serial.println("[WARN] Failed to set TXDEN pin");

    if (!rs485Serial.setMode(UART_MODE_RS485_HALF_DUPLEX))

        Serial.println("[WARN] Failed to set RS485 half-duplex mode");

    Serial.println("RS485 initialised");

    Serial.println("================================================================\n");

}

// ─────────────────────────────────────────────────────────────

//  loop()

// ─────────────────────────────────────────────────────────────

void loop() {

    float distance = readDistanceMM();

    if (!std::isnan(distance)) {

        if (distance >= 25.0f && distance <= 35.0f) {

            Serial.print("Distance: ");

            Serial.print(distance, 3);

            Serial.println(" mm");

        } else {

            Serial.println("Distance: OUT OF RANGE");

        }

    } else {

        Serial.println("Distance: READ ERROR");

    }

    Serial.println();

    delay(POLL_INTERVAL_MS);

}

Having said that, I had the wrong Baud rate set for the RS485 interface to the Bojke sensor and I have to say it took me round the houses for a couple of hours in all. Finally, I changed the display language on the sensor to English and was able to see and change the Baud rate, at which point it all worked.

That's not the end of it (yet) - but for now I seem to have a sensor that is talking to me. Now let's have a go at talking to the HX711 load cell device....