Getting an ESP32-S3-Mini to talk to an HX711 load cell amplifier and the Bojke laser distance sensor

It's all very well using that large DIN Rail-mounted ESP32-S3-POE-ETH-8DI-8DO to talk to the laser sensor and load cell but it feels a bit over the top. There's also a problem with this product when you want to connect to an HX711. This device uses I2C to connect up its 8 digital outputs, rather than go directly from the ESP32's GPIO. The HX711 uses a proprietary 2 wire serial protocol (not I2C or SPI), just clock and data, so requires "proper" GPIO digital outputs to work.

How about simply running both the HX711 and the Bojke sensor on one device, namely the ESP32-S3-Mini? I have a couple of these (and some other flavours eg RP2040) that I acquired for the MIG torch driver ("Motorhead"). That would allow me to drive the HX711 using the GPIO and talk to the Bojke sensor over RS485.

Rabbit hole warning - Claude Code:

I asked Claude Code to draw it up as a simple schematic but TBH it's not very good at that kind of task. To do so, it actually created a Python sketch that it then ran to create this graphic. Took a few minutes too:

I said I wasn't quite there with its effort, so I asked it to come up with a table in JPG format. I suppose it's a bit better in some respects:

Hmm, that's better but I'd rather work from some sort of schematic when it comes to wiring the thing up. So it then came up with this:

...and this:

Not sure that's much of an improvement from where I stand. It offered me the schematic in Eagle (Fusion 360), so in the interests of science I then gave that a go. That caused my GMKtec NUCbox9 to hang and stutter badly (a known issue with a recent Windows "update" and the on-chip Ryzen graphics) and the resulting schematic was pretty shit. I was only able to grab this screenshot by opening the schematic on my XPS15 (which has Nvidia graphics, so wasn't stricken by the same Windows conflict):

It suggested replacing the blocks with pukka Eagle symbols but that turned out to be a fool's errand that finally finished me off - talk about shit results! The original block diagram is the best I can get from it, alongside the connection table as a tabular version.

Stop buggering about, Fatty:

After that rather fruitless diversion, perhaps it's time to get on with wiring the thing up. I think I'll use a breadboard for this to start with, otherwise I'll end up with several boards all hanging together with a spider's web of wiring.

Bojack to the rescue! No idea when I got this one but it saves stripping out the other breadboards I used for the Motorhead.

So without much more pointless buggerage, let's try and lash this thing up, using the table and block schematic.

Before I forget, here's the Arduino code for the combined sensors:

It seems to compile and upload to the ESP32-S3-Mini without issues - but of course it won't do anything without the HX711 and Bojke sensor connected up.

/**

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

 *  Waveshare ESP32-S3-Zero

 *  HX711 load cell + BOJKE BL-30NZ-485 laser — stiffness logger

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

 *

 *  WIRING

 *  ──────

 *  HX711

 *    VCC  → 3.3V

 *    GND  → GND

 *    DT   → GPIO2

 *    SCK  → GPIO3

 *    RATE → 3.3V for 80Hz, GND/float for 10Hz

 *

 *  MAX485 module

 *    VCC  → 5V

 *    GND  → GND

 *    DI   → GPIO1  (UART1 TX)

 *    RO   → GPIO0  (UART1 RX)

 *    DE+RE tied together → GPIO4

 *    A/B screw terminals → BOJKE green(A+) / white(B-)

 *

 *  BOJKE BL-30NZ-485

 *    brown  → +12-24V DC

 *    blue   → GND

 *    green  → A(+) on MAX485

 *    white  → B(-) on MAX485

 *

 *  CALIBRATION

 *  ───────────

 *  Set CALIBRATION_FACTOR to 0.0 on first flash.

 *  Follow Serial Monitor prompts (115200 baud).

 *  Paste the printed factor back in and re-flash.

 *

 *  CSV OUTPUT (USB Serial, 115200)

 *  ───────────────────────────────

 *  # timestamp_ms, distance_mm, force_g

 *  1000, 28.450, 0.0

 *  1050, 28.451, 12.3

 *  ...

 *

 *  POLL RATE

 *  ─────────

 *  POLL_INTERVAL_MS 50  → 20 Hz (safe default)

 *  POLL_INTERVAL_MS 12  → ~80 Hz (requires RATE pin HIGH on HX711)

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

 */

#include <Arduino.h>

#include <HX711.h>

// ── HX711 ────────────────────────────────────────────────────

#define HX711_DT_PIN    2

#define HX711_SCK_PIN   3

#define HX711_READINGS  3     // averages per sample (lower = faster)

// ── MAX485 / RS485 ───────────────────────────────────────────

#define RS485_TX_PIN    1

#define RS485_RX_PIN    0

#define RS485_DE_PIN    4

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

#define MODBUS_BAUD              115200

#define LASER_SLAVE_ID           0x01

#define LASER_REG_ADDR           0x0000

#define LASER_REG_COUNT          0x0002

#define LASER_RESPONSE_TIMEOUT   50    // ms

#define LASER_EXPECTED_LEN       9     // bytes

// ── Poll rate ─────────────────────────────────────────────────

#define POLL_INTERVAL_MS   50

// ── Calibration ──────────────────────────────────────────────

// Set to 0.0 to run calibration on boot.

// After calibration paste the printed value here and re-flash.

#define CALIBRATION_FACTOR   0.0f

// Known weight used during calibration (grams)

#define CALIBRATION_WEIGHT_G  500.0f

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

HX711 scale;

HardwareSerial rs485(1);

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

//  CRC-16/IBM (Modbus)

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

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;

}

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

//  Read laser distance (mm) via Modbus RTU FC04

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

float readLaserMM() {

    // Flush any stale bytes

    while (rs485.available()) rs485.read();

    // Build FC04 request

    uint8_t req[8];

    req[0] = LASER_SLAVE_ID;

    req[1] = 0x04;

    req[2] = LASER_REG_ADDR >> 8;

    req[3] = LASER_REG_ADDR & 0xFF;

    req[4] = LASER_REG_COUNT >> 8;

    req[5] = LASER_REG_COUNT & 0xFF;

    uint16_t crc = modbusCRC(req, 6);

    req[6] = crc & 0xFF;

    req[7] = crc >> 8;

    digitalWrite(RS485_DE_PIN, HIGH);

    delayMicroseconds(100);

    rs485.write(req, sizeof(req));

    rs485.flush();

    delayMicroseconds(100);

    digitalWrite(RS485_DE_PIN, LOW);

    // Wait for response

    uint8_t resp[LASER_EXPECTED_LEN];

    uint8_t n = 0;

    uint32_t deadline = millis() + LASER_RESPONSE_TIMEOUT;

    while (millis() < deadline && n < LASER_EXPECTED_LEN) {

        if (rs485.available())

            resp[n++] = rs485.read();

    }

    if (n < LASER_EXPECTED_LEN)                   return NAN;

    if (resp[0] != LASER_SLAVE_ID)                return NAN;

    if (resp[1] != 0x04)                          return NAN;

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

    uint16_t calcCRC = modbusCRC(resp, 7);

    if (rxCRC != calcCRC)                         return NAN;

    uint16_t raw = ((uint16_t)resp[3] << 8) | resp[4];

    return raw * 0.001f;

}

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

//  Calibration routine

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

void runCalibration() {

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

    Serial.println("  HX711 CALIBRATION");

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

    Serial.println("Step 1: Remove ALL load from the cell.");

    Serial.println("        Send any character when ready...");

    while (!Serial.available()) delay(100);

    while (Serial.available()) Serial.read();

    scale.set_scale();

    scale.tare(20);

    Serial.println("Tared.");

    Serial.println("\nStep 2: Place known weight on the cell.");

    Serial.print("        Known weight: ");

    Serial.print(CALIBRATION_WEIGHT_G, 1);

    Serial.println(" g");

    Serial.println("        Send any character when stable...");

    while (!Serial.available()) delay(100);

    while (Serial.available()) Serial.read();

    float raw    = scale.get_value(20);

    float factor = raw / CALIBRATION_WEIGHT_G;

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

    Serial.print("  CALIBRATION_FACTOR = ");

    Serial.println(factor, 4);

    Serial.println("  Paste this into the sketch and re-flash.");

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

    // Apply immediately so it works this session without re-flashing

    scale.set_scale(factor);

    scale.tare(10);

}

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

//  setup()

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

void setup() {

    // USB CDC serial — required for S3-Zero

    // In Arduino IDE: Tools → USB CDC On Boot → Enabled

    Serial.begin(115200);

    delay(2000);

    Serial.println("# Waveshare ESP32-S3-Zero — stiffness logger");

    // RS485 direction pin

    pinMode(RS485_DE_PIN, OUTPUT);

    digitalWrite(RS485_DE_PIN, LOW);

    // RS485 UART

    rs485.begin(MODBUS_BAUD, SERIAL_8N1, RS485_RX_PIN, RS485_TX_PIN);

    // HX711

    scale.begin(HX711_DT_PIN, HX711_SCK_PIN);

    Serial.print("Waiting for HX711");

    while (!scale.is_ready()) { Serial.print("."); delay(100); }

    Serial.println(" ready.");

    if (CALIBRATION_FACTOR == 0.0f) {

        runCalibration();

    } else {

        scale.set_scale(CALIBRATION_FACTOR);

        Serial.println("Remove all load — taring in 2s...");

        delay(2000);

        scale.tare(20);

        Serial.println("Tared.");

    }

    Serial.println("# timestamp_ms, distance_mm, force_g");

}

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

//  loop()

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

void loop() {

    static uint32_t lastPoll = 0;

    if (millis() - lastPoll < POLL_INTERVAL_MS) return;

    lastPoll = millis();

    uint32_t ts    = millis();

    float distMM   = readLaserMM();

    float forceG   = scale.is_ready() ? scale.get_units(HX711_READINGS) : NAN;

    Serial.print(ts);

    Serial.print(',');

    if (!isnan(distMM)) Serial.print(distMM, 3); else Serial.print("ERR");

    Serial.print(',');

    if (!isnan(forceG)) Serial.print(forceG, 1); else Serial.print("ERR");

    Serial.println();

}

That's it for now...

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.

It's worth noting that when the target is out of range, the reported distance is 65mm, whether the true distance is greater or less than 25-35mm. Hence the sanity check can't actually discern which side it is out of range of.

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....