Using the MH-ET LIVE Scanner 3.0 (QR/Barcode) with Arduino

Updated: December 1, 2025

This guide shows how to interface the MH-ET LIVE Scanner V3.0 with Arduino using the UART serial interface. This scanner can read 1D barcodes and 2D codes including QR, and outputs the decoded text through UART or USB.

1. Overview of the Module

Your MH-ET Scanner board includes:

• 2D scanning engine (CMOS sensor + decoder)
• Two Micro-USB ports
  • UART USB → Virtual COM port
  • HID USB → Emulates a keyboard
• 6-pin interface block containing:
  • UART-TX / UART-RX
  • S-TX / S-RX (raw TTL UART, ideal for Arduino)
  • HID-TX / HID-RX
• Two jumper headers
  • Selects which interface connects to the scanner engine
• RST pin for hardware reset
• VCC / GND for power (5V required)

2. Understanding the 6-Pin Header & Jumper Settings

The key to using this module is understanding how data flows.

6-Pin Header (left → right)

Jumper Selection

There are two jumpers:

• UART ←→ S: Connect S-TX/RX to USB-UART chip
• HID ←→ S: Connect S-TX/RX to USB-HID chip

For Arduino, we do not use the jumpers at all — we directly wire to S-TX and S-RX, which always connect to the scanner engine.

3. Power Requirements

The scanner must be powered at 5V, not 3.3V.
At 3.3V, the LED driver and CMOS sensor do not get enough current → QR codes fail to scan.

Recommended:

• 5V / 500mA supply
• Add 100 µF capacitor across VCC–GND if using long wires

4. Wiring the Module to Arduino

Arduino UNO / Nano WIRING

S-TX → Arduino RX
S-RX → Arduino TX
(TX always goes to the other device’s RX)

5. Arduino Code (Tested & Working)

This code:

• Initializes serial communication
• Listens for decoded data
• Resets the scanner if needed
• Prints QR/barcode results to Serial Monitor

#include <SoftwareSerial.h>

#define SCANNER_RX 2   // S-TX from scanner → Arduino D2 (RX)
#define SCANNER_TX 3   // S-RX from scanner → Arduino D3 (TX)
#define RST_PIN    4   // Reset pin for scanner engine

SoftwareSerial scanner(SCANNER_RX, SCANNER_TX);

void scannerReset() {
  digitalWrite(RST_PIN, LOW);
  delay(20);
  digitalWrite(RST_PIN, HIGH);
  delay(500);  // scanner reboot time
}

void setup() {
  pinMode(RST_PIN, OUTPUT);
  digitalWrite(RST_PIN, HIGH);

  Serial.begin(9600);
  scanner.begin(9600);    // Some units use 115200

  Serial.println("Scanner ready...");
  scannerReset();
}

void loop() {
  if (scanner.available()) {
    String data = scanner.readStringUntil('\n');
    data.trim();
    if (data.length() > 0) {
      Serial.print("Scanned: ");
      Serial.println(data);
    }
  }
}

6. Confirming Baud Rate

Most units default to 9600, but some ship at 115200.

If you see:

• Random characters
• Half-printed QR values
• Nothing at all

Try:

scanner.begin(115200);

7. Reset Pin (RST) Details

The scanner’s RST pin is active LOW:

• Pull LOW 10–20 ms → module resets
• Releases HIGH → boots in ~500 ms

This is helpful if:

• Scanner stops responding
• Power dips
• Switching between HID/UART modes
• After scanning configuration QR codes

8. Testing QR & Barcode Scanning

For reliable scanning:

✔️ Use 5V power

3.3V causes QR detection to fail.

✔️ Ideal scan distance

10–20 cm away
(QR is most sensitive to focus distance.)

✔️ Best QR size

25–30 mm square

✔️ Avoid shiny screens and reflections

If scanning fails:

• Increase ambient lighting
• Move slightly farther/closer
• Try a simpler QR (Hello World)

9. Using USB Modes (Optional)

A. USB-UART Mode

Jumper UART ↔ S
Then connect UART microUSB → PC
Open PuTTY / TeraTerm, baud = 9600

B. USB-HID Mode

Jumper HID ↔ S
Then connect HID microUSB
Scanner types text like a keyboard.

10. Troubleshooting

❌ Scanner reads no QR codes

✔ Fix: Use 5V, not 3.3V
✔ Fix: Correct distance (15–20 cm)

❌ Only 1D barcodes read

Scanner may be in 1D-only mode
→ Scan configuration QR to enable 2D.

❌ Arduino receives gibberish

✔ Baud rate mismatch
✔ Long wires → noise

❌ Scanner freezes

✔ Call

scannerReset();

11. Bonus: Auto-Recover Watchdog

If scanner becomes idle/unresponsive:

unsigned long lastScan = millis();

void loop() {
  if (scanner.available()) {
    char c = scanner.read();
    Serial.write(c);
    lastScan = millis();
  }

  if (millis() - lastScan > 7000) {
    Serial.println("Resetting scanner...");
    scannerReset();
    lastScan = millis();
  }
}

12. Testing Other Modes and Configurations

The MH-ET Live QR code scanner supports a lot of configuration options. You can switch between the options by directly scanning pre-defined QR codes. The configuration QR codes can be viewed in this document.

Finished!

You now have a complete working setup for:

• Reading QR codes
• Reading 1D barcodes
• Hardware reset via RST
• UART communication via S-TX/S-RX
• Arduino-compatible powering
• Full troubleshooting and configuration process