What should I do if the fixed scanner fails to read the code?

(Applicable to lightweight scenarios such as express lockers, access control gates, self-service terminals, OEM equipment, etc.)
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0-3 seconds: User-side self-help
① Screen/buzzer prompt
• Red light flashes + text: "Please rescan or aim at the light"

② One-click rescan
• Touch the button "Scan again" to trigger a soft restart (no power off).
3-30 seconds: Operator/maintenance personnel intervention
③ Check the 4 most common reasons
Barcode is dirty → Change paper or clean the surface
Scanning window is dirty → Gently wipe the lens with alcohol cotton pads
Fill light is not on → Check if it is blocked; if the lamp beads are damaged, replace spare parts on site
Focus offset → Loosen the bracket screw, fine-tune up and down 5 mm and then lock

④ Temporary replacement
• Plug the spare USB handheld gun into the terminal USB port, scan and go, and mark "manual rescan" in the background.
30 seconds - 2 minutes: Software-level recovery

⑤ Reset/restart
• Most modules support serial port command AT+RST or GPIO pull-down for 200 ms to reset.

⑥ Firmware rollback
• If the firmware has been upgraded recently, use the configuration tool to roll back to the previous version (you can flash the firmware by plugging the USB flash drive into the terminal).
More than 2 minutes: Root cause investigation

⑦ Log keywords
• Use the serial port debugging assistant to check whether Decode Timeout or Illumination Error is continuously reported.

⑧ Replace module
• Always have 1 module of the same model on site, and you can hot-swap and replace it by plugging and unplugging 4 wires (VCC, GND, TX, RX).
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Appendix: 2 lines of code example (Arduino/ESP32)
cpp
Copy
if (scanResult == "") { // Decoding failed
digitalTrigPin = LOW; delay(200); digitalTrigPin = HIGH; // Soft reset scanner
}