A scanner can read the same QR code in both modes, but the way scanning starts can change how the whole machine works.

Auto sensing is easier when the scanner should read any code placed in front of it. Command trigger is better when the equipment software needs to decide exactly when scanning is allowed.

How Auto Sensing Works

In auto-sensing mode, the scanner waits for a barcode, phone or object to enter its reading area. It then turns on the light and starts scanning automatically.

This is useful for:

• Retail price checkers

• POS equipment

• Simple ticket readers

• Devices without two-way software control

• Equipment that should always be ready to scan

Auto sensing is not the same as keeping the scanning light on continuously. The scanner can stay in a waiting state and start reading only after it detects something.

The sensing method also matters. Many compact modules use image changes to detect an object. In a very dark enclosure, an IR-sensing model such as XTIOT XT203BM may provide more reliable automatic triggering.

When Auto Sensing Causes Problems

Automatic scanning may start before the equipment is ready to receive data.

For example, an access gate may detect a QR code while it is still processing the previous user. A kiosk may read a barcode from someone standing nearby, or scan the same code again before the software changes to the next page.

The scanner is working correctly, but the trigger mode does not match the software process.

How Command Trigger Works

With command trigger, the host system sends a command when scanning is required.

A typical process is:

1. The kiosk opens the scanning page.

2. The host sends a trigger command.

3. The scanner turns on and reads the barcode.

4. The decoded data is returned to the host.

5. The software accepts the result and closes the scanning process.

This gives the kiosk software control over when the scanner starts and when barcode data should be accepted.

Which Interface Is Needed?

Command triggering normally requires a two-way communication interface because the host must send commands to the scanner and receive barcode data.

USB CDC, TTL UART and RS232 can be used for this type of control. USB HID keyboard is easier for basic data entry, but it is not usually the best choice when the software needs full control of the scanner.

XTIOT scanner modules use a default baud rate of 9600 for serial communication. Other baud rates can be configured when required.

XTIOT provides the communication protocol and command format. An SDK is not required for the host software to send trigger commands or receive decoded data.

Command Trigger Is Part of Command Control

Triggering a scan is only one serial command function. Depending on the module and firmware, the host can also control or configure:

• Start and stop scanning

• Automatic or command-trigger mode

• Enabled barcode types

• Barcode prefixes and suffixes

• Other scanner settings

XTIOT models such as XT206M1, XT206H1 and XT2003D can support serial command control through the selected communication version.

Choosing the Right Mode

Choose auto sensing when the scanner should always be ready and the software does not need to control each scan.

Choose command trigger when scanning is connected to a specific step, such as payment, identity verification, ticket checking, parcel collection or access approval.

After receiving a valid result, the host software should close the scan step or ignore repeated data. Command triggering controls when the scanner reads, while the host software still controls how each result is used.