Chapter 7: QR Code Scanning

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Chapter goal: Have the NanoCam scan QR codes/barcodes and output the decoded result to the serial port and the web image.

Principle

Uses the precompiled esp-code-scanner library to decode QR codes (QR Code / Barcode) in the image in real time. The RGB565 frames output by the camera are passed directly to the scanner — no grayscale conversion is needed. A brand-new scanner object is created for every frame and destroyed as soon as the scan finishes, preventing internal state from accumulating.

The decoded result is delivered through:

1. Serial log output

2. The shared buffer g_last_code stores the latest result for overlay display on the HTTP/MJPEG stream

3. A green text label overlaid at the bottom of the web image

Steps

7.1 Switching the Mode

ai_mode:5

For the complete commands, see the Serial Protocol Manual.

7.2 Scanning a Code

Place a QR code in front of the camera; the serial port outputs:

I (xxxxx) qrcode: Decoded [QR-Code]: https://example.com

At the same time, green text showing the decoded content appears at the bottom of the web image at http://<IP>/.

7.3 Continuous Scanning

Aim at the next code and it is decoded and output automatically; the scanner is rebuilt on every frame, so it can keep working continuously without crashing.

Code

Core Scanning Logic

main/ai/nano_qrcode.cpp:

// Create a brand-new scanner object for every frame
esp_image_scanner_t *scn = esp_code_scanner_create();
esp_code_scanner_config_t cfg = {
    ESP_CODE_SCANNER_MODE_FAST,
    ESP_CODE_SCANNER_IMAGE_RGB565,
    fb->width, fb->height
};
esp_code_scanner_set_config(scn, cfg);
int count = esp_code_scanner_scan_image(scn, fb->buf);
// Decoding succeeded
const esp_code_scanner_symbol_t result = esp_code_scanner_result(scn);
ESP_LOGI(TAG, "Decoded [%s]: %s", result.type_name, result.data);
// Save to the shared buffer for web overlay
snprintf(g_last_code, sizeof(g_last_code), "%s: %s",
         result.type_name, result.data);
esp_code_scanner_destroy(scn);

Result

Aim at a QR code → the decoded content is output over serial + overlaid on the web image.

Next chapter: Chapter 8: Face Recognition

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