Camera Modules: OV7670 & OV2640

Working Principle

The OV7670 (VGA 640×480) and OV2640 (2 MP 1600×1200) are CMOS image sensor modules from OmniVision. A grid of photodiodes (pixels) converts incoming light to electrical charge proportional to intensity. Each pixel has a colour filter (Bayer pattern: RGGB) and a row/column address circuit. The sensor outputs pixel data frame-by-frame over a parallel interface (OV7670) or via an integrated JPEG engine (OV2640).

Key difference: The OV7670 outputs raw pixel data requiring significant bus bandwidth, while the OV2640 can compress to JPEG internally, drastically reducing data transfer requirements.

Electrical Characteristics

Parameter	OV7670	OV2640
Resolution	VGA (640×480)	2 MP (1600×1200)
Supply Voltage	3.3 V	2.5–3.0 V (core), 1.7–3.0 V (I/O)
Output Format	Raw Bayer, RGB565, YUV422	Raw, RGB565, YUV422, JPEG
Interface	8-bit parallel + SCCB (I2C-like)	8-bit parallel / DVP + SCCB
Frame Rate	30 fps (VGA)	15 fps (UXGA), 30 fps (SVGA)
Control Bus	SCCB (≈ I2C, addr 0x21)	SCCB (addr 0x30)
Current Draw	~20 mA (active)	~30 mA (active)
Lens	Built-in M12 lens	Built-in lens (swappable)

Interfacing with an MCU

Camera modules require significant resources: 8 data lines (D0–D7), PCLK (pixel clock), VSYNC, HREF, XCLK (master clock input), SDA, SCL. The OV7670 needs an external 8–24 MHz clock (XCLK).

Calibration

• White balance: Configure SCCB registers for AWB (auto white balance) or manual WB for consistent colour
• Exposure: AEC (automatic exposure control) handles most scenarios; override with manual exposure for specific lighting
• Focus: The OV7670 has a fixed-focus lens; the OV2640 may support auto-focus on some modules
• XCLK frequency: Higher XCLK gives faster frame rates but may introduce noise; 12–20 MHz is typical

Code Example

/*
 * ESP32-CAM (OV2640) JPEG Capture — Arduino IDE
 * Board: AI Thinker ESP32-CAM
 * Captures a JPEG frame and prints size
 */
#include "esp_camera.h"

/* AI Thinker ESP32-CAM pin definitions */
#define PWDN_GPIO    32
#define RESET_GPIO   -1
#define XCLK_GPIO     0
#define SIOD_GPIO    26
#define SIOC_GPIO    27
#define Y9_GPIO      35
#define Y8_GPIO      34
#define Y7_GPIO      39
#define Y6_GPIO      36
#define Y5_GPIO      21
#define Y4_GPIO      19
#define Y3_GPIO      18
#define Y2_GPIO       5
#define VSYNC_GPIO   25
#define HREF_GPIO    23
#define PCLK_GPIO    22

void setup() {
    Serial.begin(115200);

    camera_config_t config;
    config.ledc_channel = LEDC_CHANNEL_0;
    config.ledc_timer   = LEDC_TIMER_0;
    config.pin_d0       = Y2_GPIO;
    config.pin_d1       = Y3_GPIO;
    config.pin_d2       = Y4_GPIO;
    config.pin_d3       = Y5_GPIO;
    config.pin_d4       = Y6_GPIO;
    config.pin_d5       = Y7_GPIO;
    config.pin_d6       = Y8_GPIO;
    config.pin_d7       = Y9_GPIO;
    config.pin_xclk     = XCLK_GPIO;
    config.pin_pclk     = PCLK_GPIO;
    config.pin_vsync    = VSYNC_GPIO;
    config.pin_href     = HREF_GPIO;
    config.pin_sscb_sda = SIOD_GPIO;
    config.pin_sscb_scl = SIOC_GPIO;
    config.pin_pwdn     = PWDN_GPIO;
    config.pin_reset    = RESET_GPIO;
    config.xclk_freq_hz = 20000000;
    config.pixel_format = PIXFORMAT_JPEG;
    config.frame_size   = FRAMESIZE_VGA;
    config.jpeg_quality = 12;
    config.fb_count     = 1;

    esp_err_t err = esp_camera_init(&config);
    if (err != ESP_OK) {
        Serial.printf("Camera init failed: 0x%x
", err);
        return;
    }
    Serial.println("ESP32-CAM (OV2640) Ready");
}

void loop() {
    camera_fb_t *fb = esp_camera_fb_get();
    if (fb) {
        Serial.printf("JPEG: %d bytes (%dx%d)
",
                       fb->len, fb->width, fb->height);
        esp_camera_fb_return(fb);
    }
    delay(2000);
}

Real-World Applications

Limitations

• OV7670 resource demands: Needs 300+ KB RAM, fast GPIO, and DMA — not feasible on basic Arduino.
• Low light performance: Small pixel pitch means poor sensitivity in dim conditions. No night vision without IR illuminator.
• Fixed focus: Neither sensor has hardware autofocus; depth of field is fixed by the lens.
• Parallel interface: Uses 8 GPIO pins for data alone; consumes most available pins on smaller MCUs.
• SCCB register complexity: Register configuration for OV7670 is notoriously complex with undocumented registers.