The **RPR-08-R** is a specialized electronic component primarily used as an **Optical Surface Mount Reflective Photosensor**. It is manufactured by ROHM Semiconductor and is designed for high-precision detection of objects at close range. --- ## 1. Internal Configuration The RPR-08-R is a "Photointerrupter" (Reflective type) consisting of two main internal parts housed in a single package: | Component | Part Type | Function | | :--- | :--- | :--- | | **Emitter** | Infrared LED | Emits infrared light toward a target surface. | | **Detector** | Phototransistor | Receives the reflected light and converts it into electrical current. | --- ## 2. Technical Specifications The device is optimized for low power consumption and surface mount technology (SMT). ### Key Electrical Parameters * **Peak Emission Wavelength:** Typically around **940nm** (Infrared). * **Collector Current ($I_C$):** Usually ranges between **0.5mA to 2.0mA** depending on the distance and reflectivity of the target. * **Maximum Forward Current ($I_F$):** Generally around **50mA**. * **Response Time:** Fast switching speeds suitable for pulse detection. --- ## 3. Working Principle 1. The **Infrared LED** is biased to emit a continuous or pulsed IR beam. 2. When an object comes within the detection range (typically **1mm to 5mm**), the IR light reflects off the surface. 3. The **Phototransistor** detects the reflected light, causing it to become conductive. 4. This change in conductivity creates a voltage drop across a load resistor, which can be read by a Microcontroller (MCU). --- ## 4. Physical Characteristics * **Package Type:** Leadless, surface-mount (SMD). * **Size:** Extremely compact (approx. 3.4mm x 2.7mm x 1.5mm), making it ideal for mobile devices. * **Filter:** Often includes a visible light filter to reduce interference from ambient lighting. --- ## 5. Common Applications * **Paper Detection:** Used in printers to detect the presence or edge of a sheet of paper. * **Disc Detection:** Used in CD/DVD drives. * **Rotation Sensing:** Monitoring motor speed via a reflective strip on a shaft. * **Proximity Sensing:** Detecting if a lid is closed or a module is docked. ---