The **RPR-04-R** is a specialized electronic component primarily categorized as a **Reflective Photosensor** (also known as an Optical Proximity Sensor or Photointerrupter). It is manufactured by ROHM Semiconductor. --- ### 1. Key Internal Components The RPR-04-R is a composite device consisting of two main semiconductor elements housed in a single molded package: | Component | Type | Function | | :--- | :--- | :--- | | **Emitter** | Infrared LED (GaAs) | Emits infrared light at a specific wavelength. | | **Detector** | High-sensitivity Phototransistor | Detects the IR light reflected back from an object. | ### 2. Technical Specifications Below are the typical electrical characteristics for the RPR-04-R: | Parameter | Symbol | Maximum Rating / Value | | :--- | :--- | :--- | | **Forward Current (LED)** | $I_F$ | 50 mA | | **Reverse Voltage (LED)** | $V_R$ | 5 V | | **Collector-Emitter Voltage** | $V_{CEO}$ | 30 V | | **Collector Current** | $I_C$ | 30 mA | | **Operating Temperature** | $T_{opr}$ | -25°C to +85°C | | **Detection Distance** | $d$ | 1mm to 4mm (Optimal) | --- ### 3. How It Works 1. **Emission:** The internal IR LED sends out a beam of infrared light. 2. **Reflection:** When an object passes in front of the sensor, the IR light bounces off the surface of the object. 3. **Detection:** The reflected light hits the base of the internal phototransistor. 4. **Output:** The phototransistor becomes conductive, allowing current to flow from the Collector to the Emitter. This change in current (or voltage, depending on the circuit) is used to trigger a digital or analog signal. ### 4. Physical Features * **Compact Size:** It features a small, surface-mount or lead-type form factor (depending on the specific revision), making it ideal for space-constrained electronics. * **Visible Light Filter:** The housing usually includes a filter to block ambient visible light, reducing "noise" and false triggers from room lighting. ### 5. Common Applications * **Office Equipment:** Detecting paper presence in printers or copiers. * **Industrial Automation:** Counting items on a conveyor belt. * **Consumer Electronics:** Detecting the rotation of a wheel (with a disc) or a "lid-closed" state. * **Robotics:** Line following or short-range obstacle detection. ---