The **TSOP21** series belongs to a family of miniaturized receivers for infrared remote control systems. These components are highly integrated and designed to simplify the process of decoding IR signals in consumer electronics. --- ## 1. Internal Architecture The TSOP21 integrates several electronic stages into a single 3-pin package. This removes the need for complex external circuitry. | Component | Function | | :--- | :--- | | **Photo Detector** | A high-speed PIN diode that converts IR light into electrical current. | | **Preamplifier** | Amplifies the weak current signals from the photo detector. | | **Band Pass Filter** | Filters out noise and only allows specific frequencies (e.g., 38kHz) to pass. | | **Demodulator** | Extracts the digital data (bits) from the carrier frequency. | | **Automatic Gain Control (AGC)** | Adjusts sensitivity to compensate for distance and ambient light. | --- ## 2. Technical Specifications Commonly, these sensors operate on a standard 5V logic level and are optimized for specific carrier frequencies (the most common being 38kHz). * **Operating Voltage:** 2.7V to 5.5V. * **Supply Current:** Typ. 0.7 mA (very low power). * **Carrier Frequencies:** Available in 30, 33, 36, 38, 40, and 56 kHz. * **Transmission Distance:** Up to 45 meters (under ideal conditions). * **Output:** Active Low (The output pin drops to 0V when a signal is detected). --- ## 3. Pinout Configuration The TSOP21 typically features a 3-pin layout (though physical orientation may vary by specific sub-model): | Pin Number | Name | Description | | :--- | :--- | :--- | | **1** | **OUT** | Data Output (Connects to Microcontroller) | | **2** | **GND** | Ground (0V) | | **3** | **Vs** | Supply Voltage (VCC) | --- ## 4. Basic Circuit Implementation To ensure stability, a simple RC filter is recommended for the power supply to prevent noise from interfering with the high-gain amplifier inside the sensor. ```c // Example Connection logic for Arduino // VCC -> 5V (via 100 Ohm resistor) // GND -> GND // OUT -> Digital Pin 2 // Note: Place a 4.7uF capacitor between VCC and GND near the sensor. ``` ### Key Application Features: * **High Immunity:** It is designed to ignore "optical noise" from fluorescent lamps or sunlight. * **Compatibility:** Works with almost all standard IR remote protocols like RC5, RC6, and NEC.