## Overview of the TSOP321 Series The **TSOP321** is a miniaturized IR (Infrared) receiver module designed for infrared remote control systems. It belongs to a family of devices that integrate a PIN diode, a preamplifier, and a band-pass filter into a single epoxy package. --- ### 1. Key Technical Specifications The TSOP321 is highly regarded for its ability to filter out ambient light and provide a clean digital signal to a microcontroller. | Parameter | Value/Range | | :--- | :--- | | **Supply Voltage (Vcc)** | 2.5 V to 5.5 V | | **Supply Current** | 0.7 mA (Typical) | | **Carrier Frequency** | 30 kHz to 56 kHz (Specific to sub-model) | | **Transmission Distance** | Up to 45 meters | | **Directivity** | Angle of half sensitivity: $\pm$ 45° | | **Output Type** | Active Low (Digital) | --- ### 2. Internal Functional Components Inside the TSOP321, several electronic stages process the incoming infrared light: 1. **PIN Photodiode:** Converts IR light pulses into tiny electrical currents. 2. **Preamplifier:** Amplifies the weak current from the photodiode. 3. **Automatic Gain Control (AGC):** Adjusts sensitivity to prevent saturation from strong IR sources or interference. 4. **Band-pass Filter:** Only allows frequencies near the carrier frequency (e.g., 38kHz) to pass, blocking sunlight and DC light. 5. **Demodulator:** Removes the carrier wave and outputs the original data envelope as a digital signal. --- ### 3. Pin Configuration The TSOP321 typically follows a standard 3-pin layout: | Pin Number | Name | Function | | :--- | :--- | :--- | | **1** | **OUT** | Data output; connects to MCU input pin. | | **2** | **GND** | Ground connection. | | **3** | **Vs** | Power supply (2.5V - 5.5V). | --- ### 4. Typical Application Circuit To ensure stable operation, a low-pass filter (R1 and C1) is recommended to suppress power supply noise. ```text Vs (2.5V - 5.5V) | [R1: 100 Ohm] | +-------+----------- Pin 3 (Vs) | | [C1: 4.7uF] [TSOP321] | |----------- Pin 1 (OUT) ---> To MCU +-------+----------- Pin 2 (GND) | GND ``` --- ### 5. Selection Guide (Frequency Variants) The "321" designation often implies a specific internal AGC algorithm. However, the carrier frequency is usually denoted by the last two digits (e.g., TSOP321**38** for 38kHz). * **TSOP32130:** 30 kHz * **TSOP32136:** 36 kHz * **TSOP32138:** 38 kHz (Most common for TV remotes) * **TSOP32156:** 56 kHz