## TSOP1138: Infrared Receiver Module The **TSOP1138** is a miniaturized receiver for infrared (IR) remote control systems. It belongs to the Vishay TSOP family and is designed to detect IR signals modulated at a specific carrier frequency. --- ### 1. Internal Functional Components The device is not just a sensor; it is an Integrated Circuit (IC) that includes several stages to process incoming light: | Component | Function | | :--- | :--- | | **Photo Diode** | Converts IR light pulses into electrical current. | | **Preamplifier** | Amplifies the weak signal from the photo diode. | | **Automatic Gain Control (AGC)** | Adjusts sensitivity to compensate for ambient noise and distance. | | **Band Pass Filter** | Filters out all frequencies except the carrier frequency (38 kHz). | | **Demodulator** | Removes the 38 kHz carrier and outputs the original data envelope. | --- ### 2. Technical Specifications Understanding the electrical limits is crucial for circuit design. * **Carrier Frequency:** 38 kHz (Standard for most TV remotes). * **Supply Voltage ($V_S$):** 2.7V to 5.5V. * **Supply Current ($I_S$):** ~0.7 mA (Low power consumption). * **Transmission Distance:** Up to 45 meters. * **Output Type:** Active Low (The output stays HIGH when idle and drops to LOW when a signal is detected). --- ### 3. Pin Configuration The TSOP1138 typically features a 3-pin package (epoxy molded): | Pin Number | Name | Description | | :---: | :--- | :--- | | 1 | **OUT** | Data output to Microcontroller (e.g., Arduino). | | 2 | **GND** | Ground (0V). | | 3 | **$V_S$** | Supply Voltage (usually +5V). | --- ### 4. Basic Circuit Connection To ensure stable operation and protect against noise on the power line, a simple filter circuit is recommended: ```text +5V Receiver Supply | [R1: 100 Ohm] | +-------+----[ Pin 3: Vs ] | | [C1: 4.7uF] | [ TSOP1138 ] | | GND [ Pin 2: GND ] | [ Pin 1: OUT ] ----> To MCU (Digital Pin) ``` --- ### 5. Key Features & Advantages * **Internal Filter for PCM Frequency:** It effectively ignores sunlight, fluorescent lamps, and other IR noise sources. * **TTL/CMOS Compatibility:** The output can be directly connected to a microprocessor without additional transistors. * **Shielding:** It includes internal shielding against electrical field interference (EMI). ---