Introduction: Embracing the Digital Age
The introduction of digital television revolutionized home entertainment, but it posed challenges for households with multiple TVs. Each set required its own digital receiver and subscription, leading to inconvenience and extra costs.
The Solution: A Unified Viewing Experience
This innovative solution allows viewers to enjoy television in multiple rooms using a single digital receiver. The setup enables seamless control from different locations, enhancing user experience and eliminating the need for multiple subscriptions.
Setting Up the Circuit: Simplifying Connections
The circuit, powered from one of the TVs, involves a four-way shielded cable connecting the digital receiver to the second TV. Shielded conductors transmit audio signals (L and R), video signal, and remote control signals, ensuring high-quality transmission.
Remote Control Integration: Streamlining Operation
A secondary programmable remote control unit replaces the need to constantly move the original remote control. The infrared sensor on the second TV captures signals from this remote and transmits them to the digital receiver, simplifying control and enhancing user convenience.
Utilizing SCART Connectors: Maximizing Compatibility
Digital receivers often come with SCART connectors. By utilizing these connectors for TV and video recorder connections, the setup becomes compatible with standard devices, ensuring a seamless and hassle-free viewing experience.
Incorporating this solution into your home entertainment system not only saves money but also enhances the way you enjoy digital television, making your viewing experience more convenient and user-friendly.
Utilizing the Second SCART Connector: Efficient Signal Routing
Figure 3 demonstrates an effective method of utilizing the second SCART connector to transmit signals to the secondary TV set. In cases where this connector is already occupied, an alternative approach involves extracting audio and video signals from the available Cinch connectors, ensuring flexibility in signal routing.
Converting Infrared Signals: Enhancing Remote Control Functionality
Figure 2 illustrates the circuit required to convert the infrared signal received by the secondary TV set into a new signal, driving the infrared LED at the digital receiver location. Infrared signals from remote control units comprise short pulse trains of modulated infrared light, with modulation frequencies ranging from 30 to 56 kHz. Commonly, frequencies between 36 and 40 kHz are employed.
Understanding Modulation Frequencies: Precision in Signal Reception
Infrared sensors, such as TSOP1736 (36 kHz) and TSOP1738 (38 kHz), are designed to respond to specific modulation frequencies. Figure 4 displays various IR receivers and their pinouts. These sensors exhibit sensitivity to frequencies close to their designated modulation frequency. For the sake of practicality, a modulation frequency of 38 kHz is assumed in this context, covering the entire range from 36 to 40 kHz. The IR receiver plays a crucial role in demodulating the received infrared signal, ensuring accurate and reliable signal transmission.
The demodulated signal forms the input to our circuit, which uses it to generate a new modulated signal for the IR LED located next to the digital receiver. The author opened up his second TV set (watch out for possible sources of high voltage inside the set!) in order to use the set’s built-in IR receiver and tap off power for the modulator circuit. However, you can also fit the circuit with its own IR receiver and use a separate power supply (AC power adapter).
IR Signal Processing with 555 Timer IC
The output signal from the IR receiver serves as the trigger for an astable multivibrator circuit, featuring the versatile 555 timer IC. In the quiescent state, the data line of the IR sensor remains High and switches to Low upon receiving a modulated IR signal. As the Reset input of the 555 requires an active-low signal, an inverter is created using components T1, R2, and R3.
Setting Modulation Frequency and Duty Cycle
Modulation frequency for IR LED D2 is precisely tuned to around 38 kHz, regulated by components P1, R1, and C1. Diode D1 ensures the output signal’s duty cycle stays below 50%, a feat unachievable without its inclusion. The rise and fall times of the oscillator signal are set by P1, R1, and C1. The duty cycle, approximately 30% in this setup, is determined by the ratio of P1 to R1.
Adjusting Parameters for Voltage Variations
With a 5-V supply, P1 is calibrated to 1 kΩ. However, with reduced supply voltage, such as 3.3 V, P1 must be lowered to approximately 500 Ω. It is advisable to use an oscilloscope for precise adjustment of the oscillator frequency to 38 kHz (period: 26.3 μs). To generate a test signal at the 555 output, momentarily connect the circuit input to ground. Position IR LED D2 in front of the digital receiver, aligning it with the receiver’s IR sensor. The fourth shielded conductor of the cable connecting the receiver and TV2 serves as the negative lead for D2.
Current Regulation and Alternative Applications
Resistor R4 is dimensioned to maintain a current of around 100 mA through the IR LED. In cases of a 3.3-V supply, R4 must be reduced to 3.3 Ω. This circuit can also be repurposed for remote control of audio or video devices placed within enclosed cabinets, enhancing its versatility and practicality.