Build a TV Muter Circuit with IR Control
Description
Many residences still utilize valve-based television sets. To connect one of these large displays to a hi-fi system for enhanced audio, this is typically manageable due to the availability of SCART to Cinch adapters from accessory vendors. However, certain models frustrate users as the audio outputs associated with the SCART connector are not muted during channel changes.
This can occasionally result in undesirable signal spikes, leading to irritating popping and crackling noises emanating from the loudspeakers of the audio system. In such situations, incorporating a mute circuit is advisable. Fortunately, the opportune moment for activating this circuit is defined by the fact that the enthusiastic user presses buttons on the remote control to change channels, and the remote transmits infrared signals.
Ready-made infrared receiver modules are readily accessible, such as the TSOP1136 employed here, which generates sequences of active-low pulses in response to these signals. Concerning the circuit: when no IR signal is present, a capacitor is charged via P2 and a diode. IC1 functions as a comparator, comparing this IR voltage (applied to its non-inverting input on pin 3) to a reference voltage applied to its other input on pin 2.
IC1 – Comparator
IC1 is a comparator. The comparator is a dual-input analog integrated circuit that compares two input voltages and outputs a high or low logic level depending on which voltage is greater. It’s a fundamental building block in many electronic circuits, used for signal detection, level shifting, and noise cancellation. Its versatility makes it a frequently used component in various electronic designs.
Circuit diagram:
This reference voltage, adjustable with P1, determines the switching threshold for the comparator. If IC2 receives an IR signal, T2 conducts, and consequently, the voltage on C1 drops rapidly below the threshold established by P1. This causes T1 to transition from its previous ‘on’ state to the ‘off’ state. As a result, the relay disengages, and the audio link to the stereo system is interrupted for the duration of the noise interval.
The design is quite straightforward, as you can observe. If a stabilized 5-V supply voltage isn't available, the circuit can be utilized as shown in the schematic diagram (with a 5-V voltage regulator) alongside a basic (unstabilized) AC mains adapter that provides a voltage in the range of 9 V to 12 V to the 7805 (IC3). Alternatively, a relay with normally-closed contacts can be employed instead of normally-open contacts.
In this scenario, simply swap the signals on pins 2 and 3 of IC1 so the relay engages when an IR signal is received rather than disengaging. This conserves power because the relay is only energized during channel switching. If the second comparator of IC1 isn’t needed, it’s advisable to connect pin 6 to +5 V and pin 5 to ground. To bolster noise immunity, shield the IR sensor to prevent direct exposure to light from a fluorescent fixture.