Light Fidelity (Li-Fi) is a new paradigm in wireless communication. In this article, we describe the design of a Li-Fi dongle (transmitter) and speaker (receiver) for audio and music applications. The proposed system is a replacement for wired speakers that plays audio signals received through light. The dongle can be designed for less than ₹ 350.
This Li-Fi system scores over Bluetooth speakers as follows:
- The room’s LED lighting not only illuminates the space but also doubles as a music player, offering the advantages of both functions. LED bulbs are highly energy-efficient, consuming 85% less energy than incandescent bulbs and lasting up to 20 times longer. In contrast, most Bluetooth modules rely on batteries that typically last only a year or two before needing replacement. Therefore, the proposed system is more energy-efficient than the Bluetooth version.
- You can receive Li-Fi data as long as you are within the range of the light emitted by the LED light source. Consequently, the range is determined by the intensity of the emitted light.
- Establishing connectivity is necessary between the Bluetooth transmitter and the receiver, whereas with Li-Fi, any user can receive data and play music on their speaker by simply placing the receiver within the range of the LED light source.
- The proposed system can be used with any audio system by connecting the Li-Fi dongle to its audio output jack, eliminating the need for pairing and connectivity requests. This solves the challenge of connecting a Bluetooth speaker to audio systems lacking USB ports and Bluetooth support, which can otherwise be a more challenging task.
5. The Li-Fi dongle and speaker system we propose comes at a more affordable price compared to a Bluetooth dongle and speaker combination.
The concept we present is depicted in Figure 1. It involves utilizing a Li-Fi dongle to transmit audio signals from a source, such as a mobile phone. At the receiving end, a Li-Fi speaker equipped with solar cells is used to receive audio signals wirelessly.
The proposed Li-Fi dongle is connected to the audio jack output available on mobile phones. It has an LED through which audio/music signals are transmitted as light signals. These light signals are captured by the Li-Fi speaker through the solar cell array. The authors’ prototype is shown in Fig. 2.
Circuit and working
Figure 3 depicts the circuitry of the Li-Fi dongle. It employs three common-emitter (CE) amplifiers linked in parallel to amplify the input audio signal. The Li-Fi speaker is fashioned by establishing a connection between the output of a 3V, 200mA solar cell array and the audio input of the speaker. To achieve this, you can connect the terminals of the solar panel to a 3.5mm female audio socket and then connect the speaker’s 3.5mm audio jack to the female socket.
During testing, Boom KBS M2 speaker was used. It is available on Flipkart at the following link.
However, it is not necessary to purchase the exact speaker or a specialized Li-Fi speaker. Any speaker equipped with a built-in amplifier can serve the purpose. You can adapt such a speaker to function as a Li-Fi speaker by integrating a solar panel with it. By fine-tuning the band equalizer on the audio source and optimizing the distance between the solar panel and the light source, you can achieve nearly noise-free sound output from the speaker.
The maximum distance or range between the transmitter and receiver is contingent on the number of amplifier stages employed. In the case of a three-stage common-emitter (CE) amplifier, the maximum distance achievable is approximately two meters, provided the LED illuminance at the receiver side reaches 13,842.00 lux. For a five-stage CE amplifier, the range can extend up to 2.6 meters, with the LED illuminance at 17,382.00 lux. It has been observed that increasing the number of CE amplifier stages connected in parallel in the transmitter circuit leads to an increase in the intensity of the LED light. Consequently, this boost in light intensity expands the maximum distance over which sound is audible from the Li-Fi speaker.
This circuit finds following applications:
1. Stream music from a mobile phone, MP3 player, laptop, tablet or other mobile audio system wirelessly to Li-Fi speakers. A camera flashlight can be used for the purpose.
2. Transmit audio signals from a microphone on the dais to speakers in an auditorium using pre-installed LED lights.
3. Use reading lights in buses, trains, cars and airplanes to play melodious music wirelessly on Li-Fi speakers.
The system can be used in offices, hotels, auditoria, etc, where bright lighting is required throughout the day.
Construction and testing
A true-to-size PCB layout for the Li-Fi dongle is illustrated in Figure 4, while the arrangement of components is presented in Figure 5. Once you have assembled the circuit on the PCB, encase it within an appropriate enclosure and affix LED1 to the front panel of the enclosure. Then, connect the dongle to an audio source, such as a mobile phone.
When you initiate playback of the song, the white LED (LED1) will commence blinking. Direct the LED light towards the solar panel. You should be able to discern the song’s sound emanating from the speaker. Adjust the distance between the light source and the solar panel until you achieve a clear and audible sound from the speaker.