IR transmitter receiver
The main function of our product is link an audio data from a music player and it transmits audio data to another neighboring device.
We will use wireless daisy chaining device to meet project hard requirement. Wireless daisy chaining form of the products will allows for unlimited number of audiophile from a single audio data source.
When in use, the master audio linker device receive audio data from music player through Audio Input port and then the master device will be broadcasting the audio data received from the music player to a neighboring device through its transmitter. Then the neighboring device will also be able to send the received data to a headphone port and also transmit it again on it neighboring device. Sometimes, people want preserve their privacy of listing music, so this problem lead us to choose Infrared Transmission. People within appropriate distance will be able to transfer and receive their audio data each other. However IR requires a direct line of sight and transmitter and receiver need to be within close distance, therefore the device can be placed on a table in front of the users and place them in series.
Figure 1.1 
Our product will look like above Figure 1.1 simply a small box. The size of our product will similar to size of typical mobile phones. On the left side of the product are infrared receiver and infrared transmitter on the right side. We will design our product with the typical audio plug so that any type of headphones or earphones can be plugged into the device.
Figure 1.2 Block diagram
A block diagram of the interior circuitry of the product is shown in figure 1.2 The master device will pass the input audio data directly to its headphones so that preserves the quality of the sound. In the infrared reception mode, it will retransmit the audio data to its neighboring device at the output of Schmitt Trigger
The received square wave signal will just pass through an integrator. This is for reconstruction of modulated signal. We will place the Schmitt Trigger just after the IR receiver circuit, this is for distinguish between received voltage levels more precisely. As the distance between the transmitter and receiver become larger, the voltage levels at receiver will approach to zero. Schmitt trigger will also help reduce in noise and distortion when the distance between two devices is large. The Schmitt trigger will boost the voltage levels to max amplitude so that allow the integrator to produce the same amplitude range over a span of distances.
Then the received signal will pass through a filter to remove any high frequency noise and the filtered signal then goes to a gain control circuit. The aim of gain control circuit is to allow the user to adjust the volume of sound and this can be controlled by apotentiometer (perhaps 50K.
Figure 1.3 IR Transmitter
Figure 1.4 IR Receiver
2. Future Development plan
There are a number of developments to be done before final functional prototype to be finish. Furthermore, the device can be developed under group discussion and meeting.
2.1 Future development plan
Table 1 Tasks and estimated duration
Build and test a simple IR transmission circuit
In this stage we will build a simple IR transmission circuit to test whether it can transmit and receive sinusoidal signal from an LED to a phototransistor
Risks – signal cannot be transmitted or received properly
Responsibility – Hyeon
Estimated Time – 2hours
Build and test astable multivibrator
In this stage we will build and test our modulator at the transmitter part.
Risks – The risk in this stage is the square wave is not generated with appropriate values of Vth and Vtl.
Responsibility – Hyeon and Anu
Estimated Time – 5~6hours
Build and test IR transmitter with a modulator
In this stage, we will connect astable multivibrator and IR transmitter together.
Risks – Risks in this stage is modulation cannot be achieved properly and do not transmit the signal to phototransistor properly
Responsibility – Hyeon and Anu
Estimated Time – 6~8 hours
Build the IR receiver circuit
We will build Schmitt trigger, demodulator, low pass filter and gain control circuit in this stage
Each part in the IR receiver circuit is important in order to reduce distortion and noise.
Risks – Risks at this stage is accurate calculation of Schmitt trigger, low pass filter and gain control circuit. The calculations are very important to remove high frequency noise from demodulator.
Responsibility – Anu
Estimated Time – 6hours
Test the IR transmitter and receiver circuit with music files
In this stage we will try to transmit a real audio file from computer or mp3 player
Risks – Risks in this stage is the music files are not transmitted properly and the quality of sound is also important
Responsibility – Hyeon and Anu
Estimated Time – 2~3 hours
Create and test PCB
In this stage we will design and test the PCB. In this stage we will also redesign PCB if necessary.
Risks – The risk in this stage is the PCB may be too big and the worst case is built PCB does not work.
Responsibility – Hyeon and Anu both.
Estimated Time – 4~5hours
2.2 Potential development plan
Design is also important feature of the product, because to make sure our product has superiority over our competitor’s.
Also because to attract the consumers to purchase the product.
So we should consider a creative design for our product. Also size is another thing we should think about to help mobility. This task would require some design research. Research on internet or discussion with expert in design industry is required.
Estimated time: 6hours
2.3 Evaluation of the product
To evaluate the outcome of the product is successful following measure is taken to ensure the device transmit and receive audio data accurately, performance of the IR audio transmitter and receiver in various distance and safety.
The IR audio transmitter and receiver will be tested in various distance (0.5m, 1m, 1.5m and 2m). This is done to ensure that transmitter and receiver are work properly for appropriate distance and also we will test how the distance between transmitter and receiver affect the quality of the sound.
Also this design project is in daisy chaining form, we will test how the number of device linked all together in daisy chaining form affects the quality of the sound.
To ensure the device and user safety, the device will be subject to different working load to prevent electric shock and damage to the device
2.4 Gantt Chart Summary
This Gantt chart shows how the project will be developed in remainder of the session.
Figure 2.1 Gantt Chart of the future development plan