Project Preliminary Design Report

Transcription

1 EEL 4924 Electrical Engineering Design (Senior Design) Project Preliminary Design Report 01 February 2012 Project Title: Wireless Stereo Headset Team Name: WiSH Team Members: Name: Benjamin Landers Name: Barry Beinart Project Abstract: Our project will be to design a wireless audio device that will be able to send and receive wireless signals through any device equipped with a 3.5mm audio jack. A wireless transmitter box will be placed at the source, connected to it via a 3.5mm audio jack. If the source also requires a microphone input, the transmitter box will also be able to connect to it again with a 3.5mm audio jack. The transmitter box will contain an ATmega128RFA1, a microcontroller with built in 2.4GHz transceiver capabilities. The function of the transmitter box will be to receive audio signals from the source, perform necessary filtering and sampling through an A/D Converter, and finally then transmit the digital information to the wireless headset. The headset will receive the data, filter and sample with a D/A converter, and amplify to the headsets speakers. Another ATmega128RFA1 will be present as the microcontroller and 2.4 GHz transceiver for the wireless headset. If the microphone of the wireless headset is required, it will be sampled and transmitted in a similar fashion when compared to the transmitter box. However, the microphone will be targeted to the human vocal range in order to reduce both noise and the amount of information required to be sent.

2 Page 2/10 Table of Contents Project Abstract 1 Project Feature 3 Project Components 4 Hardware Digital 4 Figure 1- ATMEGA128RFA1 5 Hardware Analog 5 Technical Concepts 7 Figure 2 Small Block Diagram 8 Figure 3 Large Block Diagram 8 Distribution of Labor 9 Table 1 Distribution of Labor 9 Project Timeline 10 Figure 4 Gantt chart of Timeline 10

3 Page 3/10 Project Features This project will feature a headset, a device generally used for human speech and hearing through some connection. The goal is to construct a wireless headset to reduce wire clutter as well as enabling unrestricted movement while wearing the headset. Other features include: Wireless Communication (Minimum Feet) Lithium Ion Rechargeable Battery via USB connections Low power consumption through programming and component selection. As close to Real Time communication as possible. Headphone section of headset - Amplification and Filtering Microphone section of headset - Amplification and targeted filtering to human speech. 3.5 mm interface Allowing for near universal connectivity. Transmitter box of reasonable size with power supply.

4 Page 4/10 -Hardware Digital Components ATMega128RFA1 Project Components The ATMega128RFA1 will be the heart of the headset and the transmitter box. It has an onboard 10-Bit ADC which will be utilized for human audio input through the microphone. It is possible for this to run at 2Mb/s which will provide ample speed to provide the high quality audio desired. The chip provides the options of using ZigBee or IEEE , proving this to be a very versatile chip. As well, the clock rate of 16 MHz should be sufficient to do the processing required to transmit and receive data in real time. This Atmel chip also can be configured to use extremely low power, with the ability to operate the transmitter while the processor is asleep, waking when the buffer for the transmitter is empty. Battery life is important, and the minimum battery life of the WiSH needs to match the industry standards or better. The relatively low cost of this processor and transceiver bundle (~$9-$10) is a main design factor, especially when designing to compete with the other products on the market. There is a large feature set on the Atmel which aids in reliable data transport. As well, with the built in functions targeted to specialized pins, as seen in Figure 1, costs and required additional components can and will be minimized

5 Page 5/10 Figure 1 ATMega128RFA1 Pin-out, showing onboard features. Analog-to-Digital Converters and Digital-to-Analog Converters 16-bit ADC and DAC will be required for CD grade sound quality In order to achieve Stereo Output, it will be required to have a DAC that can provide 2 simultaneous conversion of the output so that there will not be a noticeable delay between the left and right channel. -Hardware Analog Components Headphone and Microphone Amplification In order to have reliable microphone input, the line level to the 3.5mm source will require some form of pre-amplification. The desired product for this amplification would be an IC designed for the specific microphone hardware. The Headphone amplification will require a top of the line ICs that can provide clear audio, with the lowest power consumption possible. Volume control will be a necessity.

6 Page 6/10 Headphone and Microphone Filtering Filter design for the microphone will likely include a LPF to be designed based on microphone selection. Headphone filtering will be designed to give a wide range of frequencies for the human ear, as well as preventing unwanted noise from being heard by the user.

7 Page 7/10 Technical Concepts A main requirement for this project is to achieve near real-time communications through a wireless channel. In order to achieve this, it is necessary to limit the amount of data transferred, by having at most 16-bit audio. 1. To achieve real time audio, it is necessary to not waste any processor power. There is a very limited data transfer rate, in this instance, 2 Megabits/second. In order to prevent these delays, the sampling frequency and bit rate must be below this mark. 16 bit audio and 44 khz will be able to meet in theory these requirements. 2. In order to conserve power, the microcontroller will be required to go in and out of sleep mode seamlessly. This can be accomplished thanks to the onboard buffers of the chip, but, it will still require appropriate processing times. This will need to be taken care of within the software and will likely require the most testing and debugging. 3. Digital Filtering is an option to be weighed, but based on whether the processor demands can handle the extra load will be sought throughout the project. 4. It is necessary to use as much of the built in features is a key concept to this design. In order to be competitive with the real world products, it is necessary to use as much of what is onboard the processor. In order to cut costs and remain competitive, wherever the ability to use software as hardware is utilized.

8 Page 8/10 Figure 2: Simple Block Diagram Figure 3: Large Block Diagram of Microphone communication

9 Page 9/10 Distribution of Labor The following is a breakdown of each team member's projected labor by approximate percentage. Barry Beinart Ben Landers General Paperwork Preliminary Research Board Design Component Selection Testing and Debugging Physical Assembly Table 1: Distribution of Labor

10 Page 10/10 Projected Timeline Figure 4: Gantt chart Of Timeline