Skynet Alpha Final Design Report

EEL4924 - Electrical Engineering Design 2

Ahmed Ghalib Caroline Trump

4/23/2013

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Table of Contents

Project Features 2

Components 3

Technical Objectives 4

Schematics 5

Pictures 6

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Project Features

The main goal of this project is to create a private wireless network. There will be two consoles and one tower (Repeater). The consoles can send and receive data by wireless communication. The data being sent consists of voice input by microphone that has been digitized and text input by a keyboard. The tower (Repeater) will be used to boost the wireless signal and send data from one console to the other. The main challenge of this project was combining our parts together. The voice signal that is being sampled at 11Ksps. To insure the voice was captured the device needed to have at least 8Ksps. Unwanted noise must be filtered out of the system before the input signal is digitized. A Pre-Amp will be used to boost the microphone’s signal and remove unwanted noise. The resolution of the digital signal original goal was to be at 12bits because this is what modern phones use. Due to the speed of the USART and microcontroller the resolution had to be knocked down to 8 bits to achieve the sampling speed needed. At 12bit resolution the console could only read and output the signal at a rate of 5Ksps. A amplifier is placed in-between the DAC and speaker. In terms of communication with the keyboard, the data rate (the bits per second) will not be an issue as long as the data is sent at a reasonable speed for both users to hold a conversation. Handshaking was used to guarantee that each character was sent. The user will be able read the text messages sent and received on an LCD. A switch will determine which input (microphone or keyboard) will be used to send data with to the tower and sent to the other console. When the microphone is used the user will press a button when they want to transmit. The Enter button was chosen on the keyboard to be used as the send button. A microcontroller the PIC18F4620 was used to process all inputs and outputs.

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Components XTend 900 1W RPSMA: The XTend module utilizes FHSS (Frequency Hopping Spread Spectrum) agility to avoid interference by hopping to a new frequency on every packet transmission or re-transmission. Its transmit power is software adjustable from 1mW to 1W—the maximum output power allowable by governments that use 900MHz as a license-free band. The XTend module is approved for use in the United States, Canada, Australia and other countries (contact Digi for a complete listing). The module transfers a standard asynchronous serial data stream, operates within the ISM 900MHz frequency band and sustains up to 115.2kbps data throughput. The module comes with an attached RPSMA antenna connector. MCP4921-E/P: 12 Bit DAC with SPI MCP3201: 12 Bit ADC with SPI PIC18F4620: 5v 8 bit Microcontroller NE5532: Low noise Audio Op Amp TL7401: Low noise Audio Op Amp NHD‐0420DZ‐NSW‐BBW LCD: 4x20, or a graphical screen display. Keyboard: PS/2 Antenna RPSMA: 900/1800 MHz Duck Antenna 2dBi with regular RP-SMA RF connector. Perfect for use with the XBee 900MHz units. 50 ohm impedance. 105mm long. Tenergy: 2000mAh 9.6 V Nickel-Metal Hydride Batteries

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Technical Objectives:

The main goal of our device is to communicate wirelessly on our own network. Device Size: Due to the size of the batteries and PCB consoles where built. They are put in a 8”x6”x3” box. Signal Range: The higher end wireless modules/cards claim to have a range of 20 ~ 1 miles. We would like to get as large of a range as we can. However the specs of the wireless modules are based on line of sight and special antennas in outdoor environments. We used standard duck antennas. These managed to communicate to each other while one was inside the senior design room and the other outside of the neb. Sample Speed: The minimum sample rate of the ADC will need to be at least 8k samples per second to capture the human voice. 11Ksps was achieved. Sample Resolution: Telephones use a 12 bit sample resolution and CD players use a 16 bit sample resolution. Due to speed of the uP the consoles have a resolution of 8 bits. Data Speed: In order to send a digitized voice with a wireless communication system, the device must be able to send 96k bits per second. The consoles are sending data at 115,200 bps. Power: The higher end wireless modules/cards will consume 1mW to 1W of power and they run at 3.3v to 5v. A 9.6v 2000mAH battery is used to power each console and tower.

Problems we overcame: Interupts and timing issues. EMI shielding from the transmitters. Audio Quality. Text input simplicity. Minimizing components. Analog Filtering Techniques. System Optimization.

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Schematics:

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Progress Pictures: