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Voice Over IP. By: Jon Peterson. Introduction. Voice Over Internet Protocol (VOIP) communications systems are a rapidly growing technology. Currently VOIP systems make up 1% of telephone communications in the US.
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Voice Over IP By: Jon Peterson
Introduction • Voice Over Internet Protocol (VOIP) communications systems are a rapidly growing technology. • Currently VOIP systems make up 1% of telephone communications in the US. • VOIP systems allow communications companies to merge their voice and data networks for greater efficiency.
Hardware Design Goals • Capture and replicate voice signals with quality equivalent or better to that of the Plain Old Telephone System (POTS). • Make the VOIP system easy to use – a non-technical user should be able to sit down and use it (Grandma design principle). • Must be able to store the user information in non-volatile memory. • Must be able to transfer packets over the internet…
Hardware Solution – User Interface • The VOIP System must look and feel like a typical telephone.
User Interface - continued • Sample LCD Displays • Custom Keypad
Hardware Solution – µController • To accomplish communications over the internet, I needed to pick a suitable network interface chip. • The Motorola HC9S12NE64 has integrated EMAC and EPHY network layers, so no external chip & bus designs were required. • The downside to picking the NE64 is that it does not include the integrated EEPROM necessary for saving the user’s settings, and it has a very limited amount of RAM.
µController - continued The RJ-45 connector includes integrated transformers to protect the microcontroller from network power surges. The connector also includes integrated LEDs to indicate network status.
Hardware Solution – Audio Quality • The audio samples must have a resolution of at least 8 bits. • The audio sample rate must be at least 8kHz. • The bandwidth of the reproduced audio must be 3kHz or greater (between 300Hz and 3300Hz).
Audio Hardware • For the input circuit, I chose a Motorola MC33202P dual, low-voltage op-amp. • For the output circuit, I chose two IC’s: • The Maxim MAX548A 8-bit, low-voltage, SPI Digital to Analog converter. • The Motorola MC34119, low-voltage, audio amplifier.
Input Circuit - MC33202P What the ATD Module sees:
Output Circuit - Maxim MAX548A Digital to Analog conversion stage
Output Circuit - Motorola MC34119 Amplifier and a low-pass filter at 3400Hz.
Hardware Solution – Data Storage • Since the Motorola HC9S12NE64 does not include the on-chip EEPROM necessary for saving the user’s settings, I had to pick an external device. • SPI memory devices are relatively fast (for external memory devices), and easy to implement (Easy = minimal wiring + circuitry) • I chose the Atmel AT25040A – 512 byte Serial EEPROM
Hardware Solution - Power I needed to pick a voltage regulator which would supply 3.3VDC and a peak current of over 1.035A. The reason for such a large current capacity is due to the requirements of the NE64 when the network interface is active. The National Semiconductor LM1086-3.3 was chosen to meet these requirements.
Thank-You! Now I will show you the full schematic, so that you may visualize my design as a whole.