3rd Place Winner:
Squawk Box, Jake Gunderson, USA

Download the full project abstract

Jake Gunderson's "first adventure into the 32-bit embedded world" certainly make it look like he's been around for a while. For his third place winning design he -- built an ip stack from scratch, configures the flash from the Boot File field of the DHCP message, and developed his own daughter card for the project. He tops if off by tying everything together without using a RTOS. Plug his Squawk Box into an Asterisk network and according to Jake you can "transform the LM3S811 into a Voice over Internet Protocol workhorse."

The design is centered on the LM3S811. The majority of the custom baseboard is dedicated to analog signal conditioning. Microphone audio is amplified and filtered in the analog domain and then digitized by the on chip A/D converter at a sample rate of 8kHz. Audio feeding the speaker is generated by one of the on chip PWM generators running at approximately 60kHz. By setting the PWM frequency significantly higher than the 300 to 3kHz voice frequency bandwidth an effective filter can be implemented that virtually removes all of the PWM carrier leaving only the modulated audio signal. The output filter is followed by a unity gain power amplifier to increase the speaker current drive capability.

The Squawk Box leverages several of the included modules on the EKK-LM3S811 board like the 96x16 PLED display and user push button to implement the projects simplistic user interface. In the future Jake adds his project could be enhanced with some addition project features including; the user interface to with a full DTMF keypad and larger display in order to expand the functionality of the Squawk Box into a full featured telephone instrument.

The software design of the Squawk Box is interrupt centric. All time critical tasks revolve around an 8 kHz interrupt which is driven by the A/D and D/A operations. There is no operating system implemented on the Squawk Box rather all processing is performed in a main loop. The interrupt routines were kept lean in order to ensure ample time in the main loop to process IP packets.

The Squawk Box can:

• Automatically answer incoming calls allowing Public Address functionality
• Play an alert tone when a call is answered notifying any parties in the immediate area that there is a new call in progress.
• Display Caller ID on the 96 x 16 display of the board.
• 160ms Adaptive Jitter Buffer: Allows Squawk Box Hardware to adjust its internal clock rate to match the clock rate of the distant end so no timing slips or audio drop outs occur as a result of clock rate problems. It also ensures that packets received out of order are resorted and played back in the same order as they were sent.
• 8-bit u-Law companded audio allowing the same quality of audio as standard telephone services.
• Encrypted Authentication to Asterisk Server: Ensures that only authorized users may participate in a Squawk Box conference.