SHDesigns: Embedded Systems Design, Consulting and Developer Resources Page hits:

Sample Project 10

Digital Signal Processing board for Language Lab Testing

The Problem/need:

SLSI had contracted me to redesign their entire language lab. The redesign replaced the control panel with a PC or laptop connected via a network interface. The new system was completed in 2003 and works very well.

One of the features needed was student testing. Teachers would record a group a students taking a verbal test. Later, the audio can be played back and grades assigned. The results would be exported to a spreadsheet. The teacher would not need to use the system, the files could be taken away from the lab and grading can be done on any PC with a sound card.

The new system included support for this board to be added.

The solution:

DSP - 56309 running at 100mHz
DSP Memory 768k x 16-bit, 15 ns RAM
IDE interface for up to 128 Gigs of Voice Storage, 80-Gig Typical.
RCM3200 Processor Module, Rabbit 3000 at 44.2 mHz
LED display for debug status
40 channels of audio via 10 4-channel CODECS
Audio is 64kbit muLaw PCM.
Includes switching power supplies.
Softools ANSI Compiler for RCM3200.

The above photo shows the prototype board. This board includes over 450 parts! It supports 40 channels of audio record and playback. A Motorola DSP56309 DSP processor provides the signal processing needed for the audio. this DSP operates at 100mHz and can perform multiple operations in a single clock. It does not work well as a general-purpose CPU as it is optimised for a specific use. A Z-World RCM3200 module provides a general-purpose controller for the board. This module includes a small embedded CPU, a network interface and supporting hardware and memory.

An IDE interface is attached to the DSP processor. This allows the DSP to store the voice locally. Finished recordings are sent through the RCM3200 network interface to the controlling PC.

The above board is the first prototype. Only minor changes are needed for the final version.

Development time:

This is a work in progress. It is a large design. Embedded code for the DSP and RCM3200 is extensive. Networking, audio processing, disk transfers, file systems, and multitasking operations are needed on both processors. In addition, a PC application needs to be developed to provide a user interface. A sample screen is shown below.

The program has several windows to select students, view current grades and assign grades. A tool bar at the top controls playback functions: play, stop, rewind and fast-forward.

Project Success:

The hardware works well. The first prototype only needed a few cut/jumps to work. This is typical for my designs. A lot of time is done in the initial design to "Get it right." As these are complicated boards, rework is difficult and the need for new prototypes would seriously delay the project. Only needed 2 cuts/jumps and some resistiors added to the IDE connector. Not bad for 450 parts.

The project took much longer than expeced. The DSP has software issues that took much time to debug A lot of testing and features added to the PC applications.

It is a great sucess though. SLSI is blowing away the competition with the testing feature. Before teachers would put 30 tapes in a rack of recorders. Run the language test. Label the tapes, take them home and listen to them one by one. Then write th grades. Now, highlight the students, hit test, when done take the laptop home. The run the test app, click on a student, listen and assign a grade. When done export all the grades to an Exel spreadsheat and done. Saves hours of work.

They can even export the audio to MP3 and burn them on a CD to send to State certification.

Return to main pageBack to Project list Project 11