Background

At The Hague University of Applied Sciences, the digital design learning line consists of three courses: first an introductory course, then Digital System Design 1, and at last Digital System Design 2. The first course learns the students the basics of digital technology, like number systems, boolean algebra, adders etc. The other two courses bring topics like designing digital systems, finite state machines and a simple microprocessor.

Each course also has multiple practical assignments, and for the students coming next year, all assignments are getting revamped. The electrical engineering department had the idea to use audio for most of the assignments, to let students get acquainted with digital technology and (simple) digital audio processing.

But, unlike the Altera DE2-70 FPGA board, the DE0 board doesn’t have any audio interface. Thus, six students have been assigned to design a nice PCB which can be put on the expansion headers of the DE0, to provide several interfaces for audio.

The Project

The goal of this project is to create a PCB which provides several audio interfaces to the FPGA board. Different connectors should be available on the board: a 6.3mm jack (Guitar), a XLR female connector (Microphone), connectors for RCA tulip plugs and a 3.5mm jack (CD players or MP3 players).

Not all incoming signals are the same, XLR often has balanced audio while the tulip and 3.5mm connectors are often used to transmit a line-level signal. All incoming signals should be pre-amplified and equally levelled, to make sure they can be mixed together.

The resulting audio signal should be converted to a digital value, and will be passed to the FPGA chip, which will probably make some calculations and adjustments on the signal, and the resulting value should be converted back to an analogue signal.

The resulting PCB should be placed on the expansion headers of the FPGA board.

Requirements

Must Have

• The PCB must have a XLR connector, to allow balanced audio to be connected, from for example a microphone.
• The PCB must have RCA tulip connectors to allow input from for example a CD player.
• The PCB must have a 3.5mm jack input to allow input from for example a MP3 player.
• The signal to convert to a digital value should be selectable by the FPGA
• The ADC resolution must be at least 8 bits.
• The resulting signal after the value has been processed by the FPGA must be converted to an analogue signal.
• The DAC resolution must be at least 12 bits.
• The ADC and DAC must be parallel accessed.

Should have

• The PCB size should not exceed 99.7x128.02mm (DE0 board size)
• The PCB should have three rotary encoders to adjust the parameters of the programmed effect in the FPGA.
• The board should handle both audio channels (stereo).
• Rotary encoders to set effect parameters.

Could have

• RS232 connection with computer to configure the effect parameters.

Block diagram