The DAR was designed on an EMAC MicroPac 535 board, which is a developement board that includes a 8051 microcontroller, onboard A/D and D/A converters, and several other components. It acts as an emulator, receiving information from a PC through the PC's RS-232 serial port. The software packages used for design were PSPICE (for hardware design), Keil uVision (for software design), and Keil tScope (for emulation on the EMAC board), and the DAR software was written completely in assembly language. Special considerations throughout the design included audio input amplification, audio output amplification, sampling frequency, playback frequency, device protection, and ease of use. The block diagram in Figure 1 shows more clearly some of the considerations necessary for this project.

Figure 1: Block Diagram of DAR (Digital Audio Recorder)

The DAR was completed with 100% success and was followed by a presentation observed by the instructor and the other members of that lab section. Some noteworthy features of the device are listed below.

Features:

• Three push buttons
  • Record button
  • Play button
  • Stop button (effective in both record and playback modes)
  • 100% software debounced
• 2 Indicator LEDs
  • Red record LED (on when recording)
  • Green playback LED (on during playback)
• Noise cancelling back electret condenser microphone
• 50W audio amplifier (on output)
• Adjustable gain on input and output through independent potentiometers
• Adjustable sampling rate (changed in software)
• Easily expandable design for increased memory (i.e. more recording time)

Downloadables: