Design Center:

Hard Disk Audio Player

With the growing market for digital audio players and the availability of inexpensive mass storage devices, high-capacity digital audio devices are appearing in the consumer market. Using the DataBridge™ IC, a hard disk or CompactFlash card, a digital-to-analog converter, and user interface components, an inexpensive digital audio player can be designed quickly.

Audio Player Circuit Block Diagram

Figure 1. Digital Audio Player.

Implementation

Figure 1 shows a block diagram of a digital audio player circuit. The AI2002A (DataBridge IC) communicates with any ATA or ATAPI hard drive, CompactFlash card, or PCMCIA disk, managing all aspects of low-level disk communication and DOS/Windows® file compatibility and communicating with the host microcontroller via a 3-wire serial bus.

The audio player's microcontroller provides simple application-specific services, such as user interface (buttons, LED's, display) and relaying uncompressed digital audio data from the AI2002A to the stereo DAC (the ADI1857 in this example), which converts the data to analog signals at line level.

Because the AI2002A provides high-level access to PC-compatible files, this circuit can be built using a small 8-bit microcontroller. No RTOS (real-time operating system), single-board computer, or custom code is necessary.

Benefits

The circuit shown in figure 1 provides the end-user with high-capacity, CD-quality audio at an affordable price. A commonly-available 20 GB hard disk holds 30 to 40 full CD's and an inexpensive 60 GB hard disk holds 90-120 CD's!

Hard Disk Capacity

20 GB:

30-40 CD's

60 GB:

90-120 CD's

(1 CD = 500-660 MB)

Because the circuit employs a commodity mass storage device, the user can customize and overwrite previous playlists. Standard mass storage devices also allow the user instant access to audio tracks without waiting to switch CD's, or even program custom track transitions (e.g. fade-in, fade-out).

Design Ideas

When used with FLASH data storage (or even a laptop hard disk), this circuit's low power consumption makes it suitable for battery-operated operation. A microcontroller capable of directly-driving a custom LCD display can be used to minimize costs. For applications that require it, several MP3 decoder IC's are available and can be inserted between the microcontroller and DAC.

Windows® is a registered trademark of Microsoft Corp.

ADI1857 is a trademark of Analog Devices Inc.

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