OrCAD Schematics and Layout Files

Main Schematic (GIF) (OrCAD)

This schematic contains most of the functionality of the eRaj board. U6 is a temperature compensated crystal oscillator with an output frequency of 32.768 KHz (Dallas Semiconductor - DS32KHz). This chip drives the X1 input of the eRaj's real time clock. U5 is a serial alarm real time clock also made by Dallas Semiconductor (DS1305). This IC can be programmed with two alarm times and serves as the timekeeper of the MP3 clock. It communicates with the microcontroller via the standard 3-wire interface.

U7 is the 1 line x 16 character LCD panel with LED backlit capabilities controlled by a momentary pushbutton. This Hantronix part (HDM16116L-7-L30F) contains a standard embedded Hitachi display controller (HD44780).

U3 is the 24LC08B 8K Serial EEPROM made by Microchip. This EEPROM is used to store the microcontroller firmware and the initialization data for the MP3 decoder. The EEPROM also needed in autobooting the microcontroller upon power-on.

U12 is a standard RS-232 transceiver (Maxim MAX3232E) used to implement a serial port for board debugging. The J4 2x3 jumper block is used to redirect two programmable i/o pins for serial port communication.

U2 is the SmartMedia socket made by Yamaichi (CN015R-3013-0). This part connects to the 22-pin SmartMedia card to the PCB traces on the eRaj board.

U8, the heart of the eRaj board, is the Cypress ZEUS (AN2131QC) which contains an enhanced Intel 8051 microcontroller with a built-in USB engine. All three 8-pin ports of the controller are used to connect to: (1) SmartMedia memory (2) LCD display (3) real time clock (3) mp3 audio subsystem. Implementing the I2C communication standard, the EZ-USB connects to the 8K firmware EEPROM, the I/O Expander and the MP3 decoder.

U11 contains six Schmitt triggers (TI SN74LVC14APWR) used to implement the reset circuitry for the microcontroller. U14 is a dual USB Transient Suppressor (TI SN75240) which is required for reliable USB communication between computer host and USB device. J6 is a jumper switch used to modify the disconnection behavior of the microcontroller on reset. J9 is the USB B-connector.

Audio Schematic (GIF) (OrCAD)

The audio schematic of the MP3 Alarm Clock contains the components necessary to transform the data bits of an MP3 file into a monaural, amplified audio signal. The first step in this process is to pass the MP3 file data through ST Microelectronics' STA013 MP3 decoder. When this decoder requests input data, the microcontroller (offpage) clocks data into it. The decoder outputs digital audio data in the I2S format. The STA013 also sits on the I2C bus so that it can receive certain configuration instructions such as volume control.

The CS4331 DAC then takes this I2S information and converts it into two audio signals (left and right channels). Of course, these signals still need to be amplified. To accomplish this, the DAC delivers its output to the TPA0253 audio power amplifier. This amplifier has the added function of summing the left and right channels to produce a monaural signal that can drive our loudspeaker.

As there are both digital and analog components on this section of the board, a dotted line in the schematics represents what should be implemented as a separate analog power plane and a separate ground plane.

Power Schematic (GIF) (OrCAD)

The power section of the chip is more complicated than one would expect because of our stated goal of powering through both a wall adapter and a battery. This allows the clock to be portable if necessary, but adds complexity to the logic needed to control the power source. Luckily, Maxim has a dual-output step-down converter with battery switchover. This model, the MAX1774 (U14), uses an external P-MOSFET (Q6) to control the connection between the battery source and the input to the chip. If a wall adapter is powering the chip, pin 4 connects to the base of the P-MOSFET and disconnects the battery supply from the main power input.

In either case, the chip provides the necessary 5V and 3.3V outputs for the board; these output voltages are set by using a simple voltage divider (R52 and R53, R57 and R59). Furthermore, it can handle up to 1.5A of current draw because an external half-bridge MOSFET (Q5) is used.

Note that there are LEDs which indicate whether the 5V and 3.3V sections are powered, and these lines are also sent through jumpers in case there is a problem with this subsection. If this occurs, a power supply can be hooked up to the jumpers to power the system for debugging.

Button Interface Schematic (GIF) (OrCAD)

This schematic contains one Philips I/O Expander (PCF8574TD), six Panasonic momentary pushbuttons (EVQ-PAC04M), one CW Industries DP3T slider (SW119-ND) and a set of discrete resistors and capacitors. The Philips I/O Expander provides remote I/O expansion for the EZ-USB microcontroller. Six pushbuttons and one slider with two positions (the third position is not used) connect to the i/o expander. When the value of one of the buttons changes, the i/o expander signals the microcontroller via an interrupt pin (BUT_INT).

Board Layout File (GIF) (OrCAD)

Board Gerber Files (ZIP)

General Directories:

sch

lib

board