User`s guide

MPLAB Starter Kit for dsPIC

DSCs User’s Guide

4.3.2.4 PWM LOW PASS FILTER (U8:A,B)

The PWM signal from the Output Compare module on the dsPIC33F device on the

board is demodulated by the PWM low-pass filter (Ref A4). This fourth-order filter uses

two op-amps (U8:A and U8:B) on the MCP6022 quad op-amp IC.

4.3.2.5 OUTPUT SELECT JUMPER (J6)

The Output Select Jumper (Ref A5) determines whether the input signal for the

Headphone Amplifiers comes from the PWM filter or the audio codec. Default setting

is CODEC.

4.3.2.6 CODEC (U9)

The starter kit includes an audio codec (Ref A6) that interfaces to the DCI module (data

interface) and I

C bus (control interface) of the dsPIC33F device. It is AC coupled to

the output of the Line/Microphone Amplifier (MIC2).

The codec is a Wolfson WM8510 and uses a 12 MHz clock signal generated by U2 for

clocking.

4.3.2.7 HEADPHONE AMPLIFIER (U11)

The Headphone Amplifier (Ref A7) is a National Semiconductor LM4811 70-mW stereo

amplifier with digital volume control. The input to the amplifier is controlled by the

setting of Output Select Jumper J6. The output of the amplifier is available at

Headphone stereo jack (J8).

Gain is controlled by the logic levels applied through the device I/O ports to the CLK

and UP/DN pins of U11. Each time the CLK line goes logic high, the gain increases or

decreases by 3 dB, depending on the logic level of UP/DN line. The gain can be

adjusted over a range of +12 db to -33 db in 16 discrete gain settings.

4.3.2.8 LINE/MICROPHONE INPUT SELECT JUMPER (J7)

The Line/Microphone Input Select jumper (Ref A8) determines if the Microphone/Line

Pre-Amplifier (U10-A) operates as a line amplifier or a microphone amplifier. If the MIC

option is selected, a bias voltage of +3.3V is applied to the Microphone/Line Input

Socket (J9). Default setting is MIC.

4.3.2.9 HEADPHONE OUTPUT JACK (J8)

The Headphone jack (Ref A9) is a 3.5 mm stereo connector. A 32-ohm headphone can

be connected to this socket.

4.3.2.10 LINE/MICROPHONE INPUT PHONE JACK (J9)

The Line/Microphone Input (Ref A10) is a 3.5 mm mono input phone jack (SJ3504).

This connection accepts either a condenser microphone or a line level signal.

4.3.2.11 USER LEDS (D3,D4 AND D5)

The starter kit features three general purpose LEDs which are connected to the I/O

ports on the dsPIC33F device. The user application can use these LEDs for indication

purposes.