Datasheet
Audio PICtail
™
Plus Daughter Board User’s Guide
DS70297A-page 16 © 2007 Microchip Technology Inc.
2.2.12 Line Output Jack (J9)
Line out jack J9 (Ref 15) is a 3.5 mm stereo socket that can be used to connect the
output of the line output amplifier to an external power amplifier or recording
equipment.
See Figure A-4 for a complete schematic of the Line Output Amplifier.
2.2.13 Headphone Amplifier (U5)
The Headphone Amplifier (Ref 18) 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 (J4). The output of the amplifier is available at
Headphone Output Jack (J10).
Gain is controlled by the voltage levels applied through the CLK switch (S1) and VOL
UP/DN switch (S2). Each time the CLK switch is pressed, the gain increases or
decreases by 3 dB, depending on the status of the VOL UP/DN switch. If both switches
are pressed, the gain increases on the leading edge of the CLK signal. If only the CLK
switch is pressed, the gain decreases on the leading edge of the CLK signal. The gain
can be adjusted over a range of +12 dB to -33 dB in 16 discrete gain settings.
See Figure A-4 for a complete schematic of the Headphone Amplifier.
2.2.14 Headphone Amplifier Digital Volume Control
Volume is increased by pressing and releasing the CLK switch (Ref 17) while holding
down the VOL UP/DN switch (Ref 16). Volume is decreased by pressing and releasing
the CLK switch without operating the VOL UP/DN switch.
See Figure A-4 for a complete schematic of the Headphone Amplifier.
2.2.15 Headphone Output Jack (J10)
The Headphone Jack (Ref 14) is a 3.5 mm stereo connector. A 32 ohm headphone can
be connected to this socket.
See Figure A-4 for a complete schematic of the Headphone Amplifier.
2.2.16 DAC Differential Amplifier (U3:C)
The DAC Differential Amplifier (Ref 7) allows the Audio PICtail
Plus Daughter Board to
interface with the Digital-to-Analog Converter module on dsPIC33F devices. Audio
output from the DAC module is a pair of buffered differential analog signals. The DAC
Differential amplifier converts this complementary signal pair into a single-ended audio
signal for the Microphone and Line Output amplifiers.
This amplifier uses one of the four op amps (U3:C) on the MCP6024 quad op amp IC
(Ref 7). The DAC Differential Amplifier provides 0 dB gain.
See Figure A-4 for a complete schematic of the DAC Differential Amplifier.
2.2.17 Codec (U2)
The Audio PICtail
Plus Daughter Board includes an optional codec (Ref 21) that
interfaces to the DCI module (data interface) and I
2
C bus (control interface) of the
dsPIC33F device on the Explorer 16 board. It is also AC coupled to the output of the
Line/Microphone Amplifier (MIC_SIG).
The codec is a Wolfson WM8510 and uses oscillator Y1 for clocking.
See Figure A-5 for a complete schematic of the Codec.