Specifications

CONSTRUCTION
76
At frequnecies higher than f2 (f>f2,
high end of audio range), capacitors
C2 and C3 overcome the effect of potenti-
ometer VR1. As C2 and C3 behave
as short, potentiometer VR1 has no
effect on the output response. Now, the
gain is controlled by treble potentiometer
VR2. The frequency f2, below which
treble potentiometer VR2 has no
effect on the response, is given by the
equation:
The output of this module is sent to
the final 2-watt audio power amplifier
(LM380) stage through potentiometer VR3
which is used as the volume control. The
power output of this module is fed to an 8-
ohm speaker. The
output-end audio
power amplifier is
designed to give a
gain of around 50.
One can also use
LM380 in various
other configurations
as per one’s require-
ments. Another
popular configura-
tion is the ‘bridge
configuration’—in
which two LM380s
can be used to ob-
tain larger power
output with a gain
of 300.
Parallel port
The output of the
parallel port is TTL
compatible. So, logic
level 1 is indicated
by +5V and logic
level 0 by 0V. The
current that one can
sink and source var-
ies from port to
port. Most parallel
ports can sink and
source around 12 mA.
The software assumes 0x378 (378H)
to be the base address of the parallel port
to which the device is connected. Another
possible base address is 0x278 (278H). It
is advised to modify this address of the
parallel port in the software program, af-
ter checking the device profile.
Actual-size PCB layout for audio play-
back circuit of Fig. 1 is given in Fig. 2
and its component layout in Fig. 3.
Software
The software accompanying this construc-
tion project is written in Turbo C/C++ for
DOS. It can be used to
play simple 8-bit PCM
wave files. 16-bit wave
files are converted into 8-
bit PCM data before pro-
ceeding.
Even stereo wave
files can be played; but
not the stereo way. Only
one channel is chosen.
Up to six-channel PCM
data can be read and con-
verted into mono 8-bit PCM data. This
software is accompanied with a C
T
UI-
based interface.
The wave file format is probably the
least undocumented sound format since
there are different schemes with differ-
ent number of chunks of related informa-
tion in the file. Even the chunks can be
of variable size. Therefore it is difficult to
get documentation on all available
chunks.
This software can be used only on
PCM data with data chunk. Every wave
file has some minimum chunks (see Table
II). These chunks will be present in every
wave file. Then there are other chunks
which are actually non-standard. In PCM
itself, the above chunk may be followed
either by DATA chunk or by LIST chunk
which, in turn, has lots of sub-chunks.
(Any information obtained on these
chunks by the readers may please be
shared with the authors.)
During playback, the speed with
which the processor in the PC can ex-
ecute the main loop is first studied using
a dummy loop and thus the delay is
adaptively varied with respect to the speed
Pin No. Pin No. SPP signal Direction Register
(D-type 25) (centronics) in/out
2 2 Data 0 Out Data
3 3 Data 1 Out Data
4 4 Data 2 Out Data
5 5 Data 3 Out Data
6 6 Data 4 Out Data
7 7 Data 5 Out Data
8 8 Data 6 Out Data
9 9 Data 7 Out Data
18 - 25 19-30 Ground Gnd
TABLE I
Relevant Details of Parallel Port
PARTS LIST
Semiconductors:
IC1 - DAC0808 8-bit D/A converter
IC2 - LF353 JFET input wide-band
op-amp
IC3 - LM380, 2-watt audio amplifier
Resistors (all ¼watt, ±5% carbon film, unless
stated otherwise)
R1 - 4.7-kilo-ohm
R2, R9 - 47-kilo-ohm
R3 - 1-kilo-ohm
R4-R6 - 10-kilo-ohm
R7, R8 - 39-kilo-ohm
VR1 - 100-kilo-ohm potmeter
VR2 - 470-kilo-ohm potmeter
VR3 - 50-kilo-ohm potmeter
Capacitors:
C1 - 1µF, 25V electrolytic
C2, C3 - 0.05µF ceramic disk
C4 - 0.005µF ceramic disk
C5-C7 - 2.2µF, 25V electrolytic
C8, C9 - 470µF, 25V electrolytic
Miscellaneous:
- 25-pin D connector (male)
- Loudspeaker 8-ohm, 2W
- Power supply: (a) +12V, 500mA
- (b) –12V, 100mA
- (c) +5V, 100mA
Fig. 2: Actual-size PCB layout for M-player
Fig. 3: Component layout for the PCB