
	Sound Digititizer for IBM PC and compatibles

You are free to copy this packet as long as it stays unmodified.
Personal use is allowed.
Commercial use of the circuit diagrams is forbidden without written permission
from both of the authors. It is also forbidden to commercially use anything
else in this packet.
You are allowed to copy parts of the software to your program as long the
pograms are Public Domain.

DISCLAIMER

I take no responsibility for this infomation contained here.
I don't consider myself as responsible for any damage caused to your
equipment/yourself or anyone/anything else by using the information, drawings
or programs contained in this packet.

The files contained in this packet:

SD0809.GIF	Original circuit diagram for Amiga digitizer. The picture
		was originally in Amiga IFF-format.

AD-CONV.GIF	Circuit diagram for PC digitizer. It is a modified and
		enhanced version of SD0809.

PREAMP.GIF	Preamlifier stages for above circuir diagram.

DA-CONV.GIF	A simple D/A-converter to Cetronics printer port. This
		design is found to be compatible with Covox Speech Thing.

README.TXT	This text file.

LUEMINUT.TXT	Same text file in Finnish.

DIGITIZE.PAS	Pascal source for Turbo Pascal 5.0. This program digitizes
		a short sound and plays it back through D/A-converter.

SCOPE.PAS	Pascal source for Turbo Pascal 5.0. This program makes your
		computer screen look like oscilloscope. EGA display
		is needed.

TESTER.PAS	A simple testing and alligning program. It simply prints
		the results of A/D-conversions to computer screen. The
		program stops when you press any key.

TESTER.EXE	Executable version of above program. This program assumes that
		you have your digitizer in LPT1 port.


The digitizer is capable to take about 15 000 samples per second when the
switch in the circuit diagram is left open. The maxium sample rate in about
22 000 samples per second when the switch is closed. Some disortion is caused
in the sampling process because ADC0809 was originally designed for maxium
sample rate of 10 000 samples per second.
It is a good idea to fit the circuit into a metal enclose to pervent possible
radio interference caused by high frequency clock oscillator in the circuit.
The leads from the oscillator to the switch should be as short as possible.
Connect the circuit only to bidirectional Centronics port. Original
IBM PCs, ATs and nearly all compatibles have bidirectional Centronics port.
(I have heard some rumous that some portables have unidirectional Centronics
port. If you connect this device to that kind of port, it does not work at all.
It may even damage the port.)

You should allign your digitizer to give values 127 or 128 when no signal is
fed into the digitizer analogue input. You can use TESTER program to do this.
It is also possible to use SCOPE. The red point in the left side of the screen
shows the right value.

D/A converter is very simple and inexpensive. The values shown in the circuit
diagram are not the exact ones (they are the nearest E96 values).
The exact resistor values are:
R1=640kOhm, R2=320kOhm, R3=160kOhm, R4=80kOhm, R5=40kOhm, R6=20kOhm, R7=10kOhm,
R8=5kOhm
Connect the circuit to your stereo system and enjoy the sounds. The output
has signal level of about 0.2V and is suitable to connect directly into
LINE IN socket.
It is a good idea to build this D/A converter in the way that it can be used
with other equipments connected after it. So it should have a through
connector. I have build my D/A converter into a small RS jumper box, which
is connected between the computer and the printer cable. I never have to
remove it because it does not interfere with any equipment conncted to
Centronics port.

The connector pin numbering in the circuit diagrams is drawn according to
Centronics printer port connector in the back of an IBM PC or compatible.
So use use D-25 connector and connect your digitizer directly to your
computer.
It is possible to use the digitizer only in bidirectional Centronics ports.
Nearly all Centronics ports in PCs and compatibles are bidirectional, but
there are some exceptions to this rule. If you connect this digitizer to an
unidirectional Centronics port, the Centronics port may damage permanently.


I hope that this digitizer type will become popular. I have suggested that
every succeeding digitizer shoud be compatible with this one. I have named
my suggestion as PPD-1 standard. It stand for PC Parallel Port Digitizer 1.
More precise information about this standard should be available soon.


If you have any suggestions how to improve this circuit or anything else
related to the information given in this packet, let me know.

	Tomi Engdahl
	Kalliomentie 8bF
	01800 Klaukkala, Finland

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