Hi!
Here is a circuit scheme for a parallel port DAC converter.
I don't remember where I got it from and I haven't tested it but
I think it should work. I have a very similar one which was sold
at the newsagents for 2 quids together with the first number
of a multimedia language course.
Bye,
Arne
P.S: I hope the circuits are understandable, I had to convert them
from the PC grafics charset to normal ASCII...
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This is the most basic D/A converter. Just a bunch of resistors.
So that's about compatibility. It is commonly known as COVOX,
tough COVOX is really a DAC&ADC card, but as D/A converter is
configured to printer port addresses, simple resistor network
can do the job.
This is schematics to build the COVOX compatible D/A converter
into printer port. It's using the well-known R-2R ladder method
to convert TTL outputs into analog signal. Resistor values are
not important, any pair will actually do as long as one is two
times less than another. However, with 15k and 7.5k the output
voltage is just right to feed into audio equipment for amplifying.
Filtering is a problem due the power requirements of active
filters, but my experiments have shown, that a simple capacitor
will do the job good enough. Electrolytic capacitor is not a must,
but you may add it if you're afraid for you HiFi equipment.
In such case don't forget the resistor after capacitor.
( I'm using this converter without these two and works fine ).
On faster AT computer clones I've encountered unfilterable
noise in printer port, it's probably caused by fast transitions
on motherboard. In such case put the wire 4-5 times through small
ferro ring.
All resistors will easily fit into D25 socket, so if you have
cable with socket which can be opened you can build this
converter parallel to your printer and leave the printer attached.
PRINTER PORT
-----, + - ANALOG OUT
| 15k ,---------------------+-||-----, ,------->
9 |--#####--+--#####-,7.5k | 5.0F | |
| 15k ,--------' | ###<-'
8 |--#####--+--#####-,7.5k === ###
| 15k ,--------' | 4700pF | 100K
7 |--#####--+--#####-,7.5k | |
| 15k ,--------' _|_ _|_
6 |--#####--+--#####-,7.5k
| 15k ,--------'
5 |--#####--+--#####-,7.5k
| 15k ,--------'
4 |--#####--+--#####-,7.5k
| 15k ,--------'
3 |--#####--+--#####-,7.5k
| 15k |
2 |--#####---+-------'
| ###
| ###15k
18 |----------|--------------------------------------> GND
-----' _|_
AdLib is based on single chip called FM Operator Type-LII
(OPLII). OPLII is capable of voicing 9 FM sounds or 6 melody
sounds plus 5 rhythm sounds.
SoundBlaster has additional C/MS music chip (12 voices)
and DAC/ADC subsystem.
DAC can do DMA transfers.
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| Arne Di Russo Internet..: [EMAIL PROTECTED] (changes after 14/1/95) |
| Rome, Italy Fidonet...: 2:335/311.55 and 2:335/21.55 |
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| Computer Science student at "La Sapienza" University, Rome, Italy |
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