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input to PC parallel port

Y

yoavshe

Jan 1, 1970
0
Hi,
I've been trying to read a signal by a parallel port.
The signal is the output of a comparator LM339, by a 21k resistor
connected to 30V, and then 10k connected to ground.
The problem is - whenever I connect the parallel port - the signal dies
(0V read).
What am i doing wrong?
What should I check?
Can anyone refer me to an example circuit where data is read by a
parallel port?
Thanks!
 
L

linnix

Jan 1, 1970
0
yoavshe said:
Hi,
I've been trying to read a signal by a parallel port.
The signal is the output of a comparator LM339, by a 21k resistor
connected to 30V, and then 10k connected to ground.
The problem is - whenever I connect the parallel port - the signal dies
(0V read).
What am i doing wrong?

Not knowing the details. Here is my guess: You are comparing against
a 10V signal (21K,10K divider). So, your LM339 is at least 10V VCC,
and the output is almost 10V.
What should I check?

Check if you parallel port is still working (not smoking).
 
Y

yoavshe

Jan 1, 1970
0
linnix כתב:
yoavshe wrote:

Not knowing the details. Here is my guess: You are comparing against
a 10V signal (21K,10K divider). So, your LM339 is at least 10V VCC,
and the output is almost 10V.


Check if you parallel port is still working (not smoking).

I tried it with a 5k-25k voltage divider as well - no good. And it's
not smoking...
How do I check whether the comparator is "strong" enough to raise the
pin to '1'?
 
L

Leon

Jan 1, 1970
0
yoavshe said:
linnix כתב:

I tried it with a 5k-25k voltage divider as well - no good. And it's
not smoking...
How do I check whether the comparator is "strong" enough to raise the
pin to '1'?

Try it without the comparator, by connecting the pin to +5V and ground
and checking that you can read the values with your software. Then
check that the comparator is working by testing the output with a DVM
or scope.

Leon
 
Y

yoavshe

Jan 1, 1970
0
Try it without the comparator, by connecting the pin to +5V and ground
and checking that you can read the values with your software. Then
check that the comparator is working by testing the output with a DVM
or scope.

Leon

Without the comparator (Directly from a power source ) it reads ok,
although only from about 7V.
I was thinking maybe the 20k and 10k resistors are too large. could
this be a reason?
Thanks
 
P

petrus bitbyter

Jan 1, 1970
0
"yoavshe" <[email protected]> schreef in bericht

linnix ???:
yoavshe wrote:

Not knowing the details. Here is my guess: You are comparing against
a 10V signal (21K,10K divider). So, your LM339 is at least 10V VCC,
and the output is almost 10V.


Check if you parallel port is still working (not smoking).

\I tried it with a 5k-25k voltage divider as well - no good. And it's
\not smoking...
\How do I check whether the comparator is "strong" enough to raise the
\pin to '1'?

If you tried to push 10V onto a parallelport pin it might as well been
blown. What pin did you use anyway? What mode is the parallel port suppose
to work in? For a comprehensive treatment of PC ports see:
http://www.beyondlogic.org/
 
S

Sjouke Burry

Jan 1, 1970
0
yoavshe said:
Hi,
I've been trying to read a signal by a parallel port.
The signal is the output of a comparator LM339, by a 21k resistor
connected to 30V, and then 10k connected to ground.
The problem is - whenever I connect the parallel port - the signal dies
(0V read).
What am i doing wrong?
What should I check?
Can anyone refer me to an example circuit where data is read by a
parallel port?
Thanks!
Fisrt, you should select in your bios setup
SPP for the printer port.
thats short for Standard Parallel Port.
That ensures that the outputs and inputs
behave like standard TTL .
Then if you want some software and info to
horse around with, get laplink.zip
at
http://home.planet.nl/~burry004
Source code included.
That software uses a cable between printerports,
to send /receive computer files.
 
C

CheapscateDave

Jan 1, 1970
0
yoavshe said:
Hi,
I've been trying to read a signal by a parallel port.
The signal is the output of a comparator LM339, by a 21k resistor
connected to 30V, and then 10k connected to ground.
The problem is - whenever I connect the parallel port - the signal dies
(0V read).
What am i doing wrong?
What should I check?
Can anyone refer me to an example circuit where data is read by a
parallel port?
Thanks!

The LM339 is opencollector and requires a pull up resistor to +5 volts.

+5------2K resistor ------output of LM339 and input pin to port.

Dave
 
S

Si Ballenger

Jan 1, 1970
0
Hi,
I've been trying to read a signal by a parallel port.
The signal is the output of a comparator LM339, by a 21k resistor
connected to 30V, and then 10k connected to ground.
The problem is - whenever I connect the parallel port - the signal dies
(0V read).
What am i doing wrong?
What should I check?
Can anyone refer me to an example circuit where data is read by a
parallel port?
Thanks!

A simple setup below.

http://www.geocities.com/zoomkat/status.htm
 
L

Leon

Jan 1, 1970
0
yoavshe said:
Without the comparator (Directly from a power source ) it reads ok,
although only from about 7V.
I was thinking maybe the 20k and 10k resistors are too large. could
this be a reason?
Thanks

Looks like you have a problem with that input. It should respond to TTL
levels.

Leon
 
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