using serial or parallel port for TTL input

[[email protected]]

HI,

I would like to be able to use my PC to detect when a transistor is
high. I have found several circuit designs on how to control a
transistor from a serial or parallel port, but none for detecting the
state of transistor.

I want to build a laser beam break detector like this
:http://repairfaq.ece.drexel.edu/sam/laserexp.htm#expbbd

When the beam is broken, a transistor will be triggered and I would
like the computer to sense when the line is high.

Can this be done with a serial or parallel port?

thanks
chad

 

[[email protected]]

I would like to be able to use my PC to detect when a transistor is
high. I have found several circuit designs on how to control a
transistor from a serial or parallel port, but none for detecting the
state of transistor.

If you have a logic level signal, simplest thing is to use one of the
status bits that the printer sends to the computer. There are ways on
many parallel ports to reverse the data lines too, but you shouldn't
need to resort to that when you already have dedicated inputs.

You could alternatively use a control input on the serial port, but may
need a larger voltage swing for that (or may not - despite outputting
larger voltages, PC serial ports can often read TTL level signals fine
in low noise circumstances)

 

[Rich, Under the Affluence]

HI,

I would like to be able to use my PC to detect when a transistor is
high.

Shouldn't you give it a blood test, or urinalysis?

;-)

 

[DaveM]

HI,

I would like to be able to use my PC to detect when a transistor is
high. I have found several circuit designs on how to control a
transistor from a serial or parallel port, but none for detecting the
state of transistor.

I want to build a laser beam break detector like this
:http://repairfaq.ece.drexel.edu/sam/laserexp.htm#expbbd

When the beam is broken, a transistor will be triggered and I would
like the computer to sense when the line is high.

Can this be done with a serial or parallel port?

thanks
chad

Chad, since you're obviously a bit uneducated about controlling a parallel
port, I suggest you look at Jan Axelson's web site at www.lvr.com
Jan has several books on using the parallel and serial ports on a PC to
control external circuitry, as well as using these ports to monitor external
events. Check out the parallel port links and you'll learn a lot about
what you're trying to do. A copy of her book Parallel Port Complete will
teach you more than you ever wanted to know about the parallel port.

Cheers!!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

[[email protected]]

thanks for the link. I think I will order the book.

thanks
chad

 

[scada]

HI,

I would like to be able to use my PC to detect when a transistor is
high. I have found several circuit designs on how to control a
transistor from a serial or parallel port, but none for detecting the
state of transistor.

I want to build a laser beam break detector like this
:http://repairfaq.ece.drexel.edu/sam/laserexp.htm#expbbd

When the beam is broken, a transistor will be triggered and I would
like the computer to sense when the line is high.

Can this be done with a serial or parallel port?

thanks
chad

Yes, this can be done very easy with the parallel port. You can use any one
of the five status inputs on the connector. For example S3 (S7-S0 byte,
S0-S2 not accesable) is on pin 15. The pin is normally high. I suggest you
use an opti-isolation IC to interface the port, that way you will protect
the computer if something goes wrong in your circuit. Use an opto with an
NPN transistor output, such as the 4N28. Connect the transistor's collector
to pin 15, and the emitter to any one of the ground pins (18-25). The led
inside the opto can be connected to your monitored circuit. Now have your
software poll the port and do it's routine on the bit change.