optoisolator input -> PC

Discussion in 'Electronic Basics' started by shmoppy, Sep 24, 2003.

1. shmoppyGuest

Hello, I'm very new to electronics so I thought this would be a good
place to ask some "basic" questions about a circuit I'm trying to
design.

I have 15 12v bulbs in my car that come on at different times (check
engine, low coolant, low oil, service ABS, etc). I would like to
replace these bulbs with 15 optoisolators that will output a logical 1
or 0 to a PC based on whether or not the "bulb" is hot. Then the PC's
software would display an ON/OFF status for each of the 15
optoisolators. This being my first ever project, I've got plenty of
questions about how to do this. to start:

- is there anything I can read or reference that would help in
learning how to do this?

- would serial or parallel be better to get the data into the PC.
would I use a 16 bit number to represent the 15 inputs? ('0100 0000
0010 0110' means bulb 2, 3, 6 & 15 are "on". 16th bit is not used.)

- what components will I need to do this?

any info is GREATLY appreciated. I'm excited to get started, but don't
really know where!

2. Robert MonsenGuest

Yes, go buy a book like "Practical Electronics for Inventors" by Sherz.
Fairly straightforward with no real math to speak of. Better, but a bit
outdated is "The Art of Electronics" by Horowitz and Hill. This one is
harder, but better for those wishing to get exact results.
There is a great page on interfacing to the parallel port here:

http://www.doc.ic.ac.uk/~ih/doc/par/

Somebody just posted it here recently, and its fairly helpful.
Look at some circuits that use the parallel port to interface to external
sensors. They will give you some idea.

3. shmoppyGuest

thanks for the reply and info Robert! I'm starting to get a better
idea of how to do this. I've still got a couple more questions:

1) there are at least two dozen optoisolators to choose from. will
just a plain jane 4N32 work ok for this?

2) how can I get the 15 separate optoisolator outputs into one 16 bit
number that my software will handle?

3) will I need an ADC or can the serial/parallel port already
understand the output from the optoisolators.

thanks!

4. Robert MonsenGuest

You can simply use the bits directly, yes?
I don't think you'll need an ADC. If the 12V wires power the optoisolator,
(through a resistor, choose the resistor to limit the current to whatever
the datasheet recommends) the optoisolator can be used to signal a high to
the PC through the parallel port.

Regards,
Bob Monsen

5. shmoppyGuest

ok good, no need for an ADC. the simpler the better I don't think
I'll be able to tie the output bits from optoisolator directly to the
parallel port because I am going to need 15 different inputs. It's my
understanding that the parallel port only has 9 inputs. This is why I
was thinking I'll need to consolidate those 15 separate 1 bit inputs
into a single 16 bit number. I'm only guessing that's how to do it,
and it's not a very educated guess at that So I'm open to
suggestions of how to get the 15 optoisolator outputs into the PC.

thanks very much for all your help so far!

6. Robert MonsenGuest

Look at

http://www.geocities.com/killedbyvb/

you'll need to write some software to select a register. Circuit posted on
alt.binaries.electronics.schematics.