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Adding a manual/computer control toggle; optoisolator help

D

davidd31415

Jan 1, 1970
0
Hi,

I have a circuit that controls several motors and lights (all 12VDC, 2A
max) through push buttons and switches. I'd like to expand the circuit
to allow for computer control through a rs232c parallel port.

What should I be concerned about with the parallel port/opto isolator
(input resistances, maximum currents, etc). Since I am controlling
motors would it be least expensive to use low-current opto isolators to
energize relays? If someone has knowledge of (or a site that
discusses) the most significant details of wiring up a circuit such as
this, I'd appreciate a few pointers; identification of the various opto
isolator variables would be helpful too ('If' for example).

I am also looking for a way to implement the "manual/automatic" mode
switching. I'll need a total of 10-15 relays if I add one in for each
button/switch, so suggestions on a simpler method to implement this
would be helpful.

Thanks

David.

E

Eric R Snow

Jan 1, 1970
0
Hi,

I have a circuit that controls several motors and lights (all 12VDC, 2A
max) through push buttons and switches. I'd like to expand the circuit
to allow for computer control through a rs232c parallel port.

What should I be concerned about with the parallel port/opto isolator
(input resistances, maximum currents, etc). Since I am controlling
motors would it be least expensive to use low-current opto isolators to
energize relays? If someone has knowledge of (or a site that
discusses) the most significant details of wiring up a circuit such as
this, I'd appreciate a few pointers; identification of the various opto
isolator variables would be helpful too ('If' for example).

I am also looking for a way to implement the "manual/automatic" mode
switching. I'll need a total of 10-15 relays if I add one in for each
button/switch, so suggestions on a simpler method to implement this
would be helpful.

Thanks

David.
Looking through the Jameco catalog results in finding part #174449CF
which is a 5 volt/125 ohm coil relay with 24 volt/2 amp contacts.
$1.79 each. The relay draws 40 milliamps at 5 volts. I don't know if the computer can supply this current but I think it can. ERS R Rich Grise Jan 1, 1970 0 Looking through the Jameco catalog results in finding part #174449CF which is a 5 volt/125 ohm coil relay with 24 volt/2 amp contacts.$1.79 each. The relay draws 40 milliamps at 5 volts. I don't know if
the computer can supply this current but I think it can.
ERS

Not the parallel port. But you can still get ULN2803s to drive relays
with, and that's a darlington input, so the parallel port would
drive it easily.

Oh, and just FYI, rs232c is the protocol on the serial port. It and
the parallel port are very different things.

Good Luck!
Rich

B

Bob Monsen

Jan 1, 1970
0
davidd31415 said:
Hi,

I have a circuit that controls several motors and lights (all 12VDC, 2A
max) through push buttons and switches. I'd like to expand the circuit
to allow for computer control through a rs232c parallel port.

What should I be concerned about with the parallel port/opto isolator
(input resistances, maximum currents, etc). Since I am controlling
motors would it be least expensive to use low-current opto isolators to
energize relays? If someone has knowledge of (or a site that
discusses) the most significant details of wiring up a circuit such as
this, I'd appreciate a few pointers; identification of the various opto
isolator variables would be helpful too ('If' for example).

I am also looking for a way to implement the "manual/automatic" mode
switching. I'll need a total of 10-15 relays if I add one in for each
button/switch, so suggestions on a simpler method to implement this
would be helpful.

Thanks

David.

This will be much easier with a parallel port. The serial port is
designed to talk RS232, and uses strange voltage levels.

If you are really using the RS232 port, you can use a chip like a MAX232
to interface with the computer.

http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf

It takes +5V, and generates the odd voltages required.

Now, your serial port will want to talk async, so you'll need a uart
chip of some kind to handle all the RS232 protocolish stuff. Programming
a uart isn't trivial, so you will want to use a microcontroller or
something like that. Some PICs have built-in uarts, so using one of
those would give you a lower chip count.

Yet another way to go would be to use a pre-built USB interface module,
like these:

http://www.futurlec.com/USB.shtml

The bottom one has up to 24 I/O points, which you can undoubtedly
program arbitrarily.

--
Regards,
Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877

D

davidd31415

Jan 1, 1970
0
Bob said:
This will be much easier with a parallel port. The serial port is
designed to talk RS232, and uses strange voltage levels.

If you are really using the RS232 port, you can use a chip like a MAX232
to interface with the computer.

http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf

It takes +5V, and generates the odd voltages required.

Now, your serial port will want to talk async, so you'll need a uart
chip of some kind to handle all the RS232 protocolish stuff. Programming
a uart isn't trivial, so you will want to use a microcontroller or
something like that. Some PICs have built-in uarts, so using one of
those would give you a lower chip count.

Yet another way to go would be to use a pre-built USB interface module,
like these:

http://www.futurlec.com/USB.shtml

The bottom one has up to 24 I/O points, which you can undoubtedly
program arbitrarily.

--
Regards,
Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877

I'll probably end up going parallel with this instead of RS232; sorry
for the confusion in the OP. Are there certain optoisolator
specifications I should look out for and is it as simple as just
putting the optoisolator in line with the parallel port output or do I
need a resistor (or other component) in there as well?

R

Rich Grise

Jan 1, 1970
0
....
I'll probably end up going parallel with this instead of RS232; sorry
for the confusion in the OP. Are there certain optoisolator
specifications I should look out for and is it as simple as just
putting the optoisolator in line with the parallel port output or do I
need a resistor (or other component) in there as well?

http://www.google.com/search?q=pc+parallel+port+interface

Have Fun!
Rich

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