High speed opto-coupler/buffer circuits.

[bigandy]

Good Evening all,

I was just wondering if anyone knows of any reasonably high speed opto-coupler/buffer circuits out there in DIY land? I'm looking for something that will be used as an interface between a laptop parallel port, a high speed port emulator (running at 4Mhz absolute max!) and a number of stepper and servo drives that take a pulsed input.

I want to make sure that no damage can occur to my laptop, and in the port emulator, so my first thought was to use an opto coupler of some sort. I have no experience of working with these in anything other than RC pulse speeds (50Hz), so can anyone recommend any parts that are reasonably priced and work well at speeds up to 4Mhz?

Cheers
Andy

[JohnMuchow]

Check out Texas Instruments. They have several digital isolators that go up to 150Mbps.
http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=897&uiTemplateId=NODE_STRY_PGE_T

IIIC, they're capacitive isolators but that shouldn't be any problem in your application.

John

[Hugh P]

Well 4N35's will not cut it.

A quote form the Gecko drive Yahoo group. There was a discussion about optoisolaters. These are used to isolate the drive (servo or stepper) from the controlling PC printer port. Mach 3 CNC software can put out a 45 Khz 4 axis pulse train and these work well with that system.

"I consider using the HCPL-0531 or HCPL-0630. They are a bit more expensive than the HCPL-2531 opto isolator"

Note that most new laptops have 3.3 volt output logic on their printer ports that may not drive an opto correctly. Also some new laptops do not have a true classic printer port they are now faking it with USB to parrallel printer port chip and the timing for CNC is all messed up. Some laptops video messes with the CNC timing.

I am in the final stages of a round ram 1968 Bridgeport vertical mill conversion to CNC with Mach 3 control, CNC4PC C11G breakout board and three Gecko stepper drives and 1200 oz in steppers with ball screws installed.

Watch your grounding and isolation if you use it. Check out and study "star grounding" systems aka single point or equipotential grounding.

Hugh

[kfong]

We have an opto breakout board we designed for CNC use for laptops and PC's
http://www.embeddedtronics.com/opto.html

Kin
http://www.embeddedtronics.com/

[Unterhausen]

you can look up midi circuits. I'm using the 6n139 in some reasonably high speed circuits, and it seems to work fine.