Opto-coupler Question
Posted: Wed Apr 21, 2010 4:52 pm
Is anyone able to recommend some fast opto-couplers appropriate for relatively high speed digital signals (say 100,000 pulses/sec)?
I'm nearing completion of a project, but I've hit a hurdle; I think that I'm using the wrong opto-coupler. I have a PC communicating with a CNC lathe over the parallel port. For those who know a bit about CNC, I'm using Mach 3 on my PC, and I'm trying to build a "break-out board" (yes, one can buy breakout boards, but this is a 25 year old lathe with some oddball innards and building the board myself is a learning experience). The parallel port is 3.3V, and the output of the opto-coupler will be 5V.
I'd like to use opto-couplers to isolate the PC from any errant high voltage coming from the lathe. My circuit works provided that I take the opto-couplers out of the system, but when I put the opto-couplers into the system, the output is either full on or full off, with no pulse detection. Here's the datasheet for the ones that I'm using now:
http://www.vishay.com/docs/83638/83638.pdf
These are Vishay part number ILQ66-4 (the quad-channel IC).
My guess is that the source of the problem is that the pulses coming over the parallel port are less than 5 usec long, but this opto-coupler isn't fast enough to respond. The datasheet is vague on the response time. The only numbers that I can find (3rd page) say that the rise and fall time could be as much as 200 usec, max, and that's obviously *way* too long.
Would this work instead:
http://www.vishay.com/docs/84732/6n137vo2.pdf
or maybe
http://www.vishay.com/docs/83604/83604.pdf
Thanks,
Randall
I'm nearing completion of a project, but I've hit a hurdle; I think that I'm using the wrong opto-coupler. I have a PC communicating with a CNC lathe over the parallel port. For those who know a bit about CNC, I'm using Mach 3 on my PC, and I'm trying to build a "break-out board" (yes, one can buy breakout boards, but this is a 25 year old lathe with some oddball innards and building the board myself is a learning experience). The parallel port is 3.3V, and the output of the opto-coupler will be 5V.
I'd like to use opto-couplers to isolate the PC from any errant high voltage coming from the lathe. My circuit works provided that I take the opto-couplers out of the system, but when I put the opto-couplers into the system, the output is either full on or full off, with no pulse detection. Here's the datasheet for the ones that I'm using now:
http://www.vishay.com/docs/83638/83638.pdf
These are Vishay part number ILQ66-4 (the quad-channel IC).
My guess is that the source of the problem is that the pulses coming over the parallel port are less than 5 usec long, but this opto-coupler isn't fast enough to respond. The datasheet is vague on the response time. The only numbers that I can find (3rd page) say that the rise and fall time could be as much as 200 usec, max, and that's obviously *way* too long.
Would this work instead:
http://www.vishay.com/docs/84732/6n137vo2.pdf
or maybe
http://www.vishay.com/docs/83604/83604.pdf
Thanks,
Randall