2009/10/8 Kirk Wallace <[email protected]>: > That seems risky to me because generally the LED in the opto-coupler > needs 10 to 20 milliamps to turn on well enough to switch the coupler's > output. You have three LED's to sink current for, which is 30 to 60 mA. > Generally, a parallel port pin is designed to sink or source about 3mA > (some can do much more, but which ones?). I would prefer to see the > parallel port pin connected to three inputs of a driver chip like a > 74LS244.
I did these sums last night and came to much the same conclusion. I will see what I have in the way of buffers (I definitely have some Op-Amps I can configure in voltage-follower mode, but I will see what the 74LS255 is) When I wired up the drives last year I was thinking very much in terms of TTL logic, +5 =1 0V = 0, not in terms of opto-isolators, source and drain currents etc. In the meantime I have built a few opto-isolated interface boards and have a better feel for the subject, but hadn't really realised until last night that I need to revisit my original wiring scheme. It was working, but on reflection I have no idea how. -- atp ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
