On Sun, 2 Mar 2014, John Kasunich wrote: > Date: Sun, 02 Mar 2014 19:39:35 -0500 > From: John Kasunich <jmkasun...@fastmail.fm> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] This sparkfun opto kit, > 2 channel. Question re led polarities. > > >> On Sunday 02 March 2014 18:12:42 Peter C. Wallace did opine: >> >>> On Sun, 2 Mar 2014, Gene Heskett wrote: > >>>>> If you have a 5V push-pull output, another way would be to connect >>>>> this output to Cathode1 and Anode2 and connect Anode1 to 5V through >>>>> a resistor and Cathode2 to ground through another resistor. >>>> >>>> But the i limiting R can also be in the common signal input line I'd >>>> assume? Or will that common voltage drop eat my lunch? OTOH, >>>> resistors in 500 packs from the shack are cheap. :) >>>> >>> >>> Sure, one resistor is fine for the second method. Slight advantage of >>> two is that the LED drives can be individualy adjusted. > > Wait a minute. It sounds like you are suggesting anode 1 to +5V. > Cathode 1 to anode 2, with a resistor to the signal source. And > cathode 2 to ground. That won't work, there is a path from +5V > thru both LEDs to ground, with no current limiting resistor. That > will let the smoke out of both LEDs. > > If you are using a single ended source, you want two limiting > resistors. +5V, thru resistor 1, to anode 1. Cathode 1 to anode 2 > and input signal. Cathode 2 thru resistor to ground. > > You can put the resistors on the inside if you want: +5 V to > anode 1. Cathode 1 thru resistor to input, then another resistor > from input to anode 2. Cathode 2 to ground. But you still need > two resistors. > > If the input signal is differential, then you can hook the LEDs > back-to-back, and use a single limiting resistor. > > -- > John Kasunich > jmkasun...@fastmail.fm
Absolutely right inless you do the first scheme (2.5 vref with 2 resistors) the LEDS are not connected together (I should have drawn the second suggestion before suggesting it!) > > ------------------------------------------------------------------------------ > Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce. > With Perforce, you get hassle-free workflows. Merge that actually works. > Faster operations. Version large binaries. Built-in WAN optimization and the > freedom to use Git, Perforce or both. Make the move to Perforce. > http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce. With Perforce, you get hassle-free workflows. Merge that actually works. Faster operations. Version large binaries. Built-in WAN optimization and the freedom to use Git, Perforce or both. Make the move to Perforce. http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
