On Sunday 02 March 2014 17:21:41 Peter C. Wallace did opine: > On Sun, 2 Mar 2014, Gene Heskett wrote: > > Date: Sun, 2 Mar 2014 16:10:23 -0500 > > From: Gene Heskett <[email protected]> > > Reply-To: "Enhanced Machine Controller (EMC)" > > > > <[email protected]> > > > > To: "Enhanced Machine Controller (EMC)" > > <[email protected]> Subject: [Emc-users] This sparkfun > > opto kit, > > > > 2 channel. Question re led polarities. > > > > Greetings; > > > > leds are something I'll have to plead less than a full understanding > > of. > > > > So, if I connect these 2 channels of this sparkfun kit such that the > > anode of one is connected to the cathode of the other, effectively > > placing them in parallel, add a current limiter in series with the > > common of one end, do I need to also put in a reverse voltage > > protection diode, or will the one that needs to light up, will light > > up without being shorted out by the other polarity led across it? > > > > The C1G can put out sufficient currant (24 ma) but I believe its > > programming jumpers cannot allow both polarities, its a one or the > > other deal per data line, so I'll have to invert the signal to get > > the opposite drive external to the C1G, but that doesn't seem to be a > > show stopper. > > > > The idea is to have the 2 optos outputs in totem pole for a > > bidirectional drive +12 volts or 0 volts, both active on an exclusive > > basis into the Gemini controller. > > > > The question is, do I need to polarity protect the leds in the opto > > package? The pdf I downloaded on the opto package is less that > > informative on this particular detail. > > > > Cheers, Gene > > > > NOTICE: Will pay 100 USD for an HP-4815A defective but > > complete probe assembly. > > Back to back LEDs should work fine (usually they have a 5V max reverse > voltage spec and about 1.1V forward drop so one protects the other. but > back to back LEDs need a bipolar source (say 2 equal resistors for a > 2.5V reference/current limit and a push pull 5V output) > > > 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. > Thanks Peter, that will solve the single ended signal source problem too at the cost of another conductor from the 5 volts in the C1G.
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. :) Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> NOTICE: Will pay 100 USD for an HP-4815A defective but complete probe assembly. ------------------------------------------------------------------------------ Flow-based real-time traffic analytics software. Cisco certified tool. Monitor traffic, SLAs, QoS, Medianet, WAAS etc. with NetFlow Analyzer Customize your own dashboards, set traffic alerts and generate reports. Network behavioral analysis & security monitoring. All-in-one tool. http://pubads.g.doubleclick.net/gampad/clk?id=126839071&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
