On Tuesday, March 27, 2012 07:07:43 AM Kirk Wallace did opine: > On Tue, 2012-03-27 at 01:46 -0400, gene heskett wrote: > > What do we normally assume to be the fwd drop of the usual LED, I > > assume IR, opto-isolated input? > > > > Setting up stuff for the 2M542's target 10 ma thru its input opto's, I > > come up with about 360 ohms for the current limiter R when the 5 > > volts is 5.27, and the diode drop is nominally 1.6 volts. > > > > My old meter seems to have taken a hit, and my new one doesn't have > > the beans to measure a diode with more than about .85 volts for its > > band gap, so the diodes in the 2M542 are measuring either .75 volts > > if reverse biased, or open when conventional 'led' bias polarity is > > applied. To say I am a bit disappointed is an understatement, it is > > a $120 meter with all sorts of bells and whistles! > > > > Thanks guys. > > > > Cheers, Gene > > The manual I found here: > http://www.scribd.com/doc/47247471/2M542-Manual > Thanks Kirk.
> says at the bottom of page 6, that 5 Volts can be applied to the inputs > without a limit resistor, unless I'm missing something. Maybe there is > already a limit resistor inside. I suppose I'd just add a resistor and > guess at a conservative limit resistance, measure the voltage across the > resistor to see what kind of current is is going through it when the > signal is On. Then reduce the resistance until you get your 10ma. But > that's just me. I can set the voltage from that LM317-T down some, 5.29 volts ATM. Looks as it it should be happy without any limiters if I set it down to 4.9 or so. I have a copy of that printed out in the mills binders and I don't recall seeing that note about the 270 ohm builtins before, so either it has been added or I forgot. In the mills setup, I believe I used 180 ohms which still gave over 10 mills. It seems to be happy. I hesitated to check with this new meter since its 5+ seconds settling time is more than long enough to kill something if its too high. 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) My web page: <http://coyoteden.dyndns-free.com:85/gene> The best portion of a good man's life, his little, nameless, unremembered acts of kindness and love. -- Wordsworth ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
