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 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. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
