G> How about link 8 of them serially, 8 LED * 2.2V(Vfwd) = 17.6V ;-) Peter Chong http://ww.ezxmlwizard.com "Dennis Heidner" <[log in to unmask]> wrote in message news:01c0d9ee$b691dbb0$031e82c0@bigbird... > Rich, I haven't seen the reply that Steve has made. > > The LED should have a published spec for the voltage drop (Vfwd) and "MAX" > voltage drop. The term forward is general added to indicate that the > device is wired and biased so that it should operate (light up). It will > also have a spec for the current that will flow when the device has the > correct voltage across it. We can call that Ifwd. > > Your resistor value should then be Rdrop = (17.5 - Vfwd)/Ifwd > > Or using the value that Steve provided (820 ohms). > Vfwd is typically 2 volts -- for most LED's, (higher for some laser > devices and the new super bright LED's) > > 820 = (17.5 - 2.0)/Ifwd or Ifwd = 15.5/820 = (rough) 19 milliampere's > current. > > The resistor will see about a 1/3 watt heat generation. > > > * To join/leave the list, search archives, change list settings, * * etc., please visit http://raven.utc.edu/archives/hp3000-l.html *