NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Heath Hezzanith question
From: Greg R_
Date: 2007 Oct 22, 21:41 -0700
From: Greg R_
Date: 2007 Oct 22, 21:41 -0700
--- "Greg R."wrote: > a current of 20 mA (0.2 A) Oops, dropped a zero from the previous post - that should obviously be 0.02 A, not 0.2. -- GregR > --- Chuck Taylor wrote: > > > Bonus question: What size resistor would I need? > > Bonus answer: It's a simple voltage divider/Ohm's Law problem. You'll > be dropping 1.3 V across the resistor (3.0 - 1.7), and a current of > 20 mA (0.2 A) through the series circuit gives a resistance of 65 ohms > if I did the math right. > > -- > GregR > > > > > Why not use an LED? Radio Shack sells a 5 mm red LED for $1.99. It > > draws 20 ma at 1.7 volts (typical). My sextant takes two penlight > > batteries (3 volts). To make this work without smoking the LED, I > > would need to solder in a resistor of the proper value in order to > > drop the voltage to 1.7 volts. But first I would have to do the > math > > to compute the proper value for the resistor. I think I'll stick > with > > the red marker. :-) > > > > Bonus question: What size resistor would I need? > > > > Cheers, > > Chuck Taylor > > 48 N > > 122 W > > > > > > > > > > > > > > > > > > > > Gary LaPook writes: > > > > > > > > Why not use this opportunity to join the 21st century and use a red > > LED > > (light emitting diode) cheap at Radio Shack, uses almost no current > > and > > lasts forever? > > > > > > > > gl > > > > > > > > > > > > Chuck Taylor wrote: > > > > > > red nail polish on the bulb or lens. > > > > > > > > I use a red felt-tip marker for coloring the bulb on my boat's > > compass. It works well. It would likely work also on a sextant > light. > > I picked up that trick from a compass repairman at a boat show. > > > > Chuck Taylor > > 48 N > > 122 W > > > > > > > > > > > > > > > > __________________________________________________ > > Do You Yahoo!? > > Tired of spam? Yahoo! Mail has the best spam protection around > > http://mail.yahoo.com > > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---