Fred,
Just a tip from experience; initially I had the same idea as you about
using the shoot bolt to complete a circuit to warn you of any doors
open. I found that after a few weeks' use, oxidisation, lubricant, dirt
or whatever makes the contact very poor quality - after a month it was
useless, intermittently reading infinity or several Megohms. Eventually
I had to install a micro switch operated by the full travel of the shoot
bolt in its socket - but you have to be careful not to end up with too
much pressure on the end of the shoot bolt.
This was just my experience - you may have more luck but the shoot bolt
remains a dodgy proposition in my view!
Not sure about your abuse of transistors though!!
Best Regards
Roger Mills
-----Original Message-----
From: forum-owner@europaclub.org.uk
Subject: Re: LEDs
Hi, Troy -
LEDology simple for autos and planes, as you can assume the extra volts
when the alternator is working equals the forward voltage of the LED.
Divide 12 volts, not 13.75V, by .020 (typical current figger), and
that's a 620 ohm, 1/2 watt resistor.
Some LEDs have internal dropping "resistor," and your "12 volt rating"
sounds like just that, and they should take 13.75. No drop resistor,
but I have some suggestions that can deny their use.
Another factor is viewing angle. Too wide are dimmish. Too narrow can
be annoying, esp with clear lens, or miss the warning cue. Color, too,
in sunlight, and there's whites and blues nowadays. LEDs are so cheap,
for sunlight use, I buy an assortment and make them show me something
outside. And there's .4" square, white diffused lens jobs that can be
black-letter, clear-labeled on the face. Real cool are LEDs with
built-in flasher chip.
Alt warning lite may be a problem, as its operation may depend upon the
low resistance of the incandescent lamp (Tony, Rotax Dealer?). Wouldn't
bet what an LED will do when the "L" line goes low on all faults, thus
requiring a 10# sledge hammer to fully test. Safer bet is an NPN
transistor circuit, reverse biased to off at the emitter when that line
is high, like when alternator is OK, equivalent lamp resistance emitter
to ground, unfortunately wasting c. 1/4 amp. LED/dropper in collector.
Further details on request.
For door ajar, you can pop-rivet springy tangs or coils, out of a
battery compartment from junk electronic stuff, to contact each shoot
bolt, wired in series from through the internal metal of bolt
mechanisms, port to starboard, to a ground. You'll need an NPN
transistor circuit to sense an open:
Tie base and collector together to really annoy the transistor. 14V
through LED dropping resistor to base-collector. LED from emitter to
ground. Base-collector to the shoot bolt circuit open end. It's an
unswitch - when shoot bolt switch turned on, grounding base, it doesn't
do anything. The triple-duty resistor also limits current flowing
through exposed door hardware and minimizes effect of dirt/grease on the
shoot bolts.
Further, seems you can take the ground from the shoot bolt circuit
through a lever-type microswitch in the throttle housing, affixed to
close at above runup throttle position. No door alert until plane
thinks you're taking off; could even quick-nudge the throttle in runup
to check the doors. But that could make you insufferable at a fly-in,
showing off features like that.
For oil press, there are oil pressure switches like to fire up a Hobbs
meter. But you don't want to plumb a tee in the Rotax oil pressure
sender, a potential engine failure looking for a time to happen. To
electrically tap the Rotax sender, your oil pressure gauge circuit would
have to see at least .7V there, at alert PSI, and an add-on transistor
circuit must not load or bias it so as to cause inaccurate gauge
reading. A more complex IC comparator circuit may be the only
way.
For "master on," an LED always on, off when shutting down, is not a good
alert. I'd try to invert the logic, with flashing LED (or see below),
by grounding LED circuit through again the "L" thing on the alt reg. It
looks good on paper, and would alert only between engine and master off.
For vital warnings, there's also "Sonalert" type devices. Whistles,
warbles, buzzers, chimes, sirens, and up to enough decibels to cause
soiling of the shorts. We go to power transistors where needed then,
due to current.
Best,
Fred F.
TroyMaynor@aol.com wrote:
>
> Hi Gang,
> I have searched but can't find it in the archive. Someone mentioned
> the 12v 3w lamp that is the alternator warning lamp being changed to
> an LED and that you had to add a resistor, I think, to make the
> regulator function correctly. Does anyone know what will work for sure
> on this? I have some nice LEDs that are 12 volt rated that I want to
> use. In fact I want to make a series of 5 or 6 warning LEDs on a
> little panel to operate at the correct intensity with a 12 volt input
> to each. I am planning to use one for oil press./master on; one for
> alternator; one for door ajar; one for engine monitor; and starter
> engaged. The alternator one is the one I was concerned about. Is this
> no big deal to do? I am electronically challenged. Please help if you
> can. Best Regards,
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