Today's Message Index:
----------------------
1. 05:55 AM - Re: warning lights for engine T&Ps (Eric M. Jones)
2. 06:19 AM - Re: Half failed LEDs (Robert L. Nuckolls, III)
3. 06:39 AM - Re: warning lights for engine T&Ps (Robert L. Nuckolls, III)
4. 08:35 AM - Re: Half failed LEDs (rayj)
5. 03:03 PM - Re: Half failed LEDs (Robert L. Nuckolls, III)
6. 03:47 PM - Re: Half failed LEDs (rayj)
Message 1
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| Subject: | Re: warning lights for engine T&Ps |
> Before I embark on this though I thought I'd
> check if there is already an established way of doing this?
> Sacha
Sacha,
There is a common op amp circuit called a "window discriminator" that is used to
do this. It is easy to set this up for many variable input voltages or currents.
National Semiconductor publishes online collections of op amp circuits which
is a good place to start.
ps When red and green are mixed, yellow is the visible result...although some color
deficient people might have an issue with this.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=422234#422234
Message 2
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| Subject: | Re: Half failed LEDs |
At 07:09 AM 4/21/2014, you wrote:
>
>I just removed about 8 blue LEDs from a string of lights that no
>longer emitted light, but still have continuity. If any one wants
>them to investigate, I'll mail them out.
When you measure them with an ohmmeter, do they
show the same or similar resistance for either
polarity of the test leads?
Bob . . .
Message 3
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| Subject: | Re: warning lights for engine T&Ps |
>I am determined to do some bench tests to see whether I can make things work
>better by incorporating a 12V voltage regulator upstream of the circuit to
>get more repeatable readings. Before I embark on this though I thought I'd
>check if there is already an established way of doing this?
>Sacha
Good for you! Suggest you start by quantifying
the sensors. Most automotive sensors are of the
variable resistance type intended to drive
fairly low-sensitivity instruments . . . read
operating currents in the tens of milliamps.
My favorite approach is to first bias up such
sensors with a constant current source (LM317
wired like the Lo Ohms adapters described
on my website).
Select a bias current that is as large as
practical (means output delta-V in relation
to delta-R is greatest). Using constant
current excitation eliminate variability
of readings due to variations in bus voltage.
Then get yourself some rough calibration
curves for each style of sensor. Water bath
on stove works for temp sensors, air tank plumbed
to pressure sensor with some needle valves in the
pressure/bleed controls is handy.
Once you have ball-parked the voltages of
interest, you're ready to tackle the detection/
lamp drivers. The device you linked seems like
it should do the job. You may have a wiring
error . . . or perhaps are wrestling with outside
influences for not having stable excitation
sources for the sensors.
Another approach to consider is using a
micro-controller like the PIC12F683 . . . a
$1.00 device that will resolve a voltage,
deduce significance of its magnitude and
then do the appropriate hat dance to drive
the LED.
The cool thing is that you can put calibration
variables into separate, easily modified
memory locations such that no potentiometers
are needed. Takes a little more head-work to
calibrate the critter but once it's set,
you're all done and it won't drift. The task
you've described can probably be done with
no more than a single chip.
There are talented, experienced folks here
on the List that can help with your software
education. I probably have some etched circuit
boards laying around that are 95% of what
you need . . . already in existence along
with enclosures like . . .
http://www.aeroelectric.com/Catalog/AEC/9024/9024_Four_Fuction_
Perhaps this is more new te4rritory than you wanted
to explore but getting a couple of these things
up and running to your task would greatly expand
your horizons.
Bob . . .
Message 4
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| Subject: | Re: Half failed LEDs |
Most of them were in the 4-8k range both ways. A couple were in the 90k
range both ways, and one was about 90k one way and about 150k the other.
They were in series with other LEDs and all carried enough current to
allow the other LEDs to continue to light.
Raymond Julian
Kettle River, MN
The things we admire in men, kindness and generosity, openness, honesty,
understanding and feeling are the concomitants of failure in our system.
And those traits we detest, sharpness, greed, acquisitiveness, meanness,
egotism and self-interest are the traits of success. And while men
admire the quality of the first they love the produce of the second.
-John Steinbeck, novelist, Nobel laureate (1902-1968)
On 04/22/2014 08:18 AM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 07:09 AM 4/21/2014, you wrote:
>>
>> I just removed about 8 blue LEDs from a string of lights that no
>> longer emitted light, but still have continuity. If any one wants
>> them to investigate, I'll mail them out.
>
> When you measure them with an ohmmeter, do they
> show the same or similar resistance for either
> polarity of the test leads?
>
>
> Bob . . .
>
>
Message 5
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| Subject: | Re: Half failed LEDs |
At 10:31 AM 4/22/2014, you wrote:
>
>Most of them were in the 4-8k range both ways. A couple were in the
>90k range both ways, and one was about 90k one way and about 150k the other.
>
>
>They were in series with other LEDs and all carried enough current
>to allow the other LEDs to continue to light.
Interesting. I'm not familiar with the failure modes
in LEDs . . . so getting first hand look at the
parts would probably not be useful. The fact that
your readings were so high but with conductivity in
both directions suggests that there's some degree
of P/N junction activity going on . . . in other
words, I suspect they failed in some low energy
event as opposed to high energy that tends to fuse
things into more solid pieces of material.
Bob . . .
Message 6
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| Subject: | Re: Half failed LEDs |
They just weren't lit one day when I looked at them. They were on 24/7.
I'll just recycle them, unless someone else wants them.
Raymond Julian
Kettle River, MN
The things we admire in men, kindness and generosity, openness, honesty,
understanding and feeling are the concomitants of failure in our system.
And those traits we detest, sharpness, greed, acquisitiveness, meanness,
egotism and self-interest are the traits of success. And while men
admire the quality of the first they love the produce of the second.
-John Steinbeck, novelist, Nobel laureate (1902-1968)
On 04/22/2014 04:59 PM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 10:31 AM 4/22/2014, you wrote:
>>
>> Most of them were in the 4-8k range both ways. A couple were in the
>> 90k range both ways, and one was about 90k one way and about 150k the
>> other.
>>
>>
>> They were in series with other LEDs and all carried enough current to
>> allow the other LEDs to continue to light.
>
> Interesting. I'm not familiar with the failure modes
> in LEDs . . . so getting first hand look at the
> parts would probably not be useful. The fact that
> your readings were so high but with conductivity in
> both directions suggests that there's some degree
> of P/N junction activity going on . . . in other
> words, I suspect they failed in some low energy
> event as opposed to high energy that tends to fuse
> things into more solid pieces of material.
>
>
> Bob . . .
>
>
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