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nuckolls.bob(at)aeroelect
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 Posted: Tue Apr 30, 2013 12:33 pm Post subject: Feedback Request on Push-to-talk circuit... |
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At 12:17 PM 4/30/2013, you wrote:
| Quote: |
Would you guys be so kind as to tell me if the attach wiring diagram
looks like it will work? I just need a simple push to test circuit
for a few LED's I have. Thanks.
- Matt
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Why are you doing press to test on LEDs?
Incandescent bulbs as warning devices begged
for press to test given that their demonstrated
service life was a fraction of that for the
airplane. On the other hand, LEDs will outlive the machine.
All of those LEDs can be tested during normal
pre-flight procedures. In other words, NOT
seeing a light when it is expected to be operating
is a more relevant test than having the light
respond to a press-to-test switch.
Press-to-test circuits test a button, a bulb
and in your example, a relay. The fact that the
light DID come on says nothing about the electro-
whizzy that drives it.
On the other hand, seeing one of those lights
illuminate when it is EXPECTED to do so is 100%
assurance for both the bulb and the integrity
of the annunciator signal that drives it.
Bob . . .
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idleup
Joined: 06 Aug 2011
Posts: 19
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| Posted: Tue Apr 30, 2013 1:39 pm Post subject: Re: Feedback Request on Push-to-talk circuit... |
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| nuckolls.bob(at)aeroelect wrote: | At 12:17 PM 4/30/2013, you wrote:
| Quote: |
Would you guys be so kind as to tell me if the attach wiring diagram
looks like it will work? I just need a simple push to test circuit
for a few LED's I have. Thanks.
- Matt
|
Why are you doing press to test on LEDs?
Incandescent bulbs as warning devices begged
for press to test given that their demonstrated
service life was a fraction of that for the
airplane. On the other hand, LEDs will outlive the machine.
All of those LEDs can be tested during normal
pre-flight procedures. In other words, NOT
seeing a light when it is expected to be operating
is a more relevant test than having the light
respond to a press-to-test switch.
Press-to-test circuits test a button, a bulb
and in your example, a relay. The fact that the
light DID come on says nothing about the electro-
whizzy that drives it.
On the other hand, seeing one of those lights
illuminate when it is EXPECTED to do so is 100%
assurance for both the bulb and the integrity
of the annunciator signal that drives it.
Bob . . . |
The best answer I could give you is because I thought you were supposed to have a "Push to test" function for your annunciators. If it is not necessary for LED's than I am more than happy to ditch the whole thing. Less parts, less complexity...
- Matt
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nuckolls.bob(at)aeroelect
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| Posted: Wed May 01, 2013 7:10 am Post subject: Feedback Request on Push-to-talk circuit... |
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| Quote: |
The best answer I could give you is because I thought you were supposed to have a "Push to test" function for your annunciators. If it is not necessary for LED's than I am more than happy to ditch the whole thing. Less parts, less complexity...
- Matt |
Aha! But of course . . .
A common design pit-fall for the OBAM aviation community
is to study and understand (1) what features are part
of a well considered failure mode effects analysis,
(2) what features are there just because the designer WANTS
them and (3) what features are being considered just because
that's the way it's been done for decades.
The fundamental tool for system design is the
Failure Mode Effects Analysis (FMEA). It's
a simple design process that runs in background
while seeking the elegant solution. The process is completely
intuitive. Briefly stated:
1. How many ways can this part fail? 2. How will each failure affect system operation? 3. How will I know it failed? 4. Is the failure pre-flight detectable? 5. Is failure of this part, in any failure mode, likely to create a hazard to flight? 6. Will failure of this part be likely to overtax my piloting skills for comfortably terminating the flight?
These questions are excerpted from an article at
http://tinyurl.com/ch547rn
which explains their utility in more detail.
Considering your constellation of LED annunciators in light of the above exercise will allow YOU to decide which of the three design goals are applicable to inclusion of a press-to-test system.
In the dual battery discussion earlier this week, we wrestled with a constellation of ideas that spanned decades of product evolution . . . ideas that may now be obsolete as a byproduct of new opportunities in technology and capabilities of modern accessories.
But in EVERY case, filtering your deliberations through the array of questions above is the simplest, clearest path to understanding value of the design feature being considered.
Bob . . . [quote][b]
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