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warning lights for engine T&Ps

 
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uuccio(at)gmail.com
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PostPosted: Mon Apr 21, 2014 11:38 am    Post subject: warning lights for engine T&Ps Reply with quote

Aero-Electrics,
Is there an easy/robust way of incorporating "idiot" warning lights for the
engine T&Ps? When I first designed the panel I had in mind tri-colour LEDs
which would turn blue if a value was below normal, green if in the normal
range and red if above the normal range (e.g. for CHT temps or fuel
pressure).
I experimented with this circuit
https://www.spiyda.com/magento/index.php/three-colour-warning-light.html
which I used to measure the various senders resistances
but was not able to reliably calibrate the readings to get anything useful.

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


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Eric M. Jones



Joined: 10 Jan 2006
Posts: 564
Location: Massachusetts

PostPosted: Tue Apr 22, 2014 4:53 am    Post subject: Re: warning lights for engine T&Ps Reply with quote

Quote:
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.


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Eric M. Jones
www.PerihelionDesign.com
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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 22, 2014 5:39 am    Post subject: warning lights for engine T&Ps Reply with quote

Quote:
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 . . .



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 . . . [quote][b]


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user9253



Joined: 28 Mar 2008
Posts: 1437
Location: Riley TWP Michigan

PostPosted: Wed Apr 23, 2014 7:11 am    Post subject: Re: warning lights for engine T&Ps Reply with quote

While looking for the collection of Op Amp circuits that Eric referred to, I found this that might be useful to someone:
http://www.ti.com/lit/an/snla140b/snla140b.pdf
Joe


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PostPosted: Wed Apr 23, 2014 9:42 am    Post subject: warning lights for engine T&Ps Reply with quote

At 10:11 AM 4/23/2014, you wrote:
Quote:


While looking for the collection of Op Amp circuits that Eric
referred to, I found this that might be useful to someone:
http://www.ti.com/lit/an/snla140b/snla140b.pdf
Joe

--------
Joe Gores

Good find. This document is a classic. AN-31 has been
around for decades and updated many times. It's a great
teaching/learning tool!

Bob . . .


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uuccio(at)gmail.com
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PostPosted: Thu Apr 24, 2014 1:49 pm    Post subject: warning lights for engine T&Ps Reply with quote

Quote:

The device you linked seems like
it should do the job. You may have a wiring error...

I tested the circuit on the bench by simulating the senders with a bunch of 1k ohm potentiometers wired in parallel (the resistance range of interest is 30-230 ohms approx in the case of the Rotax senders).
Turns out I had indeed made a wiring error.

The circuit I linked does the job perfectly as it's designed to measure resistance so it's output is pretty much independent of bus voltage, so there was no need for the dc-dc voltage regulator upstream.

I calibrated them by simulating the senders with the 1k pots and connecting them to the gauges and the tri-color LED circuit. The sensitivity can be very finely adjusted with the two 33-turn pots that are on the (approx 1x2 inch) circuit board.

I also managed to adapt the circuit to measure absolute bus voltage (for the high/low voltage light) by wiring a 7805 5v regulator thingy with three legs to get a fixed reference voltage.

All in all I'm very satisfied with the results!


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nuckolls.bob(at)aeroelect
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PostPosted: Thu Apr 24, 2014 3:21 pm    Post subject: warning lights for engine T&Ps Reply with quote

At 04:45 PM 4/24/2014, you wrote:
Quote:


>
> The device you linked seems like
> it should do the job. You may have a wiring error...

I tested the circuit on the bench by simulating the senders with a
bunch of 1k ohm potentiometers wired in parallel (the resistance
range of interest is 30-230 ohms approx in the case of the Rotax senders).
Turns out I had indeed made a wiring error.

The circuit I linked does the job perfectly as it's designed to
measure resistance so it's output is pretty much independent of bus
voltage, so there was no need for the dc-dc voltage regulator upstream.

I calibrated them by simulating the senders with the 1k pots and
connecting them to the gauges and the tri-color LED circuit. The
sensitivity can be very finely adjusted with the two 33-turn pots
that are on the (approx 1x2 inch) circuit board.

I also managed to adapt the circuit to measure absolute bus voltage
(for the high/low voltage light) by wiring a 7805 5v regulator
thingy with three legs to get a fixed reference voltage.

All in all I'm very satisfied with the results!

Good for you sir . . .

Bob . . .


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fatimaameen0
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PostPosted: Wed Sep 04, 2019 2:10 am    Post subject: Re: warning lights for engine T&Ps Reply with quote

Matronics Email Lists Forum Index -> AeroElectric-List is the topic of my assignment and I don’t know anything about it. I am looking forward to give it a start but really don’t know what to write and mention in my assignment as an opening base. I have https://easywritingservice.com/buy-term-papers/ . Any help would really be appreciated here!

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PostPosted: Wed Sep 04, 2019 4:56 am    Post subject: warning lights for engine T&Ps Reply with quote

At 05:10 AM 9/4/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: "fatimaameen0" <lucasaiden88(at)gmail.com>

Matronics Email Lists Forum Index -> AeroElectric-List is the topic of my assignment and I don’t know anything about it. I am looking forward to give it a start but really don’t know what to write and mention in my assignment as an opening base. I have https://easywritingservice.com/buy-term-papers/. Any help would really be appreciated here!

An interloper of unknown intent . . .
IGNORE



Bob . . .


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