Flying on the Cheap - Instruments

RST Engineering wrote:
Sadism & Machochism?

The problem resolves itself to dicking around with a thermocouple probe that
puts out millivolts and then picking out the microvolt rise that indicates a
rate increase. Can it be done? Sure. Easily? Perhaps. Trivially?
Probably not.

The second problem, generated by the first, is simulating such a rise and
setting the trigger in the simulation. I'm presuming that you don't want to
sacrifice an engine to calibrate the rascal. Then the question becomes,
what rate do you want to trigger? One degree a second? Ten? A hundred?
Or what rise over what time are you interested in?

Form the problem and I'll try and come up with a solution.

Jim

Tie the engine temp to a flashing LED or maybe an audible beep. Rate of
flash/beep increases as temp rises. Thing goes crazy as it's warming
up, but a button allows you to set the "this is good" steady state. If
the temp rises after that, the beeping/flashing starts going again.
Maybe the pilot wants to just shut it off again...maybe he decides that
danger is clear and present.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

If it helps you to see this as a very difficult challenge, then go
ahead. I know what the "H" in RAH stands for, but if designing your own
circuit from discrete transistors that you've carved out of wood is
beyond your interest, then why not look around for a plug 'n' play
option? Have you *really* already done that and come up empty handed?
I've got a shelf full of catalogs of temperature control hardware. I
haven't actually looked for one with a rate alarm option, but since rate
is monitored and used by the controller, I don't see why someone
wouldn't offer such an alarm as an option.

Ok, Smitty.

Nope, not at all interested in carving transistors out of wood.

Since you have all the catalogs, my suggestion is to "go for it".

When you are all done, we can compare "budgets" and judge accordingly.
Budgets?

First, obviously, would be cost.
I'm pretty sure, should he decide to bite, Jim's solution would come in
for under 50 bucks.

Power budget?
We can assume we have a 12 volt DC electrical system. How many amps
will you need? Jim probably wouldn't need over 100 mA or so, if that.

Weight budget? (Oh Sh*t, not that again!)
What say, Jim? 3 or 4 ounces?

And then come the electrical issues!

It's a thermocouple. Output is in the millivolt range.
AND, to monitor RATE of change over a very short time (seconds) we'd
have to get down to the microvolt level!

To be able to use that, it will have to be scaled up - gain of roughly
one million or more? No freakin' way *I* would try that with desecrate
(or even wooden) transistors.

Again, it's a thermocouple!
How do you propose to "interface" to it? Single side ain't gonna get it.
You would wind up amplifying the noise as much or more than the signal!
Differential low noise high gain op amp seem to be the best solution here.

Nope, this simple circuit is way beyond anything this ol' logic mechanic
would be able to do. And, not ashamed to admit it, either.

So, let's see whatcha got there Smitty?

Richard

In article et,
Richard Lamb wrote:

If it helps you to see this as a very difficult challenge, then go
ahead. I know what the "H" in RAH stands for, but if designing your own
circuit from discrete transistors that you've carved out of wood is
beyond your interest, then why not look around for a plug 'n' play
option? Have you *really* already done that and come up empty handed?
I've got a shelf full of catalogs of temperature control hardware. I
haven't actually looked for one with a rate alarm option, but since rate
is monitored and used by the controller, I don't see why someone
wouldn't offer such an alarm as an option.

Ok, Smitty.

Nope, not at all interested in carving transistors out of wood.

Since you have all the catalogs, my suggestion is to "go for it".

When you are all done, we can compare "budgets" and judge accordingly.
Budgets?

First, obviously, would be cost.
I'm pretty sure, should he decide to bite, Jim's solution would come in
for under 50 bucks.

Power budget?
We can assume we have a 12 volt DC electrical system. How many amps
will you need? Jim probably wouldn't need over 100 mA or so, if that.

Weight budget? (Oh Sh*t, not that again!)
What say, Jim? 3 or 4 ounces?

And then come the electrical issues!

It's a thermocouple. Output is in the millivolt range.
AND, to monitor RATE of change over a very short time (seconds) we'd
have to get down to the microvolt level!

To be able to use that, it will have to be scaled up - gain of roughly
one million or more? No freakin' way *I* would try that with desecrate
(or even wooden) transistors.

Again, it's a thermocouple!
How do you propose to "interface" to it? Single side ain't gonna get it.
You would wind up amplifying the noise as much or more than the signal!
Differential low noise high gain op amp seem to be the best solution here.

Nope, this simple circuit is way beyond anything this ol' logic mechanic
would be able to do. And, not ashamed to admit it, either.

So, let's see whatcha got there Smitty?

Richard

I'll pass on your proposed "contest." It's your project; I've got enough
of my own going. It's wonderful that your apparent kinship with Jim is
sufficient to entice him to design a custom solution, from parameters
that, despite his request, you have yet to clearly state (unless I
missed it, or that conversation took place offline.) Now, if you had
*really* looked around to see what was already available, and come up
empty handed, then a custom unit might make sense, provided you can get
all the engineering for nothing, which you apparently believe you can.
Sure, you can buy a big shoebox full of electronic components for your
$50 budget.

But, that's the way some engineers think. Fifty thousand different
screws available off the shelf, and we keep the Brown and Sharpes busy
making custom screws for engineers who design absurdly clumsy and
complex mechanisms with no forethought to how to hold the pieces
together.

wrote:
...

No silk scarf nor sheep-skin jacket but it
does happen to include an inexpensive GPS unit along with a cheap
'ramp' radio. ...

Could you be specific as to which unit you use?

--

FF

wrote:


wrote:
...

No silk scarf nor sheep-skin jacket but it
does happen to include an inexpensive GPS unit along with a cheap
'ramp' radio. ...

Could you be specific as to which unit you use?

I am not Mr. Hoover but - I use a Magellan 315/320 GPS with an aviation data
base. This unit was acquired on eBay for ~$75. The data base is downloaded
from

http://home.stny.rr.com/bkw/315/

and is updated regularly. You will need the DataSend program and a data cable,
both are available on eBay for around $25.

No moving map but you will be able to get from point A to point B and have the
current airport data (frequencies, runway length, composition, etc) for any
airport in the USA.

Cheap radio is an ICOM A4 with a headset adaptor, I wouldn't recommend it to
anyone but it does the job.

CW Crane