How to connect a Moving coil gauge

[Kaellis991]

Joe,
I meant to say series as Mike Powell’s book has it shown. It was late.
The meter is definitely “captain cooked” right out of the box.
It’s going back today and the next one I order, according to the seller’s assurances, will be checked with the shake test by their quality control before they ship it.
Kirk

[jph]

Joe,
I meant to say series as Mike Powell’s book has it shown. It was late.
The meter is definitely “captain cooked” right out of the box.
It’s going back today and the next one I order, according to the seller’s assurances, will be checked with the shake test by their quality control before they ship it.
Kirk

No worries Kirk. Seems like a good book and a knowledgable chap. A good reference.
Third time's the charm.. (third time lucky)
Fingers crossed.

How many other 'real' instruments are you planning on using and what types - are you doing the full set ?
Joe

[Kaellis991]

Joe,
This cockpit I am building is emulating a Piper Arrow II. All I have room and money for is the bottom half of the panel hanging below my desk with the 3 monitors for the flight instruments displayed from Xplane above the desk.
This EGT is the only real gauge I am using from an airplane.
I purchased a custom manifold pressure, rpm gauge and transponder from Flight Illusion.
Those three are the only engine gauges I am using.
The other components from a real airplane are the autopilot switches, the panel switches, the brake lever, circuit breaker panel just for show, the gear lever along with the 12 volt gear indicator lights, the cover and handle for the gear selector and the housing for the ELT switch.
The ignition key is made from a cabinet lock, 5 way switch, a spring and some 3D printed parts.
After a year the panel is mostly built. Now comes the Arduino and power connections.
..fulcrum yoke, slaw device rudder pedals, saitek throttle, and realsimgear GNS 530 along with the custom transponder to be mounted above this panel on the desk to round out my setup.
I have to forego the engine gauges on either side of the yoke, the alternate air control and the environmental controls on the far right of the panel.

Just need to get a working EGT gauge..

[jph]

Looking good Kirk
Love the start switch. Nice job.
Awaiting number three

[Kaellis991]

Adding decals now and awaiting the third and hopefully final EGT.

[Kaellis991]

Joe,

I have another EGT gauge. This is the fourth one. The last two I tried didn’t move at all with either Mikes or your method so I sent them both back for refunds. None of the last three pass the shake test.
At least with this one the needle moves when power is added using Mikes method but it behaves differently than the first one that I destroyed with my ineptitude.
I went all the way down to a 10k resistor with your method and got zero needle movement..

This fourth instrument, from a different source, seems to work but it doesn’t deflect as far as the first one did.
When using Mikes method on the first one the needle swung all the way around the gauge and pegged out at full deflection.
The numbers I recorded from that were 1.8mA and 50mV.

With this fourth gauge and using Mike’s method a full turn of the 100k pot initially swings the needle just a little more than halfway along the scale then it oscillates back and forth for a few seconds between 1/4 way and 1/2 way up the scale. (The needle on the first instrument never oscillated)

The needle then stops bouncing back and fourth and settles in at about 1/3 along the scale.
It never fully deflects.
Where it stops with the pot full on gives me .95mA and 29.4mA….which is about half of the values I got with full deflection on the first gauge.

So where do I go from here? Any help would be appreciated.
If I can’t get this one to work, I’m going to just buy a brand new one.

Kirk

[Ralph]

Isn't it easier, as I believe Joe already suggested, to fit a x25 or x27 stepper motor into it?

[Kaellis991]

That was the original thought I had last year. But someone suggested that I can just use the moving coil meter as is.
So I went down that path. A costly path….
The first one I purchased was working out well until I destroyed it. And now trying to find another one as good as that one has proven to be troublesome and expensive.
I’ve also come to the conclusion that 5v from an Arduino will not be enough power. Joes method of testing as well as Mikes method with the Arduino does not move the needle at all.
These were designed to work in an airplane with a 12 volt electrical system. So I am guessing that these EGTs could never be powered with the 5v from an Arduino.
The testing I did on the 4 units has been with 9volts. That was enough to drive the first one to full deflection. But the same 9v is deflecting the needle on this latest meter by just over half way.
Either the circuitry inside this latest meter is different from the first one and limiting the current/voltage or the needle is sticking.
Perhaps upping the voltage to 12v could deflect it more, or opening it up and removing all the resistors inside.

But with two of these now, I can work on teaching myself how to install a stepper motor into the case of the gauge I mutilated.

[Kaellis991]

Isn't it easier, as I believe Joe already suggested, to fit a x25 or x27 stepper motor into it?

Is this what I should use along with the TB6612?

[Sling]

Kirk,

Did you read what I posted about thermocouples. The aircraft electrical system voltage is irrelevant to the operation of this type of instrument. They are purely powered by the voltage generated by the thermocouple. It is very small. Connecting more than the small signal expected will not end well. The thermocouple tables tell you exactly what value in mV you need to apply to get a given needle reading. Usually to test these things one would use a thermocouple simulator which is essentially what you are going to have to make.