Can I use this actual aircraft potentiometer?

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Kaellis991
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Can I use this actual aircraft potentiometer?

#1 Post by Kaellis991 »

I have a switch panel that came with the Piper arrow dimmer pots for nav and panel lights.
One of the potentiometers seems to be dead since I cant get an ohm reading from it.
It looks like I will need to replace it with a new flatted shaft potentiometer. That should be easy enough because the set screw for the wheel is not stripped out.

The pot that works though gives me a reading of 391 ohms. (see attached)
That reading is well below the 1k thru 20k recommendation concerning the proper rating of potentiometers to use.

Do I need to replace the working potentiometer with one in the 1k to 20k range?
If so I will need to figure out how to remove the stripped hex screw holding the wheel on. Just another hurdle to get over.
IMG_4461-3.jpg

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jph
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Re: Can I use this actual aircraft potentiometer?

#2 Post by jph »

Yes, Just checked the datasheet for the Atmel328p and you can use it as is. <=10K is ok. If less than around 1K then you need the venerable safety resistor so just add a 220 ohm resistor in series with the wiper and connect the other two pins to VCC and GND for the arduino. Job sorted.
If this is for the dim input signal to AM Kirk, then what are you proposing to use to actually drive the diming circuit (output) ? (just wondering)

Joe
Joe. CISSP, MSc.

Kaellis991
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Re: Can I use this actual aircraft potentiometer?

#3 Post by Kaellis991 »

jph wrote: Fri Jun 24, 2022 3:10 pm Yes, Just checked the datasheet for the Atmel328p and you can use it as is. <=10K is ok. If less than around 1K then you need the venerable safety resistor so just add a 220 ohm resistor in series with the wiper and connect the other two pins to VCC and GND for the arduino. Job sorted.
If this is for the dim input signal to AM Kirk, then what are you proposing to use to actually drive the diming circuit (output) ? (just wondering)

Joe
Joe,

If I understand you correctly you may be thinking that I will be dimming actual lights in my cockpit. What I am using these pots for are the lights in the sim aircraft via AM and the arduino. The pots are to change the dataref info in Xplane that activates the instrument panel lighting and the nav lights on the aircraft in the sim. I have an AM scripting code that Keith provided for that.

I was hoping that the 220 resistor would take care of that low rated potentiometer. I only wish the other pot was working...but you get what you pay for.

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jph
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Re: Can I use this actual aircraft potentiometer?

#4 Post by jph »

HI Kirk,
Well, the 220 would be there with any pot to be fair, even a 10k but no worries. The pot you have will be fine.
It will work great for that usage. It is going to be really neat when you get finished.
Looking at the pot mounting, if the failed one is the same then it will be easy to change. Just get any old linear pot with a D shaft and throw it in. ;)
Doesn't matter about the value. If you find one that's greater than 10K then you can still use it, just add a resistor in parallel across the pot to bring the value down below 10K.
Keep up the good work.
Joe
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Kaellis991
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Re: Can I use this actual aircraft potentiometer?

#5 Post by Kaellis991 »

Joe,

Thanks for the info.
One of these pots, the one that works, has a switch for the nav lights. The other pot does not have a switch but I found that it works but only on one side.
So I am thinking about replacing them both, but having a hard time finding a pot with a switch, the d shaft, the correct shaft length, the correct shaft diameter and the same 270 degree rotation with the proper rating.

I've been using the filters in mouser and digi-key and coming up short...

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jph
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Re: Can I use this actual aircraft potentiometer?

#6 Post by jph »

Hi, what do you mean by 'it works only on one side ?' - is there any reading with the meter on OHMS across the outer two terminals ?
Also, why on earth would you want to replace the pot with switch that is working ? - An ADC input does not care (within reason) as to the value of the potentiometer as it is a high impedance voltage measuring input - not current. The pot is simply acting as a simple voltage divider - a variable voltage source. It doesn't matter if it is 10K or 470ohms. The coding is EXACTLY the same.

Also, when looking for replacements you should not expect to find an exact match. Anything even close will do. ANY value up to around 100K can be used (with a suitable parallel resistor). The shaft length isn't an issue providing the D section is all along it as you simply cut it with a dremel tool or similar. Even a round shaft can be made into a D section with a dremel and the rotary wheel can be made to fit whatever pot you have. ;)
As for rotation, then ANY value will do - most are 270, but it doesn't matter in the slightest if it is 300. Looking for a pot without a switch is far more likely to give you options.

Joe
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Kaellis991
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Re: Can I use this actual aircraft potentiometer?

#7 Post by Kaellis991 »

Joe,

I wasn’t clear about the malfunctioning pot. Initially, I did not get any ohm readings across the outer terminals. Later I found that there is a variable reading between the wiper and only one of the outer terminals.

About a replacement, I can certainly modify the shaft with the tools I have. So if the rotation is not an issue there are others with 300 or 320 degree rotation. I don’t really want to modify the wheel with the set screw. That’s a much trickier operation.

If the non-switched pot with only the one side connecting to the wiper isn’t useable, it’s easier to replace that one.
I will keep the fully operational switched pot for now and give it a try.

Kirk

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jph
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Re: Can I use this actual aircraft potentiometer?

#8 Post by jph »

Hi Kirk,
Yes the pot is faulty if it is not reading across the two outer terminals. That's a shame. I would be tempted to take it apart and see if anything can be done at the end of the track. It is amazing what you can do with a 2B pencil (graphite) and conductive paint. I have repaired many that way. Yours are also - probably - wire-wound as opposed to carbon track so if the issue is the connection of the wire to the end post then it is also usually easy to fix. They were probably operating as rheostats in the real aircraft.

Do you have any hobby electronics stores near you that you can visit to compare a few pots ? - like radio shack used to be like ?

Those were the days.. every time I visited the US - Work or Holiday - I was usually more interested in a large 'radio shack' shop or a mega DIY place than the actual country :lol: - oh, and Wendy's of course..

As for rotation etc, it only needs to move and turn around the same distance to feel similar to the real one. ALL the control is in software. Same with taper, it could be linear or Log (Logarithmic). It doesn't matter at all as you can sort it all out in software.
Joe
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Kaellis991
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Re: Can I use this actual aircraft potentiometer?

#9 Post by Kaellis991 »

Joe,

It’s a lot easier for me to just spend more $$$ and replace the faulty pot. I’d probably just destroy it like I did the moving coil EGT gauge.

Unfortunately, the only place to acquire electronics these days is online. Back in the 80s when I lived in Austin they was a large electronics warehouse store that had everything you could want. But those electronic stores are history these days.

So I end up buying components that I think will work for my project only to find that I chose wrong. With the leftover stuff I’ve bought online that didnt work, I could open up my own electronics shop now.

One other thing I did notice about the working, switched pot is that I can’t figure out how the terminals are used for the switching. The typical switched pot that I have has the logical two terminals. But this used pot has four terminals and no pair of them seem to do anything when the pot clicks at the switch location in the rotation.

That was my reason for just replacing them both.

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jph
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Re: Can I use this actual aircraft potentiometer?

#10 Post by jph »

Kaellis991 wrote: Sat Jun 25, 2022 10:17 am

So I end up buying components that I think will work for my project only to find that I chose wrong. With the leftover stuff I’ve bought online that didnt work, I could open up my own electronics shop now.

:lol: :lol:

Christ on a bike, you wouldn't want to see my 'stock' :o :D - I could open a small aliexpress.................................
I have things that repair thing that repair things that test things. :D


Regarding the switch, in the image you sent the switch is the lump on the end of the potentiometer. I can't see from the angle of the image but there should be 3 terminals on the potentiometer and then the two on the lump on the end which is the switch so 5 terminals in total. - unless something weird is happening.
If you meter across the two terminal in the lump on the end of the pot then they should change OC to CC with the switch operation.
Joe
Joe. CISSP, MSc.

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