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Sea2Sky

Need help balancing analog linear slide potentiometer values

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I've been building some sim TPM controls using actual Cessna TPM controls, but mounting a linear slide potentiometer where the cable goes.
 
I have the throttle control working, but notice that the range from one end to the other is not balanced. When the throttle is off, its value is jittering between 3-5. Approximately 25% throttle on the slide pot shows a high jitter value at 976-978, 50% value at 1006-1007, 75% value at 1014-105, and 100% value at 1018-1019.
 
Flight Illusion GSA-010 I/O board. The software has range limit input from 0-1023, with a cross over value setting. Changing the cross over value doesn't make any difference. The issue looks like it's coming from the the analog signal.The picture showing the throttle lever value is with throttle at 25%. but a value of 987/1023.
 
Has anyone else had this same issue, and were they able to overcome it? I tried using both 20k and 50k linear slide pots. Am I using defective linear pot slides?
 
lxEbUml.png

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Posted (edited)

To elaborate a little more, I've tested the slide potentiometer with 20k resistance, and they are indeed linear based on the resistance value.

When I wire them up, it's still doing about 90% value reading at 25% slide increase. Even though the slide pots are tested correctly, I've tried using a few other slide pots with the same results.

Edited by Sea2Sky

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Posted (edited)

They seem to be behaving like logarithmic pots. When you tested them I assume you measured them at a number of points along the slide movement. The markings on the pots are often not very clear, so incorrect types get supplied.

I use similar linear slide pots for the throttles in my cockpit, with Bodnar boards and get very good linearity in use.  Either 20k or 50k would normally be good values to choose, so if you are sure they are linear pots you probably need to ask Flight Illusion for their view.

Just another thought, the movement applied by your throttle control to the pot must also be linear so the pot movement always corresponds to the throttle movement.

Edited by Biggles2010
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John B

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Posted (edited)
40 minutes ago, Biggles2010 said:

They seem to be behaving like logarithmic pots. When you tested them I assume you measured them at a number of points along the slide movement. The markings on the pots are often not very clear, so incorrect types get supplied.

I've set the resistance to 20k on the 20k slide pots. and the resistance values are showing up correctly. at 25% slide increase, it's showing about 5k, 50% slide increase, it's showing about 10k and 100% slide increase is showing 20k resistance.

I'm pretty stumped on this as I'm getting conflicting results from my GSA-010 I/O board. My board for analog has a 5V, ground, and input setting. I don't think the 5v is suppose to be used, as the input pin carries a voltage. If I try using just input and ground pin, I get no values appearing in my hardware. My multimeter shows a resistance value when using pin 2 and 3. But if I use input and ground on each pin 2 and 3 on the slider pins, I get a value of 0 in my software config. If I use 5v and ground on pin 2 and 3, I get a value of 0. But if I use input and ground on pin 2 and 3, and 5v on pin 1, then this is the only way I get any change of values across the slide, although not balanced correctly.

Not 100% sure why it requires the 3 wires for a value range, as the guide mentions that I only need ground and input (voltage), which doesn't appear to be the case. Any other combination doesn't seem to do anything.

taLvTO0.png

 

lLFYH6G.png

"Be sure not to connect the slider to the 5 Volts pin, otherwise the potentiometer may be damaged." - it only appears that the slide range values change with the 5v connected to pin 1. To confirm, the slide pot does not become damage based on my multimeter read out.

Edited by Sea2Sky

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Looking again at your calibration images you seem to be using a very limited range. For a simple throttle without reverse, the available range would usually be from somewhere near zero to something just above 16300.  After allowing for a null area at each end, I  would expect to have a useable range from about  400 min and about 15800 max. With the trim I would want similar min (negative trim) values and max (positive trim) values.

I'm not familiar with the Flight Illusion board, but the calibration software looks to be the standard item used for analogue controls.

Unless I have misunderstood,  your total throttle range is from 224 to 978 and the trim even more restricted from 898 to 1023.   Using the full range of the pots allows much more precise control, although you should always leave some spare at each end, so the pots never hit the stops.


John B

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Posted (edited)
8 minutes ago, Biggles2010 said:

Looking again at your calibration images you seem to be using a very limited range. For a simple throttle without reverse, the available range would usually be from somewhere near zero to something just above 16300.  After allowing for a null area at each end, I  would expect to have a useable range from about  400 min and about 15800 max. With the trim I would want similar min (negative trim) values and max (positive trim) values.

I'm not familiar with the Flight Illusion board, but the calibration software looks to be the standard item used for analogue controls.

Unless I have misunderstood,  your total throttle range is from 224 to 978 and the trim even more restricted from 898 to 1023.   Using the full range of the pots allows much more precise control, although you should always leave some spare at each end, so the pots never hit the stops.

The range is set back to 0 - 1023 (-4096 - +16384), the image should have been updated to reflect that. When testing outside of P3D, the output value reading is still the same regardless of the throttle range setting.

I'm surprised that I can't get any reading from just using slide pin 2 and 3 with the input and ground pins. If the multimeter can do a linear value with those two pins, shouldn't the IO board also do the same? So weird that the 5v needs to be also attached to slide pin 1 for any sort of value increase/decrease, even though it is very unbalanced.

Edited by Sea2Sky

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Posted (edited)

I replied to you before your second post.. and after your second post, but  haven't been approved by a moderator yet. 😕  Not sure why..

Edited by Sea2Sky

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Posted (edited)

The 5v supply should never be connected to the slider. There seems to be something wrong with the pot wiring, or the way the pins are being interpreted. I'm sure you know this, but in standard pot wiring the 5v is always between the 2 ends of the resistor element of the pot, with 5v plus at one end and the ground wire at the other. They can be either way round, but one way will give control movement in the required direction. The other way will reverse it.  The wiper connection on the pot goes to the signal input connection on the board. On a 20k pot you should always get 20k between the 2 ends of the resistance. This where the 5v plus and ground wires go.

To check the pot, disconnect it from the board and put the slider in the middle. With one meter lead on one of the pins formed from the casing, use the other lead to see which other pin gives you 20k. These are the 2 pins you need for the 5v and ground wires. Correct pins will always be 20k, regardless of wiper position.

Then you should confirm which is the wiper pin on the pot. So with the slider  still near the middle position, put one meter lead on the pot casing (ground), and  use the other meter lead to confirm which one of the other pins is giving about 10k. This will be the wiper pin, which must go to the signal input on the board. If the axis movement is in the wrong direction, just reverse the 5v and ground wires. Do not change the wiper connection.

Sorry if this sounds patronising, but it is the surest way to get the wiring correct. I do recall on my own system that a couple of the pots had slightly confusing pin markings. If this does not produce correct reaction at the board, then it does suggest a board problem, but I think that would be unusual.

Edited by Biggles2010
corrn
  • Like 1

John B

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Posted (edited)
1 hour ago, Biggles2010 said:

To check the pot, disconnect it from the board and put the slider in the middle. With one meter lead on one of the pins formed from the casing, use the other lead to see which other pin gives you 20k. These are the 2 pins you need for the 5v and ground wires. Correct pins will always be 20k, regardless of wiper position.

Placing the meter lead to pin 1 and pin 3 gives me a 20k (20.5k to be exact) readout with the slider in the middle (or any position).

1 hour ago, Biggles2010 said:

Then you should confirm which is the wiper pin on the pot. So with the slider  still near the middle position, put one meter lead on the pot casing (ground), and  use the other meter lead to confirm which one of the other pins is giving about 10k. This will be the wiper pin, which must go to the signal input on the board. If the axis movement is in the wrong direction, just reverse the 5v and ground wires. Do not change the wiper connection.

 I can't seem to get any reading when using the case, or any other metal object as the ground. But if I put the meter leads in pin 2, and pin 3, then I get the 10k readout with the slider in the middle position. At this point, I'm assuming the wiper pin is set to pin 2.

And it looks like it's working correctly and the values are now balanced. 🙂 Pin 1 and 3 use ground and 5v, and pin 2 uses the signal input.

1 hour ago, Biggles2010 said:

Sorry if this sounds patronising, but it is the surest way to get the wiring correct. I do recall on my own system that a couple of the pots had slightly confusing pin markings. If this does not produce correct reaction at the board, then it does suggest a board problem, but I think that would be unusual.

Not the slightest bit patronizing, this was great advice. Thank you so much! I can't tell you how much I appreciate your help.

Edited by Sea2Sky

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Glad it helped.  I can remember a lot of trial and error setting up my own controls, and picking up a variety of tips from here.

  • Like 1

John B

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