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Potentiometer with unstable signal...

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Hi every body,I would like to have your idea to correct a little problem that I tolerated during several years. To drive the yoke, rudder and power lever, I use a Y cable (Joystick) and 4 linear potentiometers. Every thing works relatively good but comparing to a truth joystick, the behavior of the potentiometers was always unstable. As a random species of tremor which returns the flight jerked per moment. This is especially true and visible in Flight Simulator panels if you look at the throttle lever. The throttle always move (shake) forward and backward by small increment.To summarize, it's like my potentiometer collected interferences or parasites which make the signal never really stable.Even if I can fly well most of the time, that becomes unpleasant per moment, especially in delicate operations as well as landing.I would like to prevent this phenomenon. My circuit is cut out in 2 sections: the first section is a real joystick "cable" and second section of cable consists of wire as one uses for the telephones. These telephone wire go directly to the terminals potentiometers.Does any body have trick to stabilize all the pot

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Guest MikePowell

Hi,It is quite possible you are picking up electrical noise on your wiring. Pots do get dirty and worn with age, but if you are seeing this problem at different throttle positions, I would first suspect electrical noise, especially if the cables are both long and unshielded. Shielded cable would be a good next step.Mikewww.mikesflightdeck.com

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Guest LeoL

I would have to disagree with Mike on this. Typically you shouldn't be picking up any kind of interference like that on a simple DC line. Shielded cables help only when you have a high speed communication going on. In this case all the PC does is read and convert a voltage level...in theory it shouldn't be susceptible to radio or electromagnetic interference, but theory and reality don't always see eye to eye!I would guess that you probably have a bad connection, cold solder joint or simply a dirty "scratchy" pot. Have you tried changing the pot?Are you using gameport or USB? If gameport, do you poll with interrupts enabled? Try polling without interrupts and see if the problem goes away. If you're using a USB adapter, then look for a bad connection or replace the offending pot.You cannot use a filtering condenser since the pot is connected to a capacitor already. The circuitry uses this combination of resistor and capacitor to determine your pot position. By adding another condenser, you will effectively be changing the calibration constant of the circuit and do little in the way of filtering out spikes and noise in this case. But hey, anything is worth a trying at least once..;)"Faraday screen room"...sounds like a home movie theatre setup. :DHope this helped.Great work on your site, btw!-Leo

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Leo said:"In this case all the PC does is read and convert a voltage level...in theory it shouldn't be susceptible to radio or electromagnetic interference, but theory and reality don't always see eye to eye!"Very true.I can't explain it either, but from practical experiance with my home-built throttles and rudderpedals I found that using a proper shielded cable (I use normal computer serial cable, as used to connect external modems) makes a huge difference in this low-frequency "jitter".What I found to give the best results: solder the shield wires on the 15-pins connector housing on one end, and on the potmeter housing on the other end of the cable.Rob

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Guest PeterK

PeterKHave you tried any Pot Contact restore spray...Radio Shack didsell Pot contact spray some years ago but I use The Philips ECGbrand to use on Pots that get scratchy...Iv used a squirt ofWD-40 also to got the contacts to work again..Another problem is that the shaft on the pot is damagingthe bushing on the pots mounting plate and when moving the controlthe contact is lost...Have had the same issue on my cockpit but using the analog game port.Pete Http://home.attbi.com/~fs-boneyard

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Guest

Thank you every body !Il will try all your suggestions !JP

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Guest Ramsberg

I have also seen this problem with my newly built throttle... I got the following advice from a friend thats more of an electical expert than I am:Put a small capacitor over the potentiometers connectors. by that the signal, if it is coming from a "noisy pot", should me evened out.I will try this myself. Leaving report here when done/ Olle R

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