Potentiometers that do not work with short cables and work with long cables ...  - Page 1
Forum section: electronics / beginners

author: federico
author_rank: Contributor
timestamp: December 05, 2018, 04:48:19 pm
content: Hello everyone !time ago I had a similar problem, and you had solved the problem !now I'm doing a project a little bigger, and I ran into the same problem ..Quick summary:I bought a LEO Bodnar card to create my personal joystick to drive helicopters, board + 5k potentiometers.the value read by 3 of the 5 potentiometers, does not remain stationary, dances quickly between one value and the other, so also during the game, eg: the pedals are seen that vibrate.I noticed one thing, that ironically, the most distant potentiometers from the board, those with longer cables, are those that do not dance and work well, vice versa, those with the shortest cables and closer to the card are the defective ones.So I tried to add a meter of shielded cable, lengthening the cable of the defective potentiometers ...and surprise: now the potentiometers do not dance anymore ...Not being an expert, I hypothesize that the signal is "amortized" "stabilized" during the longer cable run.Orhow can I solve the thing?It is absurd that I have to put the electronics on another side and stretch all the cables to have a fully functional joystick. can you explain to me what happens and how can I solve the problem?Thanks !

author: Andy Watson
author_rank: Super Contributor
timestamp: December 05, 2018, 05:19:11 pm
content: I would guess that the longer cables are adding capacitance between the signal and ground - thereby reducing the interferance. Is the metalwork on which the pots are mounted also connected to ground?

author: perieanuo
author_rank: Frequent Contributor
timestamp: December 05, 2018, 05:20:01 pm
content: Put small chokes series with pot wires or verify your power supply he may add noiseAnd please add details like ps used and wiringRegards,pierreEnvoyé de mon iPad en utilisant Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: December 05, 2018, 05:34:45 pm
content: How long are the cables?I suspect the added capacitance could be stabilising the control loop, therefore eliminating the oscillation.Look up frequency compensation and control theory.Try adding some capacitors. Try 100pF first and increase it, until the oscillation stops.

author: federico
author_rank: Contributor
timestamp: December 05, 2018, 06:08:03 pm
content: Quote from: Andy Watson on December 05, 2018, 05:19:11 pmthe structure is detached from the ground, resting on rubber supports.The GND of the electronics is not connected to the structure but only to the GND of the card (therefore to the GND of the USB socket)Quote from: perieanuo on December 05, 2018, 05:20:01 pmsmall chokes ?, Sorry I do not understand what you mean, I know English, but use the translator for many words and I can not understand.It does not have a PS, because it is powered by the USB cable connected to the computer, it is a Plug & play card.(actually in my PC there are problems of "electrical dispersions" that can also be heard from the speakers)and in my pc works worse than everyone, but it also gives problems with other computers that are in good condition, I tried it on 4 different PCs.The cables are a single shielded cable, with poles inside the diameter of 0.50mmQuote from: Hero999 on December 05, 2018, 05:34:45 pmThe cables are about 40 inches long, and they work.Those that do not work, have cables about 2/3 long.The company LeoBodnar replied, telling me the same thing, he told me to add a 1uf / 16volt capacitor.Leobodanr REPLYYou can reduce it by putting a capacitor across your potentiometer GND and +5V pins and across INPUT and GND pins. Something like 1uF 16V capacitors should be fine.I found from my electronics store these: 1uf / 350volt, I told him that I needed 16v, but he told me that 350v is better ....I mounted them, (I attach the design of how I connected them) and the situation has worsened, instead of improving ..I asked leoBodnar for explanations and they never answered me again.Did you mean to mount them like that?Thanks at all for your help

author: perieanuo
author_rank: Frequent Contributor
timestamp: December 05, 2018, 10:03:46 pm
content: https://en.m.wikipedia.org/wiki/Choke_(electronics)Choke=little inductor that 'eats' spikes (mounted in series with load) is equivalent to capacitor in parallel with cable in your case.If fact I suggested a simple approach for your case to reduce high frequency interference that bothers you in short cable situation.We can debate hours, but if you put just some small inductors in series or capacitors in parallel you will be good.Regards,pierreEnvoyé de mon iPad en utilisant Tapatalk

author: fsr
author_rank: Regular Contributor
timestamp: December 05, 2018, 11:59:15 pm
content: "Fluctuates between 463% and 464%"? How is that a problem?Did you ever used an analog PC joystick? On the calibration screen, the spot jumped quite a lot on both axis.

author: Nusa
author_rank: Super Contributor
timestamp: December 06, 2018, 02:01:34 am
content: I'd disconnect the cable shields from signal ground. Cable shields should be attached to the chassis of the device instead.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 06, 2018, 06:13:46 am
content: Quote from: federico on December 05, 2018, 06:08:03 pmmaybe 1uF is too much making your control laggy. try smaller value say 0.1uF (100nF) or maybe 10-1nF between pads where wires and potentiometers connected to, and then reduce the wire length. voltage rating is less relevant you can use higher rating except it will be bigger in size. agree on replies above regarding capacitive effect, maybe your potentiometer (supply or arm) is noisy. btw, Leo Bodnar is a member here, you may want to PM him from here, except be aware he is not liable on your modification and he maybe busy. ymmv.

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2018, 09:08:10 am
content: Quote from: Mechatrommer on December 06, 2018, 06:13:46 amYes, I said start with 100pF, not 1µF which is 10000 times the size.

author: federico
author_rank: Contributor
timestamp: December 06, 2018, 07:25:32 pm
content: Quote from: perieanuo on December 05, 2018, 10:03:46 pmOk, now I understand, thanks for clarifyingQuote from: fsr on December 05, 2018, 11:59:15 pmyes, I put 463% and 464% as an example, because I did not calibrate the joystick in that test, it actually moves 1% or so, but on a ray that goes from 350% to 440%, so the movement it is very accentuated.It will seem little, but with the naked eye you can see the axes vibrate! and it is not a fixed movement but sometimes it is less or more accentuated.(I have had many joysticks per pc and I've never had a joystick where the axes danced like this)Quote from: Mechatrommer on December 06, 2018, 06:13:46 amGreat ! Yes, I do not pretend to waste time for myself, I understand that they have other things to think about. But I bought their electronics, and I have mounted according to their instructions, if it does not work properly, it is right that they solve the problem.If you were not there, you kindly helped me, I would send it all back.Quote from: Nusa on December 06, 2018, 02:01:34 amI think you are right !!here's what happened:This morning we took all the electronics apart and reassembled it, and we checked the various connections.The joystick worked well, so we checked one of the pins that connects the collective to the main body, and we realized that the GND was accidentally in contact with the metal structure of the joystick.We have noticed that all joystick potentiometers work well when the GND is in contact with the metal structure of the joystick.Now I have connected the GND of the card to the metal structure, and it also passes through the GND of the potentiometers and to the cable shielding.Actually it works great, it does not vibrate anymore!Do you advise me to connect only the cable shield to the structure and leave the GNDs of the potentiometers connected to the board?I wrote to LEoBodnar what happened and they also confirmed to connect the GND to the structure.But they talk about connecting the GND card to the structure, (but actually there are no connections on the board to do this)Then I do not understand, if the joystick had been built the plastic ?? where did I connect the GND?Should I build a faraday cage for the card?

author: fsr
author_rank: Regular Contributor
timestamp: December 06, 2018, 11:12:25 pm
content: Well, it was a while since i used an analog PC joystick, but they used to beverynoisy. But they worked anyways, because the software was designed to smooth out the variations.It seems that your card picked up some noise/interference. You could expect noise pickup from the cables, as they're long and act like antennae, so they were shielded with good reason, but noise pickup from the board itself? That's curious.