What is the best material/thing to affect capacitive sensor the most?

My current purpose of LowRiderV3 is for automated test of capacitive sensor, used in large touch screens. But, because of EMI from LowRiderV3, I don’t see clearly touches on this sensor. I tried Ferit rings and will try copper “shield” on cables.

But most effective would be testing thingy, that would have such huge effect on sensor, that some EMI would not be big of a deal

Finger can be seen very clearly despite EMI

Better stylus from 2 that I have available, can be seen, but with little bit higher EMI or worse touch, I will have trouble to see, where touch occured

On this picture can be seen worse stylus but with stronger EMI than in previous picture, so touch point with 203 points is not clear with 204 point EMI distortion

the best material so far, that I found to have good impact on sensor is 10 cent coin (Euro) grounded with the plug. But that is not helpful as I have to hold grounding cable next to it, I need to mount it to LowRiderV3

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I am not an expert, but I think the ideal is something with a little resistance, and a big ground. Ideally the size and squish of a finger too. The euro coin seems close. Maybe wrapping it in paper or something would give it a sharper point.

The other option is to ground the LR EMI. Putting the controller in a grounded metal box, and grounding the motor cables would probably do the most good. I have always heard to only ground one end of the cable. But with the motors not having any connection to ground, I bet you need to ground the shield to the motor and to the control box.

It sounds like the size of the contact makes a difference, which makes sense for a capacitive sensor. You could print a flat circular button and cover it with copper foil tape to achieve the same effect as your coin.

A ferrite bead on the sensor wire could degrade the signal in addition to the noise, but you could try ferrite on the motor wires, on the end near the control board. They might transmit less.

And it won’t hurt to keep some distance between the sensor wire and the motor wires. I wouldn’t think they would need to be really far apart, but avoid bundling them together.

My local dollar store has screen styluses. Basically they are an aluminum stick with a sponge pad on the tip, covered in a fabric with a conductive mesh embedded in it.

The trick will be a sink to couple to the stylus.

I would think that the steel of the LR3 X rail may be adequate. If not maybe a jug of an electrolyte solution. (In my head, I’m thinking of one of those jugs of Gatorade that field sports teams would being to a field.)

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I may not fully grasp what all your doing, but have you seen active stylus? I have one I use on my iphone and it provides a much smaller tip than a traditional stylus. Would that solve any of your issues?


I tried active stylus, but it had worse response than non active, just standart pen with rubber top for touchscreens.

What do you mean by “sink to couple to the stylus” ?
English is not my first language so I struggle sometimes.

I tried ferrite rings on motor wires but with very little effect. Sensor wires are under LowRiderV3 as you might see on the picture, so motor wires to the sensor are relatively close by. What is not good.

Biggest problem with coin or some other self made thingy is how to ground it. Coin, by itself, has no effect on sensor but when grounded, can be seen very good. I could ground it by some wire to electric plug but there is some distance between them.

How would make a big ground you mention?

Yeah, controller into metal box would be great, but so far I have 3d printed one. Is it possible motors are releasing EMI, or their box “eats” this interference?

Grounding to the electrical ground is what I was thinking. But just wiring to anything big and metal. Maybe a desktop computer case?

I don’t think there is any emi from the motors themselves. But the motor wires are moving a lot of current (around 1A), and they pulsing around 30kHz. So they will generate some emi.

Deskrop computer case is good idea, it did not cross my mind. Do you think maybe notebook could work as well? I am doing measurements with it.
What would you recommend as good type of wire for grounding? I tried copper, but I am not sure if it was too thin or something else, but it worked worse than cable I had for connection SKR board of LowRider to computer.

Motor wires are definitely causing emi. This is standart deviation from data I measured.

Picture from the top:

and from the side

In this area was LowRiderV3. Interference is quite significant. As of right now, I am looking for statictical methods to deal with EMI somehow. I was thinking some statistical probability method, which could calculate probability of interference in certain point and if there is higher probability, lower the value accordingly. But I am not sure if anything like that exists.

@martin001 , maybe you can take some ideas from the plasma table shielding. Here are a couple examples.

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@martin001 , here’s one thing I just thought of that you can try on the stylus side. Attach the passive stylus to a container with water.

I did a quick test on my touch screen by attaching the stylus to an empty bottle. I then touched the screen with no response. Next I filled the bottle and tried it again and it detected a touch. My theory is that the water acts similar to your body so it would give a similar touch event when attached to the LR.

You may be able to play with using a metal container or a plastic container with a ground wire with one end inserted into the water and the other end connected to the stylus.

You could also try using distilled, tap and a saline solution to see if you get any additional improvement. My theory is that a solution with a higher mineral content might perform better but just a theory.

Good luck and keep us posted.

BTW, what software/hardware are you using to visualize this?

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Feh… cotton swab dipped in fresh arterial blood… Let it know you’re playing for keeps.

I see he is also going wtih tinned copper on wires approach. I am currently instaling those on my wires and just grounded them today. Will see in upcoming days whether it had any effect. Thanks for sharing.

here’s one thing I just thought of that you can try on the stylus side. Attach the passive stylus to a container with water.

Under this I imagined big bottle of water on top of stylus and lots of water everywhere haha Could you please share some photos for inspiration how you attatched bottle to stylus?

Not sure about mineral content, if I will be completly desperate I will try it hah

Thanks for you reply

(visualisation and all my work with data is done with MATLAB)

Then you should be familiar with the mineral properties of tears…

aaaaaaaand YES

@martin001 , here are a few photos.


  • Plastic water bottle
  • Drinking water
  • Painters tape
  • Cheap stylus (paper tube with metal coating on inner surface and conductive rubber tip)
  • Dell Canvas touchscreen

I used painters tape to attach the stylus to the outside of the water bottle.

Touch is not detected with empty water bottle.

Touch detected with full water bottle.

I was thinking that a setup like this attached to the LR could improve your signal. Also possibly using a metal water bottle (with a lid :stuck_out_tongue_winking_eye:) along with maybe “grounding” the stylus into the water via conductive tape or a wire could improve it even more.

I also thought about filling a latex glove with water, tying it off and attaching it to the stylus (similar to how you would hold it) could work better but I don’t have any gloves to test that theory.

Hopefully this sparks something helpful for you.


Well, that is very interesting. I will be doing some tests so might try this one as well. But not sure how would water bottle be attached to the LR easily. I am using two stylus holders which I made, to attach stylus to LR. I could imagine bottle on the top of stylus but not sure if that would have simmilar effect haha

But definitely fun idea. Thanks for sharing.

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