Hi all,

I’m trying to trigger a capacitive touch button (like on a humidifier / appliance panel) using a mechanical “finger” actuator.

Problem:

• The button works perfectly with a real finger
• But plastic or regular rubber tip does NOT trigger it
• I already tried silicone/rubber tips, but they seem non-conductive

What I understand so far:

• It’s a capacitive sensor → needs change in capacitance (like human body)
• So I probably need conductive material or something that mimics a finger

Questions:

1. What is the best material to attach to the actuator tip?
   • conductive rubber?
   • ESD foam?
   • metal + capacitor?
2. Does it need to be connected to ground / large metal mass, or should it work standalone?
3. Any reliable product recommendations (AliExpress / EU shops) that actually work?
   (I already got “silicone tips” but they were not conductive…)
4. Would a simple copper tape tip be enough, or is a more complex circuit needed?

Goal:

• Reliable triggering without touching it by hand
• Ideally simple (no complex electronics)

Thanks a lot for any advice!

 

Try touching a small capacitor (e.g. 100pF) between the button and the device metal chassis, and see if that turns it on.
If that doesn't work, you might try adding some conductive foam to the end of the capacitor where it touches the button.

 

Try touching a small capacitor (e.g. 100pF) between the button and the device metal chassis, and see if that turns it on.

well but the device is in plastic.

can you show some sample - ie its from aliexpress? conductive foam


thanks

 

but the device is in plastic.

Then you will need to go inside and find a ground point, or use the AC safety ground if it has a three-prong plug.

can you show some sample - ie its from aliexpress? conductive foam

Here.

 

Then you will need to go inside and find a ground point, or use the AC safety ground if it has a three-prong plug.

it has only 2 poles p/n no ground


the foam you posted... i still need a cap + ground? thx

 

You need a large enough capacitance between the touch pad and ground. The material does mot matter, except it cannot be an insulator. If you cut your finger off and touch it to the pad while wearing insulated gloves, it likely would not trigger it, It is the size of the whole body that provides the capacitance.

 

got it ... so any idea how to simulate it... the easiest way? thanks!

 

are you certain its capacitive , transparent screens can be resistive !
types of capacitive sensors,
you change the frequency of an oscilator
you induce a voltage from ac pickup

insulate your finger with layer of say cling film , if sencor still works , then its not resistive

 

insulate your finger with layer of say cling film , if sencor still works , then its not resistive

I don't think so – resistive touch relies on the pressure of the touch to slightly deform the surface of the screen, compressing the layer of resistive material in the touch screen, changing its resistance.

 

I don't think so – resistive touch relies on the pressure of the touch to slightly deform the surface of the screen, compressing the layer of resistive material in the touch screen, changing its resistance.

That is certainly one way. Normsly used on 2d displays of old .the other is comb of conductors used as buttons on things like washing machines.

 

got it ... so any idea how to simulate it... the easiest way? thanks!

See posts #2 and #4.

 

@BobTPH
@crutschow seems doesnt work?
i touched one leg of the 100pf cap and touched the sensor with other one, nothing....
then i connected one leg of the cap to some metal item - not the machine i want to control - also nothing?\
and i also tried one leg of the cap to the ground pole of the AC wall socket, and touching machine "button" - nothing.

no clue

 

@BobTPH
@crutschow seems doesnt work?
i touched one leg of the 100pf cap and touched the sensor with other one, nothing....
then i connected one leg of the cap to some metal item - not the machine i want to control - also nothing?\
and i also tried one leg of the cap to the ground pole of the AC wall socket, and touching machine "button" - nothing.

no clue

Could be that the capacitor leg is not wide enough to "cover" the switch sensor .
Try a bit of kitchen foil on the end that touches the button ?
A bit of experimentation might be needed

 

@drjohsmith thats why that foam was proposed?

200x200mm 3/5/10/15mm ESD Anti Static Pin Insertion High Density Foam Soundproofing Foam Sound-Absorb Noise Sponge Foam

 

Hi,
thanks ... the setup provided with 100pF works fine.

 

What's the wire connected?

 

just metal speaker stand.

i think when i disconnect that other leg of the cap it didnt work at all.

 

well its weird .. i just disconnected that other leg of the cap ... and it worked.
maybe "remaining capacitance"?

thanks