I am interested in testing a capacitive touch device for reliability by simulating touch events periodically.

I would like to do this purely electrically if possible (no mechanical parts), or with a mechanical relay. I would like to avoid servos, motors, etc.

How can I design a circuit which can switch between two states? In one state, it would generate a touch on a capacitive device, in the other it would not.

  • \$\begingroup\$ Simulating a touch would, to me, involve a mechanical part, namely "the finger". Doing it without moving parts requires you to define what you are wanting to simulate much more precisely than what you have stated. \$\endgroup\$
    – Andy aka
    Aug 9, 2016 at 10:35
  • \$\begingroup\$ I would like there to be a device that is always physically in contact with the touchscreen, however I would like to be able to toggle this between triggering a touch event and not triggering a touch event. \$\endgroup\$
    – plexer
    Aug 9, 2016 at 11:06
  • 1
    \$\begingroup\$ Just to confirm, the touchscreen senses projected capacitance and not the simpler surface capacitance? \$\endgroup\$
    – nanofarad
    Aug 9, 2016 at 11:43
  • \$\begingroup\$ I am actually unsure. Is there a simple way to test? \$\endgroup\$
    – plexer
    Aug 11, 2016 at 13:49

2 Answers 2


I think a metal pin connected to the ground would be enough.

Some Youtube videos show that it works fine, but for some systems (like smartphones) you have to simulate a real size finger.

By commuting ground on this pin you could activate or deactivate touch simulations.

  • 1
    \$\begingroup\$ OK. I edited my answer. \$\endgroup\$
    – AdriZ
    Jul 20, 2020 at 10:42

FWIW, For those in future interested in an answer for this.

The human finger is 98% water which has a dielectric constant of 80 compared to plastic which is ~ 4. The required test must provide some insulation material which is soft and has this equivalent dielectric constant and make constant, with a surface area just slightly above the minimum required to be detected.

The only dielectrics approaching or exceeding this are toxic materials inside wet capacitors. Glycolic Nitrile gloves used in medicine are about 27 would be perfect to protect glass yet thin enough to couple adequate pF to touch screen yet isolated between the contacts the size of a large straw but may be short in length to simulate a finger making contact.

However the capacitive touch screen must require a bridge capacitance across the matrix grid of the electrodes beneath the thin glass surface. To make contact with the simulated finger is easy but to modulate its local bridge capacitance is not easy without motion.

Perhaps two tiny finger contacts in close proximity can be bridged with an electronic switch to simulate a finger contact but this depends on the algorithm used to avoid false contacts such as rain drops.

enter image description here

The relationship between the size of the contact area to the tiny electrodes or in this case 2 tiny fingerpads close together than can be separated and switched electronically together to become 2 series capacitors shunting the glass surface may be possible but difficult to overcome the touchpads false detection algorithms.


simulate this circuit – Schematic created using CircuitLab


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