Make Touch Pen on a 2-Axis Lego Robot invisible to Capacitive Phone Touch Screen

Thread Starter


Joined May 4, 2024
I am seeking ideas, or thoughts, on how to make a cable connected touch pen invisible to the capacitive touch screen of a modern smartphone without mechanically lifting the pen (see illustration).

This is for a two axis (no lifting!) planer lego robot I am building to teach machine learning, in particular by showcasing how to control remote control a smartphone via various methods like "AI" (see picture). Unfortunately I don't have sufficient electro mechanical knowledge (software engineer) and am stuck now...

What I know:
  1. Modern smartphones use a Mutual Capacitance Touch Screen, sometimes called a Field Projected Touch Screen (▮). The system is the same from iPhones to Androids... though sensitivity varies.
  2. Taking the tip insert of a touch pen (○) and placing it on the screen triggers no touch.
  3. However, connecting the tip with a cable (⏚←◉▮) and that cable to even to highly isolated objects like rubber gets registered as a touch.
  4. This of course leads to an endless registration of a touch...

My Thoughts:
  1. (⏚ ←◉▮) — touch — When the tip with a cable absorbs / couples the capacitive field...
  2. (↯ →○▮) — no touch ? — ...can't we use some circuitry that puts somehow just enough "power" into the tip so it doesn't get registered by the sensing electrodes anymore? Like this:

Illustration of a touch pen tip connected with a wire.
I already plan to use a Raspberry Pi for the software aspect, but this device could drive some sort of circuit:

Picture of a lego planer cable robot with strings having a touch pen tip in the middle next to an image of a raspberry pi.

Thank for your input.