Capacitive touch trigger as an isolated system

esahakian · Jun 1, 2019

I need a way to trigger a capacitive touch screen device (like a tablet) using an isolated system without touching it. For example a kid places a small gadget on a tablet screen and the gadget will trigger a capacitive touch on the tablet without requiring anyone to be holding the gadget or the gadget being tethered to anything. So as long as the gadget is sitting on the tablet screen it is continuously emitting a touch trigger to the tablet. Basically a stylus that is an isolated (independent) system.

Do anyone know of such a circuit using an Arduino or something else? Or perhaps you can point me to the right resource for building such a circuit?

rjenkinsgb · Jun 1, 2019

The item touching the screen must add sufficient capacitance so the voltage in the sensing electrodes in the screen changes.
It needs to be either connected to something large, or have a capacitive connection back to the screen ground.

A small electrically isolated item will not work on a capacitive screen.

It could work with a digitiser (or dual mode) screen, as they work by detecting a resonant circuit, which could be embedded in an object.

You can (or could) also get "touchscreen" devices that did not rely on contact at all, they had an array of IR emitters and detectors around the screen and a finger (or any object) within about a mm of the actual screen surface blocked some part of the IR beam "mesh".

esahakian · Jun 2, 2019

rjenkinsgb said:
The item touching the screen must add sufficient capacitance so the voltage in the sensing electrodes in the screen changes.
It needs to be either connected to something large, or have a capacitive connection back to the screen ground.

A small electrically isolated item will not work on a capacitive screen.

It could work with a digitiser (or dual mode) screen, as they work by detecting a resonant circuit, which could be embedded in an object.

You can (or could) also get "touchscreen" devices that did not rely on contact at all, they had an array of IR emitters and detectors around the screen and a finger (or any object) within about a mm of the actual screen surface blocked some part of the IR beam "mesh".

Thanks rjenkinsgb
So it looks like I might need to pursue two alternative paths.

1) IR emitters to detect if an item within proximity of the tablet.
2) Use passive RFID

Capacitive touch trigger as an isolated system

esahakian

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Capacitive touch trigger as an isolated system

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