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Capacitive smart surface questions

Summary: 2 Replies, Latest post by Marius Ursu on 29 Apr 2016 12:51 AM PDT
Verified Answers: 1
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Marius Ursu's picture
2 posts


I am building a device that allows objects to be recognized on a smart surface. We decided to stick with capacitive sensing.
See this for an example:
The final design will be a modified version of the Magic Trackpad.
It consists of a few blocks:
Sensor for Touch (10", 10 points) -> Controller -> Raspberrypi(outputs processed data - OBJ_ID at (X,Y) )+BT -> Tablet-> Application


I have a few questions:

-Is it realistic finish integrating the Controller and Digitizer into a working prototype in 1-2 months? I am a bachelor electronic engineering student
There is an option of buying a development kit with a screen or ready products but this is not really designing. Even with this option there is a lot of work to be done still, so i am worried about the timeline.
example of controller:
example of Digitizer:

-Do you know of Capacitive Touch controllers that are able to process Z-axis data/proximity/hover as well, and output a diameter of the touch or distance from the surface? I need this in order to differentiate between merely taking your hand off the object, and taking the object off the surface. Other ways of sensing this difference are welcome.

I am waiting for the Cypress datasheets. I was considering this one:

- I am having difficulties with finding capacitive digitizer manufacturers that have them readily available at a good price: vs
Where should i seek these screens? I found 3M, AMT, DMC but they are a lot more expensive than digitizers.

yuva's picture
Cypress Employee
21 posts


Welcome to Cypress Forum. We have trackpad design with self  cap (CSD), but with this multi-touch is not possible. For multi-touch mutual cap (CSX) is required. We have CSX for keypad and are currently developing this for trackpad. You may choose the one suitable for you.

You may refer to the following details

1. Kit ->

2. Controller ->

You can also do the proximity sensing using this device. Refer to the following application note for details of using proximity.

We don't have any details about the ITO screen (digitizer). You may have to contact third party vendor for this.




Marius Ursu's picture
2 posts

Currently, i am trying to see if using an off-the-shelve touch sensor, which outputs coordinates will be enough. Example:

In case i have to delve deeper into Z-axis or diameter of the touch, i will be integrating a controller with a sensor by myself. Example:

How much time do you estimate that the integration of Plan B will take?

To go back to the objects, assume i have no access to Z-data or the diameter of the touch, thus i don't know if the object is approaching or departing. I only have binary: on/off state.

I have the issue of not being able to tell the difference between an object being off the surface, and it simply not having a human hand touching it. False state problem.

Therefore, i came up with the solution to make the object totally active. This can be done with either:

  • internal power and circuit; How does this work?
  • external power and circuit (wireless charging)
  • attach a long wire, making the object capacitive itself. 10cm was enough for me. Why does this happen?
  • connect objects to ground. perhaps with a layer of conductive foil that is grounded on top of the sensor. this layer connects to the objects through the feet. But here my EMF knowledge stops and i need to experiment.

But this brings up the issue of only having 10 touch points, so very limited nr of objects simultaneously. I attempted to solve it in the following ways:

  1. Make the object switch: capacitive/non-capacitive/capacitive with a frequency determined by me. This eliminates the limit of object nr imposed by 10 touch points. See this paper for more
  2. Make the object active only for 5 seconds after the human touches it. This eliminates the limits of object nr due to 10 touch points. But still lets us see a correct state change.
  3. Fuse sensors in order to use one sensor underneath the touch that can tell me if the object is on the surface or not. If i use magnetism, i might have interference.

So i am wondering if you knew of other ways to solve that problem, and if you know of ways to accomplish those 3 solutions.


I am currently research Wacom and more fundamental physics to understand what is happening.

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