How to Use a Samsung Note 8 Stylus

From the first day of use, I was very interested in the question. how on a regular capacitive screen that only a certain touch area perceives was it possible to achieve the work of a thin stylus, and even with a button and several degrees of depression? In this article I will try to answer this question by telling a little about interesting technical solutions applied in this phone.

See also: Samsung Galaxy Note II teaser published

In anticipation of the upcoming Unpacked event, before the start of which a little more than one week remains, the Korean company Samsung publishes a teaser Galaxy Note II. The stylus, which will be equipped with the next generation tablet phone, comes into view on the. As with the Galaxy Note 10.1 tablet, which can be seen as the older brother of the Note II, the ad focuses on creativity. Recall that not so long ago, Samsung said it had sold 10 million Galaxy Note. It is expected that the same success awaits his follower.

First, let’s recall the theory.
A capacitive screen determines the point of contact by the leakage current when the capacitor is charged, one of which is the telephone screen and the other is the human body. On the back of the glass in your smartphone, thin lines are made of transparent conductive material (they can be seen if you look at a certain angle on the screen in good light).

Capacitive sensor: mini-capacitors (in the form of the letter H) and the conductors between them.

The touch screen controller charges and discharges these capacitors many times per second with a limited current, each time measuring the capacitance of each of them, and comparing it with the standard capacity recorded in memory. As soon as you touch the glass with your finger, you become such a large lining of the capacitor that you can charge.
Naturally, this will require energy, which the controller vigilantly monitors. As soon as he discovers that a cell starts to consume a lot of energy (a lot. this is compared to normal consumption, but even for a regular LED it is crumbs), which with a limited current wraps up with an increase in charge time. he realizes that there is something to the glass then touched.

Based on information from several capacitors, you can calculate the location and area of ​​contact using fairly complex formulas. Or a few touches, the number of simultaneously determined touches is limited only by the controller and screen sizes (it is very difficult to fit 20 fingers on the screen in 3″)

This technology has several limitations. For several reasons, such as the inability to arrange the elements densely enough (transparency decreases), the limited conductivity of the glass, and the need to cut off interference from accidental touches, pickups, dirt on the screen, etc. I had to be content with a minimum touch area of ​​5×5 mm.
In addition, the object that touches the screen must have a sufficient intrinsic capacity comparable to that of the human body. What do we get as a result? Inability to use gloves (most of them have enough resistance to reduce the leakage current to a minimum that is not determined by the controller), the need for large styluses, which must be connected galvanically to the user’s body (therefore, most of them have a metal case).

What input systems work with styluses, can distinguish pressing force, and have excellent accuracy? These are electromagnetic antenna systems that are used in the vast majority of graphic tablets

Wacom graphic tablet with stylus:

The principle of their work is also not prohibitively complicated. the stylus transmits (signal) at a certain frequency, and the antenna inside the tablet receives. The controller can find out the exact position due to the cunning shape of the antenna, and information about the pressure on the stylus is transmitted by frequency or code messages.

How to Use a Samsung Note 8 Stylus

Tricky antenna inside the graphics tablet:

Exactly the same system is implemented inside the Galaxy Note (both I and II). At the top there is glass, on the back of which there is a capacitive sensor, below it is a screen, and below it is a transmitting and receiving antenna for the stylus.
So, to make it clearer, I drew a picture.

And here is the Wacom touchscreen controller (blue) that manages all this tricky economy, and the antenna cable (green):

What is interesting. a stylus with such a design does not need a screen as such, to determine the touch. just bring it to the screen and press the tip with your finger, and the controller will still register the click.
If you fix the tip of the stylus with tape. you can draw with a wave, without touching the screen.

So let’s summarize. The grid antenna located under the screen generates pulses with a certain frequency (judging by the estimates. tens of kilohertz), in the picture they are indicated as the carrier frequency. the orange arrow. These pulses are received by an inductor located in the stylus, which is part of the oscillatory circuit. The circuit is designed in such a way that after its “buildup” it is able to oscillate for some time by itself, at its resonant frequency, gradually spending the stored energy on heating and radiation. Of course, the heating there is minimal, by a fraction of a degree, as is the radiation, which is already weakening by a few centimeters. But energy is also spent little, probably a lot of work has been done on efficiency.
An oscillatory circuit, whose resonant frequency depends on the inductance of the coil (which, in turn, depends on the position of the tip), and on the capacitance of the capacitors that are part of it (it depends on pressing a button), emits at this frequency, which is accepted by anything the same antenna, and induces current in it. Now a current with a complex shape pulsates in the telephone’s antenna, consisting of two frequencies. the exact “transmitting” one and changing depending on the state of the stylus of the “receiving” stylus. over, at some points of the antenna, the receiving field strength is higher. where the stylus is closest to the surface of the screen. The controller determines this point, finds its center (this will be the place where the stylus touches), then filters the “transmitting” frequency, and after processing receives the status of the stylus. pressure on the pen and button status.
Really interesting? 🙂

You can see all the photos from the article in original resolution in the Picasa album.

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