Explained: How does a Drawing Tablet work (Wacom Disassembly)

Although drawing tables have been in the market for decades now, in the last few years we have seen a huge surge in their popularity.

Drawing tablets are used by a wide range of individuals.

Students use them for note-taking, teachers for online tutoring, artists for making digital art and large corporations use them for digital signatures and presentations.

Coming from a science background, we have spent the last two weeks taking a deep look at the internal components by disassembling our very own drawing tablet.

We also dug up some blueprints and studied circuit diagrams in order to get an understanding of how these drawing tablets work.

By the end, we were amazed by the incredible engineering that goes into making these (seemingly simple) drawing devices, and we are very excited to share out findings with you.

Before we get into details, here is an overview of how a drawing table works.

Quick overview: How do drawing tablets work (graphics tablet)

Graphic tablets consist of a tablet and a compatible stylus.

When you hover the pen above the tablet, it works like a mouse pointer.

And when you touch the tip of the stylus on the tablet surface and drag it along, it acts as a mouse with the left mouse button pressed on.

What is the main advantage of a drawing tablet?

A mouse is great for general pointing, navigation, and clicking on things. But when it comes to making accurate cursor movements (like drawing shapes/ taking notes), it can’t keep up.

The drawing tablet, on the other hand, feels as natural as writing with a pen and allows you to perform precise movements and make intricate strokes. 

Plus, it has the ability to detect pressure changes.

Probably one of the most interesting things about these graphics tablets is the fact that – “the styluses that come with pen tablets do not have batteries inside them“.

Not having batteries makes these styluses lighter, maneuverable as well as last-longer as there is no battery degradation.

But it raises some obvious questions.

1. How a stylus is able to measure pen pressure and record button clicks, in spite of not having a battery inside them?
2. And what role does the tablet plays in this whole operation?

Where does the stylus in a drawing tablet get its power from?

The battery-free stylus of the pen tablets work on a technology called “electromagnetic resonance (EMR)” where they get their power wirelessly from the tablet itself.

Inside the tablet, you will find a grid of parallel wires that transmits electromagnetic waves.

The stylus has a coil of wire that converts electromagnetic waves into electrical energy.

Electrical energy generated by the coils is then used for measuring pen pressure and button clicks.

The measured data is sent back to the tablet in the form of electromagnetic waves generated by the coils of the stylus.

The tablet scans for incoming data (electromagnetic waves). The location at which the tablet receives the signal is calculated and that is how the position tracking is carried out.

Here is a pictorial representation of the working of a drawing tablet.

This quick overview definitely paints the big picture and describes how pen tablets work. But it leaves some interesting key details that are worth knowing.

Even though the next section is a little heavy on the technical jargons and scientific terms. But we promise – it is still easy to understand even if you are not from a science background.

Drawing tablet: The fundamental building block

In order to understand how graphics tablets work there are two fundamental properties, you need to know.

1. Magnetic field due to current-carrying wire
2. Electromagnetic Induction

Magnetic field due to current-carrying wire

When a current is passed through a conductor (wire), a magnetic field is produced around it. 

The sub-atomic particles in the conductor like the electrons moving in atomic orbitals are responsible for the production of the magnetic field.

Here is a simplified diagram showing the magnetic field in a current-carrying wire.

This fundamental property of a current-carrying wire is an essential part of a drawing tablet.

It plays a big role in the transmission of electromagnetic waves from the tablet, which ultimately powers the stylus.

But as you can see the electromagnetic field generated by a wire is emitted in all directions. Plus the EM-waves generated by a single wire is way too weak.

Here is a diagram explaining how multiple parallel wires are used to generate a stronger EM wave and how their direction is controlled using an electromagnetic shield.

Now that we have seen the basic structure of how the tablet transmits electromagnetic field above the surface.

Next, let’s have a look at how the stylus converts the incoming ElectroMagnetic waves into electric current.

Electromagnetic induction

When the electric current is passed through a coil of wire, an electromagnetic field is generated around it.

But the opposite is also true.

When a coil of wire experiences a changing magnetic field – a voltage difference (ie. electric current) is induced in the wire.

Here is a representation of what the electric field in a current-carrying coil of wire looks like.

This property of electromagnetic induction is used inside the stylus for the generation of electric current as well as transmission of data to the tablet via EM waves. 

How Wacom tables work – circuit diagram and function

Contrary to popular belief, the position tracking is not done in the stylus, the tablet is the one responsible for tracking the pen.

It does so with the help of horizontally and vertically arranged wires which detect the incoming signal from the stylus. The underlying circuitry helps narrow down the location at which the signal is received.

Here is a block diagram of the wire grid (that helps transmit and receive electromagnetic waves) along with the underlying circuitry that handles the overall operation.

Introduction to the tablet circuit

– Vertical parallel wires (white) – Detects pen movement along the x-axis

– Horizontal parallel wires (yellow) – Detects pen movement along the y-axis

– Selection circuit – Selects individual wires along the x and y-axis

– Connection switch circuit – Switches between transmission and reception circuit

– Transmission circuit – Transmits electromagnetic pulses at a defined frequency

– Receiving circuit – Receives signal/ data from the pen 

– Processing device – Controls the overall operation (including wire selection and switching between transmission and receiving circuits)

Transmission of electromagnetic wave by the pen tablet

Everything starts with the transmission circuit (see the image above). 

The transmitter contains an oscillator that creates a signal of a predetermined frequency.

The transmitter contains additional circuitry which transforms this continuous signal into a”pulse signal“. 

The signal is carried forward through the connection switching circuit and reaches the selection circuit which distributes the signal to every single wire on the x-axis as well as the y-axis.

Once it travels through the wire, it is transformed into electromagnetic waves and transmitted in all directions.

An electromagnetic shield is placed at the back of the wire grid that absorbs em waves coming towards the back.

This results in EM waves only being emitted from the front – where it comes in contact with the stylus.

Once the electromagnetic wave has been transmitted, the tablet prepares itself for the reception of the signal.

The connection switching circuit switches from the transmission circuit to → the Reception circuit.

Stylus – power generation and pen measurements

In the meantime, when the stylus comes into contact with the electromagnetic wave from the tablet, it experiences a sudden change in EM-field.

The stylus has a coil of wire near its tip. When the coil experiences a pulse of electromagnetic wave, an electric current is induced into the stylus. 

This induced current is used for measuring pen pressure as well as button presses and sent back to the coil at the tip.

Next, the coil converts the electrical data-laden signal back into an electromagnetic wave and sends it to the tablet from the tip of the stylus.

How does a drawing tablet locate and track the position of the stylus? 

When the EM wave emitted by the stylus comes in contact with the wires on the tablet, it results in a small voltage increase. 

The wires near the tip experience the largest voltage increase. The induced voltage on the surrounding wires slowly tapers off as you move away from the tip.

At this stage, the Processing device sends an instruction for the selector circuit to select the number of coils that have voltage above the above-predetermined detection level along both the x and y-axis.

The peak coil (coil with the highest voltage difference) on both the x-axis and y-axis is also selected.

Finally, the Processing device mathematically maps out the exact location based on the selected coils in x and y-axis and that is how location is calculated.

Extracting pressure data from the received signal

The electromagnetic waves sent by the stylus also contain embedded information containing pressure measurement as well as button clicks.

To process this embedded data, the received signal from the pen is amplified and sent to the receiving circuit. 

The pressure data is stored in the form of phase difference (higher pressure results in a larger phase difference and vice versa).

In order to decode the pen pressure, the receiving circuit compares the received signal from the pen to the original signal from the transmitter. 

Then it calculates the phase difference between them and sends the pressure information to the Processing device.

The processing device reports the location, pressure as well as button click data to the computer, which is finally displayed on the screen.

Position detecting and path tracing in the tablet

This whole cycle runs incredibly fast, then repeats again, a couple-hundreds times a second.

On each cycle, the tablet takes the location snapshot of the stylus, then another snapshot the very next moment – and that is how it tracks the pen movements.

Every time the tablet captures location, pressure, and button press snapshot and sends it to the computer, it is counted as a 1 report.

Most of the pen tablets available in the market come with over 200 reports per second capability, which is incredibly fast.

That is how the tablet is able to track the pen movements so accurately.

Role of pen tablet drivers

If you are a digital artist or you own a pen tablet, you know that – all the drawing tablet comes with a driver.

The driver is a software application that gives you advanced tablet settings and helps you set the custom shortcut button, calibrate the drawing area as well as fine-tune the responsiveness of pressure sensitivity, etc.

In addition to providing advanced settings, the tablet driver also helps with communication with the operating system.

The computer in itself is not designed to work with data such as pressure sensitivity and tilt sensitivity. The driver helps the computer to understand, handle, and process pen and tablet data for the smoother functioning of a drawing tablet.

How do display tablets work?

While graphics tablets are just plastic tablets with pen support, a display tablet has a screen built right into the drawing surface. With a graphics tablet, you have to look at the 

With a graphics tablet, you have to look up at the monitor screen while drawing over the tablet on the side, this requires some hand-eye coordination that takes about a few days to get used to drawing this way.

Drawing on the display tablet on the other hand, is much more intuitive as you are drawing right over your characters just like you do when using paper and a pen.

While a display tablet may be called a superior technology as it has an integrated screen, but the tablet part that powers the pen tracking and pressure measurement is very similar to the normal graphics tablet.

Or in simpler words, a display tablet is just a graphics tablet with a screen slapped on top of it.

In fact here is a link to the video of a guy attaching an external display to a graphic tablet – essentially converting it into a display tablet.

Stylus and tablet compatibility

The internal components inside the stylus such as a capacitor and variable capacitor and designed as such that they only work with the resonant frequency of the tablet.

In other words, the pen and the tablet has a defined frequency on which they work.

If you try to swap the stylus with the stylus of some other pen tablet, they may not work as they are not designed to work on the same frequency.

Even different models of tables from the same graphics tablet brand might not work with each other.

With that said, most drawing tablets brands usually have a list of compatible styluses on their website and they do sell styluses saperatily in case you break the original one.

Resources(all links open in new tab)

Magnetic field due to current carrying conductor
Magnetism and magnetic field
Phase difference due to capacitors/ inductors
Resonance
ScanLime 1, 2, 3
US5028745A, US8212550B2, US8395598B2, KR101459535B1, EP2015030B1
Capacitive stylus