# EMR pressure detection

## Pressure detection

There are two techniques. The techniques have two things in common:

* The pressure is measured by the pen.
* Then transmitted to the tablet.

Their differences is in the mechanism used for pressure detection.

## Modern design

The **modern technique:** the nib contacts a pressure sensor inside the pen. The nib goes through the hollow ferrite rod and then the nib touches the pressure sensor deeper in the pen. The ferrite rod does NOT move. The pen digitally encodes pressure data into the electromagnetic signal generated by the inductor coil. The tablet then decodes the digital pressure information from the signal.

## Old design

The **very old technique:** Nib goes into the hollow ferrite rod but does not come out the other side. The nib is shaped in such a way that it is firmly embedded in ferrite rod. Ads the nib moves, so to does the ferrite rod. The movement of the ferrite rod changes the resonant frequency of the inductor coil. That change in frequency is then sensed by the tablet and translated to pressure.

## Video

In a video I published in 2022 ([**How do EMR pens work**](https://www.youtube.com/watch?v=Vv668I4LEdg)) I showed this older technique.

a specific method to detect pressure is shown. This method involves moving the ferrite core which then alters the resonant frequency of the LC circuit. This design is from a very, very old EMR pen design.

Modern designs use a separate pressure sensor which is more reliable for detecting pressure.

<figure><img src="/files/pN1z8J9grarNdXho2sUr" alt=""><figcaption></figcaption></figure>

The OLD EMR pen design can be seen in [Pen teardowns](/drawtab/guides/pens/pen-teardown-huion-pen80.md).


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