EMR

Overview

EMR technology was introduced to drawing tablets by Wacom. And they held all the core key patents to EMR. Those core patents have expired and now other manufacturers can build increasingly sophisticated EMR designs which are begin to rival Wacom products.

EMR key features

  • Powering the pen - With Passive EMR the pen gets power from proximity to the tablet. However with Active EMR: The pen gets power from a battery inside. More here: Active EMR vs Passive EMR

  • Position detection - The basics of how the tablet detects position are described here: EMR position detection.

  • Hover (i.e. proximity detection) -

  • Pressure detection - See this document for details on EMR pressure detection. It also contains a clarification of pressure detection in the video below (which depicts a very old way of doing pressure detection).

  • Tilt detection - more here: EMR tilt detection

  • Barrel rotation detection - very rare in EMR pens

  • Communication of button press information

Explanation of how EMR works

EMR Concepts vs Implementation

Think of the EMR design illustrated in the video as a baseline example that demonstrates the fundamental concepts, different manufacturers can tweak this design in their implementation.

Resonant frequency

The exact resonant frequency used by the pen will vary.

In the case of the Wacom Bamboo Fun tablet (CTH-661) the frequency is around 750KHz. Source: the last 10 seconds of this scanlime video: https://www.youtube.com/watch?v=oKVCwPn6OPI

How fast does the tablet switch between sensing the pen and sending it power?

We don't know.

We suspect this is MUCH faster than a typical pen report rate of 200Hz.

Other pen technologies

Even though EMR is used in drawing tablets, there are many other pen technologies in the market, such as AES, Apple Pencil, etc. More here: Digital pen tech

Apple Pencil

The Apple Pencil does not use EMR. Apple uses a proprietary protocol for their pen. If you are curious about what is inside an Apple pencil, see this video: https://youtube.com/shorts/M9sArtVjRps?feature=share

EMR Technical resources

More here: EMR technical resources

Circuit simulations

The companion video contains several circuit simulations.

I used the Falstad tool https://www.falstad.com/circuit/ to create those simulations

Last updated