10.1 Pen digitizers: EMR, active pens and passive styluses

Slide 66 of 157 · Pen digitizers: EMR, active pens and passive styluses

Welcome to chapter 10: Pen digitizers: EMR, active pens and passive styluses. I'm Diggy Breiling with FPD.DEV, The Future of Display and Systems Development. Our goal is to select a pen system by protocol and sensing mechanism, not by tip appearance.

Slide 67 of 157 · Three very different tools

A passive resistive stylus applies force. A passive capacitive stylus provides suitable electrical coupling and contact geometry. Neither automatically provides pen identity, hover, tilt or pressure information. Wacom's EMR approach uses electromagnetic coupling between a sensor and a resonant pen. The sensor field can power a compatible battery-free pen. This differs from an active electrostatic pen communicating with a compatible capacitive sensor system. The word 'active' is not enough to establish interoperability. Protocol, controller, firmware, operating system and application support must match. A pen that writes on one tablet may do nothing on another.

Slide 68 of 157 · Coordinate, pressure and intent

Pen systems may report hover, tip contact, buttons, pressure and tilt, depending on the hardware and protocol. Position resolution and pressure levels describe reporting capability; they do not directly establish handwriting quality. Inspect the first stroke, diagonal lines, slow curves and edge writing. Look for offset between displayed ink and the tip, jitter, delay and missing initial segments. Palm rejection should suppress unintended hand input while retaining intended pen behavior. The animation separates the sensor's field, compatible pen response and reported position. It does not model electromagnetic field strength or pen power consumption.

Slide 69 of 157 · Integrating pen and finger touch

A service tablet may need both gloved finger interaction and detailed annotation. Specify which gestures are permitted while a pen is in range and what happens when the pen battery is low or the pen is lost. Check the final display stack and nearby metal for effects on the chosen pen system. Compare optical parallax with sensor-coordinate offset; calibrating coordinates cannot remove the physical distance between tip and image. Test the intended application. A host may recognize a pen while the application ignores pressure or handles erasing incorrectly. Treat accessory replacement and protocol longevity as lifecycle requirements.

Slide 70 of 157 · Apply the idea

A specification says 'supports stylus.' What clarification is essential? Pause here and consider your answer. Identify passive resistive, passive capacitive, EMR or the exact active-pen protocol, then required pressure, hover, tilt, buttons, palm rejection and application behavior.

Slide 71 of 157 · Chapter 10 complete

Complete the chapter exercise and review any open questions. Next is Chapter 11: Force sensing, haptics and touchless extensions. I'm Diggy Breiling with FPD.DEV, The Future of Display and Systems Development. Thank you for joining me.

Identify passive resistive, passive capacitive, EMR or the exact active-pen protocol, then required pressure, hover, tilt, buttons, palm rejection and application behavior.

Accuracy

Closeness of a reported coordinate to a defined reference position.

Precision

Repeatability or spread of results under specified conditions.

Resolution

Smallest coordinate increment or representable change; not equivalent to accuracy.

Latency

Time between explicitly defined input and output events.

PCAP

Projected capacitive touch; patterned electrodes sense electrical coupling changes.

Self-capacitance

Measurement of an electrode relative to an electrical reference.

Mutual capacitance

Measurement of coupling between transmit and receive electrodes.

Baseline

Reference measurement used to identify changes associated with touch.

SNR

Signal-to-noise ratio; specify the signal, noise measure and conditions.

SAW

Surface acoustic wave sensing through controlled propagation on a surface.

APR

Acoustic pulse recognition; a touch-generated mechanical response is used to locate contact.

DST

Dispersive signal technology; a bending-wave sensing implementation.

EMR

Electromagnetic resonance, used by compatible pen digitizers.

Haptics

Tactile feedback produced by the system.

HID

Human Interface Device class/protocol family; the descriptor defines report interpretation.

Report descriptor

Data describing the structure and meaning of HID reports.

Contact ID

Identifier used to distinguish and track a contact.

I2C

Two-wire synchronous bus; raw I2C communication does not itself implement HID.

SPI

Synchronous serial peripheral interface, with device-specific protocol behavior.

UART

Asynchronous serial hardware; electrical levels and framing must be specified.

Optical bonding

Joining optical layers with a transparent material to manage the interface.

Parallax

Apparent relative position shift caused by viewing separated planes from an angle.

NVIS

Night Vision Imaging System; pronounce 'en-vis' in this course.

Qualification

Evidence against a defined set of requirements for an identified configuration.

Validation

Evidence that the system satisfies its intended use.

Verification

Evidence of conformance to specified requirements.

Ghost touch

Reported contact that does not correspond to an intended physical touch.

Palm rejection

Classification or suppression of unintended hand contact.

On-cell / in-cell

Touch structures at a display-cell surface / integrated within the display structure; verify supplier construction.

Touch plane

Geometric region in which the sensing system detects an object.