Slide 8 of 157 · The simple comparison: benefits, compromises and selection

Welcome to chapter 2: The simple comparison: benefits, compromises and selection. I'm Diggy Breiling, founder of FPD.DEV, The Future of Display and Systems Development. Our goal is to build a shortlist from the operating conditions instead of choosing a universal winner.

Slide 9 of 157 · A useful first shortlist

Resistive touch detects a physical press; it accepts many glove and stylus types but needs force and a deformable sensing structure. Projected capacitive, or PCAP, detects an electrical field change; it supports a clean glass front and rich multitouch, with tuning needed for gloves, water and electrical noise. Infrared detects interrupted light paths; it can keep sensing electrodes out of the view but needs optical paths around the perimeter. Surface acoustic wave, or SAW, detects changes to waves travelling along glass. Optical camera and shadow systems infer position from light patterns. Pen digitizers add a specialized precision tool. Force sensing and haptics add information or feedback; neither automatically supplies a complete finger-touch system.

Slide 10 of 157 · Compare conditions, not slogans (1)

Resistive touch is useful when the user may wear gloves or use a passive tool. Check the required press force, surface wear, optical performance and number of simultaneous contacts. Surface capacitive is a glass-based option often found in legacy equipment; conductive coupling, single-touch operation and replacement availability matter. Projected capacitive, or PCAP, supports a flush glass front and multitouch. Its performance still depends on sufficient signal margin through the actual cover and glove, with the expected water and electrical noise.

Slide 11 of 157 · Compare conditions, not slogans (2)

An infrared grid can cover a large area without requiring an electrically conductive touch. But the object must be large enough and block enough infrared light to be detected. Test sunlight, blocked paths and the height of the sensing plane above the glass. Camera and shadow systems combine optical views; their geometry and contamination still matter. Surface acoustic wave, or SAW, offers a glass surface and light touch. Water and other sound-absorbing material can disturb its waves, so edge construction and the operating environment are important.

Slide 12 of 157 · Compare conditions, not slogans (3)

Pen digitizers and force sensing serve different needs. A compatible pen system can support precise writing and drawing, but the pen, digitizer and host must work together. Force sensing measures how hard the user presses and can support deliberate confirmation. It does not automatically identify every contact position; that depends on the sensing arrangement. Haptics is feedback to the user, not a position measurement.

Slide 13 of 157 · Tradeoffs become requirements

Begin with exclusion criteria: a mandatory glove, a forbidden raised bezel, a required stylus, or an unacceptable emission may eliminate a candidate. Then compare the survivors using measured evidence and lifecycle cost: sensor, controller, glass, integration, tooling, qualification, service and replacement. A weighted score is useful only after mandatory requirements pass. Do not let several convenient features outweigh a failed critical requirement. Record unknowns as unknowns, not average scores. Compare matched configurations. A lab demo on thin glass and a rugged assembly with a heater, thick cover and long harness are different systems. Request test conditions with any claimed accuracy, sunlight immunity or wet-glove performance.

Slide 14 of 157 · Apply the idea

Choose two candidates for a wet outdoor kiosk with gloves. Name the evidence that would decide between them. Pause here and consider your answer. A tuned PCAP assembly and an optical/IR assembly are plausible candidates. Compare the actual gloves, water film and droplets, solar incidence, edge performance, false touches, cleaning and mechanical envelope. Resistive may also fit if the interaction and durability requirements allow.

Slide 15 of 157 · Chapter 2 complete

For help turning your requirements into a custom display, contact FPD.DEV. These are living courses. Enrolled learners will typically receive a notification when chapter content is updated, so please sign in and enroll in the course. Next is Chapter 3: Resistive touch: a press becomes a voltage. I'm Diggy Breiling, founder of FPD.DEV, The Future of Display and Systems Development. Thank you for joining me.

A tuned PCAP assembly and an optical/IR assembly are plausible candidates. Compare the actual gloves, water film and droplets, solar incidence, edge performance, false touches, cleaning and mechanical envelope. Resistive may also fit if the interaction and durability requirements allow.

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.