PHOTOSENSORS Reference Design: Next-Generation HMI Evolving with Optical Sensing — A Thorough Explanation of Three Methods: Touchless, Optical Touch, and Force Sensing —

Human-machine interfaces (HMIs) must simultaneously meet diverse requirements, including hygiene, durability, design, and reliable operation with minimal malfunctions. Optical sensing is a technology that has recently attracted attention as a way to address these challenges. Because it uses light to detect distance, contact, and pressure, it can operate stably even in environments where capacitive sensing or MECHANICAL SWITCHES are difficult to use.
Vishay provides three types of Reference Designs (design information: Quick Design Guide, BOM, schematic, PCB Gerber data, 3D Step files, and software source code) free of charge, enabling the rapid design of HMIs utilizing optical sensing.
The Quick Design Guide included in Reference Design is the latest technical document that systematically summarizes the following three methods.

• Touchless
• Optical Touch
• Force Sensing (Optical Force Detection)

This column provides a clear explanation of the mechanisms, design points, and suitable applications of each method described in the Quick Design Guide, from the perspective of a development engineer.

1. Touchless – Distance detection using VCNL36828P

Touchless Switching – System Overview

Touchless technology detects an increase in reflected light when a finger approaches a surface. Because it allows operation without touching buttons, it is increasingly being adopted in products where hygiene and design are important.

1-1. Mechanism: Detects the "amount of change" in reflected light.

Working Principle

The key feature of Touchless is that it determines touch based on the change from a reference value (delta) rather than the absolute amount of light. This makes it less susceptible to differences in cover materials and ambient light, and ensures a consistent feel even when multiple buttons are arranged together.

2. Optical Touch — Contact detection using VCNT2025X01

Optical Touch Switch – System Overview

Optical Touch is a method that detects the sudden surge in reflected light that occurs the moment a finger touches glass. Unlike capacitive touch systems, it does not rely on the electrical properties of the human body, so it reliably responds even through gloves and is highly resistant to ambient light noise.

2-1. Mechanism: Detects a "sudden increase in reflection" upon contact.

Working Principle

When a finger touches the glass, the reflected light increases dramatically. This large change reduces false detections, enabling reliable on/off detection.

2-2. Design Points

• Cover thickness, window diameter, and distance directly affect sensitivity.
  The recommended distance is 3-6 mm. Cube uses a 2 mm cover positioned 3.5 mm apart to ensure a good viewing angle.
• Pulse drive + high-pass FILTERS removes ambient light noise.
  The emitter is driven with a 50 µs pulse to FILTERS out steady light such as sunlight.
• Offset removal and threshold setting are easy.
  Measure the offset voltage caused by the cover and set 1.8 times that value as the threshold.
• Resistant to water droplets, dirt, and sunlight.
  With its wide field of view and offset correction, this system offers high stability in real-world environments.

2-3. Suitable applications (selection advice)

• Waterproof and stain-resistant touch buttons for medical devices: Reliable response even through gloves.
• High-durability SWITCHES for industrial equipment: resistant to external disturbances and less prone to malfunctions.
• Operation while wearing gloves: Overcoming the weaknesses of capacitive touch technology
• Optical ENCODERS knob: Ideal for high-precision position detection.

3. Force Sensing (Optical Force Detection) — Detection of indentation amount using VCNL4030X01

Force Feedback – System Overview

Force Sensing detects changes in the optical path that vary depending on the amount of pressure applied and reads them as an analog quantity. This allows for operation that corresponds to the amount of pressure applied while retaining the click feel of MECHANICAL SWITCHES.

3-1. Mechanism: The amount of indentation is detected as a "change in light".

Working Principle

Pressing down changes the internal light path, causing the amount of light received to change continuously. This allows for high-resolution detection of forces ranging from light to strong presses.

4. What Reference Design offers for PHOTOSENSORS HMI

BOM

Schematic

Step files and assembly

Pseudo-Code

Algorithm description

PCB Files

Documentation Overview

PHOTOSENSORS Reference Design is a comprehensive collection of documentation for implementing optical sensing in a short timeframe.

• User Manual
• Quick Design Guide
• Application Note (Operating Principles and Design Challenges) → Scheduled for release in April 2026
• Circuit diagrams, BOMs, PCB data, and 3D STEP files.
• SW source code and algorithm explanation
• Software/Hardware Integration Guide

By utilizing these tools, development can proceed smoothly from initial verification to mass production design.

5. Summary: PHOTOSENSORS reference designs will further advance HMI design.

The three methods are: Touchless, Optical Touch, and Force Sensing.

• Mechanism design
• Signal processing
• calibration
• Countermeasures against external disturbances

While sharing a common design philosophy, they can be clearly differentiated and used according to their intended purpose.

• If you prioritize contactless and hygienic options, choose Touchless.
• For reliable on/off detection, use Optical Touch.
• For operations that utilize the amount of pressure applied, use Force Sensing.

A major advantage of this newly released Reference Design is that it allows for the rapid implementation of HMIs using highly reliable and aesthetically pleasing PHOTOSENSORS.
We can assist you with selecting the appropriate system and comparing components based on your application, and we can also provide proposals that take future technological trends into account. Please feel free to contact us for a consultation.