FDIT™ - Field Disturbance Input Technology
Product Introduction

Technology Overview
Technology Benefits
Contact Information

Entire contents Copyright © 1993-1998 Epsilon Group Inc.  All rights are reserved worldwide. IBM, IBM AT, and AT are trademarks of the International Business Machines Corporation.  Field Disturbance Input Technology, FDIT, is a registred trademark of Epsilon Group Inc.  The technology presented herein is covered by U.S.patent number 5,469,364 and 5,586,042.  Other patents pending. 


What would you think of a keyboard with no moving parts? A keyboard that uses the disturbance of an electromagnetic field to sense a finger? That could be mounted behind, and operated through bullet-proof glass, plastic, fiberglass, or even wood? A keyboard that doesn't have to be flat, and can be of virtually any geometry?

How about a keyboard that does all of that, yet cost about the same to manufacture and integrate as most current types? A keyboard that requires no special parts, materials, or manufacturing procedures other than for regular circuit board fabrication? A keyboard technology that is adaptable to pen-input and touch screen uses? A keyboard technology that will yield an exceptional competitive advantage for the next 17 years? It's hard to believe such a keyboard could exist...


Epsilon Group Inc.'s Field Disturbance Input Technology, or FDIT™, simply represents a revolution in the human to machine interface. Conventional capacitive, mechanical switch, rubber dome, and membrane type keypads have now been rendered obsolete. FDIT™ provides a non-contact, solid-state, through-barrier solution that is a cost-effective replacement for even premium membrane technology in any application where absolute reliability, shock resistance, fluid resistance, and survivability are important.

The FDIT™ Keypad is essentially a proximity sensing device. When an operator's finger "presses" a key, the keystroke is detected by measuring the disturbance of an electromagnetic field. No actual contact with the device is required. There are no moving parts. The FDIT™ Keypad is virtually maintenance free, and in most cases will outlast the equipment to which it is interfaced.

Section through a FDIT sensor Cell

The FDIT™ Keypad array itself can be fabricated from ordinary printed circuit board material, shown as element (C) in the above figure. The cells in the array (D) produce a very low energy electromagnetic field (A) through a suitable, rigid facing material, such as polycarbonate or tempered glass (B). When an operator's finger penetrates this field, a keystroke is detected.

Although there are some analogies to the function of a capacitive keypad, the FDIT™ Keypad should not be confused with conventional capacitive products. Historically, capacitive keyboards held the promise of through-barrier design, but exhibited many disadvantages. Among these disadvantages were false triggering, design complexity, and high cost. Epsilon Group Inc. has created a technology that eliminates all of these problems, allowing a highly survivable keypad that can virtually last forever. 

Field Disturbance Input Technology Overview

Essentially, all keypads are based on an array of electrically similar devices that change value when pressed by an operator's finger. In a conventional keyboard, the devices in the array are mechanical switches, and these switches change their resistance to electric current when pressed.

Capacitive keyboards, as their name suggests, are constructed from an array of capacitors that change value when pressed by, touched by, or at the approach of, an operator's finger. The variable capacitors in the array are constantly measured, and if one changes its value more than a certain amount, it is considered to be "pressed".

The known problems with prior art capacitive keyboards arise because the change of value when a capacitive "key" is touched is very small. Many other factors, such as a change in humidity, can cause the capacitors to change value enough to "press" a key. This false keystroke detection potential in prior art capacitive keyboards caused them to be "fooled" by their environment quite often, leading to their reputation for instability.

Many early capacitive keyboard engineers recognized this problem, and all manner of environmental adjusting mechanisms have been attempted. None were ever very successful; all were cumbersome, complex, and expensive. Those that relied on separate temperature, humidity and other environmental transducers were particularly unsuccessful. It seems that only the capacitive key itself knows exactly how much its value will shift with environmental change.

Some prior art capacitive keyboard engineers tried to incorporate capacitance value magnifiers, or "touch plates" into their variable capacitors. This was in an attempt to cause a wider variation of capacitance when the key was actually touched, "desensitizing" the key to the environment. This did increase stability somewhat, but conversely reduced the key's ability to act as an environmental transducer. When the environment changed too quickly, false keystroke detection still resulted.

Epsilon Group Inc. has solved all of these problems by combining several solutions into one elegant technology.

We start with a new method for measuring capacitors. A method which is uniquely suited to measuring infinitesimally small variations in the magnitude of value of a capacitor. It is sensitive in the extreme. We call it, naturally,

The FDIT™ Method of Capacitance Measurement.*

Next, we have designed a very unique variable capacitor-like proximity detector and environmental transducer. It is very simple to construct, very easy to incorporate into an array, and is very sensitive. It is referred to as

The FDIT™ Sensor Cell.*

We couple The FDIT™ Method of Capacitance Measurement,an array of FDIT™ Sensor Cells, and a common, off-the-shelf micro-controller, together into a keypad device. After exhaustive development, we arrived at the perfect logic means (software algorithm) to determine, based on the measurements of the Cell values, what is a key press, what is an environmental shift, and what is noise. We call this logic means

The FDIT™ Software Algorithms.*

Together, these three attributes, any one of which represents a significant improvement over prior devices, form a truly revolutionary advance in the state of the art of keypad design.

*Patents granted and pending. 

Technology Benefits

The FDIT™ Keypad allows an OEM manufacturer or system integrator to greatly enhance the quality and reliability of their products. FDIT™ Keypad is a "specify and forget" proposition. The result is increased customer satisfaction, and lower warranty expenses for the OEM.

Recognizing the trend toward "off-the-shelf" component integration, FDIT™ Keypad was developed in a modular fashion, separating the scanning and key detection modules from the host communication section. So far host communication modules for FDIT™ Keypad have been developed for IBM PC/ATs using the keyboard interface, Neuron™ network interface chips, SPI, full hand-shake serial bi-directional communication, and membrane encoders (for drop-in membrane keypad replacement). Custom FDIT™ Keypad layouts are easily generated, and any host communication software module may be selected. Naturally, a custom designed FDIT™ Keypad can be interfaced to any logic standard, such serial Async communication.

Field Disturbance Input Technology results in many benefits over existing keypads, just some of which are listed below:


The FDIT™ Keypad is a perfect solution where durability and protection are major considerations. The FDIT™ technology is so flexible, that the applications are limited only by the designer's imagination.

Contact Information

Thank you for your interest in

Field Disturbance Input Technology

To find out more, and have a "Hands On" experience with a keypad build using FDIT™ you will need to endorse a non-disclosure agreement (attached, Word for Windows and pdf formats) and forward an original copy to Epsilon Group Inc.

Epsilon Group Inc. stands ready to assist you at every turn. We offer a complete array of engineering design and support services. We can help you at every stage of product development, from product concept to customer support.