Quoted:
Part 2... a button is a contact point in a switch, and the switch is activated by the pressure you apply to the button. There are three basic button circuit design types. All three rely on shorting two metallic objects together to make the circuit. The quality of that point of contact is where problems arise. If a contact is cheap, dirty or damaged, the contact starts to introduce increased resistance to that contact circuit. That resistance shifts the output voltage result, and if it's really bad, the voltage will fall outside the correct range. So, the "3" button may result in a lower voltage, due to higher than normal contact resistance, and then become interpreted as the next button down the voltage array. So, say the "5" button is represented by the output voltage range from 2.61-3.11 volts. The dirty "3" button is now getting interpreted as a "5" button.

Quoted:
That's the voodoo. You can't see it and have no clue this started happening, except that the combo that used to work is now getting rejected as wrong. It is, in effect, like you are pushing the wrong button...  High quality button contacts are expensive. Contacts are made from high value precious metals. Low cost means less or thinner precious metals used. Cheap keypads fail early. You get the idea. These contacts decay as they are used. Cheap ones fail earlier.

Quoted:
We test our keypads to 1 million cycles. I seriously doubt many of the other lock makers have even tested their keypad endurance. When that checkpoint is not part of your quality control process, your vendors that make the keypads cheat, use less and less precious metal, and you get reduced cycle life and don't even know it until a year or two later when your customers begin to report problems. By then, you have produced scads of bad parts that are already in the field on safes. [/span][/span]

BACKGROUND OF THE INVENTION

Rubber dome pressure actuated switches are often used in field consoles and other telephone applications, most often over rigid circuit boards, especially where the use of hard plastic keys or hard plastic key caps are not practical, or where their incorporation into a push button type switch is not economically feasible. In addition, size and space restrictions often make the use of hard plastic caps unfeasible. It is often the case that sealants are used to impregnate the rubber dome, but the use of such materials and the process of impregnation are too costly, especially where the number of switches is extremely large, as in most telephone applications involving, for example, telephone consoles or terminals.

Heretofore, circuit board assemblies using rubber dome keys have been subject to mechanical and electrical failures in large numbers over an extended period of use, or where the use, i.e., actuation of the switch by an operator pressing on the dome, is of a high frequency of occurrence. Such failures are costly, especially in the field, both as to replacement of the defective switch and also as to repair of the switch or the circuit board itself. Thus, in prior art arrangements, any defects necessitating repair of the switch generally require replacement of the entire circuit board to which the switch is affixed.

Recent studies have shown that the circuit board containing the switch pads and upon which the switches are mounted and, more particularly, the switch pads themselves, are being contaminated during use by a foreign substance which chemical analysis has shown to be squalene, a salt that is expelled through the skin of the human body, most often as a component of sweat. Squalene is also found in some types of cosmetics and is thus quite prevalent. This substance or salt has an oily consistency and a very high viscosity which allows it to be readily absorbed by the silicone rubber of the domes. Over a period of time or of frequent operation, the rubber dome becomes saturated with the salt and, upon continued actuation of the switch, the salt becomes deposited on the circuit board, especially the switch pads, and almost invariably leads to failure of the switch pads or even of other components on the circuit board.  One type of rubber dome switch that is susceptible to such contamination is shown in U.S. Pat. No. 4,818,829 of Nopper et al. In FIG. 2 of that patent, there is shown a structure wherein the dome, upon actuation, i.e., depression, bears against an active component of the circuitry on the circuit board. Over time, the squalene contamination will reach and probably contaminate this element.

We don't want to make the keypad a logic processing device and communicate with the lock inside using complex serial communications. It must be kept simple, to control cost and reliability, as well as meeting the physical limitations.

Also, the I/O capacity is a cost barrier. As you increase the number of I/O points, you have more processor, you increase cost. We have worked tirelessly for the last 10 years to finally produce e-locks that are equal to the cost of the mechanical safe locks they displace. Every penny counts. The safe lock we produce today is the product of a long trail of research and development. So, the product I describe, even though it has fundamental design compromises, is the state of the art. If cost were no concern, and we could manage to route 11-12 conductors thru the small hole in the safe door, and had unlimited space to accommodate the huge connectors that would support that wiring, then things might be different.