7-2 Modes and Cables


Human Interface, The: New Directions for Designing Interactive Systems
By Jef Raskin
Table of Contents
Chapter Seven.  Interface Issues Outside the User Interface

Software runs on hardware. If you can't figure out how to connect the hardware, the software is just so many lost bits. Among the simplest piece of hardware is the cable, a few wires or fiber-optic strands bundled together with a connector at each end. Cables should be able to be plugged and unplugged without having to worry about whether the computer was on or not. (Cables that are not "hot-swappable" are modal!) You should not have to configure devices, as is required for SCSI connections. With the USB and FireWire standards, these desiderata are finally being addressed. But there are still interface issues that have not been addressed, even with the new standards. For example, it is frustrating to have a cable with the right kind of connector but of the wrong sex. Because there are male and female ends to cables and because some pieces of equipment have connectors that mate with the male ends of cables and others that mate with the female ends of cables, you end up owning a surprising number of variations of each kind of cable. Many computer owners find themselves also purchasing sex-changing adapters because adapters are smaller and less expensive than cables. For example, say you own only male-to-female cables but you need to connect two devices that both have female connectors. You might choose to purchase a male-to-male cable, or you might choose instead to buy a male-to-female adapter and attach it to the female end of the cable you already own. Attaching the adapter results in a cable that is, effectively, male to male.

This dilemma is avoidable, but the methods usually proposed do not work. One solution I have heard is that all connectors on equipment could be standardized to be, say, female, and therefore all connectors on cables would be male. Even so, you would still need female-to-female adapters to join two short cables into one longer one, and a manufacturer would be wise to supply male-to-female cables to act as extensions for existing cables. Following this logic, you can construct situations that require every possible combination of male and female ends on cables and adapters, even with the convention specifying that all connectors on equipment will be female.

A conventional connector pair is typically built as a male connector with pins and a mating female connector with sockets. This approach results in an inventory of eight kinds of parts that can be used as connectors on equipment or cables:

  • Male connector for equipment

  • Female connector for equipment

  • Male connector for cables

  • Female connector for cables

  • Male-to-female adapters

  • Female-to-male adapters

  • Male-to-male adapters

  • Female-to-female adapters

With hermaphroditic connectors, any two cables connect together, and any cable connects to any connector on a piece of equipment. The inventory is reduced to two items:

  • Connector for equipment

  • Connector for cables

Electronic requirements force us to have different cables for different kinds of signals, but within each class of cables, nothing in the nature of electronics or manufacturing keeps us from designing hermaphroditic connectors, which are neither male nor female. Any two hermaphroditic connectors of a given class will mate. Surprisingly, any kind of electronic signal connection or electrical power connection can be made via hermaphroditic connectors. This includes multiple-pin connectors, power connectors, and coaxial cables.[1]

[1] Some cables used in setting up widely spaced components, such as a photographer's remote strobe lights, have hermaphroditic connectors. The now obsolete GR coaxial power radio frequency connectors are another example.

If you have two hermaphroditic cables of a given class, you can use the cables either as two separate cables or joined together into one extended cable. In some cases, the hermaphroditic connector would be no more expensive or complex than a standard, sexed connector. This will not always be true; in many cases, a hermaphroditic connector will be somewhat more complex and more expensive to manufacture, but the added expense is counterbalanced by such factors as

  • Increased user satisfaction

  • Simpler manuals

  • Fewer manufacturing setups are required

  • Distributors and retailers needing to stock fewer different items

Figure 7.1 shows the schematic of a four-conductor linear hermaphroditic connector. For n conductors in a linear arrangement, you need a minimum of 2n ?1 contacts. You can trace the conductors in Figure 7.2 to see how it works. Figure 7.3 shows the conductors for a hermaphroditic coaxial connector. The idea can be extended to multiple coaxial conductors. To make better human-computer interfaces possible, we are willing to pay for more complex computers. The same reasoning should be applied to the maddening tangle of wires and cables in which computer and electronics users are perpetually enmeshed. It may seem that some linear scheme with fewer than 2n ?1 contacts is required, but keep in mind that connecting cables have also to work as extension cables.

Figure 7.1. A hermaphroditic four-conductor connector. The four conductors are labeled a, b, c, and d.


Figure 7.2. Hermaphroditic connector-equipped cables can be used to connect to units (at top and bottom of each column) or as an extension cable (right column).


Figure 7.3. Conductors for a hermaphroditic coaxial connector. An outer, insulating sheath with four prongs, similar to the ones shown but with enlarged tips and matching widenings on the bottom (not shown), serves to lock the units together.



    The Humane Interface. New Directions for Designing Interactive Systems ACM Press Series
    The Humane Interface. New Directions for Designing Interactive Systems ACM Press Series
    ISBN: 1591403723
    EAN: N/A
    Year: 2000
    Pages: 54

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