Dual-in-line (DIL) switches
The miniature DIL or DIP type of switch is designed specifically for PCB mounting, and is used as a pre-set mainly in digital equipment, although it is equally well suited for pre-set applications in analogue circuitry. The main feature of the switch is its very small size. This makes operation with the finger very difficult, so the usual method is to use a screwdriver blade. These switches should preferably be mounted where a slip with the screw- driver blade will cause the least possible damage, electrical or mechanical, to the rest of the circuit. The usual formats are 4-pole or 8-pole onjoff, and the action is a slide or a lever toggle. A changeover action can be obtained on suitable types (in which one lever operates two switches) by connecting a pair of switch pins together. DIL switches are not intended for continual use, and have a comparatively low life expectancy of around 20 000 operations. To put this in perspective, you might expect to alter the settings once or twice a year, at the most once a week.
One of the main problems attending DIL switches is mechanical damage. Designers have an unfortunate knack of placing these switches where they are difficult to see and even more difficult to operate. One printer mechanism, for example, requires the casing of the printer to be removed simply in order to set the line-feed switch, and many users of this printer cut a hole in the casing above the switch so it can be operated without dis- mantling the machine. This, however, means that the switch is being operated by a screwdriver stuck through a hole in the casing, which is the main source of damage to the switch and to surrounding circuitry. It is not usually possible to make amends for inconsiderate design, but in some instances the switch can be replaced by a miniature socket and the switch relocated at the end of a cable.