|This article relies largely or entirely upon a single source. (December 2011)|
A DIP switch is a manual electric switch that is packaged with others in a group in a standard dual in-line package (DIP). The term may refer to each individual switch, or to the unit as a whole. This type of switch is designed to be used on a printed circuit board along with other electronic components and is commonly used to customize the behavior of an electronic device for specific situations.
DIP switches are an alternative to jumper blocks. Their main advantages are that they are quicker to change and there are no parts to lose.
There are many different kinds of DIP switches. Some of the most common are the rotary, slide, and rocker types.
Rotary DIP switches contain multiple electrical contacts, one of which is selected by rotating the switch to align it with a number printed on the package. These may be large like thumbwheels, or so small that a screwdriver must be used to change them (although there are also small potentiometers of this type).
The slide and rocker types, which are very common, are arrays of simple single pole, single throw (SPST) contacts, which can be either on or off. This allows each switch to select a one-bit binary value. The values of all switches in the package can also be interpreted as one number. For example, seven switches offer 128 combinations, allowing them to select a standard ASCII character. Eight switches offer 256 combinations, which is equivalent to one byte.
The DIP switch package also has socket pins or mounting leads to provide an electrical path from the switch contacts to the circuit board. Although circuits can use the electrical contacts directly, it is more common to convert them into high and low signals. In this case, the circuit board also needs interface circuitry for the DIP switch, consisting of a series of pull-up or pull-down resistors, a buffer, decode logic, and other components. Typically, the device's firmware reads the DIP switches when the device is powered on.
DIP switches were used extensively in ISA architecture of PC expansion cards to select IRQs and memory addresses. Before the advent of cheaper, battery-backed RAM, DIP switches were also often used on arcade games in the 1980s and early 1990s to enter game settings such as difficulty or the number of credits per coin. DIP switches were very commonly used to set security codes on garage door openers as well as on some early cordless phones. This design, which used up to 12 switches in a group, was used to avoid RF interference from other nearby door opener remotes or other devices. Current garage door openers use rolling code systems for better security.
Recently (since the late 1990s), DIP switches have become less common in consumer electronics. Reasons include the trend toward smaller products, the demand for easier configuration through software menus, and the falling price of non-volatile memory. However, DIP switches are still widely used in industrial equipment because they are inexpensive and easy to incorporate into circuit designs, and because they allow settings to be checked at a glance without powering the system on.
DIP switches are still used in some remote controls to prevent interference; for example, to control a ceiling fan (and its light fixture) that was retrofitted to a single-circuit junction box. The DIP switches set a different radio frequency for each transmitter/receiver pair, so that multiple units can be installed in different rooms of the same house, or different units of the same apartment building, without unintentionally controlling each other.
Rotary switches are also used in X10 home automation to select house and unit numbers. Rotary switches are also used in some radio transmitters (particularly VHF and FM broadcast) to select the DC bias used to set the voltage-controlled oscillator, which determines the center frequency of the carrier wave output.
|Wikimedia Commons has media related to DIP switches.|
- US Patent 4012608 Miniature switch with substantial wiping action
- ATARI Airborne Avenger Service Manual, TM-102, 1st printing 1977
- US Patent 5010445 Patent for a DIP switch with built-in active interfacing circuitry