Jumper ( German and jumpers ) are small plug-in bridges which are inserted as a form of short-circuit plugs on the contacts of headers. This causes the pins to which these jumpers are plugged electrically connected together ( "closed "). Applications are primarily in the area of electronics, such as is in computer technology and digital technology application to specify certain settings or functions of components such as the SCSI ID of a hard drive or an off state. Configuring with jumpers is called in technical jargon as jumpers. The size of a jumper is in the range of a few millimeters, standard pitch is 2.54 mm.
Jumpers are a special form of short-circuit plugs, which are distinguished by the shape, size and application. While jumpers are designed as a socket, short-circuit plugs are fitted with pins. Larger types of short-circuit plugs are used, among others, also in electrical installations or in the area of electrical prototyping on breadboards.
The jumper usually consists of a small, slightly curved leaves of spring steel that connects to bridging contacts (pins) directly. To build up the necessary spring pressure on the protection against short circuits with adjacent contacts, and because of the better handling of the metal bridges are provided with a housing made of plastic. The jumper is placed on two adjacent pins, thereby via the spring, an electrical contact is established. The pins and springs are usually gold-plated to minimize contact resistance and to prevent corrosion.
The same function as jumpers can also meet the DIP switch. However jumpers are much cheaper, more reliable and take less space. These advantages are, however, a - compared to more cumbersome to use - founded in the small size of the jumper.
Jumpers are manufactured in different sizes to match pitch and the pen thickness of the pin connectors used. Common grid dimensions are 2.54 mm, 2 mm and 1.27 mm.
Jumpers are used to configure an electronic assembly or adjustment of operating parameters, provided that such determinations are rarely or even only once performed at start-up. Generally be prepared for this purpose on the mass jumper connections. Together with a pull -up resistor is provided a corresponding to one bit of information is available in this manner.
Thus, the determination of the ID number is performed at the SCSI drive by a combination of three or four jumpers, which together form the three or four bits of the ID number. In parallel ATA hard drives, the jumper settings used for determining the ATA device number (0 for master and 1 for slave), which determines whether it is the first or second drive to the corresponding ATA / ATAPI bus.
Mechanically show jumpers often a handle on edge, to allow drawing with the finger nail. In the middle there is a recess in order to pull out the jumper in space is limited with a small hook can. Both features can be seen in the photo on the right.
Jumper not be connected by jumper, but with a sufficient amount of solder. With soldering iron and desoldering pump this connection is just as easy to be separated. Jumper are less flexible configuration means and are typically rare changed as a plug jumper. If you take a pure Lötzinnbrücke soldered short pieces of wire or jumpers used, one also speaks of strapping.
Depending on the basic setting is between the solder pads already a conductive path for the initial connection is available. This must be for a desired break with a sharp object - be separated - for example, a cutter; therefore stirred in the jargon, the term Schnitzbrücke.
The typical use of solder jumpers are assembly variants. This means that the re-soldering of another component is required for meaningful change a solder bridge anyway. For automated assembled printed circuit boards and soldering Schnitzbrücken be displaced in favor of zero ohm resistors.
With a jumper, a switch can be realized. To this end, the pin headers must have three pins. The changeover is the middle pin. He is selectively connected to the right or the left by the jumper.
Undocumented jumper settings
Manufacturers of hardware documentation in general all possible or meaningful combinations of set and unset jumpers. However, there are a number of cases where the time of manufacturing, although certain features were implemented in hardware, but these were deactivated by ( unset ) jumper and also not included in the documentation. Possible reasons may be:
- Imperfections of additional features;
- Marketing aspects: The same product can be sold in two versions at different prices, but is due to higher production numbers overall still cheaper than actually two different product variants;
- Advanced features can not be used by the other components at the time of delivery;
- Functions are needed only for service purposes or factory internally to manufacture and are for the owner of the product provided is not important or not its use.
Resourceful and experimental users find undocumented jumper settings again and publish them on the Internet. Most often this is when the main boards of the case, but also in CD -ROM drives or host bus adapters to find appropriate examples. For boards are mostly to voltage values for the CPU or to settings that affect the clock frequency.