Gourt Home::Gourt :: Ribbon cable
- For the 300-ohm antenna cable, see twin-lead.
A ribbon cable is a cable with many conducting wires running parallel to each other on the same flat plane. As a result, the cable is wide and flat, rather than round like more "traditional" cables. Its name comes from the resemblance of the cable to a piece of ribbon (which is likewise wide and flat). Generally the cable is marked only with a red stripe down one side though rainbow colored cables have also been made which make life easier if only one end is going to be terminated with an IDC connector. In order to avoid damage to hardware due to ribbon cables plugged in the wrong way, the red stripe designates wire no. 1 of the cable indicating the correct position to plug the cable into its corresponding socket.
Ribbon cables are commonly seen for internal peripherals in computers, such as hard drives CD drives and floppy drives. On some older computer systems (such as the BBC Micro) they were commonly used for external connections as well. Unfortunately the ribbon like shape makes them awkward to handle especially when there is a lot of them and so round cables have almost entirely replaced ribbon cables for external connections.
Cable sizes
Ribbon cables are usually specified by two numbers: the spacing or pitch of the conductors, and the number of conductors or ways. Conventionally a spacing of 0.05 inch (1.27 mm) was the norm allowing for a two row connector with a pin spacing of 0.1 inch (2.54 mm). This size is still seen today in floppy cables and older ATA cables as well as many more specialist applications.
The high-speed ATA cable used for ULTRA-ATA 66 and above has 0.025 inch (0.64 mm) pitch and 80 ways. The 40 pin connection is still used but with special connectors that ground every other wire in the 80 way cable. Finer pitches, as small as 0.3 mm, are found in portable electronic equipment such as laptops, however portable electronic equipment usually uses Flexible Flat Cables or FFC.
Cable connectors
The main point of ribbon cables is to allow mass termination to specially designed insulation displacement connectors (IDC connectors) in which the ribbon cable is forced onto a row of sharp forked contacts. (The phrase 'IDC connector' is widely used, even though it is redundant - an example of RAS syndrome.). Most commonly this is done at both ends of the cable though sometimes (for example when making a lead that needs to change wiring between the two connectors) only one end will be IDC terminated with the other end being terminated in a regular crimp or solder bucket connection. Although it is sometimes possible to dismantle and re-use IDC connectors, they are not designed to allow this.
Popular types of connectors available with IDC termination suitable for ribbon cable include:
- BT224 connector - also defined by BS9525-F0023, DIN41651, MIL-C-83503 standards; these are the type used on ATA cables and are often simply called 'IDC connectors'. They mate with either a purpose-made plug or a two-row grid of header pins with 0.1 inch (2.54 mm) spacing.
- D-subminiature connector - used for serial ports and printer ports (however IDC D connectors are far less common than crimp and solder bucket types).
- DIN41612 connector - used for Eurocard buses.
- PCB transition headers - has two rows of pins with the same spacings as BT244 connectors. Intended to be soldered directly into a PCB.
- DIL headers - Has pins with the same spacings as standard DIL ICs. Generally used where for some reason it is desired to replace an IC with a connection to an external device (e.g. in-circuit emulators). Can also be used like a PCB transition header especially on stripboard (fitting a standard spacing header to stripboard is tricky because you have to cut the tracks between two holes rather than on a hole)
"Ribbon cable"