Cables and Connections Explained


With projections systems come a variety of cables and connections which can be a little confusing so here we explain some of the basics. If you need to discuss anything to a more technical level we will be pleased to help.

The signal inputs to a projector fall into the following groups: computer, video, audio and control. Computer and video inputs feed the projector with images while the control can either represent a computer mouse or tell the projector what to do. Control is optional, computer or video feed is necessary to generate images.

Computer Signal
The most common form of computer input is via Analogue RGB (Red, Green, Blue), sometimes referred to as VGA or SVGA (Video Graphics Array or Super VGA). This is generally terminated with 15 pin HD (high density) connections or sometimes BNC connections as illustrated below.

15 pin HD male 15 pin HD female RGB cable 15 pin to 5 x BNC

With this type of interface the signal is separated into its red, green, blue, horizontal and vertical components and each is fed down a dedicated core in the cable. Using high quality cable it is possible to run up to 30m without noticeable signal loss. For runs over 30m we recommend the use of a distribution amplifier or line driver (signal booster).

A recently introduced alternative to RGB input is Digital or DVI (Digital Visual Interface). Not all projectors can accommodate this and not all computers can output for DVI. The advantage is a faster data transfer rate and cleaner signal giving sharper, fast response images. The disadvantage is that distance is restricted to around 10m unless using boosters/converters. To complicate matters there are 3 types of DVI; DVI-A (Analogue), DVI-D (Digital) and DVI-I (Integrated - both Analogue and Digital). Most projectors and monitors accommodate DVI-I. However, some video processing equipment requires DVI-D.

DVI standard DVI connection DVI cable

Video signal
Video signal to a projector generally takes one or more of the following types (in ascending order of quality): Composite, S-video and Component.

Composite is the most universal signal type and most peripherals generating video signal (e.g. VCR, DVD, camcorder) can output in composite form. Usually terminated with phono (RCA) or BNC connections, composite signal is a combination of all of the components fed down a coax cable (RG59U 75Ω low loss). With good quality cable distances of up to 100m can be achieved without noticeable signal loss. Improvements can be made using a line driver (booster).

Composite phono (RCA) connections are usually colour coded yellow. If your equipment only has Scart out then a Scart adaptor is necessary to channel the signal via composite.

Phono/RCA plug Composite video + audio

Scart adaptor

S-video is a step up from composite in quality terms and is generally found on higher quality versions of the latest equipment (e.g. VCR, DVD, digital camcorder). S-video separates out red and green components and by deduction calculates what the blue component should be. Horizontal and vertical components are fed with the red and green signals. Connections are 4-pin mini DIN plugs/sockets. Using high quality cable it is possible to achieve 30m distances before needing signal boosting. 

If your equipment only has Scart out you will need a Scart adaptor that accommodates s-video (provided that your equipment supports s-video).

4-pin mini DIN plug 4-pin mini DIN socket S-video cable

Component takes the signal separation a stage further by utilising 3 cables to channel each of the basic signal 'components'. Most high-end video equipment will output in component form and by nature this offers the highest video quality. Connection is usually by phono (RCA) or BNC's and colour coded red, green and blue. Scart to RGB/component cables are available but will only work if your equipment supports RGB/component out.  

Component phono

3.5mm audio plug

Audio signal
Most projectors will offer audio support with low power speakers. These are intended primarily for use in small meeting rooms where sound quality is not a major requirement. Speakers are usually 1-3 watts output and sound tends to be tinny. For audio support in a larger environment or for showing video's/DVD's we recommend feeding directly into your PA system or using active multimedia speakers.

Control signal
Many projectors these days have some form of control system for the purpose of using the remote control as a computer mouse (useful for stand up presentations), or for controlling the functionality of the projector.

In the first case, mouse control (if supported) is achieved simply by connecting the computer's mouse port to the projector's mouse port using the appropriate cable (serial, USB or PS/2). The remote control then communicates with the computer via infra red to the projector and cable to the computer. Remember to point the remote at the projector, not the computer!

In the second case, control is via RS232 (command protocol) and generally using a serial connection (9-pin D-sub). It is necessary to have the right software to send RS232 commands if you want to control the projector from the computer. Signal transmission is limited in length according to transfer speed but can be increased using a line driver (booster) 

9-pin D-sub serial plug Serial cable PS/2 cable USB cable

Wireless technology
There are an increasing number of projectors now capable of wireless data transfer and the technology is improving all the time. This method eliminates the need for extensive wiring (except power) and is fine for still images and presentations/song display but has some way to go on video streaming due to the limited bandwidth available. This is likely to improve.

It is possible to achieve wireless video connectivity using a video signal transmitter system - essentially a transmitter connected to the source, converting the signal to radio frequency (RF), sending to a receiver which is directly connected to the projector. Reliability is good but restricted to around 30m for standard models or up to 5km with appropriate amplification.

Networkable projectors
Some manufacturers are introducing networkable projectors which gives the advantage of being able to display via the projector from any computer on the network. Wireless networkable projectors are also being introduced.

PROmotivations can provide all of the above products and advise on your specific requirements. We offer a full professional installation service to bring you the best solution according to your requirements and environment.