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How to solve problems with data projectors and laptops

Lots of people now bring their laptops into the department to give presentations, and have trouble getting them to work with the data projectors. They often find this out five minutes before the presentation is due to start! Here is a short list of things to try to get your laptop to talk to the data projector when it doesn't happen automatically.

It is always best to try the laptop on the projector in advance if you can as some machines simply will not work with some data projectors.

  • Always start by booting the machine with the data projector already plugged into it and switched on. Many machines autodetect the projector and will set themselves up. This method is particularly important with Macs, which often don't have an external monitor switching button.

  • Check you've actually told the laptop to use an external monitor. Many models won't send video signals to the external monitor connector automatically. On PCs you usually do this with one of the function keys and a modifier key. The function key you need sometimes has a picture of a monitor on it or says something like CRT/LCD. On machines like this there are usually three ways the video output can be set: LCD panel only, external monitor only, or both, and so you may need to press the function key a few times to cycle through the possibilities to the correct one.

    On some Macs you need to go into the monitor control panel to make them display on the external monitor. In the control panel you get a picture of two monitors. You can drag one on top of the other to make the Mac display the same picture on the external monitor as the LCD panel. You may also need to change the resolution that the Mac uses for the external monitor to get the best picture.

  • Make sure the projector cables are firmly attached to the laptop.

  • Check that the data projector is displaying the correct input; some have A and B inputs. Most will detect the signal from the laptop if there is one plugged in and switch to that input, but not always. Do not be tempted to check if the data projector is really on by hitting the power switch. They generally go into standby mode if you do this; this is so that they can cool down properly before switching off entirely. This means that you then have to wait for them to cool before you can switch them back on again.

  • Check your display resolution is not too high for the projector. Some can cope with higher resolutions and refresh rates than others; but if you're having trouble try setting your screen to 1024x768 at a low refresh rate, eg 72Hz. On a Windows PC you do this by going into the Display Control Panel and selecting 'Settings'; there will be various options for screen size.

    On Linux machines, it depends on whether you have multiple video modes configured. If you have, you can switch between them with CTRL, left ALT and the + symbol on the numeric keypad. You may find that one of your modes will work with the projector. This procedure won't resize the screen, so it's only good for a quick test to find out what modes the projector qwill do. The xrandr program can then be used to reconfigure the screen size and the resolution together for you. This will not stick once you log out.

    If you don't have multiple modes then you will need to reconfigure X to display the right mode for the projector. This is very distribution dependent, so if in doubt ask the computer officers for help. On SuSE running YaST is the way to go.

  • If you have got a picture but it is distorted then you probably need to change your video settings. This is extremely dependent on your operating system and video drivers so it's hard to give advice. The laptop manufacturer's website is often a good place to go at this point. If it's a Windows machine, try looking under Settings in the Display Control Panel.

  • Some laptops seem to require a plug and play device on the external video port to configure the external display properly. This is a problem in LT2 and 3 where the projectors are set up in such a way that their plug and play signals don't get to the laptop. In this case, plugging the laptop into a spare PnP monitor, allowing it to configure itself, and then putting it into the projector should work.

  • A problem increasingly seen with Linux machines running recent distributions is that if you boot them while attached to the projector, the projector will pick up the resolution of the boot time splash screen and configure itself to display that resolution only. Once you start X, which uses a higher resolution than the splash screen, the projector display is distorted or the wrong size because the projector isn't expecting the resolution it's now getting. The answer in this case is not to plug in the laptop until after X is started. Older Linuxes that don't display a splash screen on boot don't have this problem.

  • New 12" iBooks have a special cable to link the data projector to the iBook as they don't have the normal video ports. It seems that it is necessary to boot up the Mac, log in, plug the cable into the Mac, wait a few seconds while the Mac detects the cable and reconfigures itself, and only then plug the cable into the data projector.