The Raspberry Pi is a full computer in itself but, as with any computer, it needs to be able to interact with the real world. Most people will therefore want to connect it to a screen, keyboard, mouse and so forth. This Entry will look at the peripherals you'll need to run a Raspi.
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Some websites officially licensed to sell the Raspberry Pi are also able to provide bundles that include various cables and peripherals.
USB Hub
A USB hub will allow you to plug additional devices into a single USB port. A powered USB Hub can supply devices with power itself, saving the Raspberry Pi from the extra load.
Screen and Cable
In order to see what your computer is doing, you'll need a television screen or a computer monitor1. There are several options for connecting a Raspi to a screen:
- Composite cable – if your television has a little round yellow socket next to matching white and red ones, you can use a yellow composite cable to connect from the Raspberry Pi's composite (RCA) output. This cable will carry the video signal. For sound, you'll need a 3.5mm jack to RCA cable – this cable has a headphones-style jack to plug into the computer on one end, and the white and red cables that will plug into your television on the other.
- SCART – most televisions that don't have composite sockets will use SCART cables to link to DVD players and the like. Simple adapters are available that will convert the red/white/yellow composite cable endings (see above) into a single SCART ending.
- HDMI cable – if you've got an HDMI television, you can connect it to the Raspberry Pi's HDMI output. This shouldn't really cost more than £10 and can carry both audio and video.
- DVI – some computer monitors will have a socket for a DVI cable, which normally carries a mix of digital and analogue signals. The digital part of DVI uses the same specifications as HDMI, and so you can use a simple HDMI to DVI adaptor to connect the Raspberry Pi to a DVI monitor.
Some readers will note that a DVI output can be converted to VGA, which is used by many computer monitors. This is true, but the VGA uses the analogue part of the DVI signal. This is not present when the DVI cable is itself being fed by a digital HDMI output. In other words, you can't convert from HDMI to DVI and then to VGA using simple adaptors.
There's also a problem with converting from composite to VGA. While the colour data (red, green and blue) is present in both, they use different forms of interlacing (the way in which the lines of colour appear on your screen). As a result, a powered signal converter is generally required, possibly costing a few times more than the Raspi itself.
The Raspberry Pi Foundation have stated they plan to look at ways of providing a VGA output, so check before you buy a new monitor!
Speakers/Headphones
If you aren't using a television for both the picture and sound, you'll probably want to connect some speakers or headphones. A large number of these will work without any trouble, as the 3.5mm jack used by the Raspi is the standard used by most audio devices. If your headphones have got one of the much chunkier '1/4' jacks, then a simple adaptor will do (1/4 socket to 3.5mm jack – a metal adaptor with a big 1/4 socket and a little 3.5mm pin). If instead you want to connect to the red and white RCA sockets on a TV or stereo, you'll need a 3.5mm jack to RCA adaptor cable.
Mouse and Keyboard
You'll need at least a keyboard in order to type commands and, if you're using a Graphical User Interface (GUI – an interface that lets you click on things with a mouse) then you'll also want a mouse. A wired USB mouse and keyboard set will be sufficient2, though if you've only got one USB port you'll need to buy a USB hub.
Alternatively, wireless keyboard and mouse sets will attach via a single USB port. It's worth checking that a wireless set uses the standard Human Interface Device (HID) input; fortunately, most sets that use a little USB stub wireless receiver use HID and are thus Linux-friendly.
SD Card
The Raspi comes with a memory card reader that takes SD and MMC memory cards. You'll need somewhere to store your operating system and files, and a memory card is a little more practical than an external Hard Drive Disk. SD cards can be bought cheaply online for less than a pound per gigabyte, so it's worth getting at least 16GB if not more. Reputable names include Secure Digital and Kingston. To make life easier, the Raspberry Pi Foundation will be selling memory cards pre-loaded with a GNU/Linux operating system, removing the need for you to download these onto a formatted and partitioned memory card using a normal PC.
Internet Access
This isn't obligatory, as you can run the Raspi using programs copied onto the memory card without ever connecting to the Internet. However, if you want to connect there are a couple of ways of doing it:
- Wired Internet – the Model B comes with a 10/100 ethernet card, which means you can use an ethernet cable to connect it to a broadband router or modem and thus access the Internet. Ethernet cables are very cheap, and the longer ones can cover a number of metres. A note for those looking at powering their Raspberry Pi using the ethernet card (so-called Power over Ethernet or 'PoE') – the Model B's ethernet card does not support this.
- Wireless Internet – a wireless adaptor is a tiny piece of equipment that will plug into the USB port on the Raspberry Pi and allow you to connect to any wireless hotspot or wireless router. There are a number of websites that will tell you which wireless adaptors will work with a Linux computer. The current (and fastest) standard of wireless communication is 802.11n – wireless 'N' devices have maximum speeds of 300 megabits per second (equivalent to 37.5 megabytes/second) and are claimed to work up to around 75 metres apart (less if there are walls in the way). An 'N' adaptor costs £15–20 at the time of writing, and a wireless router capable of communicating with multiple adaptors costs around £80, assuming you don't already own one.
Power Supply
A 5V Micro USB power supply is probably the simplest solution. You may already have one, as they are commonly used as chargers for various tablets, phones and 'satnavs'. Such chargers will usually provide at least one ampere of power – greater than the 500mA and 700mA required for models A and B respectively. One word of caution: if you don't already own a 5V Micro USB charger, make sure you buy from a reputable supplier, as there are knock-off versions out there that can cause damage to both yourself and your computer.
An alternative is to use a USB 'A' to Micro USB cable, often used to plug mobile phones into a USB slot on a computer in order to transfer data. You may be able to use this cable to power the Raspi using another computer's USB slot, or anything else that can be rigged to safely provide power via USB.
Case
Though not technically a peripheral, a case is highly recommended. The ideal case should act as an insulator to prevent anything touching the circuit board while allowing access to the peripheral slots. You could make your own case out of almost anything, or alternatively buy a case either from the Raspberry Pi Foundation or a third party retailer.
Optional Extras
- A Microphone – as the 3.5mm jack is used for output only, this will need to be a Linux-compatible USB microphone.
- A Hard Drive Disk – a Linux-compatible external HDD can be connected by USB.
- The Gertboard – this is the Raspberry Pi Foundation's first add-on component, which provides the hardware needed for controlling sensors, motors and LEDs. Note that it connects directly to the low-level peripheral pins, which may be separate and need soldering onto the Raspberry Pi.
- Many, many other things – there are numerous other USB devices that could be attached, and users with the know-how could use the machine to produce all kinds of things based upon the Raspberry Pi.
1 It is also possible to connect the Raspi to a touchscreen or LCD screen, but this is beyond the scope of this Entry.
2 For those with old PS/2 mice and keyboards, there are cheap PS/2 to USB adaptors. Be careful to choose a 'double female PS/2 to single male USB' adaptor. Note that very old PS/2 mice and keyboards will not work via USB.
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