Hardware

Power:

The Raspberry Pi is powered by micro-USB connector.  It requires up to 700mA (5V),  so many smartphone chargers will work with the Raspberry Pi. (Some chargers can only supply up to 500mA, but it is important that the power supply be capable of supplying at least 1000mA) There is no power button on the device, so when power is connected, Raspberry Pi will start to work automatically. It can only be turned off by physically removing the power cable. (Many problems with the Raspberry Pi can be traced back to an inadequate power supply with USB power adapters.)

It is possible to check with a voltmeter if Raspberry has enough Power on the voltage test points.

The two test points (TP1 and TP2) are are connected to the Pi’s 5 V and ground circuits. The positive (red) meter probe should be put on TP1, and the black (negative) meter probe to TP2. The reading on the voltmeter should be between 4.8 V and 5 V. If it’s lower than 4.8 V, this indicates that the Pi is not being provided with enough power.  (If  the voltmeter shows a negative number, it means the positive and negative probes are in the wrong place. You can swap themor just ignore the negative sign.)

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Display and Audio:

Composite Video

Composite video, available via the yellow-and-silver port known as an RCA phono connector. It is designed for connections  to older display devices. (The connector creates a composite of the colours (red, green, blue) found within an image and sends it to the display device (usually to an old cathode-ray tube (CRT) TV).

HDMI Video

HDMI port provides a high-speed digital connection for monitors and TVs. HDMI port can display images at Full HD (1920x1080) resolution and also transmits the audio on the same cable.

(As the digital signals present on the HDMI cable map to the standard DVI (Digital Video Interconnect),  an HDMI-to-DVI cable can be connected to a monitor with DVI-D connectivity.)

DSI Video

DSI (Display Serial Interface) is the video standard used in flat-panel displays of tablets and smartphones. A DSI connector can be found on the Raspberry, and a DSI display can be connected to there by inserting a ribbon cable into the connector on the Pi.

Connecting Audio

If you’re using HDMI, the HDMI port carries both the digital video and audio signal. For DVI monitors, or for composite video output, a 3.5 mm audio jack provides analogue audio. (Connecting a pair of powered speakers will help to increase the volume of the sound.)

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Network:

Newer models have Wifi adapters, but older models are usually connected by an Ethernet (RJ45) cable to the network. The cable can be connected to a switch (or a router), or to a laptop if no router available. For these connections any type of ethernet cable is suitable, a crossover cable is not necessary. (Without a switch or router usually a crossover cable is needed, where the receive and transmit pairs are swapped so that the two devices are prevented from talking over each other. This task usually handled by a network switch or hub.)

The Raspberry Pi is smart enough and the RJ45 port includes a feature known as auto-MDI, which allows it to reconfigure itself automatically so any RJ45 cable is suitable and it will adjust its configuration accordingly. (If the Pi directly connected to a PC internet will not be available automatically,  the PC needs to be configured to bridge the wired Ethernet port and another (typically wireless) connection.)

If it is connected to a router, during the start up the Pi will automatically receive configuration details through DHCP protocol. This assigns the Pi an IP address on the network, and tells the gateway it needs to use to access the Internet (typically the IP address of the router).

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Storage

Raspberry Pi has no hard disk it uses an SD card (or micro SD) which holds the entire operating system. (Installing an operating system to the SD card is called flashing or imaging and it requires some additional steps.)

Beside the SD card, there are devices that can provide an additional storage space when connected via a USB cable. (Like USB Mass Storage (UMS) devices, physical hard drives, solid-state drives (SSDs) or even portable flash drives.)

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USB

With the help of USB ports many devices can be connected to the Pi (keyboard, mouse, Wifi adapter...) and also a USB hub which provides more ports for connections. An USB can be used also to provide the power to the Raspberry Pi. This way, the Pi can draw its power directly from the hub, rather than needing its own dedicated power socket. To achieve this, a hub is needed which can provide 700mA to the Pi’s USB port.

The USB ports on the Pi have a component called "polyfuse", which protects the port if a device attempts to draw too much power. (It can shut off the USB port if needed. For example if a keyboard draws much power, it may operate strangely, which can be a problem for keyboards that have built-in LED lighting, which require far more power to operate than a standard keyboard.)

USB ports  can’t cope with the speed of a gigabit Ethernet connection so it is not useful to by a gigabit USB Wifi adapter.