Raspberry Pi

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Revision as of 14:46, 18 January 2015 by Rpeters (talk | contribs) (added ref to Ver 2 & B+ models)

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A growing body of information is available at http://www.raspberrypi.org

Only a few critical issues, that are easily overlooked, are summarised below

Models

Most will purchase the model B, which has Ethernet and more USB ports

The second release of model B has 512 MB RAM in lieu 256 MB

  • likely to increase the variety of OS that are usable
  • earlier boards are not upgradeable, because all components are soldered in place

Case

The basic product is sold without a case. It does not fit in any "standard" blank case and has sockets on both sides as well as all four edges, making construction of a suitable case not a simple task.

Cases are now being sold on the Raspberry Pi site. Alternatively, third-party cases are also marketed

The two (only) chips on RPi can get quite hot in operation. Small, self-adhesive heatsinks are now available from:

http://geekroo.com/site/

Heat Load

Quick Start Guide from distributor RS Components recommends:

  • "use in well-ventillated area"
  • "should not be covered"

It's debatable whether or hot the majority of cases being sold meet the above criteria.

Alternatives to Cases

A DIY cover can be made usiing discarded CD media. The original concept was at

http://discpi.vkspartak.sk/

That "case":

  • applies to the original (ver 1 - although not labelled as such) RPi
  • does not anchor the RPi down and dimensions for accuately positioning the plastic supports are not provided. A variation, including critical dimensions is below

Ver 1 and model B+ have two and four mounting holes respectively.

  • conventional plastic standoffs could be used in any "case"


Raspberry Pi CD Case.png

Some construction factors to note, In either variant

  • RPi have been produced on at least two production lines
    • precise dimensions of the board might vary
    • check prior to construction, preferably using plastic vernier calipers
    • adjust position of supports accordingly
  • single plastic disks/CD media, although quite tough, are fairly flexible
    • two can be "laminated" together to form each of the top and base
    • the plastic in them is not tolerant of most solvents/glues - alternative is to place near the perimeter:
    • several small dots of hot-melt glue or
    • several strips of (non-foam) "double-sided" tape
  • metal components of the case must be well insulated
  • surprising force is required to insert/remove the SD Card & USB plugs, in particular. The supports must resist horizontal movement of the board
  • the board is offset longitudinally towards the USB/RJ45 end, in order to:
    • facilitate insertion removal of USB/Ethernet plugs
    • prevent SD card overhanging case
  • a minimium standoff of about 7 mm is required for board above lower CD.to facilitate insertion/removal of plugs
  • if actual CD media are used (in lieu of plastic spacers from CD stacks) then the reflective sides must face inwards
    • top sides of media can be conductive aluminium
    • clear any drillled holes of flaked aluminium swarf
    • reflective surfaces aid monitoring of the RPi's five tell-tale LED
  • drill CD media at slow speed
    • otherwise the plastic is inclined to melt and clog drlll bits
  • on early production (at least) of the RPi model B, the Ethernet socket is not well anchored
    • desirable to adhere plastic spacers above it so the top CD holds it down
  • a discarded case from a stack of 20/25 CD/DVD media can be used to protect the "CD-RPi" during transport
    • need to cut off the central spigot of the media case

Circuit Board

Power is supplied via the micro-USB connector at one end. The surface-mounted capacitor behind that connector is a known physical weak-point.

  • do not grip the board by that capacitor
  • preferably leave the micro-USB power cable permanently plugged in and power ON?OFF by either
    • powering the plug-pack/USB-hub ON?OFF or
    • disconnecting the other end of the power cable

Power Supply

  1. A raspberry pi draws 0.7A (700 mA) of regulated 5V power, which is beyond the capacity of most:
    • USB sockets on a computer
    • mains-USB plug packs
  2. Suitable power supplies include
    • mains-USB plug packs rated at 1A
      • preferably having a single USB socket only
    • USB-hubs capable to delivering 1 A to a single USB socket
      • "Zipp" brand from Big W does - but check before purchasing
  3. although the use of a USB-hub as a power source is deprecated by the manufacturers, it has been used sucessfully by the developers at http://www.ipfire.org. Critical factors are:
    • regulated power to the hub
    • 1 A available to a single socket

Rpeters12:53, 26 January 2013 (EST)