Difference between revisions of "RPi Hardware"
m (→Power Supply Problems: moved link - PSU construction)
(Removed the part about the iPhone PSU - it's more likely the cable, and this belongs in Verified Peripherals.)
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====Things that can cause problems====
====Things that can cause problems====
Revision as of 04:08, 6 August 2012
Hardware & Peripherals:
Hardware - detailed information about the Raspberry Pi boards.
Hardware History - guide to the Raspberry Pi models.
Low-level Peripherals - using the GPIO and other connectors.
Expansion Boards - GPIO plug-in boards providing additional functionality.
Screens - attaching a screen to the Raspberry Pi.
Cases - lots of nice cases to protect the Raspberry Pi.
Other Peripherals - all sorts of peripherals used with the Raspberry Pi.
The first product is the size of a credit card, and is designed to plug into a TV or HDMI monitor. It comes in two variants, model A and B, with B having more features. The expected price is $25 for model A and $35 for model B. The GPIO pins on each board allow the use of optional expansion boards.
Those who are looking to set up a Raspberry Pi for the first time, see RPi Hardware Basic Setup.
|Model A||Model B|
|Target price:||US$25 Ext tax (GBP £16 Exc VAT)||US$35 Ext tax (GBP £22 Exc VAT)|
|System-on-a-chip (SoC):||Broadcom BCM2835 (CPU + GPU + SDRAM)|
|CPU:||700 MHz ARM11 ARM1176JZF-S core|
|GPU:||Broadcom VideoCore IV,OpenGL ES 2.0,OpenVG 1080p30 H.264 high-profile encode/decode|
|Memory (SDRAM)iB||256 MiB (previously listed as 128 MiB for model A, but an upgrade to 256 MiB was announced on 29 Feb 2012)|
|USB 2.0 ports:||1(provided by the BCM2835)||2 (via integrated USB hub)|
|Video outputs:||Composite video | Composite RCA, HDMI (not at the same time)|
|Audio outputs:||TRS connector | 3.5 mm jack, HDMI|
|Audio inputs:||none, but a USB mic or sound-card could be added|
|Onboard Storage:||Secure Digital|SD / MMC / SDIO card slot|
|Onboard Network:||None||10/100 wired Ethernet RJ45|
|Low-level peripherals:||General Purpose Input/Output (GPIO) pins, Serial Peripheral Interface Bus (SPI), I²C, I²S, Universal asynchronous receiver/transmitter (UART)|
|Power ratings (provisional, from alpha board):||500 mA, (2.5 W) ||700 mA, (3.5 W)|
|Power source:||5 V (DC) via Micro USB type B or GPIO header|
|Size:||85.60 mm x 53.98 mm (3.370 × 2.125 in)|
(Provisional - some of the expansion interfaces won't be available on production boards) (PCB IDs are those of the Model B Beta board)
- SoC: Broadcom BCM2835 media processor (datasheet, BCM2835 datasheet errata, unofficial pinout) system-on-chip featuring:
- CPU core: ARM1176JZF-S ARM11 core clocked at 700MHz; ARM VFP. The ARM11 core implements the ARMv6 Architecture. For details on ARM instruction sets and naming conventions, see ARM architecture and List of ARM microprocessor cores.
- GPU core: a Broadcom VideoCore IV GPU providing OpenGL ES 1.1, OpenGL ES 2.0, hardware-accelerated OpenVG 1.1, Open EGL, OpenMAX and 1080p30 H.264 high-profile decode. There are 24 GFLOPS of general purpose compute and a bunch of texture filtering and DMA infrastructure. Eben worked on the architecture team for this and the Raspberry Pi team are looking at how they can make some of the proprietary features available to application programmers
- DSP core: There is a DSP, but there isn't currently a public API (Liz thinks the BC team are keen to make one available at some point)
- 256MiB of (Hynix MobileDDR2 or Samsung Mobile DRAM) SDRAM. The RAM is physically stacked on top of the Broadcom media processor (package-on-package technology). Here is a photo of the SDRAM (left) and BCM2835 (right) ball grid arrays on JamesH's finger. You are looking at the bottom side. The BCM2835 top side has a land grid array which matches the SDRAM ball grid array.
- LAN9512 (Data Brief | Data Sheet) (Model B) providing:
- 10/100Mb Ethernet (Auto-MDIX)
- 2x USB 2.0
- S1: Micro USB power jack (5v - Power Only)
- S2: DSI interface. 15-pin surface mounted flat flex connector, providing two data lanes, one clock lane, 3.3V and GND.
- S3: HDMI connector providing type A HDMI 1.3a out
- S4: Composite Video connector: RCA
- S5: MIPI CSI-2 interface. 15-pin surface mounted flat flex connector.
- S6: Audio connector: 3.5mm stereo jack (output only)
- S8: SD/MMC/SDIO memory card slot (underside)
- S7: Either 1x USB 2.0 (Model A) 2x USB 2.0 (Model B)
- P1: 26-pin 2.54 mm header expansion, providing: see Low-level peripherals
- 8 GPIOs at 3v3
- 2-pin UART serial console, 3v3 TTL (debug); or 2 GPIOs at 3v3
- I²C interface (3v3); or 2 GPIOs at 3v3
- SPI interface (3v3); or 5 GPIOs at 3v3
- 3v3, 5v and GND supply pins
- ARM JTAG (if pins are reconfigured in software and one signal is taken from S5)
- Second I²C interface (3v3) (if pins are reconfigured in software)
- I²S interface (if pins are reconfigured in software, hardware hack may be required)
- 6 pins reserved for future use
- P2: 8-pin 2.54 mm header expansion providing GPU JTAG (ARM11 pinout, pin 7 is nofit for locating)
- P3: 7-pin 2.54 mm header expansion (header not fitted), providing LAN9512 JTAG (pin 6 is nofit for locating)
- P4: 10/100Mb RJ45 Ethernet jack (Model B)
- TP1 and TP2: Test Points giving access to +5V and GND respectively
- 5 Status LEDs:
- D5(Green) - OK - SDCard Access (via GPIO16)
- D6(Red) - PWR - 3.3 V Power
- D7(Green) - FDX - Full Duplex (LAN) (Model B)
- D8(Green) - LNK - Link/Activity (LAN) (Model B)
- D9(Yellow) - 10M - 10/100Mbit (LAN) (Model B)
- Board size: 85.60 mm x 53.98 mm. Overall height expected to be less than 25 mm. 
- A model B between highest points (USB connector to card slot) measured 21 mm.
- Weight: under 40 g?
- Alpha board weighs approx. 55 g.
- A sample model B weighed 39.45 g.
- 6 layer PCB 
Schematic / Layout
- PCB screenshot
- PCB screenshot, labelled version
- PCB screenshot, Alpha board
- Preliminary power supply schematic, Beta board
- High-resolution PCB front photo, production board
- High-resolution PCB back photo, production board
- GIMP project containing properly aligned versions of the high-res PCB photos and Gerbers on separate layers (117MB)
- "Xray style" image of the beta board, created from the above GIMP project | desktop wallpapers
- Official schematics PDF | errata | breakdown
- 'Module groups' of the PCB photos
The board takes fixed 5V input, (with the 1V2 core voltage generated directly from the input using the internal switch-mode supply on the BCM2835 die). This permits adoption of the micro USB form factor, which, in turn, prevents the user from inadvertently plugging in out-of-range power inputs; that would be dangerous, since the 5V would go straight to HDMI and output USB ports, even though the problem should be mitigated by some protections applied to the input power: The board provides a polarity protection diode, a voltage clamp, and a self-resetting semiconductor fuse.
Premier Farnell recommend the following power supplies:
- Model A: 5V dc, 500-700mA
- Model B: 5V dc, 700-1200mA
Power consumption of the Raspberry Pi device is
- Board A: 5V, 500 mA (2.5W) without any devices connected (e.g. USB, Ethernet, HDMI)
- Board B: 5V, 700 mA (3.5W) without any devices connected (e.g. USB, Ethernet, HDMI) (Is this correct? These  links  suggest that the 700mA is only required if "using networking and high-current USB peripherals" .)
You will need to provide a power supply that can provide enough current to power the device plus any connected peripherals, and taking into account inefficiencies of the supply itself and the cable between the power supply and Raspberry Pi. The community advises opting for a power supply that can supply at least 1A if using USB peripherals or Pi plates that draw more than a few tens of milliamps of current.
- As the 5V rail is brought out in the GPIO pins, you can power the Rpi from there too. You should mind however, that those are behind the power protection circuitry, so you should provide your own.
- It is possible to power the Rpi from a powered USB hub the Rpi controls, but only on 'dumb' devices, that allow the port to supply the full current without waiting for the usb device to ask for it. As the power input of the Rpi doesn't have its data leads connected, there is no chance for a communication loop of some sorts.
- POE (power over ethernet) is currently not available for the Rpi (but nobody stops you from taking your soldering iron and doing it yourself - mind though that the Ethernet jack on the board is a 'magjack' - http://www.sparkfun.com/datasheets/Prototyping/MagJack.pdf - which means that the usual 'dumb or passive PoE' power pins 47 and 78 are *not* wired through to the board. So this is not an entirely trivial exercise).
Power Supply Problems
There have been a number of problems reported that seem to be caused by inadequate power, this is an attempt to explain what is needed and the consequences of not having enough power.
The power required by the Pi will vary depending on how busy it is and what peripherals are connected.
- Running a GUI will take more power.
- The USB devices and Ethernet connection will take power.
- Running the GPU will take extra power.
This means that it's difficult to say exactly how much power is needed. People have reported current requirements of between 300mA and 550mA. But it could in reality take more, especially for short periods. A simple multimeter will not show short surges on the power requirement. A surge in the power requirement for a few milliseconds will not be detectable by a meter but will be enough to cause problems. If the board does not get enough power the voltage will drop. If it drops enough parts of the system will run unreliably because data can get corrupted. The USB IC runs on 5V and handles the USB and Ethernet ports so it's likely that this will be the first thing to fail. Problems seen are unreliable Ethernet connection and unreliable operation of the Keyboard and/or mouse.
Each of the two USB ports on the Pi has a polyfuse rated at 140 mA, so any connected USB devices should draw less than this amount of current. In addition the polyfuse will cause a significant voltage drop, so that USB devices get less voltage than is available on the RPI itself, sometimes up to half a volt less (maybe more if the fuse has recently been hot). For regular "low power" USB devices this doesn't cause a problem as they are designed to work with voltages as low as 4.4 Volt. This isn't the case however with some USB devices such as WiFi dongles which may need 4.75 Volt, and are also known to draw more than 150 mA when configured and active.
The microUSB input port also has a 1.1 A polyfuse (700mA "hold current") which may also have enough resistance (although much smaller than the 140mA fuses) to cause a significant voltage drop on the board, even below its 1.1 A total current.
A extended explanation of the consequences of the use of these polyfuses can be found here Polyfuses explained
There are several reasons why the power to the board may be inadequate:
- The PSU may not deliver enough power. Although the maximum power requirement is said to be 700mA, that is with no peripherals connected (USB, Ethernet etc), so a 1000mA PSU should be regarded as a minimum. This allows some leeway in case the power supply cannot deliver its full power without the voltage dropping.
- The PSU is not regulated.
- The cable connecting the PSU to the Pi may not be good. People have reported cables with 4 ohms resistance on the power connections. At 500mA drain this would reduce a 5V supply to 3V.
How Can I tell if the power supply is inadequate?
Common symptoms of an inadequate power supply are
- Unreliable Ethernet or keyboard operation, especially if it's OK at first but not when the GUI is started.
- SD card errors at start up seems to be another symptom of poor power.
If you think you have a problem with your power supply, it is a good idea to check the actual voltage on the Raspberry Pi circuit board. Two test points labelled TP1 and TP2 are provided on the circuit board to facilitate voltage measurements.
Use a multimeter which is set to the range 20 volts DC (or 20v =). You should see a voltage between 4.75 and 5.25 volts. Anything outside this range indicates that you have a problem with your power supply or your power cable. Anything inside, but close to the limits, of this range may indicate a problem.
Things that can cause problems
- A USB connection on a TV or PC. The USB power supply specification is for up to 500mA and if the TV implements this then it can cause problems. The system may work initially but be unreliable because as it becomes more active the power requirement increases.
- A single supply from a powered hub. Most hubs seem to deliver more than the specified current but there's no guarantee. Check the power supply rating, it must be enough to supply everything that's connected to the hub.
- A power supply that is rated for less than 700mA may work some of the time.
- Adding a USB hard disk drive. A HDD will take quite a lot of power as it starts, maybe an amp or more. It the power supply for this also supplies the Pi then this could overload things and cause trouble.
- Some complex keyboards have been reported to take a considerable amount of power, maybe up to 500mA. The Pi cannot deliver this amount of power. Simpler budget keyboards may be better. If the system works with no keyboard attached but not with a keyboard then it's worth trying a different, simpler, keyboard.
- If you are having unreliable operation the first thing to do is check your power supply.
- Start with a good quality regulated power supply that is rated to provide 5V and at least 1A (1000mA).
- Use a good quality micro USB cable. Cables are notorious for giving trouble so be prepared to swap for another one.
- Not all power supplies will deliver what they claim.
Behind the microUSB power connector on the Model B is a metallic grey component called a capacitor, marked as C6. This capacitor helps stabilise the DC power on the board, but for some it has also become a place for their thumb when removing the RPI's power lead; unfortunately, this can result in the capacitor breaking off! It has been stated in the forums that the type of capacitor used for C6 will be changed on later RPi models for one with sturdier leads. If you do break off your C6 capacitor, it's highly likely that your RPi will still work properly, unless you have a particularly unstable power supply, but the general advice is to not use C6 as a leverage point when removing the power connector and also take care when storing or transporting your RPi if it's not fitted in a case - try not to stow the board where C6 could be knocked by other items - for example in a laptop carry case or in amongst some books.
It's unlikely that replacing a broken off C6 capacitor will be covered under warranty, but fortunately they are easy to replace if you have average soldering skills, but remember that reworking your RPi will void its warranty too. C6 is a surface mount electrolytic capacitor with a capacitance of 220 microfarad (μF) and a voltage rating of 16 volt (V). The capacitor is polarised and so must be fitted the right way round - notice the black marking on one side in the picture above. A replacement capacitor can be purchased from numerous sources - for example:
If you prefer to make your own PSU - see: Power Supply construction - HowTo
- Forum:Sad about removal of I2S. Why was this change made?
- Final PCB artwork
- RPiBlog Post: High-res pics of the PCBs
- TwitPic:Photo of Board Powered
- Forum:What do the status indicator LEDs indicate the status of?