Over current protection are resettable polyfuse/ PTC that will break the circuit temporary when too much current flowing thru it...

With so many types of USB hub at different price level/ design/made in China, it is hard to determine which ones have over-current protection at port or device or any protection at all..

See this example for the PTC
( http://dangerousprototypes.com/docs/ATX_Br...design_overview )

The standard USB current was suppose to be 500mA (0.5A) per port but these days using as a charger, some USB power supply will spill out 2A/1A via the USB port...

Except the Apple computers (not sure about the latest laptops), most standard USB port only supply 500mA via its USB port...

So the current protection question, should it be 500mA or 2000mA ??

A picture of the mentioned plug will tell a thousand words...

Don't like linux or raspbian on yr RPi ?

Just write your own operating system from the beginning...

A beginners tutorial to program the RPi using ARM assembly language...

http://www.cl.cam.ac.uk/freshers/raspberrypi/tutorials/os/

Learn Python from M.I.T. Prof teaching students programming using Python... like learning another language... spanish, english, french...etc...

http://ocw.mit.edu/courses/electrical-engi...video-lectures/

Thanks to the Internet, we can to access the best minds around the world for almost free ( you still pay fo electricity & yr internet access )...

Nowdays, all USB chargers are 5V...

See the Ampere rating... mobile charger are usually 1A ( or 1000mA ) or 2A ( 2000mA ) for tablets.. RPi needs like 1500-2000mA bcos the RPi already taken up like 700mA... when you plug in other sutff like keyboard, USB hard disk, USB Wifi adapter, other USB accessories... it will need to draw power from the adapter...

If you do not plug anything to the USB port, then it should be okay...

I might have missed something important here... what's wrong with powering the RPi from the backfeed ??

Power surge on the 5V USB power... are you sure ??

This is not 220V mains...

Unless u r using the 1st revision....

As of Model B Revision 1.0 + ECN0001 onwards, the polyfused WAS removed ...

http://www.raspberrypi.org/archives/tag/polyfuses


USB Output Power

The resetable fuses protecting the USB outputs have been removed. This feature was implemented on some later revision 1.0 PCBs by replacing the fuses with links; revision 2.0 permanently implements this modification. It is now possible to reliably power the RPI from a USB hub that back feeds power, but it is important that the chosen hub cannot supply more than 2.5A under fault conditions

So the USB power adapter you choose is important too....

Thanks for the clarifications about the input polyfuse...

My RPi with USB Wifi, Bluetooth module as serial console and Nordic Wireless module nRF24L01 with external antenna via SPI connecting wireless to Arduino wireless nodes...

Running Adafruit Occidentalis V0.2 http://learn.adafruit.com/adafruit-raspber...ntalis-v0-dot-2


Photo 08-02-2013 09 42 17 PM by stanley_seow, on Flickr

Arduino Wireless remote node :-

IMG_1083 by stanley_seow, on Flickr

First thing to check is the USB power supply/USB hub... when not enough power, it causes other issues...

Check yr ip address, ifconfig, look at eth0 , what is the ip addr ...

In command line, type tail -f /var/log/messages

Look for eth0 and other errors like below...



I face this strange problem, when I plug in my USB mouse, the eth0 get a lot of errors and when I plug out, everything works fine... I suspect it could be power supply issues but even using 2A iPod USB power supply still same issue...

Now running command line mode with HDMI to DVI converter to LCD monitor...

Why this circuit diagram so complex...

Actually... to make the circuit simple, the LM7805 itself will output 5V without any other components...

Those capacitors like 2200uF, 100nF and 10nF are just filtering capacitors to smooth the noise on the circuit..

The rest are for just for protection purposes...

Diode prevent short circuit, either accidentally, component failure or reverse current ( when a motor switch off )..

Zener at 5V8 will only allow current flow to ground when the voltage is above 5.8V

Another one is PTC resettable fuse.. this is found in the RPi, it cut off current and heat up when too much current is flowing thru it.. once cool off, the circuit is closed again...

These are all the component used in design that differentiate between an expensive Apple power supply/charger vs no-name cheap "similar looking" power supply/charger...

An example, I was using a green "USB Power" 2-ports 2.1A USB charger from ALL IT mall to power up my RPi... to my surprise, it is giving me lots of power issues like network disconnect errors... once I changed to a TP-Link 1A USB power supply from HuntKey ( http://www.huntkey.com/en/products/c149/index.html ), everything was back to normal...

ALFA seems to have very high power USB Wifi with external antenna, some are 1000mW or even 2000mW output power... and reference back to elinux.org for compatibility...

Search for them on lelong.com.my or buy/sell section here or even google for it...

http://www.lelong.com.my/alfa-awus036nhr-2...3-07-Sale-P.htm

How do you plan to connect the GPS to the RPi ?? USB version ?


You will need a powerful battery/power bank if you need it to be portable....

Do you want a tutorial to design yr own OS or just tutorials on RPi ?

Yr questions is a bit vague..

Start with this : http://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/

Write yr own RPi OS from zero...

HDMI are "digital signals" e.g. 1 and 0, unlike those analog audio cables interconnect... so "normal" price ones will do...

Unless you need to run HDMI for a very long length, 3-10m, then u might need "better" cable to prevent signal loss..

Gold/yellow colour or no gold plated doesn't matter la, but it just looks nicer... haha

Turning_the_Raspberry_Pi_Into_an_FM_Transmitter

This is a fun thing to try out with yr Pi..just need a 10cm wire plugged into GPIO4 (not pin4).. and run the fm binary from the links below... and a mono 22Khz wav file... then tune yr radio to that freq... the FM range is very good for such a simple antenna...

http://www.icrobotics.co.uk/wiki/index.php..._FM_Transmitter

*** Use with care as you might disrupt your neighbour FM radio too at the same FM frequencies..

I'm not sure if this is related to yr issue, see this forum topic :
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=7799

I once had the polyfuse blown and it takes a long time to recover... once recovered, everything was back to normal...

You might also want to measure the current ( with correct Ammeter settings ) too as suggested by someone else...

RPi had most of their product return issues are related to "power" issues....

The RPiCluster

I love the blinking LEDs and how it powered the Pi using a PCB into the header pins without the micro-USB connector..

http://www.youtube.com/watch?feature=playe...d&v=i_r3z1jYHAc

Those Sunwa "analog" multimeters are pretty cheap and good... around RM25-28 only... can be use for testing electronic components too...

http://www.jestineyong.com/bought-electronic-products/

Yes, I hv both Sanwa for accuracy measurements and Sunwa analog MM for testing stuff like capacitors bcos the analog needle is much faster than auto-ranged digital MM for testing faulty capacitors.. it was a trick used by electronic repairers to test faulty electronic components...

*** sorry for off topic from RPi...

Anyone purchased or tried the new camera module ???