Raspberry Pi logo raspberry pi

Running Raspberry Pi, occasionally you find error detected during the Linux OS (operating system) boot up process?

Sometimes it happen, sometimes it don't.

For some reason, your running program behave very odd and give weird result?

Your program hang (freeze) or crush suddenly.

Your network is working perfectly but Raspberry Pi fails to detect the network.

Your keyboard does not seems to work suddenly.

These are some of the common problems faced by many Raspberry Pi users.

Edited by Lim Siong Boon, last dated 22-Sep-2013.

email:    contact->email_siongboon  

website: http://www.siongboon.com

Topic Discussion Overview

I will be listing down the possible error that can be cause by a poor power supply to Raspberry Pi, and also the solution to check on this power supply problem.

Errors Occured while booting up Raspberry Pi.


Type of error messages and symptoms encountered during bootup.
Raspberry Pi boots and reboots again.
USB keyboard cannot be use
ERROR::dwc_otg_hcd_urb_enqueue:514: Not connected error dwc_otg_hcd_urb_enqueu   error dwc_otg_hcd_urb_enqueue   error dwc_otg_hcd_urb_enqueue
EXT4-fs error (device mmcblk0p2): ext4_iget:3811: inode #3099: comm sh: bad extra_isize (3387 != 256) EXT4-fs error
Kernel panic - not syncing: Attempted to kill init! Problem relating to SD card
unable to handle kernel null pointer dereference at virtual address 00000000

Solution to the problem listed above.
The root cause to most of the symptoms and error messages are simply cause by the power supply. It is important that the electronics components receive enough voltage in order to allow them to function properly. An ideal power supply will always supply consistent voltage given any current load. A voltage is similar to pressure, you can imagine it as an electrical pressure. Current is like the amount of presurised air flowing through within a period of time.

For example, a 5V 1A power adaptor is suspose to supply a 5V and is capable of supplying up to 1A of current to the load. A Raspberry Pi without any peripherals (devices attached to Raspberry Pi will consume current) will typically consume about 0.35A. An ideal power supply is able to supply the 0.35A while maintaining its 5V. However in this physical world, this kind of perfect power supply adaptor does not exist.

There will always be some voltage drop when the current is drawn. Even a power supply of the same brand and model, using the same components, they may have slight difference is the voltage drop. A good power supply will remains as close to 5V as possible, when current drawn is within its rated value of 1A. You can certainly use the 5V 1A to power up a higher load (5V 1.2A device for example), however the voltage will not be guarantee

Power Supply to take note for Raspberry Pi.

Ensure to use a good stable power supply for your Raspberry Pi.
Minimum recommended power supply is 5V 1A.
Voltage measure on the test pin TP1 (5V, near the micro USB socket) and TP2 (Gnd, near the composite video RCA socket) should range between 4.75V - 5.25V when in operation. See the illustration on the right. Measure this test pin while the Raspberry Pi is booting after the boot up has complete. You will see the voltage fluctuating, because the device may draw more or less current during the operating process. It is ok for the voltage to drip below 4.75V, but it will be real bad if it drips below 4.5V.

Voltage (TP1, TP2) 4.5V and below will be too low for the Raspberry Pi to operate normally. This is because there is a 3.3V LD1117-3v3 linear regulator which requires a minimum voltage drop of 1.2V in order to regular voltage properly. This means that the supply voltage has to be at least 4.5V. If it drips lower than this 4.5V, the components that are supplied with the regulated 3.3V may starts to fail. There are actually two more regulators that are used in the Raspberry. They are LP2980-2v5 (2.5V) and NCP1117-1v8 (1.8V). Components powered by these two regulators are usually not quite that affected, unless the supply voltage is much lower than 4.5V. You can actually study the schematic here to understand about the electronics used in a Raspberry Pi.

If the voltage is not high enough, the network module will fail to retrieve network information, and other peripheral may fail during bootup time. Even if it can run, you may encounter suddenly failure in the process of operating the Raspberry Pi device.

Any change in the Raspberry Pi configuration, where you attached other electronics or USB device, you will need to measure the voltage again to ensure that the power adaptor is able to handle it.

Extra care should be taken to the USB micro cable as well. If the resistance of the cable is more than 1
Ω, it should not be used to run the Raspberry Pi. The high ohm will result in a higher voltage drop. Failure can happen, even a good quality power supply adapter is used. USB micro cable should be about 0.5Ω or less.

Raspberry Pi test pin 5V Gnd
Check out the location of TP1 (5V) and TP2 (Gnd)
Setup Oscilloscope to measure power supply voltage.
measuring raspberry pi power supply from oscilloscopeprobing tp1 tp2 raspberry pi measuring voltage
ADC-320HTU power supply, 5V 2.0A, to power up Raspberry Pi

USB power supplyUSB power supply
This 5V 2A power supply specification shows that it can supply 2A of current to the load, which is double the requirement for a typical Raspberry Pi configuration. This adaptor is rated
for I.T.E. (Information Technology Equipment) equipment use.

Voltage measurement

raspberry voltage measurement using power adaptor 1
However when it is plug to run the Raspberry Pi, the voltage is measured at 4.57V. This is too close to the lower voltage limit of 4.5V. It will run Raspberry Pi most of the time, but is not recommended to use it. There will be time when the voltage dips lower. 
Any slight drips may cause your Raspberry Pi to malfunction.

Such dip can happen due to a short AC power drop, extra current consumption due to the software routine controlling the electronics or extra peripheral plugged onto the Raspberry Pi. It is hard to tell. For example the AC lighting switch being turned off, can send electrical noise across the room, resulting in a slight AC power drop to the power adaptor, therefore affecting your Raspberry Pi. It is almost impossible to predict when your device will give you the headache.

In this case, it is better to change to another reliable power adaptor although it seems working fine now. You will never know when it crush your system with errors.

Power stability of Power Adaptor

power adaptor 1 supply voltage power adaptor 1 supply noise
The open load power supply voltage is measured to be 4.96V
Voltage measured when the supply is loaded with a Raspberry Pi load is about 4.5 to 4.61V. Noise seems ok, at 55.2mVp-p.

When running the Raspberry Pi, the device's operating current is about 0.35A up to 0.38A peak. Voltage measure during booting is about 4.8V. When the booting process is completed, the stable voltage stay at about 4.54V.

The 4.61V measured across TP1 and TP2 is quite close to the limit of 4.5V. Chances of failure due to the power supply will be high.

When deploying the Raspberry Pi using this power supply adapter, it had operated well most of the time. At times, weird things starts to happen. Unable to retrieve network information at start up. The boot up process would print out error messages. The Raspberry Pi might also  terminates abnormally.

Raspberry Pi power adaptor 5V 1A

best raspberry pi power supply adaptor
Specially designed 5V 1A micro USB power supply adaptor for Raspberry Pi use. Specially for I.T.E. equipment use (Information Technology Equipment). I.T.E. means that the adaptor is designed for information technology equipment use. Noise generated by these adaptor is low. Click on this link for the technical specification of this Raspberry Pi power adaptor.

Voltage measurement

raspberry voltage measurement using Raspberry Pi power adaptor
The voltage reading measured using this power adaptor is 4.82V, which is much better than the previous adaptor above.
Any voltage measure between 4.75 to 5.25V is considered ok for Raspberry Pi operating.

Power stability of Power Adaptor

best power adaptor supply voltage best power adaptor supply noise

This Raspberry Pi power supply adaptor is the best that I have found so far. The open load voltage is about 5.06V. Open load voltage is the voltage of the power adaptor when no load is connected to it. When operating the Raspberry Pi, the measured voltage (across TP1 & TP2) stays between 4.75 to 4.90V. This is much higher than the failure voltage of 4.5V.

The micro USB plug is wired directly to the power adaptor, minimising any ohm lost due to numerous connection contact point. The power from the adaptor is directly delivered to the Raspberry Pi.

The noise of this adaptor is only measuring 56.8mVp-p, which is about the same as the previous one.

This kind of adaptor is also commonly available for charging mobile phone. Be careful to take note of the rating of the power adaptor. Those adaptor that are designed for charging mobile phone is typically 5V and less than 0.5A. Be sure to get one that have a higher current rating. Always measure the voltage at the Raspberry TP1 and TP2, to ensure that it has a minimum voltage of about 4.75V. The same power adaptor model is possible to have some slight variation in its performance. When operating in different temperature environment, the voltage can change slightly also. The voltage may also gets degraded over its operating lifespan. It is always good to measure to ensure the minimum power supply requirement has been met before troubleshooting other software problem. You might not find any, as the bug could come out of the blue due to incorrect power supply voltage.

So far, this power adaptor is the most suitable one for Raspberry Pi.
You can buy this quality power supply adaptor (5V 1A) specially designed for Raspberry Pi at PIC-STORE.

Best Recommanded
Power Supply Adaptor
for Raspberry Pi
Other adaptors power supply measurement.

rasapberry pi power adaptor 2
power adaptor 2 supply voltage power adaptor 2 supply noise
This adaptor 5V 1A is use for charging a HTC phone. Open load voltage is 5.13V. Performance is good, voltage measuring 4.77V with noise 51.2mVp-p

rasapberry pi power adaptor 3
power adaptor 3 supply voltage power adaptor 3 supply noise
This adaptor is rated at 5.2V 0.5A. Open load voltage is 5.26V. Voltage is slightly higher than the normal 5V. The voltage dip is high at 0.3V but because it is a 5.2V power supply adaptor, the final voltage drops to 4.9V, which is still fine for Raspberry Pi operation. Beware as the voltage may go down even further with other devices plugged to the Raspberry Pi. Noise is higher at 124mVp-p, propably it is not design for I.T.E equipment.

rasapberry pi power adaptor 4
power adaptor 4 supply voltage power adaptor 4 supply noise
This adaptor is rated at 5V 0.8A. Open load voltage is 5.25V. The measured voltage is 4.87V which is sufficient for Raspberry Pi operation. Noise is very high at 376mV. Not recommanded for use which Raspberry Pi, as the noise may cause intermediate problems. You can see the large negative dip from the noise. This noise dip may go beyond the minimum voltage of 4.5V which can cause problem for your Raspberry Pi project.

Measurement of micro USB cable
micro usb cable 5V wire<0.5
Ω>, Gnd wire<0.5Ω>
micro usb cable 5V wire<0.5Ω>, Gnd wire<0.5Ω>
micro usb cable 5V wire<0.5Ω>, Gnd wire<0.4Ω>
micro usb cable 5V wire<1.6Ω>, Gnd wire<1.6Ω>. faulty cable.

If the micro USB cable that is used to power up the Raspberry Pi has a ohm too high, some of the built-in peripherals will fail. This can be observed during the boot up process. The booting takes longer than usual, and many error and unusual messages can be seen during the boot up. Retreiving network information from the gateway or router may fail as well.

The internal miniSMD 6A fuse between the micro USB socket and pin TP1 is about 0.3Ω. This means that the total resistance from the power supply to the Raspberry Pi can be able 0.5Ω + 0.5Ω + 0.3Ω, which will be about 1.3Ω. If the Raspberry Pi is drawing about 0.4A, the voltage drop across the cable can be about 0.52V.

Other References
- Raspberry-pi-usb-power-cables-crashing-and-other-problems
- http://techtips.easycloudsolutions.com/2012/07/17/raspberry-pi-no-display/
- http://inductible.wordpress.com/2012/07/13/raspberry-pi-unresponsive-keyboard-problem-solved-with-a-customised-usb-cable/
- http://www.hoeser-medien.de/2013/04/raspberry-pi-power-problems-elinux/
- http://www.youtube.com/watch?v=XX3kiRUf7mg&noredirect=1
- http://www.aoakley.com/articles/2014-02-25-raspberry-pi-power-wifi.php