MORE ON RASPBERRY POWER SUPPLIES

 

Onboard fuse

There are fuses on the raspberry PCB they are a self resettable fuse called a Polyfuse. If your raspberry doesn’t work and you think that you have done something to cause it to draw to much current and trip the fuse the first to do is  disconnect the power supply and everything else and wait for a while before reconnecting the power to the raspberry ( anything from a few minutes to a few hours dependent on how much the over current surge  was  ) the chances are it will then work ok when you reconnect everything.

On the earlier raspberry p1 the fuse ( f3 ) is marked t075 (which means it is rated at 750 ma )

Some raspberry pis have fuses marked f1 and some marked  f1 & f2. revision 2 board there are no USB Polyfuse .The fuses can be replaced if needs be, but it’s difficult if you are not used to working with SMD’Ssto check if the fuse has  actually blown measure with a multimeter for 5 volts either side of it - 5 volts one side zero volts the other then the fuse has blown

The voltage regulator could also fail if for example more than 5 volts has been applied to the raspberry or a reverse polarity voltage accidentally applied

^{IT’S UN-LIKELY YOU WILL EVER NEED TO REPLACE THE FUSE, IF YOU DO CHECK THE FUSE RATING AND REPLACE WITH THE EQUIVALENT VALUE}

^{THE ABOVE IS ONLY AN INDICATION, I THINK THE PCB LAYOUTS HAVE CHANGED A LOT FROM ONE MODEL TO THE OTHER OVER THE YEARS}

 

POWERING VIA THE RPIO PINS AND FROM A BATTERY

it's possible to power the raspberry pi via it's rpio pins - it's important to note that this will by pass the fuse on the raspberry PCB so you need to be confident you are using a well regulated power supply, the raspberry pi ideally needs about 5.1 volts. Connect to pins 2 ( 5 volts ) and 6 ( ground )

Try at your own risk - I power My Entire Raspberry Pi from the RPIO pins and have never had a problem but I have gone back to powering them from the USB C connector on the pi 4

If you want to power the Raspberry pi from a battery for portable operation you can try the below - do not try and power it directly from a 6 volt battery

 

 

The 7805 comes with various current ratings - 1 amp, 1.5 amp  or 2.2 amp select one with  a high  current rating i.e the mc7805btg ( 2.2 amp ) there is also the lt1085ct-5  rated at 3 amps ( also the  lt1084 rated at 5 amps ) the pin outputs are different to the 7805 - check you are buying the correct one !

CHARGING THE BATTERY FROM A SOLAR PANEL

If you are powering  your raspberry from  a battery and want to charge the battery from a solar panel you could try this circuit - note you have to flip the switch when you want to charge it thereby switching  the raspberry off - i dont like the idea of having the solar panel connected to the rpi  battery all the time. plus you can built the cct as a seperate unit - if you want your battery charging all the time leave the switch out but there is no protection against  it getting over charged

try at your own risk -

 

RPI WARNING SYMBOLS

The colour square ( on earlier builds of os )  is telling you have a under voltage/cpu hot

a yellow 'lightning bolt' in the top right hand side corner of your screen -is telling you that there is an under voltage ( less than 5 volts ) this can cause problems such as a corrupted sd card or programs not working correctly. before you change the psu try a new usb power lead

 a red thermometer symbol on the screen is telling you the cpu is getting to hot - maybe you are running to many applications at the same time - stop what you are doing and switch the raspberry off for a few minutes - when you reconnect things the chances are all will be ok again

to check the cpu temperature type at the command line

vcgencmd measure_temp

or 

nano /home/pi/.bash_aliases

type below in terminal, save then exit terminal

alias temp='/opt/vc/bin/vcgencmd measure_temp'

type at new terminal

temp

The raspberry pi 3 and definitely the Pi4 runs hotter than the other versions - 54c is common - as can be seen from one of my rpi 3 ( which has VRS server running and is also processing VDL2 ACARS signals so it’s using a fair bit of processing power  )

 

 to monitor the temperature at a 5 second interval type ( change the number for your requirement )

watch -n 5 vcgencmd measure_temp

 

you could also add a fan to your raspberry pi - follow this link - read the below first

 

 

RTL1090MHZ DONGLE PROBLEMS DUE TO LACK OF POWER

You may have a problem running dump1090  which you may at first  put down to the program crashing,  you might see something like this

 cb transfer status: 1, cancelling

However this is not usually anything to do with the actual program it's because the rtl1090 dongle is demanding to much power from the usb port. if you have a wi-fi dongle, keyboard, mouse, audio sound card dongle plus the rtl1090 mhz dongle  all connected to your usb ports then that's a lot of power that you are asking the  rpi usb ports to supply. the solution is simple use a powered usb hub.

 

 

RESETTING A RASPBERRY PI WHEN ITS 'FROZEN' 

If your raspberry pi freezes you can reboot it by typing at the command line

reboot

or

sudo reboot

if it will not allow you to do this you could also do this simple modification to reboot a hung raspberry pi if you have  future issues

If your raspberry pi does hang before you buy a new power supply or suspect some software as to being the cause just change the usb cable from the power supply to the raspberry, some cable are known to cause problems

 

WHY IS IT IMPORTANT TO USE A GOOD QUALITY USB POWER CABLE ?

If you have problems with the rpi crashing or you see the yellow under power symbol flashing then before replacing the psu try replacing the usb power cable first

the raspberry pi will draw some where aound 700 ma to 1000 ma when working correctly – taking 700 ma as being the average - you can easily now see a potential problem caused if

 

The psu needs to give a constant 5.1 volts ( which a high quality unit will do ) and an  ideal cable with good connectors should have 0 ohms resistance but if it does not you drop voltage along its length on top of the voltage loss due to the psu voltage not being regulated correctly - result is the rpi is not being powered correctly now

You can check the voltage supplies to the rpi on rpio pins 2 & 6 with a volt meter - be careful you do not short anything out

to check the core voltage from the command line type

vcgencmd measure_volts core

As far as i know there is no way of checking the voltage applied to the RPIO  pins 2 & 6  other than using a volt meter

USB flatbed scanners can give a problem if they are not powered correctly - typically it thinks the scanner lock is on because the scanner has not moved forward quickly enough when it does its home position check - solution dont use a poor or overly long usb cable

There is a possibility that some of the really cheap 5 volt 'phone charger' psu's can fail - they still give 5 volts out but I think the filter capacitors go short cct putting high voltage onto what should be earthed metal. Bear in mind that these units maybe are  running  a remote raspberry ads b / dump1090  installation 24x7  so it’s worth checking threes no safety issue ( with a neon screwdriver for example )

 

 

 

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