I have been trying to get a simple led project to work on my pi 3 using a 5 volt 6 amp power supply and a 510 ohm resistor in front of the led to reduce the current going to it. Now after trying different tutorials, my pi 3 goes off on it's own from being powered up.
If I remove the power lead and restart the pi 3 the red comes on and the green led flashes as well as the ethernet port flashing green led.
I ssh into the pi 3 to try and run a python program, but then the pi dies, and there are no lit up leds anywhere at all on it.
Is there any way it can be fixed or should I just forget about it.
I'm not convinced it's broke, the fact it boots, initialises the USB/ethernet, loads the OS and starts the sshd service indicates it's far from dead.
Seems more like a major crash when your try to run the Python script. Does Python work? Just enter "python" at the command prompt, you should get version info and a >>> prompt. Enter "print 'hello world'" "hello world" shoould eco back and return to the >>> prompt. Enter "quit()" to get back to the OS prompt.
If that works start looking at what your script is up to.
The GPIO ports on a pi are 3.3 V if you have driven them at 5V without protection you may have damaged the port & possibly other parts of the CPU (current limiting with a resistor may not be sufficient protection).
this could easily result in erratic or unpredictable behaviour.
--
A baby is God's opinion that the world should go on.
-- Carl Sandburg
I have booted up the pi 3 and left it running for a while now. I did try a couple of python files but neither did anything out of the ordinary. So as you say it is not dead or dying.
On Sun, 21 Jan 2018 19:10:48 +0000, RobH declaimed the following:
Active High or Active Low wiring?
IOWs, what is the voltage source for the LED?
GPIO -> limit resistor -> LED -> ground (active High -- LED is on when GPIO is high/3.3V)
V+ -> limit resistor -> LED -> GPIO (active Low -- LED is on when GPIO is low/ground/0V)
In the former, the processor GPIO provides the voltage, so you should be seeing the 3.3V maximum, and need to limit the current to that available on a GPIO (If the calculator was based on 5V, you should be safe, as you are running the LED on less than maximum current given a 3.3V source). In the latter, the voltage is provided by some power supply bus -- and if that is 5V, and the GPIO is High (conceptually off), you would still have 2.8V passing through the resistor/LED being sinked by the GPIO. {Note: my use of source/sink may be inconsistent -- I tend to think in terms of higher voltage flowing to lower voltage... But electron flow itself is in the opposite direction).
--
Wulfraed Dennis Lee Bieber AF6VN
wlfraed@ix.netcom.com HTTP://wlfraed.home.netcom.com/
Boot the Pi, login, run a few programs - just to make sure the Pi itself is running OK.
Halt and power down.
Connect from GPIO pin 11 (physical pin 11) to the LED to a resistor then to 0v.
Boot Pi & login:
Run this command in a terminal
gpio -1 mode 11 out gpio -1 toggle 11
Run the last command a few times. LED ought to go on/off.
Your 510 ohm resistor ought to be fine - as a general guide for most generic red/yellow/green LEDs you can use a value of Voltage * 100 ohms, so for the 3.3v Pi, then 330 ohms is fine.
More pictures here which might help you get started:
Thats odd, as the red led is directly connected to the 3.3v power, and thus
*cannot* be switched off.
... which leads me to believe that the problem might very well not be your PI, but somehow no power being supplied to it.
In other words, check the power supply and the wiring from it to the PI (wire breakage comes to mind, but maybe even something as simple as a bad contact on the connector).
On the other hand, if the powerlines on the PI somehow got shortcutted the red led will ofcourse go dark too - but thats not something I see happening when an output pin gets destroyed. Especially not when its intermittent.
Not according to the Pi 3 schematic. There is FET between the LED and ground, the gate fed from the active low !RST output of a APX803-46SAG supply supervisor device. If the 5 V supply drops below
4.6 V it asserts the active low !RST and thus turns the LED off. If the supply rises above 4.6 V it waits at least 140 ms before lowering !RST. The same signal goes elsewhere as the PWR_LOW_N line.
The documentation is incomplete but dig about for gpiovirtbuf to at least monitor the PWR_LOW_N line and in principle be able to control the LED via that line.
As has been mentioned the GPIO's on a Pi are 3.3 V and don't take kindly to 5 V. I assumed that the 5 V supply was only fed to the 5 V USB input or to the 5 V pins on the GPIO header. If you connected the
5 V to the LED, then reistor then to a GPIO you might have fried that GPIO but with a 510 ohm resistor I find that unlikely.
Try running the LED Python script with no resistors/LEDs connected, does the Pi still fall over? Change the script to use a different GPIO, try again with no R's or LEDs, if that works repeat with R's and LED's connected (to 3.3 V...).
Damn. I googled it and went with the "I feel lucky" result. I guess I wasn't ... A later result mentions its actually connected to something switchable. So, my bad.
It would still not not be a bad idea to check the power supply though, starting with placing a led on the +5v power pins (to see if power is actually present). Apart from the wiring problems I mentioned, if the Pi is connected to that 6Amp power supply its just possible that it doesn't work/stabilize all that well on lower currents, and as such causes the Pi to brown-out.
On Mon, 22 Jan 2018 11:49:33 +0000, RobH declaimed the following:
I had provided the description... In short, active high presumes ground is the "normal/off" state for a signal, and one sets the voltage to high to turn it on. Active low presumes the "normal/off" state is high voltage, and the signal is on when pulled to ground.
But what state were those GPIOs commanded to be in. 0.0x appears proper for a GPIO commanded to a Low state, and 3.25 looks appropriate for those commanded to be in a High state.
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That is: using the sysfs access (export those you were testing), set DIRECTION to OUT, then set VALUE to 1... You should now measure around 3.3V on the GPIOs (make sure to look at the correct pin mapping to the GPIOs). Finally, set VALUE to 0 and measure -- they should now be near 0.0.
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(note that the RPi package supports use of the board/socket pin numbers, or the chip set internal pin numbers -- if you are wiring using the board numbers, but are in chip mode when commanding, you could be corrupting something critical to operation)
Note -- in that link they are using a transistor as an electronic gate to avoid drawing much current from the GPIO itself.
--
Wulfraed Dennis Lee Bieber AF6VN
wlfraed@ix.netcom.com HTTP://wlfraed.home.netcom.com/
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