tristate gpio

[boblei...@gmail.com]

I am trying to set up a GPIO pin on the raspberry pi using quick2 wire.  I need the pin to not assert high or low until needed in my code.  I have tried to do this by initially setting the pin as an input, the plan being to change it to an output when I need to assert the pin to work my hardware.

My problem is that I can't work out how to change the direction of the pin.   My code goes something like this:

from quick2wire.gpio import pins, In, Out
mypin = pins.pin(5, direction=In)   #Pin 5 set as input, this works fine and the pin works as an input ok

and later I want to switch it to an output with something like

mypin = pins.pin(5, direction=Out)

this causes a runtime error (IOError pin(5) is closed)

I have tried various other syntax without any luck.  Can anyone help me with this?

Bob

[Andrew Scheller]

It's much simpler than that :) The pin's direction is just a
property of the object, i.e. you need to do:
mypin.direction = Out

Andrew

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[boblei...@gmail.com]

Hi Andrew, thanks for replying

I tried using mypin.direction = Out but I get another runtime error. 

The traceback is:

Traceback (most recent call last):

  File "/home/pi/Desktop/SelectorKeypadTest.py", line 31, in <module>

    mypin.direction=Out

  File "/usr/bin/quick2wire/gpio.py", line 151, in direction

    self._write("direction", new_value)

  File "/usr/bin/quick2wire/gpio.py", line 192, in _write

    with open(self._pin_path(filename), "w+") as f:

IOError: [Errno 2] No such file or directory: '/sys/devices/virtual/gpio/gpio24/direction'

I'm a bit lost at this point.  My system does not have a gpio24 directory in the /sys/devices/virtual/gpio directory.  (The only directory in gpio is  called gpiochip0, and it does not contain a file called direction.)

Bob

[Romilly Cocking]

The sysfs system (twhcih controls the files under /sys) is a bit wierd. Files and directories are created and destroyed as gpio pins are exported or released. If you can' see a directory called /sys/devices/virtual/gpio/gpio24/ all that means is that the pin is not currently exported. perhaps because your code has not yet opened it (or has opened it and then closed it).

It might be easier to see what's wrong if you could post the SelectorKeyPadTest code in its current form.

Romilly

--

[boblei...@gmail.com]

Hi Romilly, thanks, I can see my problem now

I won't post the whole code because it is massive (and embarrassingly messy, a masterpeice in progress).  In a nutshell though I tried to change the direction of the pin before opening it like you said, In essence my code boiled down to:

from quick2wire.gpio import pins, In, Out

mypin = pins.pin(5, direction=In)

mypin.direction=Out      --> causes runtime error, but works fine if I move this line to after the 'with mypin:' statement

with mypin:

    mypin.value = 0

    print('mypin set to out, value 0')

    time.sleep(20)

    Print('exiting')

Thanks for your help, I appreciate it.  

Bob

PS I've had fun monitoring in a terminal when the gpio24 folder appears and disappears from /sys when my code runs - never realised this happened. 

[Romilly Cocking]

I'm glad the problem is solved.

best regards,  Romilly

[Chen Jason]

Hi,

   Can Raspberry's GPIO pin really be tristated ?  I tried to put the direction as 'in', but that does not work.  There's

still voltage on the pin.

boblei...@gmail.com於 2013年10月2日星期三UTC-7上午3時17分35秒寫道：

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[Jeffrey Herr]

Until it is connected to ground, it might look that way...  Connect with a pull-up or down resistor and it should work as expected. 

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