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Simple method of turning on a led with gpio needed

cityswift

Hi I have made up a simple interface for my Pi gpio and now want to turn a led on and off. I have tried the Cambridge University tutorial on this topic http://www.cl.cam.ac.uk/freshers/raspberrypi/tutorials/ but fail at the first apt-get command as my Pi will not allow the command. Can anyone suggest an alternative or explain why this problem is occurring? What I find is that there is little or no explaination of what the commands are doing and why they are needed. image

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  • in reply to johnbeetem

    Thanks for your replies but I wanted to write a very basic bit of code rather than copying a large comprehensive programme. This is the Cambridge tutorial which I have tried but nothing happens when I input it.

     

    Turn on the Pi

    Open a root terminal from the menu,or by running sudo su in a normal terminal

    Now type in these commands, where "18" is replaced by whichever pin the led is connected to.

     

    cd /sys/class/gpio/

    echo "18" > export

    cd gpio18

    echo "out" > direction

    echo "1" > value

    The led should now be turned on.

     

    To turn the led off

    echo "0"  > value

    cd ..

    echo "18" > unexport

     

    Everthing appears to go OK when I input this but the led does not light.

     

    Can anyone help? Have I missed something obvious? Thanks

  • in reply to cityswift

    I also tried the RPi Low-level Peripherals approach like John and it worked for me, I used Python coding and it was very simple.

    Your problem could be that you used the wrong pin, you can check my experiment from my blog here

    Cheers

  • in reply to cityswift

    cityswift wrote:

     

    Can anyone help? Have I missed something obvious? Thanks

    You might try copying the C example and compiling and running it, just so you can see if the hardware is working.  I just cut and pasted the code into "gpio.c", compiled it using "gcc -o gpio gpio.c", and ran it using "sudo ./gpio".  Worth spending three minutes.

     

    If "gpio" doesn't work, here are some obvious hardware errors that are easy to miss:  (1) Check that the LED lights using just RasPi +3.3V, a current-limiting resistor (330-470 Ohm is a good starting value), and RasPi ground.  Maybe your LED is dead.  (2) Check that the LED's anode is high and cathode is low.

     

    Caution: one of the easiest ways to destroy a RasPi is to short the +5V and +3.3V pins on the GPIO connector.  I recommend stripping some insulation off a wire and sliding it over the +5V pin before messing around with other GPIO connections.