Raspberry Pi Using the GPIO pins with Wiring Pi and openFrameworks

Using WiringPi with OpenFrameworks for Raspberry Pi to access the GPIO-pins

Important: The GPIO pins on the Raspberry Pi is 3.3V, even though there is also a 5V supply. Be sure not to connect a higher voltage than 3.3V to the GPIO pins or you could severely damage your Pi.

WiringPi is a C-library by Drogon making it easy to read and write to the GPIO pins in an Arduino style. See https://projects.drogon.net/raspberry-pi/wiringpi/ for details.

To get and install the library do the following (from projects.drogon.net):

To obtain WiringPi using GIT:
git clone git://git.drogon.net/wiringPi

If you have already used the clone operation for the first time, then cd wiringPi git pull origin

Will fetch an updated version then you can re-run the build script below. To build/install there is a new simplified script:

cd wiringPi
./build

The new build script will compile and install it all for you – it does use the sudo command at one point, so you may wish to inspect the script before running it.

Then in your projects config.make-file include the following line (in bold) in the PROJECT LINKER FLAGS-section:

################################################################################
# PROJECT LINKER FLAGS
#	These flags will be sent to the linker when compiling the executable.
#
#   Note: Leave a leading space when adding list items with the += operator
################################################################################

# Currently, shared libraries that are needed are copied to the 
# $(PROJECT_ROOT)/bin/libs directory.  The following LDFLAGS tell the linker to
# add a runtime path to search for those shared libraries, since they aren't 
# incorporated directly into the final executable application binary.
# TODO: should this be a default setting?
PROJECT_LDFLAGS=-Wl,-rpath=./libs
PROJECT_LDFLAGS += -lwiringPi

Then in your testApp.h include the library by placing the following line near the top:

#include “wiringPi.h”

and while you’re in there let’s prepare the example:

bool sensor0;
bool sensor3;
bool sensor7;

Now in your testApp.cpp an example of the use could be the following. In the setup-function put:

if(wiringPiSetup() == -1){
	printf("Error on wiringPi setup\n");
	}

	pinMode(0,INPUT);
	pinMode(3,INPUT);
	pinMode(7,INPUT);

This will make it possible to read the pins 0, 3 and 7 (see connections for the GPIO pins on https://projects.drogon.net/raspberry-pi/wiringpi/pins/ ). Also put:

bool sensor0 = false;
bool sensor3 = false;
bool sensor7 = false;

Now in the update-function:

if(digitalRead(0)!=0){
	sensor0 = true;
} else {
	sensor0 = false;
}

if(digitalRead(3)!=0){
	sensor3 = true;
} else {
	sensor3 = false;
}

if(digitalRead(7)!=0){
	sensor7 = true;
} else {
	sensor7 = false;
}

And in the draw function:

ofBackground(ofColor(0,0,0));

ofSetColor(190);
    if (sensor0 == true){
    	ofDrawBitmapString("Sensor at pin 0 activated", 50, 50);
    }
    if (sensor3 == true){
	ofDrawBitmapString("Sensor at pin 3 activated", 50, 70);
    }
    if (sensor7 == true){
	ofDrawBitmapString("Sensor at pin 7 activated", 50, 90);
    }

That’s it. Note that some of the pins should be treated different than others e.g. pin 8 and 9 have pull-up resistors. In general you should read https://projects.drogon.net/raspberry-pi/wiringpi/special-pin-functions/ to be sure you understand how you are using the pins.