CPPToPigpio is a library that maps the functions used with the mbed microcontroller to be used on with the GPIO ports of a Raspberry Pi.

Installation

To install the library:

1. After installing pigpio, download this repo as a zip file and unzip to some directory. You can download the zip file here
2. Make sure install.sh is executable by running $ sudo chmod +x install.sh
3. Run $ sudo ./install.sh from that directory. Should see a message that install has finished successfully.
4. Projects should be ready to compile now. Add in include <CPPToPigpio.h> in your main file, and ensure that Build->Set Build Commands->Build in Geany contains g++ -std=c++11 -Wall -Wextra -o ‘%e’ ‘%f’ -pthread -lpigpio -lrt -lCPPToPigpio

To enable full I2C functionality (being able to use both sets of I2C pins), do the following:

1. In Preferences->Raspberry Pi Configuration->Interfaces tab, make sure I2C is enabled. By default, this only enables I2C1 (p2/p3).
2. Reboot the pi (you can use $ sudo shutdown -r now)
3. Edit /boot/.config.txt with super user
   1. Add dtparam=i2c_vc=on above the line matching dtparam=i2c=on
   2. Reboot
4. In the terminal enter i2cdirect -y 0 and then i2cdirect -y 1 to scan the two I2C buses. You should get something similar to this image:

Testing the code

On top of writing your own code to test the library, here is an mbed repo containing some test programs - including details for setting up the testing circuits - that can be used to ensure that the library is fully functional. It also contains an example I2C driver for the MPR121 Touch Keypad."

Classes

DigitalIn

The DigitalIn interface is used to read the value of a digital input pin.

API

Code Example

This test takes in a DigitalIn signal and outputs a PWM signal that will control a servo. The servo should go to it's "maximum" position when the button is pressed and to its "minimum" position when it is released

#include <iostream>
#include <CPPToPigpio.h>

using namespace std;

CPPToPigpio::DigitalIn switchPin(p18);
CPPToPigpio::PwmOut servoPin(p20);

int main() {
    switchPin.mode(PullDown);
    
    // 20 Hz
    servoPin.period(0.05);
    
    servoPin = 0.03;
    
    while(1) {
        if(switchPin) {
            // servo on
            servoPin = 0.04;
            cout << "servo pin high" << endl;
        }
        else{
            servoPin = 0.02;
            cout << "servo pin low" << endl;
        }
        time_sleep(1);
    }
}

DigitalOut

The DigitalOut interface is used to configure and control a digital output pin.

API

Code Example

Uses a DigitalIn signal to read a button press, and lights up an LED using DigitalOut if the button is pressed.

#include <CPPToPigpio.h>

using namespace std;

int main() {
    
    CPPToPigpio::DigitalIn input(p18);
    
    CPPToPigpio::DigitalOut LED(p20); 
    input.mode(PullDown);
    
    time_sleep(1);
    
    while(1) {
        LED = input;
        
        
        time_sleep(0.1);
    }
}

BusIn/BusOut

BusIn and BusOut are used to read and write digital signals on specified pin. The MBED BusIn/BusOut has a maximum limit of 16 pins per bus, and this limit is replicated by CPPToPigpio despite it being rather artificial. In the future, the limit can easily be increased by adjusting the constructors to take more than 16 pins.

BusIn

The BusIn interface is used to create a number of DigitalIn pins that can be read as one value.

API

BusOut

The BusOut interface is used to create a number of DigitalOut pins that can be written as one value.

API

I2C

The I2C interface provides I2C Master functionality.

This interface can be used for communication with a I2C devices, such as serial memories, sensors and other modules or integrated circuits.

API

Code Example

Receives a value from an accelerometer and "plots" it on a 4-bit BusOut (it just shifts the 16-bit received value by 12).

#include <iostream>
#include <CPPToPigpio.h>

#define I2C_SDA p2
#define I2C_SCL p3

using namespace std;

int main() {
    
    CPPToPigpio::I2C acc(I2C_SDA, I2C_SCL);
    
    CPPToPigpio::BusOut LEDs(p21, p20, p16, p12);
    
    char initWrite[] = {0x20, char(0xC0)};
    char dataGet[] = {0x28};
    char dataFromStuff[2];
    
    acc.write(0x35 << (1), initWrite, 2, false);
    
    time_sleep(1);
    
    while(1) {
        acc.write(0x35 << (1), dataGet, 1, false);
        acc.read(0x35 << (1) | 1, dataFromStuff, 2, false);
        
        int superAcc = dataFromStuff[0] + (dataFromStuff[1] <<(8));
        
        cout << "acc gotten is " << superAcc << endl;
        
        int writeEm = superAcc >>(12);
        
        LEDs = writeEm;
        time_sleep(1);
    }
}

PwmOut

The PwmOut interface is used to control the control the period and duty-cycle of a GPIO pin on the Pi.

API

Code Example

This test gets a value from a BusIn and changes a PwmOut frequency based on the BusIn value. Outputs frequency to command line as well.

#include <iostream>
#include <CPPToPigpio.h>

using namespace std;

float starting_f = 8000.0f;

CPPToPigpio::BusIn switchBus(p25, p24, p23, p18);

float divisions[] = {1.0f, 2.0f, 4.0f, 5.0f, 8.0f, 10.0f, 16.0f, 20.0f, 25.0f, 32.0f, 40.0f, 50.0f, 80.0f, 100.0f, 160.0f, 200.0f};

CPPToPigpio::PwmOut outThing(p21);

int main(){
    
    switchBus.mode(PullDown);
    outThing.period(1.0f/starting_f);
    outThing = 0.5f;
    
    while(1) {
        int total = switchBus;
        
        outThing.period(divisions[total]/starting_f);
        
        cout << "frequency should be " << starting_f/divisions[total];
        
       time_sleep(1);
    }
}

Setting A Custom Period

The following periods available to be set using the 3 period functions:

0.0002s, 0.0004s, 0.0008s, 0.001s, 0.0016s, 0.002s, 0.00319s, 0.004s, 0.005s, 0.0064s, 0.008s, 0.01s, 0.0159s, 0.02s, 0.0323s, 0.04s, 0.0769s, 0.167s

Setting Duty Cycle

In order to give the ability to set duty cycle through Pigpio, internally we are converting the duty cycle to a value on the scale of 0-5000 . For instance calling write(0.4) will actually write 2000 on a Pigpio range of 0-5000 - this is equivalent to a 40% duty cycle.

Acknowledgements

This code was developed by:

• Andrew Renuart: andrew.renuart@gatech.edu
• Jason Calvert: jcalvert8@gatech.edu
• Julian Rosker: julian.rosker@gatech.edu
• Charith Dassanayake: karvin@gatech.edu