I2C LCD w/ buttons - C

Question

I'm have a 16x2 LCD button shield for RPI similar to Adafruits. It works using the provided Python library so the setup is ok.

The problem is I can't find any working C code or library to work with this setup. I've tried Gordons tutorial and some other sources I found but with no luck yet.

Has anyone got any working solution for this?

P.S. RPI is running on ArchLinux

Answer 1

I have found a workaround for this issue. Since I could not migrate the solution python I needed to get it working under C. The solution is to use Python-C API which lets you call python calls and get results.

Most of the information I found in this codeproject post

I created simple methods for my needings which included some "wait for a button press" method and such. For example if I have a method to print on a screen:

#!/usr/bin/python2

from time import sleep
from Adafruit_CharLCDPlate import Adafruit_CharLCDPlate
import sys
btnsleepcycle = 0.01

class lcdSlave():

  def __init__(self):
      self.lcd = Adafruit_CharLCDPlate()
      self.lcd.begin(16, 2)

[Some code ommited]

  def lcdprint(self, message):
      self.lcd.clear()
      self.lcd.message(message)
      return 0

[More code ommited]

Now when I want to call the code from my C code I must use the Python-C API call and make an include.

#include "python.h"

The rest is now on your C coding skills but for the same lcd print it is as easy as:

#include <Python.h>
int main(int argc, char *argv[])
{
    initPython(argv);
    int result = 0;
 PyObject *pName, *pModule, *pDict,
             *pClass, *pInstance, *pValue, *pMessage;
// Load the module object
    pName = PyString_FromString("lcdSlave");
    pModule = PyImport_Import(pName);
// pDict is a borrowed reference
    pDict = PyModule_GetDict(pModule);
    pClass = PyDict_GetItemString(pDict, "lcdSlave");
    // Create an instance of the class
    if (PyCallable_Check(pClass))
    {
        pInstance = PyObject_CallObject(pClass, NULL);
    }
    pName = PyString_FromString("lcdprint");
    char* msg = "Your message\nhere"; //  '\n' will go straight to 2nd line
    pMessage = PyString_FromString(msg);
    pValue = PyObject_CallMethodObjArgs(pInstance, pName,pMessage, NULL);
    if (pValue != NULL)
    {
        printf("Return of call : %d\n", PyInt_AsLong(pValue));
        Py_DECREF(pValue);
        result = 0;
    }
    else
    {
        PyErr_Print();
        result =-1;
    }
    // Clean up
    Py_DECREF(pModule);
    Py_DECREF(pName);
    Py_DECREF(pMessage);
    Py_Finalize();
    return result;

}

ArchLinux heads-up: I lost 2 days figuring how to compile this because there is no python-dev package. Found out it's as easy as $(pkg-config --cflags --libs python2) as stated in this solution.