MPR121 capacitive touch and Pure Data

giuliomoro I meant exactly: are you still sending to it from the other thread (that is, readMPR121()).
There are three instances for readMPR121() - I see no doubles
For documentation::

-- line 77 says --internal stuff -- do not change

 
// ---- internal stuff -- do not change -----

I2C_MPR121 mpr121;			// Object to handle MPR121 sensing
AuxiliaryTask i2cTask;		// Auxiliary task to read I2C

int readCount = 0;			// How long until we read again...
int readIntervalSamples = 0; // How many samples between reads

void readMPR121(void*);

/*********/;

-- line 389 - To have the data via i2c

	i2cTask = Bela_createAuxiliaryTask(readMPR121, 50, "bela-mpr121");

-- line 776 - to connect NUM_TOUCH_PINS to sensorValue - so Pure Data can receive these values

void readMPR121(void*)
{
    for(int i = 0; i < NUM_TOUCH_PINS; i++) {
        sensorValue[i] = -(mpr121.filteredData(i) - mpr121.baselineData(i));
        sensorValue[i] -= threshold;
        if(sensorValue[i] < 0)
            sensorValue[i] = 0;

-- Full render.cpp as it is now

/*
 ____  _____ _        _    
| __ )| ____| |      / \   

|  _ \|  _| | |     / _ \  

| |_) | |___| |___ / ___ \ 
|____/|_____|_____/_/   \_\

The platform for ultra-low latency audio and sensor processing

http://bela.io

A project of the Augmented Instruments Laboratory within the
Centre for Digital Music at Queen Mary University of London.
http://www.eecs.qmul.ac.uk/~andrewm

(c) 2016 Augmented Instruments Laboratory: Andrew McPherson,
	Astrid Bin, Liam Donovan, Christian Heinrichs, Robert Jack,
	Giulio Moro, Laurel Pardue, Victor Zappi. All rights reserved.

The Bela software is distributed under the GNU Lesser General Public License
(LGPL 3.0), available here: https://www.gnu.org/licenses/lgpl-3.0.txt
*/

/*
 *	USING A CUSTOM RENDER.CPP FILE FOR PUREDATA PATCHES - LIBPD
 *  ===========================================================
 *  ||                                                       ||
 *  || OPEN THE ENCLOSED _main.pd PATCH FOR MORE INFORMATION ||
 *  || ----------------------------------------------------- ||
 *  ===========================================================
 */

#include <Bela.h>
#include <DigitalChannelManager.h>
#include <cmath>
#include <stdio.h>
#include <libpd/z_libpd.h>
extern "C" {
#include <libpd/s_stuff.h>
};
#include <UdpServer.h>
#include <Midi.h>
#include <Scope.h>
#include <string>
#include <sstream>
#include "I2C_MPR121.h"


void Bela_userSettings(BelaInitSettings *settings)
{
	settings->uniformSampleRate = 1;
	settings->interleave = 0;
	settings->analogOutputsPersist = 0;
}

/*
 *  MODIFICATION
 *  ------------
 *  MPR121 Stuff
 */

// How many pins there are
#define NUM_TOUCH_PINS 12

// Define this to print data to terminal - function prints data from sensor
#define DEBUG_MPR121

// Change this to change how often the MPR121 is read (in Hz)
int readInterval = 50;

// Change this threshold to set the minimum amount of touch
int threshold = 40;

// This array holds the continuous sensor values
int sensorValue[NUM_TOUCH_PINS];

// ---- internal stuff -- do not change -----

I2C_MPR121 mpr121;			// Object to handle MPR121 sensing
AuxiliaryTask i2cTask;		// Auxiliary task to read I2C

int readCount = 0;			// How long until we read again...
int readIntervalSamples = 0; // How many samples between reads

void readMPR121(void*);

/*********/


float* gInBuf;
float* gOutBuf;
#define PARSE_MIDI
static std::vector<Midi*> midi;
std::vector<std::string> gMidiPortNames;

void dumpMidi()
{
	if(midi.size() == 0)
	{
		printf("No MIDI device enabled\n");
		return;
	}
	printf("The following MIDI devices are enabled:\n");
	printf("%4s%20s %3s %3s %s\n",
			"Num",
			"Name",
			"In",
			"Out",
			"Pd channels"
	      );
	for(unsigned int n = 0; n < midi.size(); ++n)
	{
		printf("[%2d]%20s %3s %3s (%d-%d)\n", 
			n,
			gMidiPortNames[n].c_str(),
			midi[n]->isInputEnabled() ? "x" : "_",
			midi[n]->isOutputEnabled() ? "x" : "_",
			n * 16 + 1,
			n * 16 + 16
		);
	}
}

Midi* openMidiDevice(std::string name, bool verboseSuccess = false, bool verboseError = false)
{
	Midi* newMidi;
	newMidi = new Midi();
	newMidi->readFrom(name.c_str());
	newMidi->writeTo(name.c_str());
#ifdef PARSE_MIDI
	newMidi->enableParser(true);
#else
	newMidi->enableParser(false);
#endif /* PARSE_MIDI */
	if(newMidi->isOutputEnabled())
	{
		if(verboseSuccess)
			printf("Opened MIDI device %s as output\n", name.c_str());
	}
	if(newMidi->isInputEnabled())
	{
		if(verboseSuccess)
			printf("Opened MIDI device %s as input\n", name.c_str());
	}
	if(!newMidi->isInputEnabled() && !newMidi->isOutputEnabled())
	{
		if(verboseError)
			fprintf(stderr, "Failed to open  MIDI device %s\n", name.c_str());
		return nullptr;
	} else {
		return newMidi;
	}
}

static unsigned int getPortChannel(int* channel){
	unsigned int port = 0;
	while(*channel > 16){
		*channel -= 16;
		port += 1;
	}
	if(port >= midi.size()){
		// if the port number exceeds the number of ports available, send out
		// of the first port 
		rt_fprintf(stderr, "Port out of range, using port 0 instead\n");
		port = 0;
	}
	return port;
}

void Bela_MidiOutNoteOn(int channel, int pitch, int velocity) {
	int port = getPortChannel(&channel);
	rt_printf("noteout _ port: %d, channel: %d, pitch: %d, velocity %d\n", port, channel, pitch, velocity);
	midi[port]->writeNoteOn(channel, pitch, velocity);
}

void Bela_MidiOutControlChange(int channel, int controller, int value) {
	int port = getPortChannel(&channel);
	rt_printf("ctlout _ port: %d, channel: %d, controller: %d, value: %d\n", port, channel, controller, value);
	midi[port]->writeControlChange(channel, controller, value);
}

void Bela_MidiOutProgramChange(int channel, int program) {
	int port = getPortChannel(&channel);
	rt_printf("pgmout _ port: %d, channel: %d, program: %d\n", port, channel, program);
	midi[port]->writeProgramChange(channel, program);
}

void Bela_MidiOutPitchBend(int channel, int value) {
	int port = getPortChannel(&channel);
	rt_printf("bendout _ port: %d, channel: %d, value: %d\n", port, channel, value);
	midi[port]->writePitchBend(channel, value);
}

void Bela_MidiOutAftertouch(int channel, int pressure){
	int port = getPortChannel(&channel);
	rt_printf("touchout _ port: %d, channel: %d, pressure: %d\n", port, channel, pressure);
	midi[port]->writeChannelPressure(channel, pressure);
}

void Bela_MidiOutPolyAftertouch(int channel, int pitch, int pressure){
	int port = getPortChannel(&channel);
	rt_printf("polytouchout _ port: %d, channel: %d, pitch: %d, pressure: %d\n", port, channel, pitch, pressure);
	midi[port]->writePolyphonicKeyPressure(channel, pitch, pressure);
}

void Bela_MidiOutByte(int port, int byte){
	rt_printf("port: %d, byte: %d\n", port, byte);
	if(port > (int)midi.size()){
		// if the port is out of range, redirect to the first port.
		rt_fprintf(stderr, "Port out of range, using port 0 instead\n");
		port = 0;
	}
	midi[port]->writeOutput(byte);
}

void Bela_printHook(const char *received){
	rt_printf("%s", received);
}

static DigitalChannelManager dcm;

void sendDigitalMessage(bool state, unsigned int delay, void* receiverName){
	libpd_float((char*)receiverName, (float)state);
//	rt_printf("%s: %d\n", (char*)receiverName, state);
}

#define LIBPD_DIGITAL_OFFSET 11 // digitals are preceded by 2 audio and 8 analogs (even if using a different number of analogs)

void Bela_messageHook(const char *source, const char *symbol, int argc, t_atom *argv){
	if(strcmp(source, "bela_setMidi") == 0){
		int num[3] = {0, 0, 0};
		for(int n = 0; n < argc && n < 3; ++n)
		{
			if(!libpd_is_float(&argv[n]))
			{
				fprintf(stderr, "Wrong format for Bela_setMidi, expected:[hw 1 0 0(");
				return;
			}
			num[n] = libpd_get_float(&argv[n]);
		}
		std::ostringstream deviceName;
		deviceName << symbol << ":" << num[0] << "," << num[1] << "," << num[2];
		printf("Adding Midi device: %s\n", deviceName.str().c_str());
		Midi* newMidi = openMidiDevice(deviceName.str(), false, true);
		if(newMidi)
		{
			midi.push_back(newMidi);
			gMidiPortNames.push_back(deviceName.str());
		}
		dumpMidi();
		return;
	}
	if(strcmp(source, "bela_setDigital") == 0){
		// symbol is the direction, argv[0] is the channel, argv[1] (optional)
		// is signal("sig" or "~") or message("message", default) rate
		bool isMessageRate = true; // defaults to message rate
		bool direction = 0; // initialize it just to avoid the compiler's warning
		bool disable = false;
		if(strcmp(symbol, "in") == 0){
			direction = INPUT;
		} else if(strcmp(symbol, "out") == 0){
			direction = OUTPUT;
		} else if(strcmp(symbol, "disable") == 0){
			disable = true;
		} else {
			return;
		}
		if(argc == 0){
			return;
		} else if (libpd_is_float(&argv[0]) == false){
			return;
		}
		int channel = libpd_get_float(&argv[0]) - LIBPD_DIGITAL_OFFSET;
		if(disable == true){
			dcm.unmanage(channel);
			return;
		}
		if(argc >= 2){
			t_atom* a = &argv[1];
			if(libpd_is_symbol(a)){
				char *s = libpd_get_symbol(a);
				if(strcmp(s, "~") == 0  || strncmp(s, "sig", 3) == 0){
					isMessageRate = false;
				}
			}
		}
		dcm.manage(channel, direction, isMessageRate);
		return;
	}
}

void Bela_floatHook(const char *source, float value){
	/*
	 *  MODIFICATION
 	 *  ------------
	 *  Empty
	 */

/*********/

// let's make this as optimized as possible for built-in digital Out parsing
// the built-in digital receivers are of the form "bela_digitalOutXX" where XX is between 11 and 26
static int prefixLength = 15; // strlen("bela_digitalOut")
if(strncmp(source, "bela_digitalOut", prefixLength)==0){
	if(source[prefixLength] != 0){ //the two ifs are used instead of if(strlen(source) >= prefixLength+2)
		if(source[prefixLength + 1] != 0){
			// quickly convert the suffix to integer, assuming they are numbers, avoiding to call atoi
			int receiver = ((source[prefixLength] - 48) * 10);
			receiver += (source[prefixLength+1] - 48);
			unsigned int channel = receiver - 11; // go back to the actual Bela digital channel number
			if(channel < 16){ //16 is the hardcoded value for the number of digital channels
				dcm.setValue(channel, value);
			}
		}
	}
}
}

char receiverNames[16][21]={
	{"bela_digitalIn11"},{"bela_digitalIn12"},{"bela_digitalIn13"},{"bela_digitalIn14"},{"bela_digitalIn15"},
	{"bela_digitalIn16"},{"bela_digitalIn17"},{"bela_digitalIn18"},{"bela_digitalIn19"},{"bela_digitalIn20"},
	{"bela_digitalIn21"},{"bela_digitalIn22"},{"bela_digitalIn23"},{"bela_digitalIn24"},{"bela_digitalIn25"},
	{"bela_digitalIn26"}
};

static unsigned int gAnalogChannelsInUse;
static unsigned int gLibpdBlockSize;
// 2 audio + (up to)8 analog + (up to) 16 digital + 4 scope outputs
static const unsigned int gChannelsInUse = 30;
//static const unsigned int gFirstAudioChannel = 0;
static const unsigned int gFirstAnalogInChannel = 2;
static const unsigned int gFirstAnalogOutChannel = 2;
static const unsigned int gFirstDigitalChannel = 10;
static const unsigned int gFirstScopeChannel = 26;
static char multiplexerArray[] = {"bela_multiplexer"};
static int multiplexerArraySize = 0;
static bool pdMultiplexerActive = false;

#ifdef PD_THREADED_IO
void fdLoop(void* arg){
	t_pdinstance* pd_that = (t_pdinstance*)arg;
	while(!gShouldStop){
		sys_doio(pd_that);
		usleep(3000);
	}
}
#endif /* PD_THREADED_IO */

Scope scope;
unsigned int gScopeChannelsInUse = 4;
float* gScopeOut;
void* gPatch;
bool gDigitalEnabled = 0;

bool setup(BelaContext *context, void *userData)
{
	// Check Pd's version
	int major, minor, bugfix;
	sys_getversion(&major, &minor, &bugfix);
	printf("Running Pd %d.%d-%d\n", major, minor, bugfix);
	// We requested in Bela_userSettings() to have uniform sampling rate for audio
	// and analog and non-interleaved buffers.
	// So let's check this actually happened
	if(context->analogSampleRate != context->audioSampleRate)
	{
		fprintf(stderr, "The sample rate of analog and audio must match. Try running with --uniform-sample-rate\n");
		return false;
	}
	if(context->flags & BELA_FLAG_INTERLEAVED)
	{
		fprintf(stderr, "The audio and analog channels must be interleaved.\n");
		return false;
	}

if(context->digitalFrames > 0 && context->digitalChannels > 0)
	gDigitalEnabled = 1;

/*
 *  MODIFICATION
 *  ------------
 *  MPR121 Stuff
 */

if(!mpr121.begin(1, 0x5A)) {
	rt_printf("Error initialising MPR121\n");
	return false;
}

i2cTask = Bela_createAuxiliaryTask(readMPR121, 50, "bela-mpr121");
readIntervalSamples = context->audioSampleRate / readInterval;


/*********/

// add here other devices you need 
gMidiPortNames.push_back("hw:1,0,0");
//gMidiPortNames.push_back("hw:0,0,0");
//gMidiPortNames.push_back("hw:1,0,1");

scope.setup(gScopeChannelsInUse, context->audioSampleRate);
gScopeOut = new float[gScopeChannelsInUse];

// Check first of all if the patch file exists. Will actually open it later.
char file[] = "_main.pd";
char folder[] = "./";
unsigned int strSize = strlen(file) + strlen(folder) + 1;
char* str = (char*)malloc(sizeof(char) * strSize);
snprintf(str, strSize, "%s%s", folder, file);
if(access(str, F_OK) == -1 ) {
	printf("Error file %s/%s not found. The %s file should be your main patch.\n", folder, file, file);
	return false;
}
free(str);
if(context->analogInChannels > 8 || context->analogOutChannels > 8)
{
	fprintf(stderr, "This project can run with a maximum of 8 analog channels\n");
	// change LIBPD_DIGITAL_OFFSET if you want more
	return false;
}
// analog setup
gAnalogChannelsInUse = context->analogInChannels;

// digital setup
if(gDigitalEnabled)
{
	dcm.setCallback(sendDigitalMessage);
	if(context->digitalChannels > 0){
		for(unsigned int ch = 0; ch < context->digitalChannels; ++ch){
			dcm.setCallbackArgument(ch, receiverNames[ch]);
		}
	}
}

for(unsigned int n = 0; n < gMidiPortNames.size(); ++n)
{
}
unsigned int n = 0;
while(n < gMidiPortNames.size())
{
	Midi* newMidi = openMidiDevice(gMidiPortNames[n], false, false);
	if(newMidi)
	{
		midi.push_back(newMidi);
		++n;
	} else {
		gMidiPortNames.erase(gMidiPortNames.begin() + n);
	}
}
dumpMidi();

// check that we are not running with a blocksize smaller than gLibPdBlockSize
gLibpdBlockSize = libpd_blocksize();
if(context->audioFrames < gLibpdBlockSize){
	fprintf(stderr, "Error: minimum block size must be %d\n", gLibpdBlockSize);
	return false;
}

// set hooks before calling libpd_init
libpd_set_printhook(Bela_printHook);
libpd_set_floathook(Bela_floatHook);
libpd_set_messagehook(Bela_messageHook);
libpd_set_noteonhook(Bela_MidiOutNoteOn);
libpd_set_controlchangehook(Bela_MidiOutControlChange);
libpd_set_programchangehook(Bela_MidiOutProgramChange);
libpd_set_pitchbendhook(Bela_MidiOutPitchBend);
libpd_set_aftertouchhook(Bela_MidiOutAftertouch);
libpd_set_polyaftertouchhook(Bela_MidiOutPolyAftertouch);
libpd_set_midibytehook(Bela_MidiOutByte);

//initialize libpd. This clears the search path
libpd_init();
//Add the current folder to the search path for externals
libpd_add_to_search_path(".");
libpd_add_to_search_path("../pd-externals");

libpd_init_audio(gChannelsInUse, gChannelsInUse, context->audioSampleRate);
gInBuf = get_sys_soundin();
gOutBuf = get_sys_soundout();


// Bind your receivers here
libpd_bind("bela_digitalOut11");
libpd_bind("bela_digitalOut12");
libpd_bind("bela_digitalOut13");
libpd_bind("bela_digitalOut14");
libpd_bind("bela_digitalOut15");
libpd_bind("bela_digitalOut16");
libpd_bind("bela_digitalOut17");
libpd_bind("bela_digitalOut18");
libpd_bind("bela_digitalOut19");
libpd_bind("bela_digitalOut20");
libpd_bind("bela_digitalOut21");
libpd_bind("bela_digitalOut22");
libpd_bind("bela_digitalOut23");
libpd_bind("bela_digitalOut24");
libpd_bind("bela_digitalOut25");
libpd_bind("bela_digitalOut26");
libpd_bind("bela_setDigital");
libpd_bind("bela_setMidi");

/*
 *  MODIFICATION
 *  ------------
 *  Empty
 */

/*********/

// open patch:
gPatch = libpd_openfile(file, folder);
if(gPatch == NULL){
	printf("Error: file %s/%s is corrupted.\n", folder, file); 
	return false;
}

// If the user wants to use the multiplexer capelet,
// the patch will have to contain an array called "bela_multiplexer"
// and a receiver [r bela_multiplexerChannels]
if(context->multiplexerChannels > 0 && libpd_arraysize(multiplexerArray) >= 0){
	pdMultiplexerActive = true;
	multiplexerArraySize = context->multiplexerChannels * context->analogInChannels;
	// [; bela_multiplexer ` multiplexerArraySize` resize(
	libpd_start_message(1);
	libpd_add_float(multiplexerArraySize);
	libpd_finish_message(multiplexerArray, "resize");
	// [; bela_multiplexerChannels `context->multiplexerChannels`(
	libpd_float("bela_multiplexerChannels", context->multiplexerChannels);
}

// Tell Pd that we will manage the io loop,
// and we do so in an Auxiliary Task
#ifdef PD_THREADED_IO
	sys_dontmanageio(1);
	AuxiliaryTask fdTask;
	fdTask = Bela_createAuxiliaryTask(fdLoop, 50, "libpd-fdTask", (void*)pd_this);
	Bela_scheduleAuxiliaryTask(fdTask);
#endif /* PD_THREADED_IO */

return true;
}

void render(BelaContext *context, void *userData)
{
	int num;
	
libpd_start_message(8);
	for(int n = 0; n < 8; ++n)
libpd_add_float(sensorValue[n]);
libpd_finish_list("sensorValue");

#ifdef PARSE_MIDI
	for(unsigned int port = 0; port < midi.size(); ++port){
		while((num = midi[port]->getParser()->numAvailableMessages()) > 0){
			static MidiChannelMessage message;
			message = midi[port]->getParser()->getNextChannelMessage();
			rt_printf("On port %d (%s): ", port, gMidiPortNames[port].c_str());
			message.prettyPrint(); // use this to print beautified message (channel, data bytes)
			switch(message.getType()){
				case kmmNoteOn:
				{
					int noteNumber = message.getDataByte(0);
					int velocity = message.getDataByte(1);
					int channel = message.getChannel();
					libpd_noteon(channel + port * 16, noteNumber, velocity);
					break;
				}
				case kmmNoteOff:
				{
					/* PureData does not seem to handle noteoff messages as per the MIDI specs,
					 * so that the noteoff velocity is ignored. Here we convert them to noteon
					 * with a velocity of 0.
					 */
					int noteNumber = message.getDataByte(0);
	//				int velocity = message.getDataByte(1); // would be ignored by Pd
					int channel = message.getChannel();
					libpd_noteon(channel + port * 16, noteNumber, 0);
					break;
				}
				case kmmControlChange:
				{
					int channel = message.getChannel();
					int controller = message.getDataByte(0);
					int value = message.getDataByte(1);
					libpd_controlchange(channel + port * 16, controller, value);
					break;
				}
				case kmmProgramChange:
				{
					int channel = message.getChannel();
					int program = message.getDataByte(0);
					libpd_programchange(channel + port * 16, program);
					break;
				}
				case kmmPolyphonicKeyPressure:
				{
					int channel = message.getChannel();
					int pitch = message.getDataByte(0);
					int value = message.getDataByte(1);
					libpd_polyaftertouch(channel + port * 16, pitch, value);
					break;
				}
				case kmmChannelPressure:
				{
					int channel = message.getChannel();
					int value = message.getDataByte(0);
					libpd_aftertouch(channel + port * 16, value);
					break;
				}
				case kmmPitchBend:
				{
					int channel = message.getChannel();
					int value =  ((message.getDataByte(1) << 7)| message.getDataByte(0)) - 8192;
					libpd_pitchbend(channel + port * 16, value);
					break;
				}
				case kmmSystem:
				// currently Bela only handles sysrealtime, and it does so pretending it is a channel message with no data bytes, so we have to re-assemble the status byte
				{
					int channel = message.getChannel();
					int status = message.getStatusByte();
					int byte = channel | status;
					libpd_sysrealtime(port, byte);
					break;
				}
				case kmmNone:
				case kmmAny:
					break;
			}
		}
	}
#else
	int input;
	for(unsigned int port = 0; port < NUM_MIDI_PORTS; ++port){
		while((input = midi[port].getInput()) >= 0){
			libpd_midibyte(port, input);
		}
	}
#endif /* PARSE_MIDI */
	unsigned int numberOfPdBlocksToProcess = context->audioFrames / gLibpdBlockSize;

// Remember: we have non-interleaved buffers and the same sampling rate for
// analogs, audio and digitals
for(unsigned int tick = 0; tick < numberOfPdBlocksToProcess; ++tick)
{
	//audio input
	for(int n = 0; n < context->audioInChannels; ++n)
	{
		memcpy(
			gInBuf + n * gLibpdBlockSize,
			context->audioIn + tick * gLibpdBlockSize + n * context->audioFrames, 
			sizeof(context->audioIn[0]) * gLibpdBlockSize
		);
	}

	// analog input
	for(int n = 0; n < context->analogInChannels; ++n)
	{
		memcpy(
			gInBuf + gLibpdBlockSize * gFirstAnalogInChannel + n * gLibpdBlockSize,
			context->analogIn + tick * gLibpdBlockSize + n * context->analogFrames, 
			sizeof(context->analogIn[0]) * gLibpdBlockSize
		);
	}
	// multiplexed analog input
	if(pdMultiplexerActive)
	{
		// we do not disable regular analog inputs if muxer is active, because user may have bridged them on the board and
		// they may be using half of them at a high sampling-rate
		static int lastMuxerUpdate = 0;
		if(++lastMuxerUpdate == multiplexerArraySize){
			lastMuxerUpdate = 0;
			libpd_write_array(multiplexerArray, 0, (float *const)context->multiplexerAnalogIn, multiplexerArraySize);
		}
	}

	unsigned int digitalFrameBase = gLibpdBlockSize * tick;
	unsigned int j;
	unsigned int k;
	float* p0;
	float* p1;
	// digital input
	if(gDigitalEnabled)
	{
		// digital in at message-rate
		dcm.processInput(&context->digital[digitalFrameBase], gLibpdBlockSize);

		// digital in at signal-rate
		for (j = 0, p0 = gInBuf; j < gLibpdBlockSize; j++, p0++) {
			unsigned int digitalFrame = digitalFrameBase + j;
			for (k = 0, p1 = p0 + gLibpdBlockSize * gFirstDigitalChannel;
					k < 16; ++k, p1 += gLibpdBlockSize) {
				if(dcm.isSignalRate(k) && dcm.isInput(k)){ // only process input channels that are handled at signal rate
					*p1 = digitalRead(context, digitalFrame, k);
				}
			}
		}
	}

	libpd_process_sys(); // process the block

	// digital outputs
	if(gDigitalEnabled)
	{
		// digital out at signal-rate
		for (j = 0, p0 = gOutBuf; j < gLibpdBlockSize; ++j, ++p0) {
			unsigned int digitalFrame = (digitalFrameBase + j);
			for (k = 0, p1 = p0  + gLibpdBlockSize * gFirstDigitalChannel;
				k < context->digitalChannels; k++, p1 += gLibpdBlockSize)
			{
				if(dcm.isSignalRate(k) && dcm.isOutput(k)){ // only process output channels that are handled at signal rate
				digitalWriteOnce(context, digitalFrame, k, *p1 > 0.5);
				}
			}
		}

		// digital out at message-rate
		dcm.processOutput(&context->digital[digitalFrameBase], gLibpdBlockSize);
	}

	// scope output
	for (j = 0, p0 = gOutBuf; j < gLibpdBlockSize; ++j, ++p0) {
		for (k = 0, p1 = p0 + gLibpdBlockSize * gFirstScopeChannel; k < gScopeChannelsInUse; k++, p1 += gLibpdBlockSize) {
			gScopeOut[k] = *p1;
		}
		scope.log(gScopeOut[0], gScopeOut[1], gScopeOut[2], gScopeOut[3]);
	}

	/*
	 *  MODIFICATION
 	 *  ------------
	 *  MPR121 Stuff
	 */

	// Keep this code: it schedules the touch sensor readings
	if(++readCount >= readIntervalSamples) {
		readCount = 0;
		Bela_scheduleAuxiliaryTask(i2cTask);
	}

		/*********/
	// audio output
	for(int n = 0; n < context->audioInChannels; ++n)
	{
		memcpy(
			context->audioOut + tick * gLibpdBlockSize + n * context->audioFrames, 
			gOutBuf + n * gLibpdBlockSize,
			sizeof(context->audioOut[0]) * gLibpdBlockSize
		);
	}

	//analog output
	for(int n = 0; n < context->analogOutChannels; ++n)
	{
		memcpy(
			context->analogOut + tick * gLibpdBlockSize + n * context->analogFrames, 
			gOutBuf + gLibpdBlockSize * gFirstAnalogOutChannel + n * gLibpdBlockSize,
			sizeof(context->analogOut[0]) * gLibpdBlockSize
		);
	}
}
}

void cleanup(BelaContext *context, void *userData)
{
	for(auto a : midi)
	{
		delete a;
	}
	libpd_closefile(gPatch);
	delete [] gScopeOut;
}


// Auxiliary task to read the I2C board

void readMPR121(void*)
{
    for(int i = 0; i < NUM_TOUCH_PINS; i++) {
        sensorValue[i] = -(mpr121.filteredData(i) - mpr121.baselineData(i));
        sensorValue[i] -= threshold;
        if(sensorValue[i] < 0)
            sensorValue[i] = 0;
#ifdef DEBUG_MPR121
        rt_printf("%d ", sensorValue[i]); //prints the values of the sensor when DEBUG_MPR121 is define at beginning of programme
#endif
    }
#ifdef DEBUG_MPR121
    rt_printf("\n");
#endif
   

// You can use this to read binary on/off touch state more easily
//rt_printf("Touched: %x\n", mpr121.touched());

}

giuliomoro
Thank you for your reply.It's this link.
Later on, I saw the MPR121 example in Bela that you mentioned earlier. After I connected the copper board, although I didn't understand C++very well, at least it made a sound......