Digital/digital-input/render.cpp

Switching an LED on and off

This example brings together digital input and digital output. The program will read a button and turn the LED on and off according to the state of the button.

• connect an LED in series with a 470ohm resistor between gOutputPin (digital pin 0) and ground.
• connect a 1k resistor to +3.3V.
• connect the other end of the resistor to both a button and gInputPin (digital pin 1)
• connect the other end of the button to ground.

Before using the digital pins we need to set whether they are input or output. This is done via pinMode(context, 0, gInputPin, INPUT);.

You will notice that the LED will normally stay on and will turn off only when the button is pressed. This is due to the fact that the LED is set to the same value read at gInputPin. When the button is not pressed, gInputPin is HIGH and so gOutputPin is set to HIGH as well, so that the LED conducts and emits light. When the button is pressed, gInputPin goes LOW and gOutputPin is set to LOW, turning off the LED.

As an exercise try and change the code so that the LED only turns on when the button is pressed.

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
 
#include <Bela.h>
#include <stdlib.h>
 
int gInputPin = 1; // digital pin 1 - check the pin diagram in the IDE
int gOutputPin = 0; // digital pin 0 - check the pin diagram in the IDE
 
bool setup(BelaContext *context, void *userData)
{
        // Set the mode of digital pins
        pinMode(context, 0, gInputPin, INPUT); //set input
        pinMode(context, 0, gOutputPin, OUTPUT); // setoutput
        return true;
}
 
 
void render(BelaContext *context, void *userData)
{
        for(unsigned int n=0; n<context->digitalFrames; n++){
                int status=digitalRead(context, 0, gInputPin); //read the value of the button
                digitalWriteOnce(context, n, gOutputPin, status); //write the status to the LED
                float out = 0.1f * status * rand() / (float)RAND_MAX * 2.f - 1.f; //generate some noise, gated by the button
                for(unsigned int j = 0; j < context->audioOutChannels; j++){
                        audioWrite(context, n, j, out); //write the audio output
                }
        }
}
 
 
void cleanup(BelaContext *context, void *userData)
{
        // Nothing to do here
}