Blinking an LED

This sketch shows the simplest case of digital out.

  • Connect an LED in series with a 470ohm resistor between P8_07 and ground.

The led is blinked on and off by setting the digital pin HIGH and LOW every interval seconds which is set in render().

In setup() the pin mode must be set to output mode via pinMode(). For example: pinMode(context, 0, P8_07, OUTPUT). In render() the output of the digital pins is set by digitalWrite(). For example: digitalWrite(context, n, P8_07, status) where status can be equal to either HIGH or LOW. When set HIGH the pin will give 3.3V, when set to LOW 0V.

Note that there are two ways of specifying the digital pin: using the GPIO label (e.g. P8_07), or using the digital IO index (e.g. 0)

To keep track of elapsed time we have a sample counter count. When the count reaches a certain limit it switches state to either HIGH or LOW depending on its current value. In this case the limit is context->digitalSampleRate*interval which allows us to write the desired interval in seconds, stored in interval.

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The platform for ultra-low latency audio and sensor processing
A project of the Augmented Instruments Laboratory within the
Centre for Digital Music at Queen Mary University of London.
(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:
#include <Bela.h>
#include <cmath>
#include <rtdk.h>
bool setup(BelaContext *context, void *userData)
pinMode(context, 0, P8_07, OUTPUT);
return true;
void render(BelaContext *context, void *userData)
static int count=0; //counts elapsed samples
float interval=0.5; //how often to toggle the LED (in seconds)
static int status=GPIO_LOW;
for(unsigned int n=0; n<context->digitalFrames; n++){
if(count==context->digitalSampleRate*interval){ //if enough samples have elapsed
count=0; //reset the counter
// status=digitalRead(context, 0, P8_07);
if(status==GPIO_LOW) { //toggle the status
digitalWrite(context, n, P8_07, status); //write the status to the LED
else {
digitalWrite(context, n, P8_07, status); //write the status to the LED
void cleanup(BelaContext *context, void *userData)
// Nothing to do here