Simple mbed amplifier for quarter-inch audio input with volume, delay, and distortion control from smartphone app via bluetooth.

Dependencies:   mbed-rtos mbed

Files at this revision

API Documentation at this revision

Comitter:
lindseysix
Date:
Tue May 02 00:28:13 2017 +0000
Commit message:
Prototype amplifier with effects and smartphone control via bluetooth

Changed in this revision

main.cpp Show annotated file Show diff for this revision Revisions of this file
mbed-rtos.lib Show annotated file Show diff for this revision Revisions of this file
mbed.bld Show annotated file Show diff for this revision Revisions of this file
diff -r 000000000000 -r a487ac94eb85 main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Tue May 02 00:28:13 2017 +0000
@@ -0,0 +1,104 @@
+//Library includes
+#include "mbed.h"
+#include "rtos.h"
+ 
+#define MAX_DELAY   10000   //Max size of delay effect sample buffer(too large can crash on compile from memory limit)
+ 
+//mbed pin declarations
+
+AnalogIn pot(p20);
+DigitalOut led(LED1);
+DigitalOut led2(LED2);
+AnalogIn input(p15);
+AnalogOut output(p18);
+Serial pc(USBTX, USBRX);
+Serial blue(p13,p14);
+ 
+//global variable declarations
+
+int inv_gain = 3;                       //scale factor for decreasing delay volume
+int delay = 0;                          //store value for delay from smartphone app
+float volume = .5;                      //store value for volume from smartphone app
+float distortion = 1.0;                 //store value for distortion from smartphone app
+unsigned short buffer[MAX_DELAY];       //declare array for storing samples for delay effect
+int scaleFactor = 30;                   //global to convert int values from smartphone app sliders
+
+/*******************************************************
+ Bluetooth thread for reading input from smartphone app
+********************************************************/ 
+void threadBluetooth(void const *args)
+{
+         while(1)
+         {
+              if(blue.readable())                       //check if new value is available
+              {
+                   int changeVal;                       //variable to hold value from smartphone app
+                   changeVal = blue.getc();             //get new value from app via bluetooth
+                   
+                   if(changeVal <= scaleFactor)         //check if new value falls in volume slider range
+                   {
+                       //convert volume to float value in range [0.0-1.0]
+                       volume = (float)changeVal/((float)scaleFactor+3);
+                   }
+                   else if(changeVal <= scaleFactor*2)  //check if value is in delay range
+                   {
+                       //convert delay to float in range (0.0 - 1.0]
+                       delay = ((float)changeVal-((float)scaleFactor+1))/((float)scaleFactor)*MAX_DELAY;
+                       
+                       if(changeVal == 31)              //if new value is bottom of delay slider
+                       {
+                           delay = 0;                   //set delay to zero (disable effect)
+                       }
+                   }
+                   else if(changeVal <= scaleFactor*3)  //check if value is in distortion range
+                   {
+                        //convert distortion to float in range (3.0 - 4.0)
+                        distortion = 3.0 + ((float)changeVal-(2*(float)scaleFactor+1))/((float)scaleFactor);
+                        
+                        if(changeVal == 61)             //if new value is bottom of distortion slider
+                        {
+                            distortion = 1;             //set distortion to one (disable effect)
+                        }
+                   }
+        }
+        Thread::wait(100);
+}                                                       //end bluetooth thread
+
+/*****
+ Main
+*****/
+  
+int main(void)
+{
+    Thread threadBlue(threadBluetooth);                 //startup Bluetooth thread for smartphone app
+    int oldDelay;                                       //global for delay comparison
+    
+    while(1)
+    {
+        int i;                                          //for loop count variable
+        
+        if(delay > 0)                                   //check if delay effect is on
+        {
+            if(delay != oldDelay)                       //if delay value has changed re-buffer
+            {
+                for (i = 0; i < delay; i++)             //buffer loop
+                {
+                    buffer[i] += input.read_u16();
+                    oldDelay = delay;
+                }
+            }
+            while(delay > 0)                                        //while delay is on
+            {
+                buffer[i] = buffer[i]/inv_gain + input.read_u16();  //scale buffer value and add to input
+                output.write_u16(distortion * volume * buffer[i]);  //write to output
+                i = (i+1) % delay;                                  //traverse buffer array(use delay number of values)
+            }
+        }
+        else
+        {
+            //with no delay write input value scaled by volume and distortion 
+            output.write_u16(distortion * volume * input.read_u16());    
+            wait_us(23);                                             //wait time based on sample rate
+        }
+    }
+}                       //end main
\ No newline at end of file
diff -r 000000000000 -r a487ac94eb85 mbed-rtos.lib
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-rtos.lib	Tue May 02 00:28:13 2017 +0000
@@ -0,0 +1,1 @@
+https://mbed.org/users/mbed_official/code/mbed-rtos/#58563e6cba1e
diff -r 000000000000 -r a487ac94eb85 mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Tue May 02 00:28:13 2017 +0000
@@ -0,0 +1,1 @@
+https://mbed.org/users/mbed_official/code/mbed/builds/794e51388b66
\ No newline at end of file