jim hamblen / Mbed 2 deprecated speaker_demo_Analog

A class to play notes on a speaker using analog out See https://mbed.org/users/4180_1/notebook/using-a-speaker-for-audio-output/

Dependencies:   mbed

Speaker.h@0:1c8118ee4106, 2013-01-21 (annotated)

Committer:
4180_1
Date:
Mon Jan 21 03:37:11 2013 +0000
Revision:
0:1c8118ee4106
ver 1.0

Who changed what in which revision?

UserRevisionLine numberNew contents of line
4180_1 0:1c8118ee4106 1 class Speaker
4180_1 0:1c8118ee4106 2 {
4180_1 0:1c8118ee4106 3 public:
4180_1 0:1c8118ee4106 4 Speaker(PinName pin) : _pin(pin) {
4180_1 0:1c8118ee4106 5 // _pin(pin) means pass pin to the Speaker Constructor
4180_1 0:1c8118ee4106 6 // precompute 32 sample points on one sine wave cycle
4180_1 0:1c8118ee4106 7 // used for continuous sine wave output later
4180_1 0:1c8118ee4106 8 for(int k=0; k<32; k++) {
4180_1 0:1c8118ee4106 9 Analog_out_data[k] = int (65536.0 * ((1.0 + sin((float(k)/32.0*6.28318530717959)))/2.0));
4180_1 0:1c8118ee4106 10 // scale the sine wave to 16-bits - as needed for AnalogOut write_u16 arg
4180_1 0:1c8118ee4106 11 }
4180_1 0:1c8118ee4106 12
4180_1 0:1c8118ee4106 13 }
4180_1 0:1c8118ee4106 14 // class method to play a note based on AnalogOut class
4180_1 0:1c8118ee4106 15 void PlayNote(float frequency, float duration, float volume) {
4180_1 0:1c8118ee4106 16 // scale samples using current volume level arg
4180_1 0:1c8118ee4106 17 for(int k=0; k<32; k++) {
4180_1 0:1c8118ee4106 18 Analog_scaled_data[k] = Analog_out_data[k] * volume;
4180_1 0:1c8118ee4106 19 }
4180_1 0:1c8118ee4106 20 // reset to start of sample array
4180_1 0:1c8118ee4106 21 i=0;
4180_1 0:1c8118ee4106 22 // turn on timer interrupts to start sine wave output
4180_1 0:1c8118ee4106 23 Sample_Period.attach(this, &Speaker::Sample_timer_interrupt, 1.0/(frequency*32.0));
4180_1 0:1c8118ee4106 24 // play note for specified time
4180_1 0:1c8118ee4106 25 wait(duration);
4180_1 0:1c8118ee4106 26 // turns off timer interrupts
4180_1 0:1c8118ee4106 27 Sample_Period.detach();
4180_1 0:1c8118ee4106 28 // sets output to mid range - analog zero
4180_1 0:1c8118ee4106 29 this->_pin.write_u16(32768);
4180_1 0:1c8118ee4106 30
4180_1 0:1c8118ee4106 31 }
4180_1 0:1c8118ee4106 32 private:
4180_1 0:1c8118ee4106 33 // sets up specified pin for analog using AnalogOut class
4180_1 0:1c8118ee4106 34 AnalogOut _pin;
4180_1 0:1c8118ee4106 35 // set up a timer to be used for sample rate interrupts
4180_1 0:1c8118ee4106 36 Ticker Sample_Period;
4180_1 0:1c8118ee4106 37
4180_1 0:1c8118ee4106 38 //variables used by interrupt routine and PlayNote
4180_1 0:1c8118ee4106 39 volatile int i;
4180_1 0:1c8118ee4106 40 short unsigned Analog_out_data[32];
4180_1 0:1c8118ee4106 41 short unsigned Analog_scaled_data[32];
4180_1 0:1c8118ee4106 42
4180_1 0:1c8118ee4106 43 // Interrupt routine
4180_1 0:1c8118ee4106 44 // used to output next analog sample whenever a timer interrupt occurs
4180_1 0:1c8118ee4106 45 void Sample_timer_interrupt(void) {
4180_1 0:1c8118ee4106 46 // send next analog sample out to D to A
4180_1 0:1c8118ee4106 47 this->_pin.write_u16(Analog_scaled_data[i]);
4180_1 0:1c8118ee4106 48 // increment pointer and wrap around back to 0 at 32
4180_1 0:1c8118ee4106 49 i = (i+1) & 0x01F;
4180_1 0:1c8118ee4106 50 }
4180_1 0:1c8118ee4106 51 };
4180_1 0:1c8118ee4106 52