High-Speed Serial Transfer

hey guys,

i'm having trouble sending serial data @ fast speed (5000 samples per second) through bluetooth serial connection , having reproduced correctly @ receiving end.

for setup, have pair of rn-42 modules (https://www.sparkfun.com/products/12577) interfacing pair of teensy 3.1 microcontrollers (https://www.pjrc.com/teensy/teensy31.html). microcontrollers communicating bluetooth modules @ 230400 baud rate.

basically, want send low quality audio mic transmitter receiver. i'm using interrupts @ transmitter end have audio sampled @ 5000 hz.

now, when send sine wave through transmitter, on receiver a square-waveish version of sine wave, along bunch of other random jumps when analogwrite() signal.

teensy has true 12-bit analog output, expected near perfect reproduction of sine wave if feed analogread values correctly receiver. thoughts on causing receiver receive poor signal? code transmitting , receiving included below.

code: [select]


//transmitter code
int led = 13; //power led
int sample_rate_hz = 5000; //sampling rate
uint16_t val; //variable microphone input
const int audio_input_pin = 14; //the signal feed pin 14
const int analog_read_resolution = 12; //12 bit resolution
const int analog_read_averaging = 12;
const int cts_pin = 17;
intervaltimer samplingtimer; //set interval timer, lets specify sampling rate

void setup()
{
  //pinmode(led, output);
  pinmode(cts_pin, input);
// digitalwrite(led, high); //turn on led o teensy
  serial.begin(115200);
  serial1.begin(230400); //begin serial communications bluetooth , usb if necessary
  analogreadresolution(analog_read_resolution);
  analogreadaveraging(analog_read_averaging); //set analog read resolution , averaging

  delay(2000);

  samplingbegin(); //begin reading audio immediately

}

void loop() //do nothing, interrupt timers handle data acquisition , sending
{
 
}

void samplingbegin() //set sampling rate, call samplingcallback function every 1000000/sampling rate microseconds.
{
  samplingtimer.begin(samplingcallback, 1000000/sample_rate_hz);
}

void samplingcallback() //continously read in analog input (noise if no input)
{
  if(digitalread(cts_pin) == low) //if bluetooth's internal buffer not overwhelmed.
{
  val = analogread(audio_input_pin);
  serial1.print("<"); //send entire integer, marker start , end recognized receiver.
  serial1.print(val);
  serial1.print(">");
  }
}

code: [select]


//receiver code
int led = 13;
char input;


void setup()
{
  pinmode(led, output);
  digitalwrite(led, high);
  serial.begin(115200);
  serial1.begin(230400); //open bluetooth comm
  analogwriteresolution(12);
  delay(3000);


}

void loop()
{
if(serial1.available())
  {
    while(serial1.finduntil("<", ">")) //find <, store values int until > met.
    {
      int val = serial1.parseint(); //create int characters between < , >
      analogwrite(a14, val);
    }
  }

}



time little math.  230400 / 10 / 5000 = 4.608 bytes per sample.  assuming perfect communications (no retries) have 4.608 bytes per sample available.

code: [select]

 serial1.print("<");
 serial1.print(val);
 serial1.print(">");

assuming input has balanced histogram on 0 1023 range, on average 4.916 bytes per sample needed.

you trying push data through pipe.  you need more efficient encoding (fewer bytes per sample) or bigger pipe (higher baud rate).

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