higher Frequency

Projects Programming
1

hi guys, i wrote a code:

int x,y;
void setup()
{
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  randomSeed(analogRead(A0)); ;
}

void loop()
{
  x=random(0,2);
  y=random(0,2);
  digitalWrite(8,x);
  digitalWrite(9,y);
  delayMicroseconds(100);
}

it supposes to be like generate random pseudo sequence with 10Khz...well the result is random yet the frequency is just like 4KHz. anyway could make it 10Khz?Thansks

2

your random and digitalWrites take time, too. reduce delayMicroseconds to adjust. or look into blink without delay to get more accurate.

3

For 10KHz, you signal must go hi & low every 50 microseconds.
digitalWrite also takes time, you could replace those with direct port manipulation.

  x=random(0,2);
  y=random(0,2);
if(x==0){
PORTB = PORTB & B11111110;  // clear D8
}
else{
PORTB = PORTB | B00000001; // set D8
}
if (y == 0){
PORTB = PORTB & B11111101; // clear D9
}
else {
PORT = PORT| B00000010; // set D9
}
  delayMicroseconds(50);

Replace PORTB with the correct port if needed.

4

Unfortunately, your random(0, 2) calls are taking 141 microseconds each. You'll need a faster pseudo-random generator.

This thread seems vaguely familiar. See this thread.

5

and generate 10khz signal - Programming Questions - Arduino Forum

6

The random pseudo sequence (white noise) is usually generated by shift registers with an XORed feedback (from a few shiftreg bits). My old pic12c508 @4MHz does 20kHz in asm (~10hrs random seq period, afair), so arduino could be faster..

http://www.elektronik-labor.de/AVR/dds/Noise.html

For example (an example of a 32-bit maximal period Galois LFSR from wikipedia above):

void setup() {
  // put your setup code here, to run once:
 Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly: 
  
unsigned long lfsr = 1u;
unsigned bit;
unsigned long period = 0;

long t = micros();

do {
  /* taps: 32 31 29 1; feedback polynomial: x^32 + x^31 + x^29 + x + 1 */
  lfsr = (lfsr >> 1) ^ (-(lfsr & 1u) & 0xD0000001u); 
  ++period;       // remove this in your code
  if (period==10000) Serial.println(micros()-t);  //  << remove this in your code then, put here the bit output
} while(lfsr != 1u);

  period = 0;
}

Prints:

35844

So a loop takes 3.58usecs. It takes less when you remove the print line there, but you have output a bit so it might be the same (or even shorter) :wink:

The actual loop:

unsigned long lfsr = 1u;
for(;;) {
  /* taps: 32 31 29 1; feedback polynomial: x^32 + x^31 + x^29 + x + 1 */
  lfsr = (lfsr >> 1) ^ (-(lfsr & 1u) & 0xD0000001u); 
  // << HERE do output a bit to an output pin
  // << HERE put a delay when required
}

The pseudo random seq period will be ~4.2hours.
A discussion on that algorithm: Talk:Linear-feedback shift register - Wikipedia
Not tested, no warranties of any kind :slight_smile: