testing Bit-banging Pulse Width Modulation

Projects General Guidance
1

testing Bit-banging Pulse Width Modulation from http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM, i started with:
void setup()
{
pinMode(13, OUTPUT);
}

void loop()
{
digitalWrite(13, HIGH);
delayMicroseconds(100);
}

however, i got 0.000 Hz and only about 1.?? mV
so i looped:
while(true)
{
digitalWrite(13, LOW); // also used digitalWrite(13, HIGH);
delayMicroseconds(i);
Serial.print(i);
Serial.print('\n');
i++;
if(i > 2000){i = 0;}
}

again, got same except a brief 7 something Hz at start, but did not repeat after loop restarted.

ok. checked 0 - 13
void setup()
{
// put your setup code here, to run once:
int i = 0;
while(i < 14)
{
pinMode(i, OUTPUT);
i++;
}
Serial.begin(9600);
}

void loop()
{
int i = 0;
int j = 0;
// put your main code here, to run repeatedly:
while(true)
{
digitalWrite(j, LOW);
delayMicroseconds(i);
Serial.print(i);
Serial.print(" , ");
Serial.print(j);
Serial.print('\n');
i++;
j++;
if(i > 2000){i = 0;}
if(j > 12){j = 0;}
}

}

pin# volts HZ
0 5.03 V 0.000
1 ~1.8 V ~2.5 kHz [very active]
2 4.1 mV 0.000
3 4.4 mV 0.000
4 4.4 mV 0.000
5 2.7 mV 0.000
6 2.9 mV 0.000
7 2.9 - 3.0 mV 0.000
8 3.1 mV 0.000
9 2.9 - 3.0 0.000
10 2.7 0.000
11 2.6 - 2.7 0.000
12 2.4 0.000
13 1.8 0.000

this makes no sense.
assuming pins 2 - 13 have different voltages due to contact of test wire to pins.
but why does pin 0 have zero Hz and 5 volts & pin 1 have ~2.5 kHz and ~1.8 V?
could someone explain what is going on?

2

void setup()
{
pinMode(13, OUTPUT);
}

void loop()
{
digitalWrite(13, ! digitalRead( 13 ) );
delayMicroseconds(100);
}

3

ok. changing
digitalWrite(13, LOW);
to
digitalWrite(13, ! digitalRead(13));
gave an output of about 2.5 V and 120 Hz down to about 30 Hz
but why did http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM say to use LOW or HIGH?
and why would ! digitalRead be pasted into digitalWrite?

4

This is the first example from that page...

void setup()
{
  pinMode(13, OUTPUT);
}

void loop()
{
  digitalWrite(13, HIGH);
  delayMicroseconds(100); // Approximately 10% duty cycle @ 1KHz
  digitalWrite(13, LOW);
  delayMicroseconds(1000 - 100);
}

Notice the pin is toggled; set HIGH then later set LOW.

5

mightyruler:
but why did http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM say to use LOW or HIGH?

The phrase "LOW or HIGH" appears nowhere on that page.

and why would ! digitalRead be pasted into digitalWrite?

The pin's state is read (digitalRead) then toggled (!) then written (digitalWrite).

6

The words LOW and HIGH are used in the code on that page, I assume the OP did meant those

7

Browse for "piano tones micros" where I did this for 13 outputs on a '1284P chip.
digitalWrite is a very slow way of getting there, is very limiting.