working of define and integer

Using Arduino Programming Questions
#1

Hello i have question about working of this 2 things. I found a code by Andrea Toscano.

#define LED_PIN 10
#define SERIAL_BAUD 115200
#define PERIOD 2000
#define OMEGA 2*PI/PERIOD
#define PHASE 0
#define OFFSET 128
#define AMPLITUDE 127
unsigned long timer = 0;

void setup() {
Serial.begin(SERIAL_BAUD);
}
void loop() {
timer = millis();
int ledValue = ledValue = OFFSET + AMPLITUDE*(cos(OMEGA*timer)+PHASE);
analogWrite(LED_PIN, checkValue(ledValue));
}
int checkValue(int val) {
if (val > 255)
val = 255;
else if(val < 0)
val = 0;
return val;
}

So,if i delete some of those define syntax (not all but only that written below)and replace it with
const int OFFSET = 127;
const int AMPLITUDE = 128;
const int PERIOD = 2000;
const int OMEGA = (2*PI)/PERIOD;

than the program doesnt work properly.Led isnt blinking but its only turned on.
Please what does make that mess?

#2

Please what does make that mess?

It means that you need to post the code you are actually running. Do NOT expect us to guess what you changed.

#3

i didnt changed anything else just deleted

#define PERIOD 2000
#define OMEGA 2*PI/PERIOD
#define OFFSET 128
#define AMPLITUDE 127

and replaced it with

const int OFFSET = 127;
int AMPLITUDE = 128;
const int PERIOD = 2000;
const int OMEGA = (2*PI)/PERIOD;

and i meant fading not blinking in post above sorry :slight_smile:

#4

Why did you change the values of AMPLITUDE and OFFSET?

What IS the value in OMEGA now that you have forced it to have a type? Is int the proper type?

#5

robot_chobot:
i didnt changed anything else just deleted

#define PERIOD 2000
#define OMEGA 2*PI/PERIOD
#define OFFSET 128
#define AMPLITUDE 127

and replaced it with

const int OFFSET = 127;
int AMPLITUDE = 128;
const int PERIOD = 2000;
const int OMEGA = (2*PI)/PERIOD;

and i meant fading not blinking in post above sorry :slight_smile:

I call BS.
The code won't even compile with the changes you said you made.

You made OMEGA a const int then try to change it with your calculation. Even if that did work it should probably be a float not an int.

#6

You made OMEGA a const int then try to change it with your calculation.

The value is resolvable at compile time, so the calculation is OK.

The type should probably not be int.

#7

I stand corrected. Learn something new every day.

#8

Hello

I noticed that (with arduino uno) the sketch with #define size is 3478 bytes , the one with constants only 2066.

I disassembled the two files.

In the second there is no cosinus calculous at all.

I can't explain it.

Regards,
bidouilleelec

#9

OFFSET, PERIOD, PHASE and OMEGA are all integer constants. OMEGA is 2PI/2000 and as an integer is 0.
Zero times timer (anything) will always be zero so cos(OMEGAtimer)+PHASE will always be 1. Nothing in
int ledValue = ledValue = OFFSET + AMPLITUDE(cos(OMEGA*timer)+PHASE);
will ever change so it’s calculated once at compile and replace with a constant. No further calculations necessary, optimized out.

#10

That makes sense

#11