I just got an Idea of trying to code rain simulation with arduino and Adafruit OLED display. When I finished it was quite messy code so I thought That maybe doing it Object Oriented would help. This code is just a sketch that MAYBE works. The thing is that I need to create an array of objects(drops) and then display them. I have tried to display just one drop and it does not seem to do anything, even Serial wont print the pos_y. I have never wrote an Arduino code with objects so I just made a quick research and tried. here is the code:

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);

class Drop{
  int pos_x = random(0, 128);
  int pos_y = random(-5, -20);
  int len = random(3, 7); 
  int speed = random(6, 13);
 void fall()
 display.drawFastVLine(pos_x, pos_y, len, 1);
 pos_y = pos_y + speed;


Drop* drop = new Drop[50];

void setup() {
// put your setup code here, to run once:
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

void loop() {

I will appreciate any suggestion or solution, spent almost entire day doing this "simple thing"..

  • 2
    I tried your code using a dummy implementation of Adafruit_SSD1306 that just prints to the serial port. It seems to work as expected. Commented Nov 11, 2018 at 12:24
  • can the display show negative y position? becose it start with -5 (you don't initialize random)
    – Juraj
    Commented Nov 11, 2018 at 15:41
  • Well, cutting out all the display code the program appears to work fine for me.
    – Majenko
    Commented Nov 11, 2018 at 15:56
  • It may well be then that the display driver hates a negative Y value. Not using that library ever I can't say... Personally I'd never use an Arduino for anything to do with a display...
    – Majenko
    Commented Nov 11, 2018 at 16:03
  • do you have 9600 baud set in Serial Monitor? add some prints to see where the code hangs
    – Juraj
    Commented Nov 12, 2018 at 6:24

1 Answer 1


The code works without the display commands. A problem could be that you start with negative pos_y and use it as parameter for drawFastVLine.

Function random returns first parameter if it is a larger value then the second parameter. random(-5, -20) always returns -5.

To have more random random values, you should call randomSeed in setup().

And you can use global array Drop drop[50];.

  • I dont think so, the messier version without objects worked fine with negative values :/ And thank you for the clarification with random!
    – kuskus
    Commented Nov 11, 2018 at 19:28
  • Okay i just used Global array and it seems that it fixed the problem ;). Thank you!
    – kuskus
    Commented Nov 12, 2018 at 17:02
  • strange. what version of IDE you have. is in Question the same sketch you use?
    – Juraj
    Commented Nov 12, 2018 at 17:22

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