LCD flickers with pulses

i trying make vending machine standard coin acceptor , 2 momentary push buttons, stepper motors , lcd.

details:
arduino mega 2560 r3
hd44780 1602 lcd character display 16 x 2 (with 10k potentiometer)
ch 926 coin acceptor
2 pin momentary push buttons x2
28byj-48 stepper motors x2

the problem having once arduino reads pulses , if function fulfilled, lcd flickers (the writing flickers). seems though pulses interfering lcd, i'm not sure how go fixing issue.

code: [select]

#include <liquidcrystal.h>
#include <stepperak.h>
#define gearratio 64
const byte stepsperrevolution = 2048;
const byte stepsperrevolution2 = 2048;
const byte coinint = 0; //this pin 2 on arduino
const byte ledpin = 13;
const byte switchpin = 30;
const byte switchpin2 = 31;
byte resetpin = 14;
stepper mystepper (stepsperrevolution, 46,47,48,49);
stepper mystepper2 (stepsperrevolution2, 50,51,52,53);
volatile float coinsvalue = 0.00;
byte coinschange = 0;
liquidcrystal lcd(7,8,9,10,11,12);


void setup()
{
  digitalwrite (resetpin, high);
  serial.begin(2400);                 
  pinmode(ledpin, output);
  attachinterrupt(coinint, coininserted, rising);
  mystepper.setspeed(0.15*gearratio); 
  mystepper2.setspeed(0.15*gearratio);
  pinmode (switchpin, input_pullup);
  pinmode (switchpin2, input_pullup);
  pinmode (resetpin, output);
  lcd.begin(16,2);
  lcd.clear();
  lcd.print("please insert");
  lcd.setcursor(0,1);
  lcd.print("coins...");
}

void(* resetfunc) (void) = 0;

void coininserted()   
{
  coinsvalue = coinsvalue + 0.20;  //1 dollar set 5 pulses, , 2 10, 1 pulse means adding 20 cents
  coinschange = 1;                           
}


void loop()
{
  if(coinschange == 1)         
  {   
   
    serial.print("amount: $");
    serial.println(coinsvalue);
    lcd.clear();
    lcd.print("$ ");
    lcd.print(coinsvalue);   
if(coinsvalue >= 2)
      {
// stepper motor code supposed go here, there needs 2 motor codes, 1 each switch & @ end, coinsvalue needs reset

 lcd.clear();
 lcd.print("press button..");
  if(digitalread (switchpin) == low)
    {
   serial.println ("button 1 pressed");
   digitalwrite(ledpin, high);
   lcd.clear();
   lcd.print("vending!");
   delay (500);
   serial.println("vend motor 1");
   motorcode1();
   delay (500);
   coinsvalue = 0;
   digitalwrite(ledpin, low);
   coinschange = 0;
   lcd.clear();
   lcd.print("thank you!");
   delay(2000);
   lcd.clear();
   digitalwrite (resetpin, low);
   resetfunc();
    }
  if(digitalread (switchpin2) == low)
    {
   serial.println ("button 2 pressed");
   digitalwrite(ledpin, high);
   delay (500);
   lcd.clear();
   lcd.print("vending!");
   serial.println("vend motor 2");
   motorcode2();
   delay (500);
   coinsvalue = 0;
   digitalwrite(ledpin, low);
   coinschange = 0;
   lcd.clear();
   lcd.print("thank you!");
   delay(2000);
   lcd.clear();
   digitalwrite (resetpin, low);
   resetfunc();
    }
   
      }
  }
}


void motorcode1()
{
  mystepper.step(stepsperrevolution); 
}


void motorcode2()
{
  mystepper2.step(stepsperrevolution2);
}


i new arduinos , code reflect that, if please explain or give examples in newbie terms, appreciated.

thanks

hi , welcome.

can tell more flickering, see ?
what mean pulses ?
do mean button being pushed ?
or mean pulse coin acceptor ?

your code control motors isn't finished yet, have controller(s) connected ?

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