LCD slight blink while refreshing

[Electro-Poleas]

Hi!

I'm having this issue with an LCD display using the Adafruit library. My program checks with a while loop if an input it's true or false. My question is if it's possible to make that blinking stop? This is the program:

Code: Select all

import RPi.GPIO as GPIO
import time
from Adafruit_CharLCD import Adafruit_CharLCD

GPIO.setmode(GPIO:BCM)
lcd = Adafruit_CharLCD()

GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
lcd.begin(16, 1)

while True:
      door = GPIO.input(5)
      lcd.clear()
      if door:
                  lcd.message ('Door Open')
      else:
                 lcd.message ('Door Closed')

      time.sleep(2)

[Laurens-wuyts]

You could try to check if it's already printed.

Code: Select all

import RPi.GPIO as GPIO
import time
from Adafruit_CharLCD import Adafruit_CharLCD

GPIO.setmode(GPIO:BCM)
lcd = Adafruit_CharLCD()

door_old = 0

GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
lcd.begin(16, 1)


while True:
    door = GPIO.input(5)
    lcd.clear()
      
    if door == 1 and (door_old != door) :
        print 'Door Open'
        door_old = door              
    else:
        if door_old != door:
            print 'Door Closed'
            door_old = door

Please correct me if something is wrong

Laurens

[rpdom]

You could try to check if it's already printed.

That's along the right lines, but I think that will still keep blinking because of the lcd.clear() in the loop.

Perhaps something like this:

Code: Select all

import RPi.GPIO as GPIO
import time
from Adafruit_CharLCD import Adafruit_CharLCD

GPIO.setmode(GPIO:BCM)
lcd = Adafruit_CharLCD()

door_old = 2

GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
lcd.begin(16, 1)


while True:
    door = GPIO.input(5)
      
    if door == 1 and (door_old != door) :
        lcd.clear()
        lcd.message( 'Door Open' )
        door_old = door              
    else:
        if door_old != door:
            lcd.clear()
            lcd.message( 'Door Closed' )
            door_old = door

Note that I initially set "door_old" to 2 which is an invalid value so that the door status will be detected as changed whether it is open or closed when you start.

[Electro-Poleas]

Hi! Thank you very much for your help.
I ran both codes and both worked. But the display still has that slight blinking every two seconds.

[Electro-Poleas]

Probably the reason for the blinking is that the program is continuously checking if the inputs changes. Is it posible to modify the code to change the LCD output only if there is a change on the input?

[rpdom]

Is it posible to modify the code to change the LCD output only if there is a change on the input?

That's what our suggestions did. They compare the current state with the previous state and only display a message if they are different.

[Electro-Poleas]

Is it posible to modify the code to change the LCD output only if there is a change on the input?

That's what our suggestions did. They compare the current state with the previous state and only display a message if they are different.

Sorry about that. Well it didn't work I'm afraid to say. If your code does exactly that, I'm beggining to think that it's an electronic issue. I've tried to put a 100nF capacitor between VCC and VSS. Maybe the problem is that it's a cheap chinesse LCD. Idon't really know.

Thanks again for your help.

[Laurens-wuyts]

Is it a flicker in the backlight or is it a flicker in the characters?

Laurens

[Electro-Poleas]

Is it a flicker in the backlight or is it a flicker in the characters?

Laurens

The characters are the ones flickering. And it's more pronounced in the characters on the right.

[sysfrank]

So, I am having a similar problem. In my case, it is the backlight that is blinking. It happens every time I update the display. Any suggestions?