Hi! I've been faffing about with an I2C LCD and an RTC module to display time, manage alarms, etc. When i'm not using the LCD i want to turn the backlight off, i've been doing this through the use of one of the digital pins to provide power to the VCC but I'm still getting flashes of light coming from the LCD.
I've read this is from the I2C pins still sending signals to the RTC, so i've also tried disabling the I2C connections using Wire.end() and Wire.begin() however i'm STILL getting flashes of light from the LCD.
I've tried the noBacklight(); and backlight(); functions and their variations which also didn't work, I'm certain the lcd I2C backpack doesn't have support for backlight control.
Is there any way to stop these quick flashes of light coming from the lcd. I should note that the flashes are very dim however the LCD is setup in my room so isn't suitable for having running during the night. I've tried using a transistor to control the ground connection from the LCD which DOES work however i've also read online that this is a bad idea to do for electrical circuit reasons I don't understand.
Looking at your non existent schematic I see where you used a backpack to run your LCD display. You can use backlighton() or backlightoff() instructions to control it. In my other library I use:
lcd.noBacklight(); // Turn the backlight off
We cannot help you given the limited amount of information you have provided about your LCD device, the library involved, and any sketch s/w you are using.
i.e. we have no idea what type of LCD device you are using.
It sounds like it could be a simple hd44780 display with a PCF8574 based backpack,
but we simply have no idea about what LCD device you are using.
But in general, it is not a good thing to yank power from a device but still have active signals connected to it.
i.e. you appear to be yanking power from the device but still have active signals (the i2c signals) going to it.
This is a bad thing to be doing.
Also, keep in mind that most LCDs need some sort of initialization so if you yank its power, it will need be re-initialized before it will work properly again.
If you provide more information about your LCD device, perhaps even a photo, we can likely provide some assistance.