I have the following problem: for some *** reason, my LCD is flashing when my fingerprint scanner turns on. Here is a video of the behavior: https://www.dropbox.com/s/mqk4u0vu8yvhiwz/IMG_3171.m4v?dl=0.
More details: I have a membrane keypad. When I start typing on it, the LCD turns on, and when I type the correct code, the fingerprint scanner turns on, and the LCD prompts the user to press a finger upon the scanner. However, then the LCD backlight starts flashing badly. Interestingly, if I just plug the wall adapter into the arduino and try the scenario, the LCD does not flash. However, if let's say 10-15 have passed since the adapter is plugged in, the LCD flickering becomes visible and irritating (again, when the fingerprint scanner is turned on). So, what could be the reason and how to fix it? Why if I just plug the adapter and execute the scenario, the LCD does not flash, and if I wait some time with the adapter plugged in, and then execute the scenario, the LCD flickers?
Just to add: My fingerprint scanner is GT511C1R (https://www.sparkfun.com/products/13007) and I am using the standard scheme for wiring it (560/1000 ohm for the RX). I am not using lcd.clear() command as I know it's heavy, and even if I don't write any text, the still LCD flickers.
Best regards, Nike