LCD character fading

I have been having some troubles with my LCD Characters fading after use with an external power supply. I have a 15V, 3A power supply connected to a 7805, 5V (1A) regulator. That is connected to my Mega 2560. I also have the 5V regulator connected to the LCD. After a given period of time (about 30-60 seconds), the characters on the display begin to fade until they no longer are visible; however, when I plug in a 12V (400mA) power supply to the DC power jack, the LCD display works completely normally. What could be the issue here?

You didn't put a heatsink on the 7805, did you? (It is a TO-220 package with the metal tab, isn't it?) It is overheating and (gradually) shutting down; there is still enough voltage to operate the LCD backlight and electronics, but the contrast voltage is much more critical.

Put a meter on the 5V line and watch it.

I am having the same issue.

Using an L7805 and a i2c character LCD from adafruit, my screen gradually loses contrast (about 50 seconds from turn on to fully faded). When I power the LCD from my 5v pin on Arduino, it works fine forever.

When I monitor the voltage coming off of my L7805 output pin, it is a steady 4.99 volts (on my multimeter).

approx. 9v in --> L7805 --> 5v out

@Paul__B any solution? are you suggesting adding a heatsink will solve the problem? I'm having trouble figuring out why the problem would occur only with external power supply and not my arduino's power supply. Any other insight (I realize this is an old thread, but need help and can't find this problem elsewhere!)

Thanks!

vwls:
Thanks!

See what happens if you keep monitoring the voltage and drive both the LCD and something else .... such as a string of LEDs....at the same time. If those other devices remain powered and working.... then the issue won't be with the regulator. Otherwise...the issue will be your regulator.

Did you use input and/or output capacitors with your 7805?

Don