16x2 lcd backlight going dim

[Vindhyachal.takniki]

1. I had made a project in which 16x2 lcd is interfaced with couple of other functions.

2. After some hours(varies) of functions correctly i had seen that lcd backlight starts going bit dim. Ten it fluctuates. It goes high & low repeatedly.
However text on it is printed correctly.

i assume:
1. Since text is printed correctly so my lcd code is fine. & it has nothing to do with lcd backlight going dim.
2. I checked 15 pin of lcd on CRO it shows correct +5V all the time.

What could be problem??

[miguelvp]

What do you have connected to pin 3?

A picture or diagram might help

[sleemanj]

2. I checked 15 pin of lcd on CRO it shows correct +5V all the time.

What could be problem??

Pin 15 is the Anode of the backlight LED, pin 16 is the Cathode, if you have connected 5v and gnd directly there, you're shoving 5v through that LED without any current limiting.

The backlight led in these usually has fairly high forward voltage (4.2v or some such) and current capability (120mA or some such) which will be why it has survived thus far, but the added heating and current will be killing it swiftly, which is what you're seeing with it coming-and-going.

Like any LED, you need to current limit it.

[Vindhyachal.takniki]

yes I haven't connected any current limitor.
My ckt is attached

[void_error]

You need a resistor between +5V and backlight anone (+), anything between 100-330ohms should do. I usually go with 220ohm regardless of the backlight color for testing purposes.