I have lots of interests, and play around with many different things. Mechanics, sewing, art, music, plumbing, you name it. I have long had an interest in electronics, and have fiddled about some. I have a basic understanding of what I am doing, but it is indeed basic.
I have a Christmas display which includes a number of pieces that are illuminated by LED's, and each piece has a pair of AA batteries, which means there is an attached battery box, and switch. The display sits on a shelf above a window in my home, so getting up there to turn all those switches on and off is a pain. I figured I would make a simple little power supply to run all of the LED's. My idea was to use a wal wart which I already owned. It supplies 12V at 500 ma. Since the LED's are powered by 2 AA batteries, I expect that they are getting just a bit over 3 volts, so I figured I would use an LM317 voltage regulator to set my voltage at 3 volts, and life would be good.
As is often the case, I apparently know just enough to get myself into trouble lol. So, I used an online calculator to get my resistor values, and set up my circuit on a breadboard to test. I started by powering it with a 9V battery, and got 3.1 volts, which I figured would be fine. I then hooked up the 12V wal wart, expecting to see that same 3.1 volts, but that was not the case. When I power the circuit from the wal wart, I am getting 2.69 volts from the LM317.
Can anyone explain to me why I am seeing the difference in voltage between the battery power, and the wall adapter? Thanks in advance!