Was reading an article in Make magazine about a guy building his own arduino board. He made a point of saying he didn’t want to use a 7805 voltage regulator but used an L4931 instead because it has low dropout and he wants to run his arduino on a 6V battery.
Low Dropout? What’s that? Started doing research and found that the 7805 has a 2V dropout. Meaning you need at least 7V to power it. Huh? How did I miss that? Surely you jest?
I put a 7805 on the breadboard and connected VOMs to the input and output. Started the input at 12V and worked down to 6V. Sure enough, at 6V, the 7805 is outputting 4.8V, not 5.0.
My motionDetector circuit is using a 7805 and I feed it 6V. My logic was the closer my input voltage is to 5V, the less power I’m wasting, or, more importantly, the less heat I’m generating, and that is a bit of a concern because this circuit resides in an already hot location.
Now that I see I’m actually feeding my circuit a with mere 4.8 volts that may very well explain why it would randomly lock up on me. Not that it has in a long time, but it has.
Luckily, the wall wart with which I am supplying power has a switch for 6, 6.5, 7, and 7.5V. I checked the circuit to make sure I wasn’t doing something dumb, and then upped the voltage to 7V to allow for a full 2V drop out.
With any luck, I will never see a hang on the motionDetector again.