# Measuring Power, 12v RGB LED strips, 7805, atmega328 and 8 AA's

This is a repost from the general electronics section, but this seems like it might be a more appropriate forum.

I've been playing with electronics for a few years now and have build a lot of things that I like, but I'm still a self taught rank amateur and could use some advice.

I'm building a battery powered RGB LED display (for a bike). It consists of 4 strands of 12v RGB LEDs, a 7805 voltage regulator an atmega328 running the UNO bootloader and some transistors.

It currently drains 8 AA's (1.5v*8=12v) in about 2 hours and I want it to last at least 8, or ideally 12 hours.

Each alkaline AA should be 2700mah or 21 Ah for the 8 AA's.

So, now I'm learning about power. I've never tried measuring power and so I think I'm doing something wrong.

I placed my multimeter between the battery and my circuit board and with the lights plugged in I'm getting a .6 reading when the meter is set to 10A and a 2.8 reading when it's set to 20m. Does that mean that I should multiply .6 * 10A to get 6 Amps or is at .6 A or 600 mAh. Most people think that it should be .6 amps which makes some sense to me since the light should use about 115 mA per color per meter and I have about four meters and one color is on at a time (on average).

If that were true then I my lights should last for days instead of hours (21600 Ah / .6 = 36 hours)

To move things further along when I measured without my lights the circuit (the 7805, 16 mhz atmega and a bunch of transistors switching nothing frenetically) is using .25 * 10A). I thought that an arduino should use something like 25 ma while it's running so I'm off by a factor of 10 or 100 depending on how my meter is reading.

That leads me to think that I should remove the 7805 and give the Arduino it's own power source. Is that recommended for minimizing battery drain.

Summary: * 4 meters of 12 RGB LED strip @ 114 mA / meter (http://tinyurl.com/12vrgbled) * 16 mhz 'breadboard arduino' (on a protoboard) * 7805 giving the arduino 5v (and the bypass to get the lights 12v) * 8 AA batteries (21600 mAh)

Power reading @ 10A .6 with lights, .25 without lights @ 20m 2.8 with lights 1.15 w/o lights

Battery life * 1.5 -> 2 hours with 8 alkaline AA's

Questions: 1. How do I read my ammeter (is .6 @ 10A setting .6 amps or 6 amps)? 2. How long would you predict the circuit would last? 3. Should I avoid the 7805 and power the arduino from a separate power source? 4. How much would I gain if I did that?