Using a 12V lipo to power LED strip and Attiny 85

Correct, you need a 5V regulator.

Yes, something like that would work, or a low cost buck converter would be more efficient

Sent from my iPhone

how about this,

L7805C-V - STMICROELECTRONICS L7805C-V - IC, LINEAR VOLTAGE REGULATOR 5V TO-220-3 | Newark element14 US

I personally have used these pulled out of old power supplies I found in the shop for projects.

Yup

That will work

Thanks for suggesting the buck converter! Looks like it could be cheaper than using a bunch of mosfets (like I already did). But still very helpful when I make more light controllers!

This example looks like it would be perfect: Simple Buck LED Driver with PWM Input

Except I'll be using N-channel mosfets, since that's what I already have... and they're within the ranges the author says are important (min 2A drain current, drain source 30V, gate threshold lower than 4V (logic gate).  ... it looks like the Gate, drain and source are all in the same spots between the two of them according to their data sheets, so I think it would be ok to just swap them..... right?

Pchannel

NTD2955T4G ON SEMICONDUCTOR Transistors - MOSFET | 10N9570 | Newark element14 Canada

Nchannel

FQP30N06L FAIRCHILD SEMICONDUCTOR Transistors - MOSFET | 20C4477 | Newark element14 Canada

The circuit will only work with a P channel MOSFET.

An N channel MOSFET needs the gate to go more positive than the source to to switch on and that isn't going to happen. But because it will be the wrong way round in the circuit it will conduct all the time if you make its source more positive than it's drain.

Find  a buck regulator that doesn't need a MOSFET at all (there are lots) - how much current do you need at 5V ?

MK

As Open Collector NPN transistor replacements, the N Channel MOSFET will work providing it meets certain critera, that being the GS voltage is low enough for logic control

for example

http://canada.newark.com/fairchild-semiconductor/fqp30n06l/n-channel-mosfet-60v-32a-to-220/dp/Search?catalogId=15003&langId=1&storeId=10196&gs=true&st=logic%20level%20n%20channel%20mosfet

this is the results of a Newark search for "logic level n channel mosfet", try it on your local site, this one is my Canadian pricing

these will easily drive your power LEDs and wont need heat sinks and has a similar circuit to the instructables site. The cange I would make is not power the FETS and LEDS through the Arduino but take the 12V direct to the LED strip and the return direct from the source pins which will be common back to the power adapter, take a separate feed to the arduino that does not involve the current for the LEDS

here is a video where I cover off using MOSFETS like this  Driving BIG loads with your micro controller - no isolation

The buck converter I was referring to was to derive the 5V you mentioned, not for driving the LEDs, if your supply is actually 5V and you need to derive a 12V for the LEDs then you will need a boost converter that would look very much like the buck converter you showed

this is the kind of BUCK converter i was referring to Mini DC/DC Step-Down (Buck) Converter - 5V @ 1A output [TSR12450] ID: 1065 - $14.95 : Adafruit Industries, Unique & fun …

Hope this helps

Peter