Quote Originally Posted by Ioannis View Post
Ok. No matter what your source is, bat or line power. You need to measure the current flow so, it is easier to do it before your regulator. In this case you do not mess with the output voltage regulation and everything is much simpler.
Of course this has the drawback that measurment would include also the regulators own consumption. But if you know it, then it can be subtracted or do not bother at all if it is << that output current.
I have to state that I tried that way and because of the components needed, a one chip solution is much more accurate, elegant and is working either at + or ground rail. But then, it is just me!
Ioannis
I smell what you're cooking (understand what you're getting at, picking up what you're laying down, and so on, I could keep going but I won't )...

I'm just looking at getting some comparison readings between running at various clock speeds down to the built-in 37khz (32, 40, whatever) oscillator for a few keyfob type devices. If I take the current readings while running off of 5v and then switch the circuit over to a coin cell, the current draw should drop on a fairly decent curve following the voltage. That way I can keep track of mAh's (uAh maybe?) used in the keyfob and flash and LED in a slightly different pattern during activation to indicate that the battery is probably near EOL and will need changing, and if this works, I can keep the whole thing buried inside the same PIC in the keyfob without adding another chip.