The merlin project. Update and tip.

[The Dark force of dance]

Y-ellow Ladies and diodes.
        Ok well after some rearrangement I've got it working fairly well.
First of all I thought I'd share this with you for those who don't know this
trick.

You can file a resistor value up. It's an old recipe that's been in the
Goodfortune family for years. What you do is take a resistor slightly lower
in value than what you need, lock it down between a couple of alligator
clips and hook it to your multimeter. Then get a small needle file and
gently file away the coating and into the resistive material. As you file
you'll notice the resistance climb. So suppose, as I just did, you needed a
3K resistor but you only had the E12 range available to you. Thus the
closest you had was a 2K7. You can easily file it up to 3K. In this case I
got it to 3001 ohms. One stroke too many. Oops. When you've got the resistor
filed up to the desired value you coat the filed away area with a little
nail polish and you're done.

Now this trick you may already know but the general wisdom is that you can
only do this with carbon film resistors. Well I thought I'd give it a go
with a metal film and see how it goes. And I'm here to tell you it works a
treat. In fact it works so well I can forget carbons altogether. The thing
is that metal films are harder to file of course. What this means is that it
takes more filing to file up the value. Which means far more accuracy. And
of course the stability of metal films as well. I'm so impressed I just
thought I'd share it with you and break a few myths.

Of course just before anyone points it out, when you file up the resistance
of a resistor, you also lower it's watt-rating slightly Usually this is
negligible and usually it doesn't matter anyway. But it is worth pointing out.

I just thought I'd make mention of this because it goes against the
conventional wisdom. But on with the show.

What I ended up doing is scrapping the idea of the low voltage op-amp in
favor of putting a second voltage reference in. One for each regulator. The
first thing I noticed was that when the first reg was loaded down, the
second reg dropped by about 200mills as well. Just like when fed from a
single reference. To cut to the chase, it was a just a function of where I
was taking the measurements from. In hind sight this should have stuck out
like a sore thumb but it escaped me. It's all working just fine now as far
as that goes.

However the drop-out is now closer to 5 volts than 4 unfortunately. Still
that's 2 volts better than 7 as it was before. And as I mentioned to Paul P
earlier, probably not much worse than we could expect from one of these 3
terminal regulators. Especially if the 78xx or worse, the 317 family of
regulators are anything to go on. With both regulators running the quiescent
current @ 12 volts is around 24ma. Not too shabby all things considered. 

I'll post the circus for y'all some time soon but now it's time to get on
with the battery charger part. Which is what brought me to mention the
resistor filing trick.

Anyway Hope this helps and once again, thanks everyone for the advice thus
far. It's all be invaluable.

Be absolutely Icebox.
 _ __        _                              
| "_ \      | |         batzman at gist.net.au / aek at gist.net.au
| |_)/  __ _| |_ ____           ALL ELECTRIC KITCHEN               
|  _ \ / _` | __|___ |  The new AEK CD, Elementary Urban sanity    
| |_) | (_| | |_  / /   is out now on Transmission Communications from
|_,__/ \__,_|\__|/ /    http://brisbane.dialix.com.au:80/~com11
                / ,__   and check out http://www.all-electric.com
Goodfortune    |_____|       Let your SANITY wear thin.