[sdiy] ML317: 12V to 10V?

[David G. Dixon]

> I'm building up VCO scale adjust tool (see idea:
> http://electro-music.com/forum/viewtopic.php?p=307414#307414 ), and
> thinking of
> precise 10V reference (I can go down to 7V, no big deal), but I can
> get only 12 pin
> rotary switch, so extra pins with ref voltage will be in good use in
> future :)
> 
> I don't want it to adjust ref voltage each time I'll use it, so in
> this case stable voltage to op-amp suits me.
> 
> I've got plenty 12V 100mA DC wall wart power supplies and wish to use
> it in this project. I can dismantle it and use only transformer and do
> other things by myself.
> 
> I'm thinking to use LM358D instead of TL082.
> 
> Other thing is: Can I change 10k 1% resistors to 100K 1%? More acuracy
> I suppose?

Aha!  I was right.  You don't need current.  You need a good voltage
reference.  I think the REF family of voltage references is just about the
best option for your application.  I would avoid using a zener like Ray
Wilson does, simply because zeners are temperature-sensitive, and the REF
chips are designed specifically not to be.

The ladder idea is OK, and in fact, that is exactly how my keyboard matrix
scanner works.  And yes, hand-selecting the resistors is very important.
You can probably get away with 1% resistors so long as you match them to the
fourth significant figure.  And yes, smaller resistors are better in this
application.  I'd go with 10k/20k.