[sdiy] Keyboard matrix decoder

[Luís Marka]

> Hi Luis...
>
> unless you are a glutton for punishment... why not use a DAC instead of
the
> R/2R ladder.

Hi Harry,
'Coz these are quite hard to get where I live... if I order them from
another place, shipping costs alone will be pretty higher than the DAC cost
itself.

> If you do the R/2R ladder you'll probably have to match the resistors to
0.1%

Yes, I can get a bunch of, say, 100K 1% metal film and match them to
something like 0.2%. Think this is precise enough. I'll make techno/trance
anyway, so precise tuning is not my main concern!   :)

> Another good trick is to make the 2R by series of two R resistors (make R
by
> parallel
> of 2R...) this way you use onlt one value...

Yes, I've been checking further, and decided to 200k (2x100K) and 100K
resistors.


> If you drive with CMOS, you need to make the ladder resistors MUCH larger
than
> the
> internal resistance of the CMOS... often hundreds of ohms... so using
50K -100K
> might
> be appropriate...
>
> Or... use a DAC ???

Hehhe.. Sure, if I can get these at a reasonable price, I will use a DAC.
Now, think it's time for a lot of protoboarding... this will be a busy
Sunday!

Seeya,
Luís Marka