[sdiy] optical retrofit for minis?

[Tom Arnold]

On Tue, Mar 22, 2005 at 01:29:17PM -0500, david at therogoffs.com wrote:
> I didn't say hall-effect sensors, I said reed switches, which are under $1 each.
>

As per my emails about 3 months ago while I was fighting with my Mini's
keyboard action, I've been playing with Hall Effect sensors and magnets.
Unfortunatly I have too many projects so it fell by the wayside after I got
my original busbars replated.

Anyhow, I forget the company name but the sensors I got have the part prefix
HAL, they give a nice voltage out depending on magnet strength.  I got tiny
magnets from Edmund Scientific because I wanted ones that were very
repeatable magnetically.  I didnt align them carefully or anything on the
keyboiard I glued them to ( J-wire version not Mini's twin bus version ).
What I found was its easy to have the microcontroller calibrate signal
strength.  Scan the voltage of each key sensor, then depress ( with a weight
not a finger so its repeatable ) and scan again.  I need to spend more time
to get the code for the Per Key aftertouch working, and I'll need some
better numbers for velocity.

Total cost?  The hall effects were $1.05ea in quantity.  The magnets were
$12 for 200.

I actually ditched the idea of using interupters because I found the
alignment was much harder then hall effect as a missalignment reqired
physical tweaking where hall effect re-alignment can be done entirely in
software.

It'll probably wait until my Mini screws up again before I gain interest,
well, maybe when I need to build a CV keyboard for driving my slowly growing
modular...

Oh, and I feel the need to mention...  When you replace those mini bushing,
clean and grease those bellcrank caps!  And replace the 3 worn flat from the
guy playing simple basslines every night for 5 years...  the feel of the
PrattReed board is incredable after some TLC...
(okay, its no T8, but it no longer feels like you're selecting bands on a
Grundig )

-- 
 -----------------------------------------------------------------
 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
 - SynthGeek        -
 - BBD Fanatic      -  "...is it a virus, a drug, or a religion?" 
 - echo evho wjxo   -    Juanita Shrugs. "What's the difference?" 
 --------------------