[sdiy] optical retrofit for minis?

[Kevin Lightner]

>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.

I did try both reed and hall switches, but ruled them out because of 
alignment and installation concerns.
Also, I have no idea how close someone may place their mini to a 
speaker or transformer.


>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.

This is interesting on the computer doing the scaling.
Some pics are woefully shy on onboard ram though.

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

I couldn't find halls for that low. :(

>
>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.

Interestingly, I found the opposite.
My considerations are not for a one-off, but for an easily installed 
product though.
There are more ideal places for me to put things if this wasn't so.

>
>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...

Yeah, I know :)
In fact, I'd kindly offer that I've rebushed more keyboards than 
anyone you could find. :)
Gone through countless thousands of bushings.
So many being done now, I taught my wife the job to help out.
I also have some techniques that can make some actions even smoother 
than you're probably used to.

-- 
Regards,
Kevin Lightner

http://www.synthfool.com