[sdiy] Touch Keyboards

[Grant Richter]

The know the Buchla 218 uses guitar fret wire between keys for a  
local ground connection.

The 221 appears to use a similar design. The fret wires have a very  
pleasant tactile feel and the close location of a ground contact is  
really needed for the touch sensing technology in the 217 and 218.

I have been testing the Freescale Design E-field technology

http://www.freescale.com/webapp/sps/site/prod_summary.jsp? 
code=MC34940&nodeId=0112698268

using their inexpensive eval board and a home made printed copper  
keyboard (sprayed with 3 coats of polyurethane varnish).

As long as the electronics has an earth ground reference somewhere,  
the single key electrodes work well with no ground needed for the  
human operator. The only problem is the 2.5 millisecond settling time  
between each key detection for the diode / LP envelope detector.

But I believe I have worked out how to scan all 32 keys in 1  
millisecond while keeping the "pressure" sensing capability. At this  
point, performance appears as good or better than the Buchla and  
Serge key feel, but I do not yet have a microprocessor connected for  
outputing CV or MIDI data that can be played in real time.

Q-prox is another source of modern capacitive key sensing technology.

http://www.qprox.com/products/qmatrix.php

The problem with these modern technologies is that they are not  
optimized for fast enough key scanning to be acceptable for  
traditional musical keyboards.

> Both Buchla 221 & Serge 115 has capacitive one conductor laquercoated
> keys!
> I know that for a fact since I had two 221:s and one 115 on my  
> workbench
> last week!
>
> /Daniel