MOTM

In a message dated 03/31/2000 3:40:57 PM, nate@... writes:

<< to somewhat mimick a ribbon controller (since that idea is now officially
out the window)  >>

Seems like it would be easier to build your own ribbon controller (they're 
pretty simple and crude) or perhaps use a Force Sensing Resistor (I'm looking 
into that now).

Ivan

In a message dated 3/31/2000 1:40:57 PM, nate@... writes:

>Does anyone on this list know what sort of technology was used on the
>metalic keypads used on microwaves made in the early 80's? I had a
>Panasonic that had a touch pad on it, the buttons required no pressure
>to
>activate, just a touch. I'm trying to find out if the keypad was made of
>some expensive material or it there was extensive circuitry required to
>make these touch sensors work.

I don't know anything about the Panasonic microwave oven (except that you 
shouldn't watch the food cook), but these types of conductive pads aren't 
uncommon. I remember seeing them on elevators in the early seventies, in 
fact. I have an old Phillips turntable which uses this type of pad.

Both types of pads (I believe) use two conductive surfaces which are 
physically isolated from one another. It's possible (if unlikely) that these 
circuits use your skin to actually conduct between the poles. The circuit is 
closed when one's finger touches both parts of the pad -- your skin acts like 
the switch mechanism by allowing micro currents to travel between the two 
conductive surfaces. 

Another (more likely candidate) kind of touch key pad is the kind that is 
sensitive to capacitance. This would include (I think -- again I'm not sure) 
my Phillips turntable, the Serge Touch Keyboard, and the patch memory pads on 
the Oberheim OB-1. 

I would never build anything of the first kind (that depends on skin to 
conduct a voltage), but I'd imagine that both circuits would require a bit of 
work since the first would more likely require a CMOS or similar circuit to 
do the actual work (so your finger only closes a control circuit.


 the reason I ask is, I was thinking about
>some type of linear controller using pads similar towhat I was describing
>hooked to a resistor chain fed through a sample & hold and a lag processor
>to somewhat mimick a ribbon controller (since that idea is now officially
>out the window) Let me know what you think. -Nate


For more information on capacitive touch sensitive circuits see the "CMOS 
Cookbook" by Don Lancaster which has a good section on how to build these. 
The circuit looks somewhat simple, but if you're going to build a keyboard 
it's going to be a very repetitive job.

As far as the pads themselves, you can probably use any conductive material. 
The OB-1 uses some kind of metal balls cut in half (about 3/8" diameter). The 
Serge TKB uses conductive paint painted on plastic. 

I still think it would be easier to build a ribbon controller in either a one 
off or a production setting, than build a touch keyboard from capacitance 
switches (especially if one wanted more than 12 notes/octave). Someone on the 
diy list came up with the idea of using two sided tape and sprinkling 
graphite powder across the top of the tape until they got about 100K across 
the length of the tape. While I'd still consider this a less than adequate 
solution (similar to Gene Stopp's conductive trash bag method I've mentioned 
before), at least there are some simple solutions for experimenters to try. 
Of course, there may be a way to get (semi-)conductive paint in smaller 
quantities than I've been able to find so far.

It sure seems there's a market wide open for someone to build/sell 
controllers with all this type of talk going on so frequently here: ribbons, 
joysticks, touch keypads, mod wheels, small ribbon, small theremin, faders, 
etectera, all remotely housed so they can be used near a keyboard (or other 
remote area). Useful for any synths out there (ARP, Moog, MOTM, etc.).

JB