Fw: [sdiy] Force Sensing Resistor

JH. jhaible at debitel.net
Sat Sep 15 13:37:14 CEST 2007

(I just saw your mail was cc'd to synth-diy, so I'm forwarding my response 
there, too.)

Hi Edward,

thanks for your mail - you're doing really interesting stuff!

I have recently played a (broken) CS80 again after many years, and decided
that I need such an expressive keyboard, too.
Either I'll buy a CS-80 (maybe soon?), or I'll build my own keyboard.
I wouldn't go so far as carving my own keys, though. Reusing something
existent, rather.

I'm pretty picky about keyboard action.
Three that I like are
Rhodes Chroma
Wurlizer EP200

What I *don't* like, despite them being loved by many piano players, are
The Prophet T8
The hammer action of mayny electronic pianos (my Kawai CA600 included)

I tracked it down to what exactly it is that I don't like, and I think I
found the difference:
On many weighted, hammer-action type keyboards, you need a lot of force to
just hold the key down.
Ideally, the key should give resistance when you hit it, but then need less
force to keep it down.
I really appreciate the keyboard action to be weighted for better dynamic
control, but my fingers are not strong enough to play for a long time, when
a lot of force is needed for just keeping the keys down.

I noticed that grand pianos and upright pianos can be very different in that
respect also, varying from model to model, and from manufacturer to

On the CS-80, the keyboard action is very good for my taste, but the
aftertouch is a little on the stiff side IMO. I'd love to have a sensitive
aftertouch like the CS-50 has, but polyphonic.

I'd love to see pictures of your work!

Best regards,


----- Original Message ----- 
From: "Edward King" <edwardcking2001 at yahoo.co.uk>
To: "JH." <jhaible at debitel.net>; <xyzzy at sysabend.org>
Cc: "Synth DIY List" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, September 15, 2007 11:40 AM
Subject: Re: [sdiy] Force Sensing Resistor


Yes, Ive built my own keyboard (actually several now) from scratch the hard
way (wooden keys, partly machined and then hand finished + keytops etc).
I dont recommend it.
I dont regret doing it, but I actually lost hair during the course of the
development and would only do it again for a "special" / "different" type of
keyboard. Some ideas I had included using replica fingerbones for a true
"frankenstein" / Goonies type thing or hand carved keys for a "rustic" look.
The concept of combining organic look and feel with modern technology lights
my little candle.
Im also still very taken with building a keyboard or two from composite
materials or even glass.

As to the sensing, monitoring and other control stuff, I really could write
a book. the conclusions I came to were as a result of years of testing
different methods. At one point I even tried a sealed conductive liquid
position sensor that my other half was kind enough to help develop with me.
It was not good.

Eventually, I got stuck into the idea of optical measurement and initially
went with the slotted optical transistor output sensors with vane attached
to the lower part of the key (as per work done by Graham Hinton for a breath
controller in the eighties and the work done more recently by Adrian Freed
at berkeley).

The vane design was a royal posterior ache and hand-manufacturing tolerances
were laffable. I was eventually left with two choices: 1) have vanes
lasercut or moulded specifically (quotes I got were ridiculous for the size
of the things) 2) go with optical distance measuring technology. I went with
the latter.

I also decided to go with the Fatar TPM10 (hammer action weighted keyboard)
available through Doepfer for my prototype because I had the opportunity to
test one out a while back and liked it very much.
Although I had difficulty dealing with Doepfer initially (confusion over
where Im located because I have a uk email address, but dont live in the
uk), they turned out to be very helpful, very professional and pleasant to
deal with.

The PCBs for my senso arrangements will be done by the time the keyboards
arrive and as long as the spec hasnt changed, they should slot right in.

Im happy to share my photos with you of the keyboard mechanisms I designed.
I dont have many (Im not much of a photographer) but I'll send them over.

Either way, my advice to you is to either buy a midi keyboard and adapt it
(cost anything from 30 bucks to 300 bucks) or go with the fatars from
doepfer (800 bucks or thereabouts) because building your own is very costly
in terms of man hours lost sleep and wood splinters.



----- Original Message ----- 
From: "JH." <jhaible at debitel.net>
To: "Edward King" <edwardcking2001 at yahoo.co.uk>; <xyzzy at sysabend.org>
Cc: "Synth DIY List" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, September 15, 2007 10:31 AM
Subject: Re: [sdiy] Force Sensing Resistor

>I came late into this thread. Edward, have you built your own keboard with
> polyphonic aftertouch ?!
> What keyboard action did you use to retrofit with QTC pills?
> Do you have any pictures of what you've built?
> I thought the Pills respond in en exponential rathe than linear way.
> Thought
> I read this somewhere.
> I've ordered some of these from Maplin yesterday. Curious to try them
> myself!
> JH.
> ----- Original Message ----- 
> From: "Edward King" <edwardcking2001 at yahoo.co.uk>
> To: <xyzzy at sysabend.org>
> Cc: "Synth DIY List" <synth-diy at dropmix.xs4all.nl>
> Sent: Saturday, September 15, 2007 5:42 AM
> Subject: Re: [sdiy] Force Sensing Resistor
> Hi Tom!
> Actually, although they make some products in the uk, they also have a
> manufacturing unit in the far east (or at least in that direction).
> I went a bit overboard with them when I came acrross them and have given
> proportional control to various objects that really shouldnt have
> it....however....
> Let me know if you want me to send you over a couple of samples as I've
> got
> to order some more in anyway.
> A nice quickie experiment (proof of concept) is find someone with a
> slightly
> earlier model car, pop off the electric window switch, shove a QTC pill in
> between the contacts and hey presto! You have (or should have depending on
> the car and switching arrangement) proportional electric window control
> :o)
> for more relevant uses, the forum on peratechs website will be helpful in
> getting the best out of the materials and if you want more hints and
> practical advice, just gimme a shout. Remember, the output is
> _very_nearly_
> linear but not quite so for finer control, you need to tweak things a bit.
> EK
> ----- Original Message ----- 
> From: "Tom Arnold" <xyzzy at sysabend.org>
> To: "Edward King" <edwardcking2001 at yahoo.co.uk>
> Sent: Friday, September 14, 2007 5:32 AM
> Subject: Re: [sdiy] Force Sensing Resistor
>> On Fri, Sep 14, 2007 at 05:26:45AM +0300, Edward King wrote:
>>> QTC cable is what Im using for keyboards that only need aftertouch for
>>> the
>>> whole board. For individual aftertouch (I can never remember whether its
>>> called poly or mono) QTC pills.
>> Oh.  Nifty, How did I miss this product??   Looks like its made in the
>> UK?
>>> Both QTC cable and QTC pills are very cheap and pretty linear.
>> For Poly I'm back to playing with Hall Effect sensors since they have
>> dropped in price.  I hope to have something to report soon...
>> -- 
>> --------------------------------------------------------------------
>> - Tom Arnold           -  "...is it a virus, a drug, or a religion?"
>> - Sysabend Caretaker   -    Juanita Shrugs. "What's the difference?"
>> ------------------------       -- Neal Stephenson,  Snow Crash
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