[sdiy] Alternatives to Faders

[Edward King]

Ive been playing around with my panel design for a little while (taking a 
break from soldering, woodwork, metalwork and the fiddly business of slotted 
switches).

One of the things that has always bugged me about any board that Ive bought 
is the limit of channel / track controls.
Since most synths are limited to 16 MIDI channels, this is usually what you 
get. Plus a master volume control.

Further, most workstations provide track / channel control through up/down 
buttons or in the case of newer DAWS, faders on a touchscreen.
Neither of these options are very friendly and certainly dont provide a 
level of fluidity required for smooth control of tracks.

The alternatives are of course faders, but herein lies the problem:
What if you have more tracks / channels than you can cater for with faders? 
They do - after all - take up a reasonable amount of space and the decent 
ones (of which I think Penny and Giles are probably the creme de la creme) 
cost a bomb. Quality does matter. A basic 100mm 0.50 pence fader will last 
only a few thousand operations before degredation is really noticeable. A 50 
dollar fader will last a lot longer (probably the lifetime of the machine) 
but would you really spend 800 dollars for faders on a homebuilt?

The problem remains though that if you have more tracks than faders, you 
have to abstract this out and use a bank switching arrangement. This 
introduces problems of its own...if you have fader #1 moved to 70% and then 
switch banks so that fader #1 is now covering track #17, the fader will 
still be at its 70% position and this will cause a jump from whatever value 
track 17 was at before to the 70% mark its controller now is.

The only practical way around this I can tell is to use motorised faders 
that - when you switch fader banks - move the faders to reflect the values 
of the tracks they now represent.
These are even more expensive and take up even more board real estate 
though, not to mention the increase in power and control and interfacing 
requirements.

So, Im open to ideas (especially ones which enable me to use 16 faders to 
represent multiples of 16 tracks).

I have a few of my own and this is the current favourite:

I was playing around with a ball mouse, cleaning out the gunk from the 
rollers when it suddenly occurred to me that the sensing mechanism was quite 
hardy, but very compact. I dont know if its common knowledge, but the 
sensitivity of mice can be adjusted from the mouse as well as the operating 
system.

So I set up an experiment to see whether I could get the right sensitivity - 
versus - input ratio and it more than suffices.

I figured that since pitch-bend or modulation wheels are commonplace on 
synths, they are immediately identifiable as control surfaces and have a 
proven track record.
They are also the right size (ish) and becuase nearly 50% of their area 
would sit above the surface of the panel, they are reasonably compact.

Of all the ball mice sensing components, some use an analogue led and 
phototransistor setup (which is then converted by the electronics), but most 
use a logic output. Both types have drive electronics (usually in the form 
of a single chip).
A quick search of components suppliers puts these sensors at a cost which 
provides a cheaper and more flexible solution than all of the above. Funnily 
enough though, it works out cheaper to buy 50 ball mice (which obviously 
contain 2 sets of sensors and electronics) than it is to buy the sensors 
themselves.

Has anyone tried this method? 


		
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