[sdiy] Substitute for pin matrixes?

[Aaron Lanterman]

On Jan 23, 2010, at 11:14 AM, Derek Holzer wrote:

> In this vein, can anyone tell me how the program cards for the Buchla Music Easel work?
> 
> FROM http://www.buchla.com/historical/music_easel/music_easel.html

I've see Magnus has already responded to this - I'll just throw in a couple other notes...

The individual daughterboards tend to have inputs that are (more or less) like op amp summing nodes on an inverting op amp configuration. One resistor is off-board and hooked to the front panel pots (which have a couple of additional tapering resistors), and another resistor, if used, it on the card. A +13.5 V supply can be fed to the front panel sliders and/or the resistors on the card, or both, as determined by a switch. The summing aspect lets you pile the front panel setting *on top* of what is set by the card. Choosing different resistor values on the card lets you emulate various slider settings. 

The switches on the front panel (to select filter routings, etc.), for the most part, don't hook dircelty into the sound generating circuitry - they create settings for various CMOS switches, so the CMOS switch settings can be set by resistor values on the card.

It's quite clever - and from the card you can do all sorts of things that you can'd do from the front panel.

- Aaron