AW: Don's interpolating scanner

[Don Tillman]

   From: Magnus Danielson <magnus at analogue.org>
   Date: Sun, 03 Jan 1999 04:21:57 +0100

   I agree, certainly an interesting piece of work!

Thanks!

   I have a little diffrent solution that does not require as many
   VCAs. In it's basic layout it only requires 2 VCAs. Let's consider a
   8-input scanner.

   First I would have two 8-to-1 analog muxes (4051's) to select two
   adjacent inputs, each being feed into the 2 VCAs. 

Yeah, this will work fine.  The big issue here is converting from an
input control voltage to the digital select lines for the mux and the
analog control voltages for the VCAs, and the circuitry to do this
accurately and without glitches is not easy.

But that's for a *linear* scanner, like the circuits JH and I did.

A *circular* scanner is where your approach becomes powerful.  A
circular scanner doesn't care about a scan control voltage so there's
no need to deal with that; a triangle wave oscillator and a counter
are all you need.  

A speed control voltage would change the frequency of the triangle
wave oscillator, and, yeah, through-zero is just begging, isn't it?

The original Hammond Chorus uses, clearly, a circular scanner.

  -- Don