From: jasen@xnet.co.nz   
      
   On 2008-08-30, none  wrote:   
   > John Fields wrote:   
   >   
   >> On Sat, 30 Aug 2008 08:18:36 -0400, none  wrote:   
   >>   
   >>>Hello,   
   >>>   
   >>>I'm putting together a circuit that uses a binary counter to cycle through   
   >>>addresses of SRAM.  I would like to vary the number of addresses used   
   >>>while   
   >>>the circuit is running.  Does anyone know of a simple way to build a   
   >>>binary counter with a variable count?   
   >>   
   >> ---   
   >> Probably, but how about some more details?   
   >>   
   >> JF   
   >   
   >   
   > I'd like to start out with a binary counter with a count of 0-255, and   
   > either with switches, or preferably a rheostat, slowly lower the maximum   
   > count, hopefully all the way down to 0-1.   
      
   run the output of the counter into a DAC (digital to analogue converter)   
   use a comparitor to compare it to the voltage from a potentiometer   
   across the same supply as the DAC the output of the comparitor feeds   
   the reset pin of the counter.   
      
   if you really need to use a rheostat instead of a potentiometer   
   there's probably a way to make that work too.   
      
   a pre-built DAC will probably give smoother tuning of the count than a   
   simple r-2r ladder, but the only one I found locally requires dual supply   
      
      
   Bye.   
      Jasen   
      
   --- SoupGate-Win32 v1.05   
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