Re: Need help with a circuit

From: John Fields (jfields_at_austininstruments.com)
Date: 12/28/04 

Date: Tue, 28 Dec 2004 13:26:39 -0600

On 28 Dec 2004 08:48:24 -0800, "Dark Alchemist"
<GhostOfACPast@gmail.com> wrote:

>Well, the posibilities of x would be a sine wave (for this test but
>could be anything in reality).
>
>If x <= 0 then y = 0 else if x <1 then y = sqrt(1 - x^2) is as far as I
>was able to simplify it.
>
>So, comparator A compares against 0 and comparator B compares <1 but we
>do not want the compare at B if A is true.
>This is as far as I got before my eyes started to glaze over, heheheh. 

---
If we assume that x is a voltage which varies over some range and that
you want to know when the voltage is less than or equal to 0 volts and
also when it's less than 1 volt, then you can set up two voltage
comparators like this:
              +2V                              
               |         Vcc                    
            [10.0K]       |                      
               |        [10K]                 
               +----|+\   |            
               |    |  >--+-->B
     x>---+---------|-/   
          |    |         Vcc   
          | [10.0K]       |       
          |    |        [10K]  
          +---------|+\   | 
               |    |  >--+-->A
               +----|-/          
               |
              GND
 
and your truth table will look like this:
   x       A     B   
--------+-----+-----
  <=0V     0     1    
         
 0<x<1     1     1     
  >=1V     1     0 
So the logic to control your function machine would look like this:
                    +2V                              
                     |         Vcc                    
                  [10.0K]       |                      
                     |        [10K]                 
                     +----|+\   |            
                     |    |  >--+----+
     x>---+--[10K]--------|-/        |
          |          |         Vcc   |  
          |       [10.0K]       |    |   
          |          |        [10K]  +--B 
          +--[10k]--------|+\   |      and Y---+
          |          |    |  >--+-------A      |
          |          +----|-/                  |
          |          |                         |  
          |         GND              +---------E--------+ 
          |                          |                  |
          +------------------------>x|  y = sqrt(1-x²)  |-->y       
                                     |                  |
                                     +------------------+
Where the line coming down from the AND would be an enable. When x was
less than 0V  it would go low, disabling the function machine, then
when x was between 0V and 1V it would go high to enable the function
machine, and when x rose to higher than 1V it would disable it again
for as long as x remained higher than 1V.
  
-- 
John Fields

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