Definition of an Analog(ue) Computer - test-drb@ccmp.vtda.org

6 May 1998

Allison quoted me as having written:

...
  <What's that got to do with it?  Diodes are
analogue parts - the output 
 <(current) is a continuous function of the input (voltage), not a 
 <discrete one (to me the difference between an analogue and a digital 

 Yes, but they don't (generally) amplify.   
I think you may be confusing my remark with Tony's.  I remarked that 
"all circuits are amplifiers" meaning that the general circuit can be 
modelled as taking an input, applying some sort of gain, and producing 
an output.  A gross oversimplification, but I wasn't talking about the 
active/passive issue (gain>1 => active, etc.)  Tony made a slightly 
different remark, "Digital circuits are built with analogue parts".  
Unlike mine, this is not an oversimplification, it is absolutely true.  
And has nothing to do with amplifiers.  You can build a digital circuit 
element with diodes; they are analogue parts, and they don't amplify.  
Clear now?

...
  <component).  In fact, Allison, you were saying
only a few days ago that  
 <you don't need any amplification to make an analogue _computer_ (with 
 <which I agree - although some of your examples I wouldn't call 
 <computers).

 I still hold that amplification is a factor in the equation that an analog 
 function may contain but it is not required. 
I never (intensionally) disputed this!

...
  This is an analogue function, take a shot at the
equation it solves. 
I couldn't quite read your diagram, I'm afraid.  Was it series capacitor 
followed by shunt diode?  Looks like it refers the input to the lowest 
value it (the input) ever takes, rather than to ground or a fixed 
reference.

...
  <For non-electronic digital computers, where do
Facit mechanical 
 <calculators lie?  I have one (which is driven by an electric motor but 

 Computers, mechanical, fixed program. 
Roughly what I thought.  I wasn't sure whether people would class it as 
a computer, but I think it is no less of one than a 4-function pocket 
calculator.

[pneumatics]

...
  You've not seen a modern production line that uses
air logic.  I've worked  
No.  I've seen some of the components in catalogues, though, and 
wondered if they'd be of use in organ building, though!

...
  on one that was used to produce pharaceuticals that
were in flamable bases 
 (ethanol).  There was some fairly complex logic in that system.  Working  
Sounds fun!

...
  with it is like designing with relays. 
I can imagine.

Philip.