Analog-to-Digital Conversion

Date: 02/07/2001 at 20:43:55
From: James Grady
Subject: Analog to Digital Conversion

I have no trouble converting an analog number such as 1234 to a 
digital number 10011010010, but I do not know how to do an A/D 
conversion of text and strings, or of tactile senses.

Can you help? I would really appreciate it.

Date: 02/08/2001 at 12:25:30
From: Doctor TWE
Subject: Re: Analog to Digital Conversion

Hi James - thanks for writing to Dr. Math.

How this is done depends on the "form" of the analog input.

In computing, text is usually entered via keyboard (technically, 
already a "digital" form - the typist is the A/D converter by pressing 
the right keys) or via scanner. If the scanned text is simply saved in 
some sort of "image" format (pdf, bitmap, gif, etc.), the _text_ is 
still analog, although the _image_ is digital. (The computer still 
can't tell what character is what.) Converting images to text is a 
tricky process because of the variety of fonts, orientations, etc. 
Programs that attempt this are referred to as Optical Character 
Recognition software, or OCR. For an introduction to OCR, visit:

   Character Recognition - Sargur N. Srihari, Stephen W. Lam
   http://www.cedar.buffalo.edu/Publications/TechReps/OCR/ocr.html   

   Optical Character Recognition (OCR) as a Digitization Technology
   - Susan Haigh
   http://www.nlc-bnc.ca/pubs/netnotes/notes37.htm   

   OCHRE - Optical Character Recognition Using Neural Networks in Java
   - Jason Tiscione
   http://www.geocities.com/SiliconValley/2548/ochre.html   

Other "analog" data (like tactile senses) are generally collected 
electronically by some form of transducer (microphone, pressure 
sensor, light-admitting diode, etc.) that "measures" the 
characteristic and produces a proportional voltage or current. This 
electronic signal is then converted to a digital value by a 
conventional A/D converter such as the TLC549 chip. For more 
information about this chip, see:

   Texas Instruments TLC549 8-bit Analog-to-Digital Converter
   - Ian Harries
   http://www.doc.ic.ac.uk/~ih/doc/adc_dac/tlc549/tlc549.html   

For more information on electronic A/D converters, visit:

   howstuffworks.com's "How Analog and Digital Recording Works"
   - Marshall Brain
   http://www.howstuffworks.com/analog-digital.htm?printable=1   

   PC-Based Data Acquisition - Datappli, Inc.
   http://www.datappli.com/data_acquisition.htm   

I hope this helps. If you have any more questions, write back.

- Doctor TWE, The Math Forum
  http://mathforum.org/dr.math/