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/
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