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From: John Woodgate
Subject: Re: Detecting black marks on paper
Date: Tue, 14 Jan 2003 20:23:37 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Tue, 14 Jan 2003 21:32:11 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that John Fields
wrote (in <email@example.com>) about 'Detecting black
marks on paper', on Tue, 14 Jan 2003:
>On 13 Jan 2003 21:31:35 -0800, firstname.lastname@example.org (Duane) wrote:
>>I am learning electronics as a hobby and was wondering what it would
>>take to make a sensor that I could move over (by hand) a sequence of
>>black lines (something like printed morse code) and make sounds or
>>flash LEDs. I don't need any pattern recognition -- it would fine to
>>light an LED when a line is detected. I am looking for something
>>simple - and cheap :)
>Shine an LED on the paper so it reflects back to an LDR. When the
>beam from the LED goes over the line some of the energy will be
>absorbed and the resistance of the LDR will increase. You may/will
>have to focus the beam from the LED or run it through a slit to get
>the sensitivity you need. Use the varying output from the LDR to
>trigger a voltage comparator and use the comparator's output to do
>whatever you want.
I would not use a Light Dependent Resistor, because of its slow
response. I would use a phototransistor.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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