Alt-BEAM Archive

Message #03864



To: beam@sgiblab.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Fri, 28 May 1999 07:14:58 -0700
Subject: [alt-beam] Re: edge detector


In this circuit, the LDRs will naturally compensate for ambient light.
If the 2 values are equal then the output is normally on (low/0V) and
turns off (high/+V) as the bottom LDR is turned on by a brighter source.
The circuit is really a difference detector and it is the edge that
supplies the difference.

regards

wilf


BotDoc wrote:
>
> Hey list,
> Here is a little edge detector schematic that uses 1
> NPN transistor, 1 resistor and 2 photoresistors. It
> has an active low output that drains 23uA at 3.1V.
> The photoresistors should be a close together in value
> as possible, facing down, and about half of centimeter
> or so above the ground. It is triggered when the
> front sensor goes off of a desk (white), assuming that
> light isn't coming from your floor. It will also avoid
> things such as ink blots on your desk etc. Flip the
> photoresistors so they are facing up, and you can
> reverse before getting stuck in a shadow... Might be
> something to thow on your photovores.
> BotDoc
> _________________________________________________________
> Do You Yahoo!?
>
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