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<div class="moz-cite-prefix">Sounds like you are building the basics
for an HO hump yard -- at least the club members at NRVMRRC would
love to see the demonstration. (Combine it with an auto-decoupler
and push-and-shove moves and you're almost there). They're in the
process of building a new yard module for the club layout.
(you'll need to detect a modulated reflected signal from a barcode
on each car)<br>
<br>
There was an article in last month's Circuit Cellar or Elektor
magazine about using an IR LED as a photosensor. The author also
compared and contrasted phototransistors, LED's, photodiodes and
photosensitive resisters as sensors.<br>
<br>
Basically you need to bias the LED, and amplify the result through
a high-gain op amp. Then a second-stage op amp uses a comparator
to give you your detection signal (to a straight digital input).
Alternately you can use a separate ADC chip and read the analog
samples from the first stage to detect beginning and end of an
object.<br>
<br>
Give me a couple of days to dig up the article for you.<br>
<br>
On 10/07/2013 03:55 PM, Grawburg wrote:<br>
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<blockquote cite="mid:4905541f6e9e91a7a08d533657448165@myglnc.com"
type="cite">
<pre wrap="">I'm working on a project to demonstrate how a basic conveyor system can separate
different size objects by using some HO train cars and electric turn-out switches.
The intention is to have a detector, either a visible light photocell arrangment using
LEDs or an infrared LED emitter/receiver. The turn-out switch will be isolated from
the Pi with a relay.
I know the photocell will give me a basic ON-OFF (high-low), but what does the IR
LED give? I will have a timer loop in my Python code that instructs the switch to remain
in the diverted position for x-seconds and then return to the default position.
Brian Grawburg
Wilson
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<br>
<pre class="moz-signature" cols="80">--
Scott G. Hall
Raleigh, NC, USA
<a class="moz-txt-link-abbreviated" href="mailto:ScottGHall1@GMail.Com">ScottGHall1@GMail.Com</a>
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