Re: [mh] Using 1-wire to sense if the boiler is running

[Jim S. <js...@sy...>]

Ben,
=20
You might look for a photo-darlington transistor - it will work with the
visible light very well.
http://www.nteinc.com/specs/3000to3099/pdf/nte3036.pdf
=20
Jim

-----Original Message-----
From: mis...@li...
[mailto:mis...@li...] On Behalf Of =
Ben
Griffith
Sent: January 18, 2007 11:06 AM
To: mis...@li...
Subject: [mh] Using 1-wire to sense if the boiler is running


Hi all,

For a while I've been trying to figure out a simple non-invasive way for =
MH
to use 1-wire to know when my oil-fired boiler was running, and I =
figured it
out last night.  The burner has an LED on it that lights up when the =
burner
is running.  I slipped a short piece of tubing over the LED, and put an =
IR
sensor from Radio Shack in the other end of the tubing.  The sensor is =
the
same shape and size as a standard LED.  The LED puts out just enough IR =
for
the sensor to detect it.  The sensor goes between ground and the PIO pin =
of
a DS2405 switch and a resistor goes between +5V and the PIO pin.  I had =
to
play with the value of the resistor to get it to work.  Too low and it
wouldn't trigger when the LED came on, too high and it would think it =
was
always on.  I ended up using a 43K resistor.  The tubing I used to hold =
the
sensor on is white, and I had to put a bigger piece of black tubing over =
it
to prevent the fluorescent lighting from intermittently triggering the
sensor (I don't have any black tubing handy that's the right size to =
slip
over the LED and sensor by itself).=20
This same technique could be used with anything that has an LED.  Some =
put
out more IR than others, and in fact the green one on my boiler puts out
considerably less than most of the others I was playing with.  If it =
emitted
more IR I could reduce the sensitivity with a smaller resistor and I
wouldn't need the black tubing as a light shield.=20
A CDS cell could probably be used instead of an IR sensor, but the need =
for
light shielding would probably be greater then.
Anyway, I thought others might find this useful or interesting.

-Ben=20