light sensitive resistor detector circuit

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Dean Huster
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Re: light sensitive resistor detector circuit

Post by Dean Huster » Sat Nov 16, 2002 9:57 am

Bildar, if your house wiring allows you do see a change of voltage across a lamp when it's on and when it's off, I'd be pretty worried about my house buring down! Your wiring should be stout and low-resistance enough that the additional 400 ma or so that a 40-watt lamp imposes shouldn't cause any easily-measureable change in voltage at all.<p>Ron, your original post's last idea I think is best. Just monitor the temperature. That will solve a couple of problems: (1) a lowering temperature on moderate days signifies a bad lamp; (2) on the days when the temperature really drops low outside and the 40-watt lamp can't compensate, the thermometer will alert you to a freezing danger and you can temporarily swap out the lamp with a 100-watt lamp, 200-watt lamp or 1500-watt screw-in heating element (with the proper fixture, of course!).<p>I wonder, though, Ron, (and let's equalize the situation) if two 100-watt lamps in series will be any more reliable than a single 50-watt lamp. As it is, lower-wattage lamps are longer-burning anyway. It's likely that they will individually last longer since incandescent lamps running with severe under-voltage have tremendously-longer lives, but on the other hand, you're inserting the odds of TWO lamps where the failure of either one will bring the whole system down.<p>You know, LEDs are a lot more reliable ... ;) <p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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Dean Huster
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Re: light sensitive resistor detector circuit

Post by Dean Huster » Sat Nov 16, 2002 10:01 am

Ooooh! Just thought of a super-cheap indicator. Use Ron's two 60-watt lamps in series. Then across ONE of those lamps, wire a 7-watt, 120-volt night light lamp and install this small lamp where you can see it glowing. Then if either 60-watt lamp goes out, the night light goes out. No fancy electronics needed here.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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Chris Smith
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Re: light sensitive resistor detector circuit

Post by Chris Smith » Sat Nov 16, 2002 12:33 pm

Dean, thats three rusty sockets that can fail! <p>One power resistor, works for years and years and years! 40 to 100 watts works for most cold climates, keeping things above 32 degrees is all it has to do, and a sealed box [or foam] around the pipe does 3/4 of that. <p>Water under 40 PSI also wont freeze at 32 degrees.

Ron H
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Re: light sensitive resistor detector circuit

Post by Ron H » Sat Nov 16, 2002 8:42 pm

Dean, it's kinda late here. I should be going to bed now, so my thinking may be even fuzzier than usual. Could you explain how the nite lite scheme works? It seems to me that when both 60w bulbs are good, the nite lite has a little more than half the line voltage across it, and glows dimly (maybe). If the bulb it is wired in parallel with burns out, the nite lite gets most of the line voltage, and glows at near-normal brightness. If the other bulb burns out, the nite lite extinguishes. Maybe I'll see the lite in the morning, after a good nite's sleep.<p>I agree with Chris (I made the same suggestion). Use a 100w resistor that's dissipating 40 to 60 watts. It will put out the same amount of heat, and should last indefinitely. Of course, if one wants to feel really secure, install a remote-reading thermometer.<p>Ron

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dacflyer
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Re: light sensitive resistor detector circuit

Post by dacflyer » Sun Nov 17, 2002 10:13 pm

hey heres one for you,,, cannot find long life bulbs?
how does 8,000 hrs sound?
i work in traffic signals here in my city..
we use 2 different kinds of lamps,,
1 is 116 watts , other is 169 watts..both rated at bout 8k hrs.. we have some 67 watt ones left too...were replacing them all with LEDS now..
contact me @ [email protected] if interested,,,<p>also heres easiest of all light meter too if you like<p>4 parts only !<p>1 wall-wart
1 led
1 resistor
1 foto cell..
all parts can be gotten from radio shack
foto cells come in a varity pack too...
wire them all in series...watch polarity and voltage... very simple...

Dean Huster
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Re: light sensitive resistor detector circuit

Post by Dean Huster » Mon Nov 18, 2002 8:39 am

Duh! Ron, I don't know what I was thinking. I was painting earlier today and fumes must have affected my thinking. What the night light will do is glow dimly when both lamps are good, blow brightly when the lamp it's across opens up and go out when the other lamp opens. Hey, it's even better than I thought! A simple three-component scheme that provides all kinds of information!<p>Chris, with this project, we're going to use brass-base lamps and solder our connections to them and not use sockets at all! No rust or corrosion problems then.<p>I suppose that if you're going to use one of those expensive, high-power resistors in there, you might as well just get a 300-ohm resistor rated for 100 watts and just slap it across the line. It'll just sit there and sputter out 50 watts or so and probably never need replaced or monitored. There: a one-part solution.<p>Say, has anyone ever considered heat tape around the pipes and tank? No power consumed at all until the temp drops below 35° or so.<p>This all kind of reminds me of the guy who wanted to electronically monitor exhaust temperature, head temperature, crankcase temperature, engine RPM, battery voltage, battery current, blade #1 RPM, blade #2 RPM, ground speed, fuel level, fuel flow rate, estimated-time-to-empty, etc. on his riding mower. Plowed through half of the shrubs around his lawn before he quit reading the meters and started paying attention to mowing.<p>Say, just thought of another option. Put a doggie door into the space and get a really big dog. He'll appreciate the relatively warm area there vs. out in a cold, drafty dog house and his body heat will keep things thawed.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

billdar
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Re: light sensitive resistor detector circuit

Post by billdar » Mon Nov 18, 2002 12:28 pm

Dean:<p>Sorry, been gone a little while and jumping back
in late.<p>All I was saying is to think about the bulb as
a switch. If the bulb is lit, the switch is
closed and (here you're correct) you shouldn't
see any voltage.<p>But if the bulb goes out, the switch opens and
there _is_ a voltage across it.<p>I hope Im not wrong in this one... It's not as
elequent as using the transformer, but the theory
should be correct...

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