light sensitive resistor detector circuit

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
forrestgump
Posts: 24
Joined: Mon Feb 11, 2002 1:01 am
Location: Nova Scotia, Canada
Contact:

light sensitive resistor detector circuit

Post by forrestgump » Fri Nov 08, 2002 6:31 am

Hello I know I have the schematic somewhere in a book on how to build this simple circuit but can not seam to find it. I know there are kits out there to purchase but I believe I have all the parts necessary already. <p>I have a water pump under my house in a little insulated box; however it sometimes freezes so I installed a 40Watt light next to the pump to keep the pump from freezing. The problem is no matter what light bulb I get they don't last the winter. So I would like to build a small circuit using light sensitive resistor and transistors to tell me if the light is working or not. I would like the have a green led if the light bulb is still on and a red if it went out. I have easy access to AC mains so I could power the circuit using a wall wart. Thanks for your help in advance. I know some of you have this already in you head! <p>
Thanks
Mark Cox
Nova Scotia, Canada

User avatar
Externet
Posts: 1842
Joined: Fri Feb 01, 2002 1:01 am
Location: Mideast USA
Contact:

Re: light sensitive resistor detector circuit

Post by Externet » Fri Nov 08, 2002 8:56 am

Hi.
I do not have the schematic you want.
Any photosensor alone can be read with a meter remotely.
You have to run the signal from the light bulb location to the place you want to monitor its working condition anyway.
Go fancy.
Get a fiber optic leftover piece from the telephone company and touch one end to the lamp bulb and the other end will shine where you want.
If the distance is not too long, some cars do have optic conduits from tail lights to the dashboard to monitor burned bulbs, pull one at the wreck yard. A couple could be joined for longer runs
Miguel
- Abolish the deciBel ! -

Ron H
Posts: 360
Joined: Tue Dec 18, 2001 1:01 am
Location: Boise, ID
Contact:

Re: light sensitive resistor detector circuit

Post by Ron H » Fri Nov 08, 2002 9:17 am

I have a few alternatives.<p>1. Put two 60 watt bulbs in series. The combination will probably dissipate about 40 watts, and they will last a LONG time.<p>2. Use a 60 watt bulb with a series diode like a 1N4004. This will also dissipate about 40 watts, and will last a long time.<p>3. Buy a 100 watt wirewound resistor in the range of 200-400 ohms. This will dissipate P=(120)^2/R (360 ohms will dissipate 40 watts, but that is not a common value), and will last a LONG time.<p>Of course, this still won't tell you if the box is warm. How about installing a remote (wired or wireless) thermometer?<p>Ron

billdar
Posts: 79
Joined: Wed Jun 19, 2002 1:01 am
Contact:

Re: light sensitive resistor detector circuit

Post by billdar » Fri Nov 08, 2002 10:46 am

How about forgetting about testing for the
presence of light?<p>When the bulb goes out, the filiment breaks,
correct? I can't think of a failsafe circuit
off the top of my head, but I would think you
could just sample the voltage accross the
bulb. <p>When the voltage is low, the bulb is good. When
goes high, bulb broke. <p>Maybe could be done with
a simple inverted comparitor. The (-) connected
to the bulb, (+) connected to to a little thevinin
voltage divider as reference voltage. Have an
open drain output connected to the center pin of
a tricolored LED. When high you'd get red/orange,
when low you'd get green/yellow depending on the
LED.<p>I'm sure there is a flaw in that particular ckt,
but the theory would be a little easier to
impliment than photosensors.

Dimbulb
Posts: 324
Joined: Sun Oct 13, 2002 1:01 am

Re: light sensitive resistor detector circuit

Post by Dimbulb » Fri Nov 08, 2002 11:00 am

An op-amp as a comparator goes high or low whenever the input exceeds the reference. The cadmium light cell adjusted to output a normally on condition (green led). The lower limit must be set so momentary change such as power glitch. and the ambient light during the brightest time of day does not effect the current generated in the cell when the heater light is on. However a meaningful condition when the light is definitly off is sensed and the op-amp output changes states (Red led). <p>The light cell could be positioned in a short length of PVC with clear plastic lense that is aimed and fixed in position at a safe distance from the heat/light source while minimizinge stray light such as spider shadows or other a mouse getting toasty.<p>Another sensor design uses only a thermistor epoxied to a short piece of copper pipe located near the light bulb and two wires extended to an inexpensive resistance meter which gives you a close approximation of the temperature of your pump. A red line is drawn on the meter. This gives you more information about the freezing conditions at a remote pump.

Dimbulb
Posts: 324
Joined: Sun Oct 13, 2002 1:01 am

Re: light sensitive resistor detector circuit

Post by Dimbulb » Fri Nov 08, 2002 12:06 pm

Going further with the thermistor.<p>If you want to take the project to a higher level
you could calibrate it by putting the small copper tubing and thermistor in a bowl of water with ice cubes and record the resistance also there usually is a chart that tells you approximate temperature value equivalents.<p>Further a dpdt switch is installed that takes the 2 wire thermistor to a small circuit which deals with milli-volts instead of resistance.
a very small stable current from 2 C cells is fed through the thermistor the mV or uV is amplified and can turn on an led or buzzard. You can flip back to resistance(temperature) for adjustment and reading the temperature.<p>LM385 1.2 V and a 10 K pot used as a voltage divivder coming off your 2 C cell pack would be precise and steady constant voltage source.
If you get this far at a hands on level then come back and ask this forum more specific questions.
My approach is that since you seem earnest are ready to make application or will you rangle in design without a tangible platform to motivate the completion. A schematic can sometimes be to rigid while a hands on step by step gives you an intuitive confidence that motivates and makes the project more interesting.

User avatar
MrAl
Posts: 3862
Joined: Fri Jan 11, 2002 1:01 am
Location: NewJersey
Contact:

Re: light sensitive resistor detector circuit

Post by MrAl » Fri Nov 08, 2002 2:44 pm

Hello there,<p>Some very interesting ideas!<p>I'd just like to add one more :-)<p>A small current transformer could be
used to monitor the current through the
bulb (or other heat source) by wiring
the primary in series with the bulb.
The secondary would be connected through
a resistor and LED, and the LED would have
a diode connected in reverse to the LED.<p>If the bulb blows out, the current stops flowing
in the primary and so the current stops flowing
in the secondary so the LED goes out.
The transformer also provides for electrical
isolation from the 120vac mains, so the LED
circuit is not in contact with the dangerous
120vac supply.<p>Total parts count comes to four parts:
1. Current transformer
2. 1/4 watt resistor
3. 1N4001 diode (or equiv)
4. LED (any color)<p>BTW, i built this very circuit once to monitor
an electric coffee maker. When the coffee was
done, the LED would go out because the coffee
maker would turn off via it's own internal
thermal switch. Once current stops flowing,
the secondary current drops to zero turning the
LED off.
This also works for monitoring other ac devices
too without introducing appreciable resistance
in the primary circuit.<p>If you cant find a current transformer, you can
probably get away with taking an older small
transformer used for 6v or something, and
wind a few turns around the core to form the
primary. The 120vac winding would be used as
the secondary, while not using the original
6v (or whatever) secondary.<p>Good luck with your circuits,
Al
LEDs vs Bulbs, LEDs are winning.

greg123
Posts: 361
Joined: Sat Sep 07, 2002 1:01 am
Location: St. John's NFLD Canada
Contact:

Re: light sensitive resistor detector circuit

Post by greg123 » Fri Nov 08, 2002 3:21 pm

Just my two cents......<p>Couldn't you put a photoconductive cell in a resistor bridge (voltage devider) so that when the light is on vs off the output voltage is different. You could then connect this output to a comparator with the threshold set at the voltage at where the bulb is on or off. The ouput from this could be used to drive an led to show weather the bulb is on or off.

Ron H
Posts: 360
Joined: Tue Dec 18, 2001 1:01 am
Location: Boise, ID
Contact:

Re: light sensitive resistor detector circuit

Post by Ron H » Fri Nov 08, 2002 4:00 pm

Two more cents...<p>Some of these ideas are good. I especially like Al's current transformer and Miguel's light pipe.<p>Regardless of what sort of failure sensor he uses, it seems to me that heater reliability is a problem. I would much rather change a light bulb under a house at my leisure, in the summer, than HAVE to do it in the dead of winter. If he uses one of the suggestions in my previous post, he can do routine maintenance annually. If he uses a power resistor(s), the heater will probably outlive the pump.<p>Cheers, y'all-
Ron<p>[ November 08, 2002: Message edited by: RonH ]</p>

josmith
Posts: 340
Joined: Tue Dec 04, 2001 1:01 am
Contact:

Re: light sensitive resistor detector circuit

Post by josmith » Fri Nov 08, 2002 4:20 pm

Move someplace warmer

forrestgump
Posts: 24
Joined: Mon Feb 11, 2002 1:01 am
Location: Nova Scotia, Canada
Contact:

Re: light sensitive resistor detector circuit

Post by forrestgump » Sun Nov 10, 2002 3:01 pm

Lots and lots of Ideas I like Externets nice simple idea of using a piece a fiber optic. I think I have an old piece at work left over from a 10baseT fiber connection? But If I can’t find a piece I think I like MrAl’s idea seams quite simple using the secondary of a transformer. All of them sounds good but I don’t have a lot of experience with op-amps etc so simple is good for me! Of coarse Joesmith has a good Idea to move somewhere warmer! Canadian winters can be cold! Thanks for all the replies I really appreciate the help and info sort of makes you think with all the great ideas what a group of professionals could accomplish if all worked on 1 project! Hmm now there’s an Idea “Online inventors” Thanks again I will let you know what I’m using soon!<p>Mark
Nova Scotia, Canada.
[email protected]

forrestgump
Posts: 24
Joined: Mon Feb 11, 2002 1:01 am
Location: Nova Scotia, Canada
Contact:

Re: light sensitive resistor detector circuit

Post by forrestgump » Mon Nov 11, 2002 5:49 pm

I actially did something a bit different, well what i was looking to try in the forst place. I made a small circuit using a photoresistor a 2n2222 2 led's 100k pot and 2 1k resistors to protect the leds and a 9v 350ma wall wart. the circuit activates a led when there is no light beening picked up by the photoresistor. I put a green led in parellel to the 9v supply with a 1k resistor to let me know the circuit is getting power. Anyway a ver simple project but for me it was great! Anyway thanks again for your ideas!<p>Mark

User avatar
Edd
Posts: 885
Joined: Sun Jan 27, 2002 1:01 am
Location: Dallas Tx
Contact:

Re: light sensitive resistor detector circuit

Post by Edd » Tue Nov 12, 2002 9:43 pm

OKJello:
Looks like U finished up before I even read Ur post, but sounds like U had to
remote it to get its photovoltaic sensing , unless you are visually confirming
the LED’s states from afar.
My slant on the solution would have been to detect lamp/circuit
continuity,using 5 cheap, common components.This could be placed at the power source
in a very small insulated box, or by virtue of being so small, built inside a
larger heat shrink tubing shroud. The circuit would consist of the AC lines hot
side feeding one lead of a 100w lamp the lamps other lamp lead would then go to
the positive leads of a pair of shunted 1N4007 diodes with the diodes other
leads going to the AC lines low side.This runs the lamp at ½ voltage for long
life/reliability.
(The shunted diodes give a 2x current cushion and the 7 series of the diodes
give a PIV cushion.) For indication a sample is taken from across the shunt
diodes.The neg term of a LED goes to AC low side then its pos term goes to a
7500 ohm 1w resistor (or 2 shunted 15k ½ w units) the res then feeds to the
cathode of a 1N4007 with its anode then connected to the common cathodes of the
shunted 1N4007’s. The current limiting res for the LED may require some tweaking
in accordance with the LED type/current specs or if an even lower degree of
luminosity is desired.
The electronics would be in a sheltered area at the AC source, and if the
lamp had to be remoted an extension cord could make one connection at the AC
line gnd and its other connection at the common diode cluster apex.If using
an extension though, from the safety factor and prevalent codes, one might
well place a 1a fast blow fuse in line at the AC hot side as well as a 130-150v
MOV across the complete AC line just past the fuse. An unlit LED is indicative of
an open lamp ckt or a power outage.
AC Hot IN..................................AC Gnd In
....O..........................................O
....|...........................................|
[1a Fuse](opt).............................|
....|................(opt)....................|
....|---------/[MOV]/--------------|
....|...........................................|
[100wLamp]................................|
....|.............(2x)........................|
....|_ _ _ _[1N4007]_ _ _ _ _ _ _ _ |
....|......(+).........(-)...................|
....|..........................................|
....|_ [1N4007]_ _/\/\/\/\_ [LED] _ |
,......(-)....(+)..7.5k 1w....(+)...(-).....

73’s de Edd
[email protected] (Interstellar~~~~Warp~~~~Speed)
[email protected] (Firewalled-Spam*Cookies*Crumbs)<p> ;)<p>[ November 12, 2002: Message edited by: Edd Whatley ]</p>

User avatar
Chris Smith
Posts: 4325
Joined: Tue Dec 04, 2001 1:01 am
Location: Bieber Ca.

Re: light sensitive resistor detector circuit

Post by Chris Smith » Wed Nov 13, 2002 11:22 am

With out re-inventing the wheel, or spending more than a buck or two, my 400 ohm power/100 watt resistor is on its third year, keeping the pipes from freezing. We get up to minus 24 degrees F. <p>"K-I-S-S" is always best.<p>Keep,...
it,...
simple,...
stupid,...<p>always a first choice in cold weather.

User avatar
jollyrgr
Posts: 1289
Joined: Thu Jan 03, 2002 1:01 am
Location: Northern Illinois
Contact:

Re: light sensitive resistor detector circuit

Post by jollyrgr » Wed Nov 13, 2002 10:19 pm

I like Chris' solution. But I have a suggestion that might prove useful. Convert the AC signal going to the lightbulb to DC. This makes lightbulbs last significantly longer. The two lights on the front of my garage use photosensors to turn them on at night, off during the day. The photosensors output rectified (DC) current to the lightbulbs. One bulb is still there from March 1999 when I installed the photosensors. The other lasted until just this past August. For your setup I would just install a single diode in series with the light bulb. You'll probably have to use a 60 or 100 watt bulb in place of the 40 watt as the diode will cut the output to less than half of what it is now. Use a diode that can handle a couple of amps.<p>Also, you could use a light dimmer to lower the output to a larger bulb. Thus use a 100 watt bulb but use a light dimmer to lower the output.<p>If you want to still make a light alarm, what you want to do is use two transistors wired as a DARLINGTON PAIR. The input of the "BASE" is a voltage divider that consists of a CdS cell and a potentiometer. If you want I can send you a basic schematic of this circuit. While I can't give you specific values for your project, I can give you the basics to get started.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

Post Reply

Who is online

Users browsing this forum: No registered users and 8 guests