# Simple but big circuit Challenge to all

#### Chris15

Joined Apr 15, 2009
252
Hi
Bear with me as i explain my tricky circuit and what i want it to do:
Ok, my dad gets up at 4:00AM every morning and it is very dark, when he is walking through our sunroom to the door to get to his car it is dark, he cant turn the lights on because he wont be able to turn them off without having to walk through the dark, i have made a timer circuit with a relay thet turns a 50W light on from 1 min to 16min's, i want 3 light activated switches to do this:
1) When the lights in that same room are on i want the LDR to turn my circuit off so you can walk around that room without wasting the batteries.

2) another LDR outside so when the sun has risen enough the circuit will turn off so people can walk aroung in that room without having to turn the circuit off and when it is dark the circuit is reactivated.

3) i want the last LDR as a trigger to the circuit so that when my dad walks through the laser beam the curcuit for my set time limit.

the curcuit seems simple but is tricky putting it all together, all the LDR switches i beleive should have relays. IMPORTANT this is another important point: i want the circuit to run off a plug pack not batteries (for obvious reasons) i have been told that with the 14VDC 450mA plug pack i need a voltage regulator with two capacitors and a 27Ω resistor, but i need the wiring diagram im not sure how to bring this voltage from 14V and 450mA to the 12V the circuit alone needs but the light i am using is 50W so i need to know how how much the circuit draws with a multimeter.

If someone could help please. (If you could please i need an answer quick because i have been at this circuit for ages trying to figure it out myself but cant plus my dad has fallen over multiple times)

Thanks, Chris

#### Wendy

Joined Mar 24, 2008
21,840

#2, you can buy off the shelf a photocell circuit that will turn the light off with sunlight very cheaply. It fits between the light bulb and the socket.

One suggestion, make a simplified layout to do this, and figure out where the sensors are to be. The rest is gravy.

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#### Oxbo Rene

Joined Feb 20, 2009
200

#### Wendy

Joined Mar 24, 2008
21,840
Oh, you mean a photocell, aka electric eye, aka CDS cell. Never heard the LDR designation, though I've played with them a lot over the years, and have 20 or so in my junk box.

#### KMoffett

Joined Dec 19, 2007
2,765
Chris,
i have been told that with the 14VDC 450mA plug pack i need a voltage regulator with two capacitors and a 27Ω resistor,
Check your other thread. My comment on the 27Ω resistor was just to test the wall wart for regulation.

Is this thread something entirely different than that thread, or part of the same project?

Ken

#### Chris15

Joined Apr 15, 2009
252
OK
Bill LDR (light dependant resistor) resistance changes depending on the light or darkness.

Oxbo, yes that is the right one

and Ken yes this is the same as the circuit on the other thread and sorry ill check the other thread

#### KMoffett

Joined Dec 19, 2007
2,765
Chris,

It helps if you keep all parts of a project in one thread. It's much less confusing for those who try to help.

Ken

#### Oxbo Rene

Joined Feb 20, 2009
200
Oh, you mean a photocell, aka electric eye, aka CDS cell. Never heard the LDR designation, though I've played with them a lot over the years, and have 20 or so in my junk box.
Yes Bill, you must learn to be "Politically Correct" these days.
Whomever is up there that makes these changes in terminology for the rest of us to live by, is always more better correct, etc.
Kinda like changing cps to Hz, it all makes perfect sense

#### steveb

Joined Jul 3, 2008
2,431
Sometimes they are your friend. I've noticed that technical proposals with acronyms get funded more often.

Whenever I propose a new device or idea, I give it a fancy acronym. Originally, I did this to save space and not have to write out long strings of words, but now I see is lends a degree of credibility to something new and unproven. When possible, I try to throw in the initial Q for quantum. For some reason, people are very impressed when they see this word even though it just means "a small amount". Hey, a dose of QBS never hurt anyone.

#### Chris15

Joined Apr 15, 2009
252
So does anyone have an answer to my problem? Apart from Ken i know you are helping me with the wall adaptor, dont worry about this thread if you know you tell me but sorry about making another thread but i wanted you to answer the regulation problem and whilst we figured that out i wanted to see if anyone knew the tricky wiring, i didn't want to ask you too much.

SO ANYONE HAVE A POSSIBLE SOLUTION? SORRY BUT YOU ARE TALKING ABOUT THE LDR/PHOTOCELL NOW THAT WE ALL KNOW WHAT IT IS ANY SOLUTIONS?

Chris

#### Wendy

Joined Mar 24, 2008
21,840
LIke I said, draw a rough sketch of your layout. I think I've answered #2, is there a reason this simple accessory will not work? Last time I bought one they were under \$2.

As for #1, they make IR sensors that fit in the light switches, replacing the existing light switch. They aren't perfect, but they do exactly what you describe, if they "see" a warm body they turn on the lights. I don't see how a photocell will do the job, other than being a door way thresh hold detector. The problems I've run into with the IR sensors is if you sit still for too long they can turn off (but they do have a timer), and if wind comes through the door they can false trigger due to temperature change.

#3 is easy enough, how long is the time limit (variable)?

Something else to consider, X10 makes a bunch of accessories that will allow your computer to turn on or off these kind of devices. Basically we need a bit more input to be able to help coherently. How experienced are you with electronics and house hold currents? The second is a major consideration, unless you are very safety concious you could end up endangering yourself or someone else. I know you intend on using low voltage for the electronics, but ultimately you will be connecting to house lines.

From what I'm reading you may be locking yourself into a box with the solutions. Define the job, then look for a solution, don't try to make the solution fit the job.

You mentioned making a timer, they make simple timers (mechanical) for bathrooms that when you turn the handle they will stay on for however long you set them for, up to 30 minutes. They are used in hotels for energy conservation.

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#### CDRIVE

Joined Jul 1, 2008
2,219
However, I would propose proximity sensors. Out in the VAB near where I work they have proximity sensors that turn on the lights whenever you come to an elevator or bathroom, they work pretty darn good, etc...
I agree. We installed them at my hospital (figuratively speaking.. I don't own it) and they seem to work surprisingly well. Not the endless flood of work orders that I invisioned at all.

Joined Jul 7, 2009
1,577
Chris, I think you're trying to break a peanut with a sledge hammer. Yes, the build-it-yourself electronics stuff is fun, but a good engineer/problem solver always asks some key questions:

What exactly is the problem that needs to be solved? And what constraints must the solution meet?

What are all of my reasonable choices of solution ideas to solve this problem?

Then one goes through various winnowing processes to pick the leading contenders.

From your description, the simplest solution that occurs to me is to add another switch so when your dad exits the room, he can turn off the lights. It sounds like your sunroom wasn't built per the US National Electrical Code (there should be a light switch by each exit). I've got a similar situation in my den in my house when I added on an addition and a new door.

Adding a new switch isn't trivial, as you've got to change from a typical single switch to a two-way switch and the wiring has to change to include a traveler wire both from the old switch to the fixture and the new switch (details will depend on exactly how the light is wired). There are many websites and books that describe what's needed or you can hire an electrician to do it (an anathema for us do-it-yourselfers!). However, some folks do this with wiring channel that can be attached to a surface rather than doing things inside the wall (less work, but uglier). Another method is to use an X10, RF, or IR switch to activate a switch where your original switch is now.

Due to my overwhelming laziness, I like the solution my wife came up with. There's an outlet near the new door and she just stuck a motion-sensing night light in there. Gives me enough light to see exactly what it was I tripped over. Since she probably paid less than a dollar for it at a garage sale, it certainly didn't hurt the pocketbook. Plus, even I could handle the installation.