Dark-Activated Switch--LDR Project

[DarkVolker]

I've been wanting to work on some kind of small project to build something useful. I've decided that I'm going to build LDR switch circuits so that my outside lights turn on when it is getting dark outside. I've got a basic schematic of how to accomplish this, but I am going to need help on the values of the components so that the circuit turns on at a specific level of darkness.

I need to know how to calculate what resistors I need and the specs of the photoresistor.





Oh and I forgot to mention that I am hoping to make this on as small of a PCB as I can manage. I am thinking I can make this really small. Do I really even need a PCB though?

[kam]

well, replace the 100K resistor with an 100K potentiometer first. This will give you freedom to setup the brightness. Also replace the 330ohm resistor with a smaller one, such as 220 or less. Also, add a 1K resistor in series with your potentiometer to prevent overcurrent through the base. And you are done.

[DarkVolker]

Edited: Please re-read.

With the potentiometer, when you say brightness, are you referring to the brightness level(or rather lack of brightness) that the switched light will turn on at? I don't want to control the brightness of the light, I just want that on or off....I want to control at what darkness level the light is turned on and what brightness level it is turned off. I'd also like to add a delay somehow to prevent lightning strikes or car headlights or whatever from making the light turn on or off.

Thank you for your help so far.


Edit: I forgot to ask about the power rating of the resistors and pot I should get. This project will be turning a 13W/120V compact fluorescent bulb on and off. Should I base the amount of watts my resistors need to be able to handle on the load of the lightbulb it is switching on?

I have some ideas, but I'm not exactly sure about how to have this circuit allow or block the 120VAC power from getting to the light socket. I might have the design all wrong for this application.

[cheerio]

put this in front of the resistors base
http://en.wikipedia.org/wiki/Schmitt_trigger

i think kam has a circuit on the page that behave like a schmitt trigger

[DarkVolker]

That is a little beyond my knowledge of this type of basic electronic circuits. I'm in network administration now so I do mostly troubleshooting on networks. I've always been interested in this type of thing and have actually made a few very basic circuits in the past, but that was a long time ago. I'm planning to go back to school and get a bachelor's degree in computer engineering(hardware not software). So, I took on this project so I can freshen up what I already know and learn some new things. I will probably do lots of projects as long as I can think of good applications for them and actually use them after they are finished and working.

So am I on the right track for what I want to do or am I way off?

[cheerio]

if you want to switch on or off depending on the daylight you need a switching circuit that behaves like a schmitt trigger. you can buy such a thing as a IC or you can read the wiki page and implement this:

the vout would connect to your transistor base
the vin would connect to where your transistor base is connected now

[kam]

Here you are

http://www.pcbheaven.com/circuitpages/Simple_Reliable_Thermostat/

R1 will be your photocell. You may want to replace R2 with a bigger one depending on your photcell. R3 controls the hysteresis. R5 sets the brightness level for ON/OFF

[DBoulanger]

It's sad to see that the author of this topic never came back with additional questions or suggestions.

It is also disappointing to see the type of help that was provided.  Let's face the facts, the original author was planning to control a 13W/120V fluorescent.

Nobody mentioned the need of some extra components such as a relay for instance.  The triggering aspect was somehow addressed, but not as clearly as a newbie would have expected it.  Referring people to external sources is a good idea, although it is mandatory to ensure that the basic concept is understood first, no ?

No wonder why this topic aged without any valid conclusion.

[MarvKern]

Hi..i am a hardware design engineer. I worked on many basic projects and as per my knowledge replace the 100K resistor with an 100K potentiometer first. This will give you freedom to setup the brightness. Also replace the 330ohm resistor with a smaller one, such as 220 or less. Also, add a 1K resistor in series with your potentiometer to prevent overcurrent through the base.

complete pcb