Making a light switch

Thread Starter

Quillion

Joined Jul 18, 2009
10
So I am currently trying to make light operated alarm clock, and I already managed to get the most annoying noises possible using 2 piezo buzzers and 2 555 timers, but now I need the switch that would activate the alarm.
So here is where I am stuck.
How would I get a photoresistor to act as a switch without the use of microcontroller?
I need it in such a way that when it reaches certain light level, then electricity will pass, and if its dark then it does not output any electricity.
I did some research and found out I have to use PNP transistor, but I am still stumped and have no idea how to use it, please help me
Thanks to everyone in advance who helps
 

spinnaker

Joined Oct 29, 2009
7,830
So I am currently trying to make light operated alarm clock, and I already managed to get the most annoying noises possible using 2 piezo buzzers and 2 555 timers, but now I need the switch that would activate the alarm.
So here is where I am stuck.
How would I get a photoresistor to act as a switch without the use of microcontroller?
I need it in such a way that when it reaches certain light level, then electricity will pass, and if its dark then it does not output any electricity.
I did some research and found out I have to use PNP transistor, but I am still stumped and have no idea how to use it, please help me
Thanks to everyone in advance who helps
I'm just a noob too but did some searching for you and found this.

http://www.scribd.com/doc/23891342/Photoresistor-Transistor-and-LED-s

If it is higher current and voltage you want to switch on and off then you could replace the LED with a solid state relay (which is actually a LED to control the "switch").

Hopefully one of the more experience forum members will weigh in and I have not set you too far astray. :)
 

Thread Starter

Quillion

Joined Jul 18, 2009
10
Thanks a lot to everyone for your amazing help, it was very very awesome and I managed to build it very well, now I wake up every time with the sun, which is perfect since all my uni classes are in the mornings:p
There is only one problem though, now whenever, someone turns on the lights(in a room near me) my alarm turns on right away. Is there any way to make it turn on a after significant amount of light falls on it rather than when it sees light it gets noisy

But holy crap I think I created something that is sexually attracted to light hehehehe
Thanks a lot guys
 

KMoffett

Joined Dec 19, 2007
2,918
You can also collimate the light sensor to shield it from room light. Place it in a tube of about the same diameter and aim the tube out the window. Should work better...assuming it's not pointed at a street light. ;)

Ken
 

VoodooMojo

Joined Nov 28, 2009
505
this is cool..

years ago my dad bought me a beautiful expensive pair of binoculars.
we lived at the time in the most awe inspiring part of the planet. So exploring the vistas was a way of life.

anyway, one day I dropped my precious binoculars and whew, luckily I didnt break any lenses or mirrors. But everytime I looked through them for more than a minute, pow, big headache.

pops sent them in for repairs. When they came back repaired (and working well) I looked at the repair ticket and learned the same word. Collimate.

I have been waiting for over forty five years now to legitimately use the word collimate in a sentence.

thank you for the fond memory and the chance to share it!
and one more time....collimate...
 
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