By using light sensor with transistor switch, you can make a “LED that turns on when dark” circuit without bothering with microcontrollers.
You will need
-1 transistor (BC546)
-1 photocell
– 100k ohm potentiometer
-LED
and pliers and soldering iron.
Here is the schematic
and here is how the components are physically connected..
You should be careful for these points when connecting the circuit. Some of them has directions and it will not work if you connect it the other way around…
This circuit is based on information from following sites. You can also just follow the schematics from these sites, and should work.
http://www.kpsec.freeuk.com/trancirc.htm
or this project is also nice
http://www.evilmadscientist.com/article.php/nightlight
I made a “Granny Throwie” with this circuit, so that the LED will turn on only in dark. I am hoping to send this piece to Stitches on the Bridge project, a massive guerilla knitting over the Skye bridge in Scotland. Perhaps “Granny Throwie” will light up the Skye bridge some day..
[…] Satomi and Hannah Perner-Wilson have posed on ‘How To Get What You Want‘ another variant of this simple sensor using a 100k ohm potentiometer instead of the 1k […]
Suggest you add a current limiting resistor to protect your circuit. There are 2 possible places:
1. Between the top end of the pot and the 3V.
2. Between the base of the transistor and the wiper of the pot.
Otherwise, with the circuit as shown, if you turn the wiper all the way to the 3V, you will either cook your transistor, drain your battery, overheat the battery, or all three at once.
Also, depending on how hard the transistor gets driven, you may want to consider a resistor in series with the LED to avoid cooking that part as well.
Thanks for the suggestion!
The schematics on this post is working (or at least it did not burn or overheat my circuit, yet:), but I am sure there can be some improvement.
This granny throwie lasted several weeks (emitting light only at dark) but maybe it can last even longer.
I will try your suggestion when I get time and post it here.
First of all I would like to say superb blog! I had
a quick question that I’d like to ask if you don’t mind.
I was curious to find out how you center yourself and clear your mind prior to writing.
I’ve had a difficult time clearing my thoughts in getting my ideas out there. I do take pleasure in writing but it just seems like the first 10 to 15 minutes tend to be lost just trying to figure out how to begin. Any suggestions or tips? Thank you!
Hey, I am very excited I located your site. I was looking around for Southern
Africa-related web sites when I landed on your 1. I’m actively considering travelling to South Africa – have you yourself been there? What do you propose I check out? I count on seeing a ton more from you later, so please keep up the great work!
I like it whenever people come together and share opinions.
Great blog, stick with it!
I would like to design LED garden lights with rechargable mobile batteries and I want to control these lights with sensor i.e. when it becomes dark the lights should automatically get switched on is there any circuit for controlling the same.
Hello mates, its impressive post about tutoringand fully explained, keep it up all the time.
my weblog; Mitchell
This website was… how do I say it? Relevant!
! Finally I have found something which helped me. Thanks!
Hello, could please help me? I have a 12v battery and two 12v led lights. Could you tell me how could I do to turn them when there’s dark/becomes night?
What’s up, I want to subscribe for this blog to obtain most up-to-date
updates, thus where can i do it please help.
my weblog; click here