# Help with LED lighting solution

#### MincePie

Joined Jan 20, 2016
3
Hey guys, I'm relatively new to circuitry (complete beginner ) and I am requiring some help with a LED lighting project.
The main aim of the project is to create a circuit that lights up an LED using a rotary switch to chose between 1 of 3 circuits.
1) a LDR that powers the LED when activated with light
2) a LDR that powers the LED when there is no light
3) and the 3rd mode provides constant power to the LED.

I was hoping that someone could help me work out a circuit that could do this, The main bit that I need help with is connecting the 3 circuits together and to the switch so that they can power the LED. I can already build the LDR circuits but if anybody has any suggestions for LDR circuits they would also be appreciated.
Cheers Tom

#### mcgyvr

Joined Oct 15, 2009
5,394
Your request while fairly simple is still a bit confusing..
How are #1 and #3 different?

You always want to feed an LED with constant current as they are not resistive loads like many other devices (lightbulbs,etc...) and will not just "draw" what they need from the power source.

#### Dodgydave

Joined Jun 22, 2012
9,854
No problem, what voltage supply are you using, what led type is it, ie current required.

#### mcgyvr

Joined Oct 15, 2009
5,394
oh.. I might get it now.. had to re-read it a few times
When mode 1 is activated the LED will ONLY light when the LDR is receiving light vs when mode 3 is on the LED is on regardless of the LDR

and maybe share your LDR circuit for critique..

#### Bernard

Joined Aug 7, 2008
5,719
Try this:
Use a 555 IC as comparator. SW in light pos., Lt, & LDR is in light pins 2 & 6 will be high, pin 3 low, LED lit.
SW in dark, Dk position , & LDR in dark, pins 2 & 6 will be low, 555 is set, pin 3 high, transistor on, LED on.
SW in O n , LED on.

#### MincePie

Joined Jan 20, 2016
3
@Bernard - thank you very much,with my limited circuitry knowledge I was able to identify the rotary switch, 555 IC timer, LDR and a resistor and transistor.
Would it be possible for you to label the different components or or just list the components you used?
@mcgyvr You are correct and I will draw it out and upload the circuit diagram later.
@Dodgydave I will be using 5v.
Thanks

Last edited:

#### Dodgydave

Joined Jun 22, 2012
9,854
Yes its a 555 chip, if your in the uk try cpc ( Farnells).