Circuit for switch between daytime active ON and OFF


I'm trying to make an LED come on when dark but have the option (via a switch) to make it stay on. I'm really confused about what type of switch to use and have to rig it up.

The following website has a dark sensor that I got to work, but trying to add a switch to it has proved mindbending.

Any ideas thanks?!

In the dark, the LDR is high resistance, so the transistor base gets the 9V and the LED goes on. So for your switch to put the LED on, you need to make it as if the LDR is high resistance even if it's light. So, a switch in series with the LDR will make it seem that it's dark

Thanks. Glad there is a simple solution. Just before I checked back here I went and set it up real fancy using a DPDT switch! At least I learned how to use them now :o

You can verify my idea by just disconnecting the ldr, of course....

It worked a treat, but without the dark sensor I was getting 480 mA into my LEDs. Now I'm only getting about 220 mA. I even tried a TIP120 instead of the BC547.

I am not using a resistor on the LED

I am not using a resistor on the LED

You must.... LEDs only handle something like 20mA.

With 9V supplied and about 2V across the LED, you need to drop 7V over the resistor. R=V/I so 7/0.02 = 350 or so.

It's a 12V RGB+W LED string 1m long. Connected through an LED controller it draws 610 mA. Not sure why I'm losing about 400 mA through the dark sensor. This power is reduced even when I flick the switch.

Worked it out lol. Even just 1 cm travel through my breadboard creates the bottleneck.