im trying to make a set of 10 LED's that will run on a 9V battery. i want it to brighten up when it gets darker like a lamp post and to be able to turn on/off and off with a 3 way slide switch. what size variable do i need and what kind of LDR to make it work without it turning on in the day?
they white superbright LED's with 470r resistors conected to each leg, it will only be turned on for about 3 hours a day so ideally, the battery should last up to 3 weeks.
you can't just put the LDR in series with the leds you will need an appropriate control circuit, battery life may be extended by using a comparator circuit to totally shut off the current so that your not in the position where the leds are just slightly on using current but have nothing to show for it.
A new 9V alkaline battery will supply 120mA and will last for about 4 hours with the LEDs dimming all the time.
A rechargeable 9V Ni-MH battery will last for about 1 hour for each full charge.
Four AA alkaline battery cells make 6V when new and will supply 120mA for about 18 hours.
Here is a circuit that detects light and turns off your LEDs. Simply put the LEDs on the collector of the transistor. You can use either an LDR or photo transistor. **broken link removed**