Light controlled tea light

Submitted by patrik on Sat, 2016-01-23 07:18

Electric tea lights are nice but they have a great disadvantage. There are small batteries in the base which dont last long and you have to replace them often. A modification is to remove the small batteries and add an external battery pack. The tea lights work on 3 volt, so two AA:s, rechargeable or not, will do.
I also tried to add a circuit that detects the light in the room and turns the light of at daytime, no need the have the candles lit then. The circuit is designed to draw as little power as possible, otherwise the gain of the power saving would be gone.
I ran this circuit with a tea light and two rechargeable GP Recyko:s in a lamp outside. I thought it would be working for a couple of months as the temperature is low from time to time, several degrees C below zero. But the lamp just kept glowing, it was almost a year and a half before it shut down! Nice indeed.
Here's the circuit used:

"LED4" is the tea light, "LPT80" is a photo transistor.