Using an LED candle timer circuit in other projects

Thread Starter


Joined Oct 15, 2018
I have a lot of LED candles, signs, etc, that do not have built in timers. Some of them are in places where it would be far more convenient to have one.

Plastic LED Christmas candles, as shown, contain this circuit board. They run off 2xAA batteries and shut off after 8 hours and then turn back on in 16 hours. In the past, they used to contain an amber flicker LED. In the past 5 years or so, they instead contain a dull neutral white LED which looks even dimmer (running off 3v) and less realistic than if it used amber. But I thought the circuit might be useful.

Testing this circuit by clipping off the LED, then connecting 3xAA rechargeables (tested 3.9v fully charged) to the underside (soldered some wires onto it and clipped to a battery pack) while using a multimeter on the remaining LED legs (positive is the leg closest to the crystal oscillator) reveals no voltage drop. So I connected the circuit to two old LED candles (not the same type) that take 3xAA, again connecting the surface on the bottom to the wires coming from the battery case, and then the other ends of the cut wires that lead into the candles (not designed to be easily disassembled, so I'm not sure if there's a circuit board in there or just LEDs with resistors) to the leads from the clipped off LED.

They both turned off earlier than 8 hours, one about 4 hours, the other about 6 hours. Strangely, I turned one back on by flipping the switch. The other one would not turn back on. I was worried I had accidentally short-circuited something, but removing a battery and putting it back in enabled the on/off switch again, so it seems that the timer circuit board was stuck in off mode?

Is using it in 4.5v (somewhat less if using rechargeables) powered items changing the timing of the crystal oscillator? While it would be nice to have a shorter timer, since if I want something to turn off before midnight I have to turn it /on/ before 4PM in the afternoon, I'm assuming that any timing errors also mean that it will no longer be on a 24 hour cycle.

ledcandles.jpgtimercircuit1.jpg timercircuit2.jpg