How do alternating Christmas tree lights work?

Question

I saw these alternating Christmas lights:

The top image has all lights on, the bottom left image has odd-numbered lights on, and the bottom right image has even-numbered lights on.

The LEDS are joined by two enameled wires, and three AA batteries power the lot.

How does the controller turn the odd-numbered lights on and off?

Dave Tweed · Accepted Answer · 2019-02-07 17:05:27Z

5

These kinds of lights have LEDs connected in an alternating polarity fashion. Take look at the following circuit.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Lights with this kind of configuration are cheaper to make and adequately serve their purpose.

The controller is able to power the LEDs in the following two ways to create the effect:

Dave Tweed

171k17 gold badges230 silver badges396 bronze badges

answered Feb 7, 2019 at 16:52

Electric_90

2,12214 silver badges25 bronze badges

2

\$\begingroup\$ Actually, it's probably AC all the time, and the controller just plays with the duty cycle in order to create a cross-fade effect. \$\endgroup\$
– Dave Tweed
Feb 7, 2019 at 17:07
\$\begingroup\$ Cheaper to make than what? \$\endgroup\$
– Misunderstood
Feb 9, 2019 at 0:59
\$\begingroup\$ @Misunderstood, cheaper than using something like addressable leds for the same effect. \$\endgroup\$
– Electric_90
Feb 9, 2019 at 4:17
\$\begingroup\$ I got hold of the lights and the power supply plugs directly to the power outlet. The sign says "U_rated=4.5V~ U_out=4.5V~" and "Combination in waves: sequential, slo-glo, chasing/flash, slow fade, twinkle/flash, steady on." I hooked a multimeter on AC voltage and I measure between 0 and 2 volts most of the time, except some 0 voltage at some points when the lights are on, so I assume those have DC. \$\endgroup\$
– miguelmorin
Feb 14, 2019 at 23:15
\$\begingroup\$ @DaveTweed How can I test your explanation with a multimeter? \$\endgroup\$
– miguelmorin
Feb 19, 2019 at 22:32

| Show 1 more comment

1 Answer 1