Why don't your Christmas lights work? Sadly, in the event of a string of lights going out on your tree, replacing the strand is usually the best option. It's pretty difficult to find that one bulb ...

This circuit uses low-voltage AC to drive a string of 50 or so bi-color LEDs (two LEDs connected in inverse parallel). Power to the LEDs is controlled by the Triac and the two optocouplers which have ...

Editor's Note: Here's another take on the transformerless AC line power supply, which finds use in some well-insulated, low-power devices. Our technical reviewer pointed out that C ac should be an ...

A 6-V battery powers a circuit with parallel branches on a board. Several wires and light bulbs plug into the board to make various series and parallel circuits. The brightness of the bulbs changes ...