Using AC for LED Christmas Lights

Posted on Feb 7, 2014

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 their photo-transistors effectively connected in inverse-parallel. Depending on which optocoupler is turned on, the Triac applies positive, negative

Using AC for LED Christmas Lights
Click here to download the full size of the above Circuit.

or both half-cycles to the LEDs and so the colours can be red, green or in-between. Switch S1 is used to select the pulses from two oscillators which are formed by the NAND gates in IC1 (4011B). This provides a variety of LED flash patterns, depending on the setting of S1.

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