5. Making an LED Flickering Candle for a Halloween Pumpkin

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Colorful pumpkin lights are very attractive, but constant luminance can be a little boring and artificial. By adding a blinking LED (also called a flashing LED) to the circuit, the pumpkin can appear as if it were lit by a flickering candle.

A blinking LED includes a tiny integrated circuit (IC) built into the LED itself. Most blinking LEDs operate from 3.5V to 9V, but you should ask the seller or manufacturer to be sure.

Blinking LEDs are available in various colors, although red is most common. Expect to pay around $0.60 each per ultra bright flashing LED.

Schematic of a flashing LED in series with two steady LEDs.

Schematic of a flashing LED in series with two steady LEDs.

Where did the resistor go in the schematic? The resistance is built into the blinking LED.

The schematic shows two red-to-green LEDs. But, you can use one white LED or one blue-to-ultraviolet LED in combination with one blinking LED if you prefer.

A single flashing LED causes two steady LEDs to blink at the same time on a solderless breadboard.

A single red blinking LED causes two steady red LEDs to blink at the same time on a solderless breadboard.

You only need to use one blinking LED to control one or two normal LEDs, so long as they are all in the same strand. In fact, it’s a waste to put two blinking LEDs in the same strand. And, sometimes they’ll mess each other up.

Combine a blinking strand of LED lights in parallel with 1 to 4 steady strands for an intermittent change in brightness. If all of the LEDs are the same color, the total light source will appear to flicker. If the flashing LED strand is a different color, then both the overall brightness and color will be altered.

The only problem with using a single blinking LED strand is that the blinks occur at a fairly constant rate (1-3 times a second). It’s not a huge problem; it just looks a little more artificial than a true candle flicker.

For a more spectacular display, make all five strands flash. The variances in the blinking LEDs cause them to become randomly synchronized and unsynchronized. The effect is fun and spooky, for just a couple of dollars.

Click to see a movie of a pumpkin with red flashing LEDs.

Click to see a movie of a pumpkin with red blinking LEDs.

As you can see, blinking LEDs add a lot to the decorative display with very little change in circuitry.

Blinking Color LEDs

Blinking LEDs are available in colors other than red. Using the same techniques presented in earlier LED schematics, you can create an LED circuit that includes a blinking red strand, a blinking green strand, and a blinking blue strand.

Flashing red LEDs control different color strands of LEDs. Black tape covers the red flashing LED for the blue and green strands.

Flashing red LEDs control different color strands of LEDs. Black tape covers the red flashing LED for the blue and green strands.

If you don’t have blinking LEDs in a variety of colors, you can simply use a red blinking LED and cover it with black masking tape for the blue strands and green strands (see above). That way, the red doesn’t interfere with the blue and green colors.

Because the brightness of the tape-covered blinking LEDs is unimportant, use the cheapest blinking red LEDs you can find, such as from BGMicro for only $0.10 each (part #LED1064).

Click to see a movie of a pumpkin with red, green, and blue flashing LEDs.

Click to see a movie of a pumpkin with red, green, and blue flashing LEDs.

Coming up, what can be accomplished in LED lighting with more complex circuitry changes, such as adding a microcontroller?