How to Make Regular Battery LED Tree Lights Flash On & Off

Make this flash.

Flashing LED Christmas lights are more efficient at stealing attention than dull static lighting. Unfortunately, stationary lights may be all that is available. With a little ingenuity and skill, any string of lights, no matter what type, can be transformed into eye-catching, pulsating bulbs.

Things You'll Need

• Electromagnetic relay
• 555 timer IC
• 47 uF capacitor
• 2 resistors, 10K ohm
• Transformer (120V to 12V)
• 7805 voltage regulator
• Generic PCB circuit board (pre-drilled)
• Solder
• Soldering iron
• #30 AWG jumper wire

Instructions

1. Determine the blink rate of the LED lights. There is no theoretical limit to the frequency of flashing. As an example, the calculations used here will assume one blink per second.

2. Select a resistor and capacitor combination which yields the desired frequency. For one blink per second (1 Hz), resistor 1 and resistor 2 should both be 10K ohm and capacitor 1 should be 47 micro-farads (uF). While this is very close to a 1 second interval it is not exact. It is important to realize that no accurate timings are possible with RC (resistor capacitor) circuits, but the values previously specified are quite close. Perform a search for 555 timer calculators for more information.

3. Place the resistors, capacitors, and 555 IC timer on the circuit board. Solder them in place and wire them up appropriately. 555 timer circuits are very common and easily found through search engines.

4. Install the relay and solder in place. The relay is required to switch the 110 to 120 volt AC supply on and off. The 555 timer's cycle should be wired to the relay to provide the appropriate relay switching rate, while the relay itself will turn the Christmas lights on and off.

5. Connect and solder in place the 7805 voltage regulator and transformer as part of the device's power supply. In general power supplies are beyond the scope of this article, but keep in mind that this circuit will tap the AC power from the user's wall outlet and convert it first into approximately 12 volts AC and then ultimately into five volts DC. This is sufficient to drive the 555 timer and relay. All subsystems are complete, and the lights are ready to begin blinking.

Tips & Warnings

• Understand the 555 timer. Read the manufacturer's documentation and experiment with flashing and LED before you consider this project. The 555 timer is the heart of this project, the rest only requires simple mechanical switching and wiring skills.

• The project previously explained requires the use of high voltage lines. Do not touch them while they are active! Doing so can potentially cause personal injury and/or death. This is a basic circuit to follow, but do not attempt if you have no prior knowledge of electronics or electrical wiring.

References

• Horrorseek.com: 555 Timer Calculator