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How to make a group of LEDS blink alternatively with a NE555 for your christmas tree

Hi friends doers,

Here we go again for a new tutorial.

You can see around you things blinking all the time if you live in a city (signs, billboards, lights and more). If you want want to know how to make the same maker project, you are the right place for a nice step by step tutorial.

Hardware

Before starting, you need to gather the following hardware:

A prototyping board (breadboard)
6 LEDs
1 68Kohm potentiometer
1 390 ohm
A NE555
1 1Kohm resistor
1 10Kohm resistor
1 2N2222 NPN transistor
12N2907 PNP transistor
1 9V battery
6 220 ohm resistor

The NE555 allows you to create a square signal. This signal's frequency can be changes with 2 simple components. A potentiometer ( a variable resitor and a capacitor).

To calculate the potentiometer's value, we need to fix a max frequency (Fmax) visible by men's eyes, usually 20Hz and a lower one (Fmin) where we can make the the frequency vary between those 2 values (Fmax and Fmin)

When you look the NE555 datasheet, the formula for the frequency is :

Frequency = 1.44/ [( Ra + 2Rb) x C]

We want a Max frequency of 20HZ and a min frequency of 0.2Hz. To do so after calculation, we found:

Ra = 360 ohm
Rb = 72 Kohm

The Normalised values for the E12 serie are: Ra = 390 ohm and Rb = 68 Kohm

Schematic

Following our schematic, you can use the breadboard to wire our differents components (diode, Resistor, battery, led) and our NE555 to create our blinking led.

Make it work

To make our project work, we need to plug our schematic to a 9v battery. The NE555 can work with a voltage going from 6V to 12V.

You can turn the potentiometer and make it vary from zero to 11 Kohm.

When the potentiometer is at 0 Kohm, our frequency is 0.2Hz, our LED stays 5 seconds on and 5 seconds off.

When the potentiometer is at 11 Kohm, our frequency is 20Hz, our LED stays only 0.0 5 seconds on and 0.05 seconds off. which is too fast for the human eye to see the change. So it appears like it's always on.

When changing the value of our variable resistor from max to min or for min to max, we can notice that the blinking frequency slows down or accelerate.

The Leds blink alternatively depending of our square signal coming from the NE555 is at 0V or VCC. If the signal is at VCC, the NPN transistor is actived and the LEDs from D1 to D3 work. When the signal is at 0V, the PNP transistor is actived and the LEDs from D4 to D6 work.

You can change the resistor Ra or Rb to put the frequency you want and have your your own application (christmas tree, signs, cars...)

If you decide to make the schematic on your prototyping board or on a PCB, share it with with or leave a comment after the article.

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