Introduction: CD4017 Based Multi-functional Bicycle Backlight

This circuit is made by applying very common CD4017 LED circuit so called as LED chaser.

But it can support diverse LED blinking methods by plugging control cables as different manners.

Maybe it can be utilized as bicycle backlight or visual indicator of Raspberry Pi or Arduino circuits.

Step 1: LED Blinking Scheme


As you can see in the video above, bi-color LEDs are blinking as bouncing manner.

Firstly 4 red LEDs are blinking one and after as clockwise.

Afterward 4 green LEDs are blinking as anti-clockwise.

This operational scheme is one example among diverse other possibilities you will see later.

Let’s start to make this.

Step 2: Schematics

This circuit is operating itself with own NE555 clock source without any control of external controller such as Raspberry Pi or Arduino.

It’s a very typical and common LED chaser circuit (Turning on LED on by one as sequential manner) using CD4017 (Decade Counter IC).

Therefore, detail explanations will not necessary for the circuit operation.

But some explanation is still necessary for the NE555 clocking circuit as it control blinking speed of LEDs.

The details are as described in the step next.

Step 3: Clock Generation Method

In the schematics shown at the step 2, small circled numbers are assigned to resistors of NE555 clocking circuit.

The 1K (number 1) is R1 and 100K VR (number 2) is R2 which are defining clock speed in the table shown in the picture above.

As you can see, R2 (100K VR) value is decreasing, clock speed (F, Frequency) is increasing.

When VR 100K value become 10 ohm, frequency increasing up to 141 per second.

With this speed, all LEDs are seems blinking at the same time as you can see in the video above.

Reversely, LED blinking becomes slow when you increase VR 100K value.

You can choose any capacitor value (10uF), VR (100K) and R1 (1K) when F (Frequency) can be in range of 1 to 100 as shown in the table above.

Step 4: Parts

For making this circuit, PCB accessories such as long pin head and IC pin head is important for supporting easy modification of LED blinking scheme. (I’ll explain later)

Others are common parts you can easily buying from internet e-stores.

- CD4017 (16 pin Decade Counter IC) x 1

- NE555 Timer IC x 1

- Capacitors: 10uF x 1, 0.1uF x 1

- Resistors: 220ohm x 1 (LED current limiting), 1K (Clock timing control) x 1, 100K (defining LED blinking rate)

- Bi-color LED x 4 (common cathode type is required)

- Universal board 30(W) by 20(H) holes size (You can cut any size of universal board to fit this circuit)

- Tin wire (I’ll example detail in “Part 2: making PCB drawing” for usage of this part)

- Long length pin head (3 pins) x 5 (I’ll explain later)

- IC 3 pin head for connecting bi-color LED x 4

- Jumper cables (Female socket at one end) x 8 and red/blue color wiring cables

Step 5: Making PCB Drawing

As like before, let’s make PCB drawing which shows wiring pattern and location of each part.

And it can support easy soldering and minimize any wiring/soldering mistakes.

When cable is not used, wiring pattern becomes a little bit complex as shown in the picture above.

As everything is ready, let start to solder parts on the universal PCB.

Step 6: Soldering Main Board

This is main PCB board including CD4017 and NE555 ICs.

As CD4017 is not inserted to IC pin head socket, you can see 8 pin length of IC pin-head socket.

This IC pin head will be utilized as bi-color LED socket in the daughter PCB board which will be made in the next step.

To make various LED blinking pattern, each output of CD4017 is tagged and numbered as shown in the picture above.

You will see importance of these numbers written on the magic tape segment as controlling of LED blinking is highly dependent on these tagged numbers.

Although PCB drawing is made differently from the main board wirings, physical connection is the same as depicted in the PCB drawing.

Step 7: Soldering Daughter Board

The daughter PCB board will be attached to main board as 90 degree position (mounted as perpendicular manner).

You can see difference between long type pin-head and short one in the picture above.

The long pin head should be inserted from the front side of PCB and soldered at the back-side of daughter board.

At the back-side, female socket of jumper code shall be inserted to soldered long pin head conductor.

When you using short one, plugging jumper code become difficult as remained pin head conductor portion is too much short.

Usually bad contact may happen when you using short pin head connector.

Therefore, please use long length of pin head connector.

As everything is ready, let’s make this circuit operating.

Step 8: RED/GREEN CROSS Pattern


Are you Christian?

Then this blinking pattern will have meaning to you.

Red LEDs are following the sign of the cross.

Subsequently Green LEDs are the following the same path of Red.

How this is possible?

Step 9: Wiring for Making RED/GREEN CROSS Pattern

Previously I mentioned numbered tags.

You can connect numbered female jumper cables to the pin head conductors located in the daughter board like above.

As I didn’t make detail PCB drawing of daughter board, pin assignment is different from what I’m originally thinking.

Later I found the actual pin layout as shown in the picture above.

That’s why PCB drawing is important and necessary to make soldered PCB is the same with intended circuit design.

Step 10: Circular Iteration Pattern


Are you Buddhist?

Then your world is iterating endlessly with reincarnation. (Of course reincarnation is finish when you become Buddha)

Anyway by changing pin connections, you can modify LED blinking pattern altogether.

What will be pin connection for the circular iteration pattern?

Step 11: Wiring for Making Circular Iteration Pattern

As shown in the picture above, you can connect jumper code cables to make circular iteration pattern.

OK. Let’s make another LED blinking pattern.

Step 12: Another Blinking Pattern

The jumper code connection is like in the picture above.

What kind of blinking pattern is this?

Step 13: Bouncing Left to Right Blinking Pattern


This blinking pattern is already seen one at the beginning of this story.

But I like the final blinking pattern as shown in the next step.

Actually I like it….

And if you’re makes this one blinking faster…. The better…..

Step 14: Chaos Pattern


Although this circuit can change its operational pattern, only one type of blinking pattern should be decided for finalization.

Still I don’t assemble main-board with daughter board.

Both boards can be connected with pin head connector and soldered together for completion.

Step 15: Finalization

Somehow many CD4017 IC and bi-color LEDs are stored in my part inventory.

I don’t know when I bought these and why.

Anyway I use several of them with this project.

But quite many remained still…

I’ll introduce some more circuit ideas later by using the stored CD4017 and bi-color LED.

Thank you for reading this story.