In this post I will discuss how to build a simple LED chaser circuit with a push pull or reverse forward sequencing effect. Also, in the later part of the article I have explained how this simple LED chaser could be upgraded to a 100 to 200 LED laser circuit with a reverse forward LED sequencing effect.
Introduction
As learned earlier, an LED light chaser circuit typically refers to an electronic configuration able to generate or illuminate a group of LEDs in some predetermined sequence. One popular IC 4017 is very commonly employed for making this type LED sequencer circuit.
Here also the IC basically is a Johnson's 10 stage decade counter/divider and can be used for many interesting light pattern generations, and may be used for various decorative purposes.
So far we have circuits using the above IC for producing chasing light effects, however making the IC create "reverse" "forward" "chasing" pattern with LEDs is something many of us might not be acquainted with. Here I have explained how to make a simple yet effective to and fro or reverse forward light chaser circuit using LEDs.
Understanding IC 4017 pinouts
But before that let's take a brief look at the IC 4017 pin out details.
The IC 4017 is a 16 pin dual in line (DIN) IC.
The IC has 10 outputs which generate the sequencing high outputs in the order of the pin outs - 3, 2, 4,7, 10, 1,5, 6, 9, 11. The sequencing takes place in response to a frequency applied at pin 14 of the iC
Pin 16 is the positive supply input, pin 8 is the negative supply input or the ground line.
Pin 13 is used clock inhibit inhibit and will stall the circuit if connected to positive supply terminal, however connecting it to ground makes everything normal, so we connect it to ground.
Pin 12 is the clock carry out, not required for single 4017a applications, so we leave it open.
Pin 15 is the reset pin, and it resets the output to the start pin in response to a positive response to it.
The pin 15 of the IC is connected to the second last pin 9 of the IC, which means the output resets every-time the sequencing reaches pin 9m,and the moment this pin goes high, the IC repeats the action by resetting the system.
Pin 14 is the clock input and requires to be fed with a square wave frequency, easy obtainable through any astable oscillator made from ICs like IC 555, IC 4049, transistors etc.
Circuit Diagram
How it Works
Looking at the shown reverse forward LED light chaser circuit, we see that basically the IC is arranged in its normal sequencing or chasing mode, however the clever introduction of the diodes at the outputs of the IC make the sequencing appear to be reversing and forwarding from start to finish and vice versa.
The smart arrangement of the diodes enables the output sequence of the IC to feed the LEDs in a way that the relevant LeDs are able to imitate a to and fro chasing pattern.
This is achieved by by forcing 5 outputs to move in a forward chasing pattern, while the following 5 outputs are redirected toward the same LEDs but in the opposite direction, making the pattern look like a to and fro chasing motion.
Parts List for the proposed 4017 LED light chaser circuit
- R1 = 1K,
- R2 = 4K7,
- R3 = 1K,
- R4 = 100K pot, linear,
- C1 = 10nF,
- C2 = 4.7 uF/25V,
- IC1 = 4017,
- IC2 = 555
Adding More LEDs
In the above example we have seen how a reverse forward LED sequencing may ge implemented over 5 LEDs, however in order to get a more interesting effect we would want to increase the number of LED to higher numbers so that the illumination increases and the visual effect is able to get much enhanced.
The following section have explained how this may be accomplished using 200 LEDs, however any number of LED could be used just by modifying the transistors and the series parallel connections for the LEDs, I have explained the details.
Circuit Operation
The circuit diagram shows a simple yet an effective configuration which is able handle up to 200 different colored LEDs and create the required to and fro chasing show.
The IC 4017 is the main part of the entire system whose outputs have been very cleverly manipulated using diodes.
Normally, in response to a clock signal the outputs of a 4017 IC would begin shifting sequentially from pin#3 to pin#11 covering ten of its pin outs in a certain random order.
If the LEDs are arranged in these ten outputs, one would acquire ordinary one direction sequencing of the LEDs.
In the discussed circuit, five of the end sequence pin outs have been diverted in such way that the connected LEDs produce a to and fro moving effect, however with this arrangement the total number of outputs get restricted to only 5, nevertheless sufficient for implementing the intriguing visuals.
Normally the outputs would accommodate a maximum of 4 LEDs, a total of 20 numbers. For handling as high 200 LEDs, transistor buffer stages have been included in the circuity.
Each transistor or the channel can hold upto 50 LEDs, the LEDs are connected in series and parallel combination as shown in the last diagram.
The LEDs are connected to the collector of the respective transistors as referred to in the last diagram.
The IC 555 is wired up as an astable for generating the required clock pulses at the input pin#14 of IC 4017.
These clocks determines the sequencing rate of the connected LEDs which may varied by adjusting variable resistor R3.
The circuit may be powered from a 12V battery or a 12V/3amp SMPS adapter unit.
Circuit Diagram with 200 LED Chaser Circuit
The basic reverse forward LED circuit using single LEDs can be studied elaborately in this LED scanner article, and the video can be witnessed below:
How to Connect the LEDs
The following diagram illustrates the connection arrangement of the LEDs to the above circuit. A single series for each channel has been shown in the diagram.
The numbers can be simply increased just by inserting more such series in parallel to the respective strings of the different channels.
Circuit Diagram for Series Parallel LED Connections
Parts List
- R1 = 1K,
- R2 = 4K7,
- R3 = 1K,
- R4 = 100K pot, linear,
- C1 = 10nF,
- C2 = 4.7 uF/25V,
- IC1 = 4017,
- IC2 = 555
- All diodes are = 1N4007
- All transistors are = BD139
- All transistor base resistors are = 1K
- LED resistors are = 150 Ohms 1/4 watt.
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