We all have probably learned a lot regarding 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 we will learn 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.
How the Circuit 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