The 8-LED Flasher is built around Timer and Counter ICs. It Flashes 8 LEDs sequentially and the flashing speed can be controlled by a potentiometer. This can be used as a design pattern for decoration. But theoretically, it clears the Timer and Counter concepts in an easy way.
· The circuit is powered with a 9 V battery.
· The monolithic integrated circuit 555 timer can be used as square-wave generator, linear saw-tooth generator, pulse generator, time delay generator, etc. here we use it to generate square waveform i.e. it is used in the Astable Mode with a duty cycle of 66.6%.
· The output frequency of 555 timer in astable mode is given by:
F = 1.44/(R1+2*R2)*C1
· We have R1=2.2K; R2=100k ; C1=1uF;
Fig. 1: Image of a Circit Showing Basic Astable Mode
· C1 charges through the resistances R1 and R2, and discharges through R2 only. The charging and discharging times are independent of supply voltage. The capacitor charges between (1/3)Vcc to (2/3)Vcc.
· The R2=100k pot is varied to change the O/P Freq. of 555 Timer
· This variation in Frequency leads to variation in Flashing speed of LEDs
The IC-CD4017 is Decade counter which comes in 16 pin Package.
· The CD 4017 is called a COUNTER or DIVIDER or DECADE COUNTER. It is a very handy chip for producing “Running LED effects” etc.
It has 10 outputs. Output “0” goes HIGH on the rise of the first clock cycle.
On the rise of the second clock cycle, output “0” goes LOW and output “1” goes HIGH. This process continues across the ten outputs and cycles to output “0” on the eleventh cycle.
The “Carry Out” pin goes LOW when output “5” goes HIGH and goes HIGH when output “0” goes HIGH.
When RESET (pin 15) is taken HIGH, the chip will make output “0” go HIGH and remain HIGH.
When “Clock Inhibit” (pin 13) is taken HIGH, the counter will FREEZE on the output that is currently HIGH.
· In this configuration, When counter IC is triggered with a clock input, it starts counting i.e. provides a HIGH o/p sequentially (one by one) on all Bits (Q0,Q1…Q7). These bits can be identified from the below Pin Configuration of the IC.
· As it reaches Q8, because the Pin 9 and 15 are shorted, so after 8 counts, the counter automatically Resets.
The 8 LEDs could be arranged in any pattern and thus be used as a decorative Light Toy in your living room. To be true, I gave it a heart shape and gifted to girlfriend.
Fig. 2: Pin Diagram of 555 Timer
Fig. 3: Pin Diagram of CD 4017
Fig. 4: Prototype of Circuit on Bread Board of 8 LED Flasher with Flashing Speed Control