Circular LED Chaser using 555 Timer and BC547

555 Modes

Basically 555 timer IC can be used in 3 modes 1. Monostable Mode 2. Bistable Mode 3. Astable Mode.

In this blog we discussed about how 555 Timer can be used as LED Chaser using Astable Multivibrator mode of 555 Timer lC and 4017 IC.

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555 Timer Pin Diagram

PIN 1 is Ground Pin, Pin 2 is the Trigger Pin, PIN 3 is Output Pin, Pin 4 represents Reset Pin, Pin 5 is the Control Voltage, PIN 6 is Threshold, PIN 7 is the Discharge PIN and PIN 8 represents Power Supply or Vcc.

555 Timer Internal Architecture

555 Timer is divided into 5 parts. First part is voltage divider circuit, second comparator block, third flip-flop circuit, fourth discharge circuit and last output driver circuit.

LED Chaser Schematic Circuit Diagram

555 timer’s PIN2 is connected to PIN6 and a capacitor(Here we used 4.7microF) is connected with PIN2 & Ground. PIN6 is also connected to PIN7 with a 100Kohm resistance. PIN7 is connected to PIN8 with a 10Kohm resistor as PIN8 is the Power Supply or VCC. 555 Timer’s PIN3 is connected to 6 LED’s and a BC547 transistors’s Base pin through a resistor.

When Pin3 HIGH, 3 Blue LED’s one side will HIGH and transistors’s base pin on so 3 Blue LED’s other side will get LOW, thus 3 Blue LED’s will glow. When Pin3 LOW, 3 Green LED’s one side will LOW and transistors’s base pin off so 3 Green LED’s other side will get HIGH through 150ohm resistor, thus 3 Green LED’s will glow.

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Further Readings

• How LED Flasher Works Internally
• Electronic Piano

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