It is the prototype model of our Indian traffic Light System in which it uses three different light to indicate three different actions. Red light indicate STOP action. Yellow Light indicate LOOK. Green light indicates GO. Here we are using two IC 555 to perform this task. It will turn ON LEDs one by one continuously.The red LED has an equal on-off period and when it is off, the first 555 delivers power to the second 555.
This illuminates the Green LED and then the second 555 changes state to turn off the Green LED and turn on the Orange LED for a short period of time before the first 555 changes state to turn off the second 555 and turn on the red LED. A supply voltage of 9v to 12v is needed because the second 555 receives a supply of about 2v less than rail. This circuit also shows how to connect LEDs high and low to a 555 and also turn off the 555 by controlling the supply to pin 8. Connecting the LEDs high and low to pin 3 will not work and since pin 7 is in phase with pin 3, it can be used to advantage in this design.
- Resistor: R1=100 Kilo Ohm
- Color code for 100 Kilo Ohm: Brown-Black-Yellow-Golden
- R2=1 Kilo Ohm
- R3=47Kilo Ohm
- Color code for 47 Kilo Ohm: Yellow-Violet-Orange-Golden
- R4,R5 = 220 Ohm
- Color code for 220 Ohm: Red-Red-Brown-Golden
- Electrolyte Capacitor: C1,C2= 100uF
- Light Emitting Diode:
- LED1= Red LED
- LED2= Yellow LED
- LED3=Green LED
- IC1,IC2= IC 555
- Battery: 9 Volts
Circuit Building Steps:
Mount two 555 ICs on Bread Boars as shown below.
Short pins 2 and 6 of both ICs.
Connect pin 1 of Both ICs to Ground.
Connect pin 4 of both ICs to VCC and pin 8 of IC 1 to VCC.
Connect Resistor R1 of 100k Ohm to pin 6 of IC1 and R2 of 47 K Ohm to pin 6 of IC2.
Connect second terminal of R1 to Pin 3 of IC1 and pin 8 of IC2 through yellow and Green wire respectively. Connect another terminal of R2 to pin 3 of IC2.
Connect Capacitors C1 and C2 of 100uF to pin 6 of IC1 and IC2. Connect positive terminal to pin 6 of IC. Polarities of capacitors are shown below. Connect negative terminal of capacitor to Ground.
Mount resistor R2,R4 and R5 on breadboard. Connect one terminal R2 to VCC. Similarly connect one terminal of R4 and R5 to VCC. As shown below:
Connect second terminals of R2,R4,R5 to Anodes of RED ,YELLOW,GREEN LED respectively. Connect cathode of RED LED to pin 3 of IC1. Connect cathode of YELLOW LED to pin 7 of IC2. Connect Anode of GREEN LED to pin 3 of IC2.
Connect Battery terminal to the bread board and observe the output.
LEDs will turn ON one by one like our actual traffic signal.It begins with RED then followed by YELLOW and GREEN.