This is a very basic traffic light circuit that is built around the TTL family 74145. The circuit is stepped by a 555 astable oscillator. The rate at which the timer IC changes is determined by the value of resistance. The Oscillators output is divided by a 74LS90 divider that produces a (BCD) output. There are four counts for RED, two counts for ORANGE and four counts for GREEN. A presentation prepared by my friend's friend. I have done no editing at all, I'm just uploading the presentation as it is.

2. TRAFFIC SIGNALS

3. Description
• This is a very basic traffic light circuit that is built
around the TTL family 74145.
• The circuit is stepped by a 555 astable oscillator.
The rate at which the timer IC changes is
determined by the value of resistance.
• The Oscillators output is divided by a 74LS90
divider that produces a (BCD) output.
• There are four counts for RED, two counts for
ORANGE and four counts for GREEN.

4. START
Is the Signal Green?
EW Signal is
green for 10s NS Signal is
green for 10s
EW Signal is
orange for 2s NS Signal is
orange for 2s
EW Signal is red
for 10s
NS Signal is
red for 10s
FLOW DIAGRAM

5. REQUIRED TOOLS
∀ • Voltage supply (+5V)
∀ • 100uF Capacitor
∀ • 0.01uF Capacitor
∀ • Green LED’s (3 required)
∀ • Yellow LED’s (3 required)
∀ • Red LED’s (3 required)
∀ • 4-8 ohm resistance (2 required)
∀ • 555 IC
∀ • 74LS90 Decade Counter
• 74145 BCD Decoder

6. IC IMPEMENTATION
DIAGRAM

7. CIRCUIT DIAGRAM