Many electronics circuits and projects for learning in simple ways.

Traffic light controller circuit using CD4027 – NE555

Today, let’s look at 2 model of Traffic light controller circuit.
They use the LEDs for display and the digital circuit as based.
This circuit include IC-4027,CD4017,IC-555 and a few parts so easy and cheap.

First model circuit.
This circuit is designed in first. We use many circuit to mix together.

As circuit in Figure 1

01-the schematic diagram of first circuit


Figure 1: The schematic diagram of first circuit.

How it works
-The IC1-NE555 will generate the square wave pulse out to pin 3, to determine the working state of IC2.

– The frequency of IC1 will depends on R1,R2,VR1,VR2 and C1.
– The VR1 is used to adjust the time of a green LED show.
– And, the VR2 is used to adjust the time of a red LED show.
– Then this signal is sent to IC2, that is connected as T-flip-flop.
– The T- flip flop will change the state every toggles on leading edge of clock signal from IC1.
– The IC2 will supply the output at pin 15. But it cannot directly drive the current to LEDs.
-Thus, we need to use IC3 as buffer circuit, to drive LEDs. This circuit can good work.
-But there are disadvantage, the yellow light will light all the time.
02-placing of LEDs in first model
Figure 2: placing of LEDs in first model.

Parts you will need
R1_______50K_1/4W Resistors tolerance: 5%_______= 1 pcs.
R2_______10K_1/4W ____”________”_____________= 1 pcs.
R3-R8____470ohms______”________”_____________= 6 pcs.
R9_______3.9K_________”________”_____________= 1 pcs.
VR1_____1M ___Miniature skeleton preset___________= 1 pcs.
VR2_____100K ___”______________”______________= 1 pcs.

Capacitors
C1______1000uF 16V___Electrolytic capacitors______= 1 pcs.
C2______100uF 16V________”________”__________ = 1 pcs.
C3_______0.01uF 50V_____Ceramic Capacitors_____ = 1 pcs.

Semiconductor and others
LED1, LED4______5mm Red LED_________________ = 2 pcs.
LED2, LED2______5mm Yellow LED________________ = 2 pcs.
LED3, LED6______5mm Green LED________________ = 2 pcs.
Q1________2N3904___NPN 40 Volt 0.2 Amp transistor__= 1 pcs.
IC1,IC3____NE555____Standard Timer Single 8-Pin_____= 2 pcs.
IC2_______CD4027_____DUAL J-K MASTER/SLAVE FLIP-FLOP__= 1 pcs.

The second model circuit.

As above, we can improve the various disadvantages and use a fewer ICs.
Which are easier to understand because as small size circuit.
This circuit include 3 main section:

1. the oscillator use IC1
2. the times generator use IC2
3. The display using LED by the transistors to drive LEDs

How it works

03-the schematic diagram of the traffic light circuit in update version
Figure 3: the schematic diagram of the traffic light circuit in update version.

In the oscillator, IC1 is connected as the astable multivibrator circuit to generate the frequencies.

This frequency is determined by R1,R2,VR1,C1.
Then, this output frequency will appear at pin 3 of IC1 into pin 14 of IC2.
Which IC2 will be connected as the decade counter circuit.
Next, the IC2’s pin 14 will continuously count the input signal, and display the output “1” on pin 3, 2, 4, 7, 10, 1, 5, 6, 9 and pin 11 respectively.

While pin 14 is “1” the pin 3 is “1”, but others pin will is “0”.
Then pin 14 get “1” again the pin 2 is “1” instead, the pin 3 and others will is “0”.
The output is “1” flash to output pins 3 to 11 as above.
Then, it will cycle back to the pin 3 again.

All LEDs is installed as Figure 4.

04-placing of LEDs in improved model
Figure 4. placing of LEDs in improved model.

-The output voltage at pin 3,2,4,7 will make Q1 works.
-Then the green-LED1 and red LED3 glow.
-Next, the output voltage at pin 10 will make Q2 works.
-Thus the current will flow to both the yellow-LED2 and red-LED3 light up.

-Next step,the output voltage at pin 1,5,6,9 makes Q3 works, so there are the current flow to the green-LED4 and red-LED6 glow up.
-Then, there are the output voltage at pin 11, so makes Q4 works.
-Next there current flow to the yellow-LED2 and the red-LED3 glow up.

-And the output will cycle back at pin 3 again.

If change from LEDs is relays will make we can control the high power lamp.

Parts you will need
Resistors
R1_______10K_1/4W Resistors tolerance: 5%_______= 1 pcs.
R2_______1K_1/4W Resistors tolerance: 5%_______= 1 pcs.
R3,R4_______180 ohms 1/4W Resistors tolerance: 5%_______= 2 pcs.
VR1_____100K ___Miniature skeleton preset___________= 1 pcs.

Capacitors
C1______1000uF 16V___Electrolytic capacitors______= 1 pcs.

Semiconductor and others

D1-D8__________1N914 or 1N4148____75V 150mA Diodes
LED1, LED4______5mm Red LED_________________ = 2 pcs.
LED2, LED2______5mm Yellow LED________________ = 2 pcs.
LED3, LED6______5mm Green LED________________ = 2 pcs.
Q1-Q4_____2N3904___NPN 40 Volt 0.2 Amp transistor__= 1 pcs.
IC1,IC3____NE555____Standard Timer Single 8-Pin_____= 2 pcs.
IC2_______CD4017_____Decade counter with 10 decoded outputs IC = 1 pcs.
B1________9-volts battery__________________________= 1 pcs.

This Post Has 4 Comments

  1. I would like to get some instructions on how to repair a simple house electric fan. I am an amateur electronic enthusiast. Thank you.

  2. Thanks to all of you for the great circuit designs.
    Rob54

  3. Hi, Robert Swatosh
    Thanks for your feedback.

  4. This circuit does work. However, the designing has to be done properly. Please short the two yellow LED’s so that they glow simultaneously in both the cases of before turning green and before turning red.

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