An car turn signal circuit with chasing effect is a crucial part for cars, helping to show when a driver wants to turn left or right.
This circuit works by making lights flash in a sequence similar to the blinking turn signals we see on modern cars.
It relies on two main components: the 555 timer IC and the CD4017 decade counter IC.
In this setup, the first component known as IC1 is set up in a way that allows it to create a continuous flashing pattern which then activates the counter IC2.
This explanation will help you understand how a simple car turn signal circuit is designed and how it works using both the 555 timer IC and the CD4017 IC.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | 47k 1/4 watt | 1 |
| 1k 1/4 watt | 2 | |
| 10k 1/4 watt | 4 | |
| Preset | 470k | 1 |
| Capacitors | Electrolytic 1μF 63V | 1 |
| Electrolytic 220μF 25V | 1 | |
| ICs | 555 Timer IC | 1 |
| CD4017 Decade Counter IC | 1 | |
| Transistors | BC547 | 4 |
| LEDs | Any 5mm, 20mA | 8 |
The circuit diagram mainly relies on two key integrated circuits: the 555 timer IC known as IC1 and the CD4017 decade counter called IC2.
The 555 timer IC1 is set up in astable mode which means it creates a continuous square wave signal.
This signals frequency is really important because it controls how fast the LEDs blink.
The timing parts R1, R2 and C1 help set this frequency.
The clock pulses from IC1 go to the clock input pin 14 of IC2.
The CD4017 acts as a decade counter turning on its output pins one by one with each clock pulse.
In this circuit we only use the first eight outputs from Q0 to Q7 to light up the LEDs which are labeled LED1 to LED8.
However, the outputs from IC2 cannot provide enough current to power the LEDs directly.
To fix this we use BC547 transistors named Q1 to Q4 as current amplifiers.
Each transistor controls two LEDs in series to make sure they shine brightly.
As the IC2 CD4017 moves through its outputs the LEDs light up in a ‘chasing’ pattern creating a cool effect like a running turn signal.
For selecting the left and the right chasing turn signal LEDs the existing automobile left, right turn signal switch can be used.
Note: Watch out when you are working with the wiring in this circuit!
If you connect something incorrectly it could cause problems with your vehicles electrical system.
Formulas with Calculations:
The below formulas with calculations are for Car Turn Signal Circuit with Chasing Effect:
Frequency Formula (for 555 Timer in Astable Mode):
f = 1.44 / ((VR1 + 2R2) × C1)
where,
- VR1 is the preset in the circuit diagram
- R2 is the resistor with 47k in the circuit diagram
- C1 is the capacitor C1 of 1μF in the diagram
Substitution Example:
For VR1 = 470k, R2 = 47k, and C1 = 1µF
f = 1.44 / ((500k + 2 × 47k) × 1µF)
f = 2.54 Hz
Resistor Value Adjustment Formula:
R1 + 2R2 = 1.44 / (f × C1)
Above formula is to achieve a specific frequency (f) formula
How to Build:
To build a Car Turn Signal Circuit with Chasing Effect follow the below steps mentioned:
- Assemble all the above mentioned circuit diagram components.
- Connect pin 1 of IC1 555 to GND.
- Connect pin 2, 6 and 7 of IC1 555 to one end of resistor R1 and other end of R1 resistor to center leg of VR1 preset and second leg of VR1 preset to positive supply.
- Connect a positive of capacitor C1 from pin 2,6 and 7 of IC1 555 and negative of capacitor C1 to GND.
- Connect pin of IC1 555 to pin 14 of IC2 CD4017.
- Connect pin 4 and pin 8 of IC1 555 to positive supply.
- Connect a positive of capacitor C2 to positive supply of +12V and negative of capacitor C2 to GND.
- Connect pin 2 of IC2 CD4017 to base of transistor Q2 through resistor R5.
- Connect pin 3 of IC2 CD4017 to base of transistor Q1 through resistor R4.
- Connect pin 4 of IC2 CD4017 to base of transistor Q3 through resistor R6.
- Connect pin 7 of IC2 CD4017 to base of transistor Q4 through resistor R7.
- Connect pin 8 an pin 13 of IC2 CD4017 to GND.
- Connect pin 10 to pin 15 of IC2 CD4017.
- Connect pin 16 of IC2 CD4017 to +12V positive supply.
- Connect the emitters of transistors Q1 to Q4 to GND.
- Connect the collector of transistors Q1 to Q4 to the cathode(-) of LED1 to LED8 and connect the same cathode of LED1 to LED8 to left indicator switch of car through resistor R2 and the anode(+) of LED1 to LED8 connect to right indicator switch of the car through resistor R3.
Conclusion:
Car Turn Signal Circuit with Chasing Effect shows how a sequential LED flasher works by using a 555 timer and a CD4017 integrated circuit.
It is affordable, simple to build and you can change it to add more features like changing the speed of the flashing lights.
Plus, the way the circuit is designed makes it useful for other things too like decorative lights or different signaling systems.
References:
Finished: Car Indicator Light (Turn Signals and Brake Light)