This circuit simulates the police car lights by alternate flashing. This circuit flashes red LEDs for three times and blue LED’s for three times. This flashing action performs continuously.
This circuit uses 555 timer and a decade counter. Here, 555 timer runs in astable mode. Decade counter 4017 counts the incoming pulses that is for first pulse Q0 becomes high and for second pulse Q1 becomes high and so on again for 10th pulse Q0 state becomes high.
555 Timer Based Police Lights Circuit Principle:
Here 555 timer produces continuous pulses via pin 3. The width of these pulses can be varied by varying the resistance (R1,R2 ) or capacitance (C1). These pulses are given as input to the decade counter. For every incoming pulse the output state of the decade counter is get incremented.
- For 1st pulse – Q0 high – blue led’s glow
- For 2nd pulse – Q1 high (no connection) – all led’s off
- For 3rd pulse – Q2 high – blue led’s glow
- For 4th pulse – Q3 high – all led’s off
- For 5th pulse – Q4 high – blue led’s glow
- For 6th pulse – Q5 high – red led’s glow , blue led’s off
- Hence blue led’s flashes for 3 times.
- For 7th pulse – Q6 high – all led’s off
- For 8th pulse – Q7 high – red led’s glow
- For 9th pulse – Q8 high – all led’s off
- For 10th pulse – Q9 high – red led’s glow
- For 11th pulse – Q0 high – blue led’s glow, red led’s off
- Hence red LEDs flash for 3 times. This process repeats continuously.