Police Lights using 555 Timer
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.
Circuit Diagram of Police Lights using 555 Timer:
Circuit
Diagram of Police Lights using 555 Timer
Circuit Components:
·
NE555 timer
·
4017 decade counter
·
1n4148 diodes – 6
·
1k Resistor(1/4 watt) – 1
·
22k Resistor(1/4 watt) – 1
·
470 ohm Resistor(1/4 watt) – 8
·
2.2uF Electrolytic capacitor(16V) – 1
·
Blue LED’s – 2
·
Red LED’s – 2
·
9v battery – 1
·
Connecting wires
555 Timer based Police
Lights Circuit Design:
555 Timer: Here 555 timer runs in free running mode. It produces pulses whose
width can be varied. 2nd and 6th pins are shorted to allow triggering after
every cycle. 4th pin is connected to Vcc to avoid sudden resets.
4017 Decade Counter: It is a 10 bit counter with ten decoded outputs. It counts the
incoming pulses. The supply voltage range is -0.5 to +22V. The high pulse on
the reset pin clears the count to zero. The speed of operation of this IC is up
to 10 Mhz.
The ouput states (Q0,Q2,Q4)
are ORed to flash the blue LED’s 3 times and the states Q5, Q7 and Q9 are ORed
to flash the red LED’s 3 times.
Based on the outputs of
4017 IC, two transistors (NPN) switches the LED’s ON and OFF.
Resistors R3, R4, R5, R6
are used to protect the LED’s from high voltage.
How to Operate Police
Lights Circuit:
·
Apply power to the circuit.
·
Now observe the LED’s, red led’s flashes 3 times and blue led’s
flashes 3 times and this process repeats.
·
If you want to set the different time delays for LED’s then vary the
resistance (R1, R2) or capacitance (C1).
555 Timer based Police
Lights Circuit Applications:
·
This circuit used as an indicator for police cars.
·
We can use it as LED flasher circuit by making some modifications.
Limitations of Police
Lights Circuit:
·
The values of the resistors R1, R2 and capacitor C1 should be same
to get perfect flashing.
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 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.
555 Timer based Police
Lights Circuit Design:
555 Timer: Here 555 timer runs in free running mode. It produces pulses whose
width can be varied. 2nd and 6th pins are shorted to allow triggering after
every cycle. 4th pin is connected to Vcc to avoid sudden resets.
4017 Decade Counter: It is a 10 bit counter with ten decoded outputs. It counts the
incoming pulses. The supply voltage range is -0.5 to +22V. The high pulse on
the reset pin clears the count to zero. The speed of operation of this IC is up
to 10 Mhz.
The ouput states (Q0,Q2,Q4)
are ORed to flash the blue LED’s 3 times and the states Q5, Q7 and Q9 are ORed
to flash the red LED’s 3 times.
Based on the outputs of
4017 IC, two transistors (NPN) switches the LED’s ON and OFF.
Resistors R3, R4, R5, R6
are used to protect the LED’s from high voltage.
How to Operate Police
Lights Circuit:
·
Apply power to the circuit.
·
Now observe the LED’s, red led’s flashes 3 times and blue led’s
flashes 3 times and this process repeats.
·
If you want to set the different time delays for LED’s then vary the
resistance (R1, R2) or capacitance (C1).
555 Timer based Police
Lights Circuit Applications:
·
This circuit used as an indicator for police cars.
·
We can use it as LED flasher circuit by making some modifications.
Limitations of Police
Lights Circuit:
·
The values of the resistors R1, R2 and capacitor C1 should be same
to get perfect flashing.
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