LED Flasher Circuits Using 555 Timer IC

IC 555 Simple LED Flasher

An LED flasher circuit can be used as an LED blinker, vehicle indicator light, signal flashlight, etc. A simple blinking circuit is basically a circuit to continuously ON and OFF the light supply on a fixed time interval. That is a periodic output of HIGH and LOW state sequences that ON and OFF the LED repeatedly.

led flasher, 555 blinker circuit

Here circuit consists of an astable multivibrator using an NE555 timer IC, which generates a square wave. The circuit has an approximate ON state time of 0.94 Seconds and OFF state time of 0.47 Seconds.

The Rate of flashing of the circuit can be calculated as,

Ton = 0.69*(R1 + R2)*C   |    Toff = 0.69*R2*C

Ttotal = Ton + Toff  = 0.69*(R1 + 2*R2)*C

The flashing rate can be adjusted by varying the values of either resistors R1 or R2 or the capacitor C1. Also, instead of using a fixed resistance value for R1 and R2, either one of the resistance can be replaced with a potentiometer. Then the rate of flash can easily be tuned

components required

IC – NE555

Resistor – R1, R2 – 6.8k, R3 – 1k

Capacitor – C1 – 100uf, C2 – 100nf

LED -Red

Supply – 9v battery

Alternating LED Flasher With 555 IC Circuit Diagram

This alternate LED flasher consists of a pair of LEDs which blink alternately. It has the same circuit of a simple LED flasher circuit using a 555 astable multivibrator. The only difference is that one more LED is added in the circuit, which ON when the 555 output is in a low state.

In the circuit, the LED1 lights when the output pin has a HIGH state and LED2 lights when the output is in a LOW state.

alternate led flasher

The rate of flashing can be adjusted by varying the ON period and OFF period of the astable multivibrator.

components required

IC – NE555

Resistor – R1, R2 –  6.8k, R3,R4 – 1k

Capacitor – C1 – 100uf, C2 – 100nf

LED – 2 Nos

Supply – 9v battery

Police Flashing Strobe Light Circuit Using 555

Strobe lights are commonly used as emergency vehicle lights for visual warnings. Their light effects are similar to the flashing light in police vehicles, ambulance, beacon light bars, etc.

The given police light circuit consists of two 555 astable multivibrators. One with a lower oscillation frequency (IC1 multivibrator section) and other with a higher frequency (IC2 multivibrator section).

The IC2 consists of a simple LED flasher circuit, which continuously flashes the LED. And using the signal from the low-frequency multivibrator, the signals from the IC2 are alternately switched to the RED and BLUE LEDs. Here the LED set consists of a 3×3 Red and 3X3 blue LEDs.

The square wave output of IC2 is connected to the RED and BLUE LEDs through an NPN transistor Q1-BC547 and a PNP transistor Q2-BC557.

The base of both transistors is biased from the output of low-frequency multivibrator. So it switches the transistor Q1 and Q2 alternatively with the high and low state at the output.

On high output state of IC1, the Q2 switches to forward active mode and drives the flashing signals to BLUE LEDs. Similarly, in the low output state of IC2, the Q1 drives the signals to the RED LEDs.

The rate of flashing of LED sets and switching time between the LED sets can be adjusted by varying the time period of the two multivibrator circuits.

Components required

Integrated circuit – IC1,IC2 – NE555

Transistor – Q1 – BC557, Q2 – BC547

Resistor – R1, R3, R10, R11 – 1K, R2 – 470K, R4-R9- 220ohms, R12- 100K

Capacitor – C1,C4 – 2.2uf, C2,C3 – 0.01uf, C5 – 220uf

Diode – D1 – D9 – Red LED, D10 – D18 – Green LED

Simple Flashing brake light Circuit

The circuit can use to make a simple pulsating stop brake light which continuously flashes as long as the brake is applied. Here we are using a 555 astable multivibrator to generate the flashing. The working of flash brake light circuit is same as simple 555 flasher circuit. With the given values for R1, R2, and C1, the circuit has an ON period and OFF period of 0.125 seconds and 0.124 seconds respectively.

flashing brake light, brake light circuit

The LED brake light has a set of 3×3 LED bulbs, 3 parallel set of 3 series LEDs and 220 ohms resistance. The 555 IC has a maximum output current of 200mA. The output current driven by an LED is about 20ma – 40 ma. Here in the set, it is about 25ma. As the total current is below 100ma, the LEDs can be connected directly to the output pin of the 555IC. Also, as the brake light is not lighting for a too long the IC does not heat as much. Even though, the circuit can work fine if it kept ON for a long period.

The switch should be placed so as to activate the circuit while applying the brake. Or replace the switch with any another easy mechanism which makes an electrical contact during braking. Also, the circuit can be connected in parallel to the existing brake light. But the power rating of wire and fuse should be considered while connecting along with it.

Flash Light – Components required

Integrated circuit – IC – NE555

Resistor – R1 – 1K,R2 – 82K, R3,R4,R5- 220ohms

Capacitor – C1 – 2.2uf, C2 – 0.01uf

Diode – D1 – D9 – Red LED

Flash and Hold Brake light Circuit

In flash and hold circuit, the light does not flash continuously as like a normal flasher. Instead, the circuit flashes initially for a few seconds and then hold the ON state until the brake switch is released.

This brake light circuit consists of an additional monostable multivibrator with the above flasher circuit. In the circuit, the output of the monostable multivibrator is connected to the base of a PNP transistor, which is connected across the capacitor C4. So, during the high state of the IC1, the Q1 is OFF. Thus the astable multivibrator generates periodic signals, which flash the LEDs. After the quasi-state period of IC1, the output return to the low state. At this time the Q1 ON and it shunts the capacitor. Thus the voltage at the trigger pin becomes below 1/3Vcc and holds the ON state at the output of IC2, which is actually interrupting the working of the astable multivibrator.

The flashing time of the circuit is equal to the time period of the monostable multivibrator. So the period of flashing can be adjusted by varying the time period of the monostable multivibrator.

Brake Light – Components required

Integrated circuit – IC1,IC2 – NE555

Transistor – Q1 -BC557

Resistor – R1 – 470K, R2,R3 – 1K, R4 – 100K, R5-R7- 220ohms

Capacitor – C1 – 4.7uf, C2 – 22pf, C3,C5 – 0.01uf, C4 – 2.2uf, C6 – 220uf

Diode – D1 – D9 – Red LED

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