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Two LED Flasher by 555 Timer

2014-12-23 18:42  
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Figure 1 

The purpose of building this circuit is to create aLEDflasher with alternating sequence from the twoLEDs where the operation is based on the functionalities of a 555 timer integrated circuit.

555 – a highly stable device for generating oscillation or accurate time delays used in pulse width/position modulation, sequential timing, time delay generation, linear ramp generator, precision timing, and pulse generation due to its features such as normally open and normally off output, temperature stability, output and supplyTTLcompatible, adjustable duty cycle, and operates in both astable and monostable mode4N25 – a general purpose optocoupler that consists of a gallium arsenide infrared emitting diode driving a silicon phototransistor in a 6-pin dual in-line package used in microprocessor inputs, digital logic inputs, and power supply regulators due to its features such as high isolation voltage between input and output, operating temperature up to 110oC, and available in wide-lead spacing

The main component of the circuit is focused on the 555 timer integrated circuit which is also being used in other circuit requiring multivibration and timing. It can be configure to three operating modes namely:

-Monostable – produces a single (one shot) pulse upon receiving a trigger signal

-Astable – produces a continuous square wave or rectangular pulses as with an oscillator

-Bistable – produces a state of set and reset as with a flip-flop or Schmitt trigger

When operating in bistable mode, it may be utilized in bounce free latched switches, pulse-type waveform processing, and railroad track designing. When operating in astable mode, it may be utilized in pulse position modulation, security alarms, tone generation, logic clocks, pulse generation, lamp flashers, and light emitting diode. When it operates at monostable mode, it may be utilized in pulse width modulation (PWM), capacitance measurement, frequency divider, touch switches, bounce free switches, missing pulse detection, and timers.

The alternating flashes produced from the twoLEDs D1 and D2 can be of different colors if desired, for added physical feature and attraction. The use of 250K ohm trimmer R3, together with the changing of the values of capacitor C1, is for the adjustment of the frequency of oscillation or alternation of the sequence of lighting.

The circuit can be supplied by a battery source or a separate power supply and because of the addition of optocouplers IC2 and IC3, an external circuit can be driven at the same time withLEDs D1 and D2 for different types of applications like the indication of an alarm. The use of optocoupler is to all the input signal to theLEDto be converted into varying light which is detected by the photodiode and uses light emitting diode to transmit light via an optically transparent barrier between two isolated circuits.


Figure 2 

The flasher circuits usingLEDs can be seen widely in motorcycles and cars for their tail, brake, turn light applications. TheseLEDs can also come in different monochromatic colors such as white, red, and amber. One of the most important use of the flasher circuit is providing a visual indication of a hazardous situation from its warning lights.


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