Some time at night it happens that we have to park our vehicle at highway because of some emergency and it may possible another speeding vehicle rams into another vehicle parked at the edge of highway. Mostly cars have flashing indicator, but heavy vehicle like trucks, buses and auto rickshaws have no such kind of indicator or warning flasher present. Here we have described a simple flashing indicator circuit which will be visible from a distance and warn the vehicle driver.
Fig. 1: Prototype of Parked Vehicle Indicator Circuit on Breadboard
This simple circuit is based on NE555 timer. In this circuit 555 timer is working in a-stable mode. In this mode 555 timer work as free running oscillator means it does not have any permanent or steady state and it is continuously changing its state from low to high and come back to its original state. This continuous switching from one state to another state from high to low and low to high produces a continuous square wave at output.
Frequency of oscillation is determine resistor R1 and R2 and capacitor C2. In this circuit we have set the 0.2 Hz frequency approx. And the period for which LED glows is about 4 seconds. In this circuit when the power supply is ON C2 charges and discharges exponentially with time. Because of this a saw tooth waveform is produce. This wave is feed to the base of transistor T1 which is working in a common emitter mode to buffer the wave preventing the loading of capacitor C2.
Now IC1 pin 6 is used as output and when it receives signals it will illuminate the LED’s gradually and smoothly illuminating and dimming the LED’s. Here we have connected 6 LED’s in parallel through the emitter of transistor T1 with 100 ohm resistor. You can also connect more LED’s by replacing the transistor with more amplification capability transistor. We have used Red LED’s because red color has the longest wavelength and Red color is also the sign of danger so it will be visible from a distance and alert people.
Be careful while choosing the value of resistor if small value is selected output from LED’s appear to clipped and if large value resistor is chosen LED’s will turn off for small period of time.