Stroboscopic Lamp using Timer 555

Introduction

A strobe light or stroboscopic lamp, commonly called a strobe is a device used to produce regular flashes of light. It is one a number of devices that can be used as a stroboscope. A typical commercial strobe light has a flash energy in the region of 10 to 150 joules, and discharge times as short as a few milliseconds, often resulting in a flash power of several kilowatts. Larger strobe lights can be used in “continuous” mode, producing extremely intense illumination.

Circuit Diagram

Working

The Stroboscopic Lamp built above uses a timer 555 in the astable mode of operation. The values of resistors R1 and R2 and capacitor C2 were chosen to given a wide range of frequencies from 0.3259 Hz to 31.369 Hz. The 100kΩ pot is used to set the frequency of the flashes. When R1 = 100Ω, R2 is set at null position, and C2 = 22µF, On-time (Ton) and Off-Time (Toff) is given as:

Ton= 0.69*{R1 + (R2 + R3)}*C2 = 16.698 ms
Toff = 0.69*(R2 + R3)*C2 = 15.18 ms
Time Period, T = Ton+ Toff = 31.878 ms
Frequency, f = 1/T = 31.369 Hz
When R2=100kΩ, On-time (Ton) and Off-Time (Toff) is given as:
Ton= 0.69*{R1 + (R2 + R3)}*C2 = 1.5347 s
Toff = 0.69*(R2 + R3)*C2 = 1.53318 s
Time Period, T = Ton+ Toff = 3.0679 s
Frequency, f = 1/T = 0.3259 Hz

 

Video Demonstration

 

Application

•  They are widely used in industry to study high-speed machinery. Machines, under moving condition, can be inspected under strobe light, where the moving parts are observed as though they are standstill.
•  If a machine or engine is to spin at a precise speed, a strobe light flashing at the same speed to check. When the speed is correct, the strobe light should make it appear motionless. Stroboscopic effect is observed when the frequencies do not match.
• As a timing light they are used to set the ignition timing of internal combustion engines.
• In medicine, stroboscopes are used to view the vocal cords for diagnosis of conditions that have produced dysphonia (hoarseness). The patient hums or speaks into a microphone which in turn activates the stroboscope at either the same or a slightly different frequency. The light source and a camera are positioned by endoscopy.
• Lights on emergency vehicles (such as squad cars, ambulance) are sometimes basic rotating lights inside coloured plastic, but strobe lights are also used for this purpose because they are brighter and more attention-grabbing.
• Telephones and doorbells for hearing-impaired people often have an attention-grabbing strobe light on them in place of (or as well as) an audible ringer.
• Flashing lamp strobes are also adapted for pop use, as a lighting effect for discotheques and night clubs where they give the impression of dancing in slow motion.
• Another application of the stroboscope can be seen on many gramophone turntables. The edge of the platter has marks at specific intervals so that when viewed under fluorescent lighting powered at mains frequency, provided the platter is rotating at the correct speed, the marks appear to be stationary.

 Harmful Effects of Stroboscopic Light

Although extremely rare, strobe lighting can trigger seizures in photosensitive epilepsy.
Studies have shown that the majority of people that are susceptible to the strobing effects can have
symptoms of epilepsy at 15 Hz-70 Hz, albeit rare. Other studies have shown epileptic symptoms at the
15 Hz rate with over 90 seconds of continuous staring at a strobe light. There have been no known
seizures at or below the 8 Hz (or 8 flashes per second) level

Conclusion

A strobe light is a very useful device for observing rotating moving parts of a machine and to
measure its frequency of rotation. A wide range of frequencies can be set choosing appropriate
values of R1, R2, R3, and C2. Most strobe lights on sale to the public are factory-limited to
about 10–12 Hz (Or 10-12 flashes per second) in their internal oscillators, although externally
triggered strobe lights will often flash as frequently as possible. Most fire alarms in schools,
hospitals, stadiums, etc. strobe at a 2 Hz rate.

Credits:

Kishore Seshadri