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# Stroboscope Uses White LEDs(BC649)

2014-12-13 18:57
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This article briefly describes the Stroboscope Uses White LEDs (BC649). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, can be more effective to grasp this principle. Do you know the circuit, for example, can understand and buy these components: BC649 , 1N4004.

This stroboscope circuit uses 16 high-brightness whiteLEDs in a torch housing and it provides a signal output to a frequency counter to provide a rev counter display. IC1 is 555 astable multivibrator and it provides a signal to IC2, a 4046 phase lock loop. IC2 and the two 4017 Johnson decade counters, IC3 & IC4, make up a frequency multiplier with a factor of 60 (IC3 divides by 10 while IC4 divides by six). The multiplied frequency is taken from theVCO(voltage controlled oscillator) output of IC2 at pin 4 and this becomes the signal to drive the frequency counter. Its output reading is the speed of the shaft being measured inRPM. A narrow positive-going pulse train to turn on Q1 and theLEDs is obtained from pin 3 of IC4. This has the advantage of giving a much sharper marker line (on the shaft) illumination. The unit can be powered from a 12V 500mA plugpack or a suitable battery.

Circuit diagram:

#### Figure 1 Stroboscope Uses WhiteLEDs Circuit Diagram

Editorial note:
At switching frequencies above 100Hz (6000RPM) the persistence of the phosphor of the whiteLEDs will make the circuit ineffective. To run the circuit at much higher frequencies, substituteLEDs without phosphors; eg, red, green or yellow or a mixture of these).