Portable Strobelight

Stroboscopes usually produce short bright flashes of light at adjustable but regular intervals. Commercial xenon stroboscopes must be plugged into a wall outlet, since the xenon-filled tube, which produces extremely bright flashes of light, requires more power than would be practical for portable use. The portable strobelight (pocket strobe) reported here is recommended for convenient field use. This pocket strobe allows from about 1 to 8 flashes per second. It is completely solid state and lightweight. It employs a high-intensity (super-bright) light-emitting diode (LED) to produce yellow light.

The LED circuit consists of three main sections - the power supply, timing circuit, and LED driver (figure above). The power supply is a 9-V alkaline battery. The timing circuit is a 7555 timer chip. The LED driver is simply a silicon PNP transistor and a current-limiting resistor. This strobelight produces short flashes of yellow light lasting only about 20 ms. The time between each flash is adjustable, but the duration of each flash is fixed by the circuitry. The 3.3k resistor connected to the LED provides a current-limited output to drive a frequency counter.

The flash rate can be read with a frequency counter. Although this method is the most accurate way to measure the repetition rate, an easier and more portable alternative method handy for portable use is to use the frequency counter only once to calibrate the dial on the strobelight. An approximate rate can then be read directly off the strobelight without need for a frequency counter.

Useful link:
ICM7555 datasheet (pdf)