Home > Circuits > LED Strobe
Modified:21:14, 22 October 2013

Strobes are useful devices for seeing fast moving components freeze or just as lighting effects. Unfortunately for a really good result you need to use a Xenon flash tube which can produce intense brief discharges of light but it needs high trigger voltages - upwards of 4KV!

However with LED technology moving on quite quickly nowadays, a simple and fairly effective strobe can be built from high power white LEDs.



Signal at the collector of Q2 which drives Q3

Download circuit simulation - Livewire

The circuit is based upon a classic astable used for years in the Alien project. Q1 and Q2 form part of the astable while Q3 is a Darlington transistor used to drive the LEDs.

The waveform shows the . The output pulses are kept at about 80ms while the space between them can be varied from 80ms to about 400ms using VR1 which alters the charge time of C2. The "on" time stays constant and produces a fairly brief pulse for the LEDs.

The current through the 8 LEDs is about 100mA each with a 4.7ohm resistor but since the pulses are brief, even when tested with a supply of 12 volts, the Darlington only got warm and the LEDs coped fine..

Component side
The PCB was designed to have the LEDs mounted on it. This saves on annoying wiring. There are 8 white hyperbright LEDs, around 30,000mcd @ 30mA.

VR1 is mounted directly to the PCB to create a neat module with only 2 wires for the supply.


PCB size: 52mm x 34mm
Copper Track side

Component side

Copper Track side

In the quest for more brightness another model was made that had exactly the same components except that the LEDs were mounted on a seperate PCB.

This time 38 LEDs were connected except this time, pairs of LEDs were wired in series and then paralleled up to make 19 pairs. This increases the voltage drop all were wired 2 were placed in series to prevent large power loss in the LEDs resistor.

The supply was 12v this time and the LED resistor was reduced to 0.47ohms. The result was fairly impressive but no where near the power of a mains strobe. However, some experiments such as a slow running tap produced some interesting images, as well as spinning wheels on motors, making them appear still.


LED PCB - 38 x 5mm LEDs

PCB size: 70mm x 70mm

PCB size: 48mm x 36mm

Designed and Written by Phil Townshend 2009
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