# LED High frequency Strobe

Discussion in 'The Projects Forum' started by Mechanic, Apr 2, 2013.

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1. ### Mechanic Thread Starter New Member

Mar 26, 2013
3
0
I am actually a mechanical engineering student and fairly new to circuits.

For my graduation project, I am building a test-setup in which we use a camera setup. To avoid having to use a high speed camera, we are looking into two exposures per frame to do PTV.
For that reason I looked into high power led-modules and am looking into a circuit that makes the LEDs flash at a clearly defined interval at a clearly defined speed.
Furthermore the circuit must accept trigger signals to be able to synchronise the camera. The camera sends out a pulse every time it takes a shot.

The pulses I need are of 0.1-1 ms and the times between the pulses in the same order, but always larger. I found the circuit posted below for the astable oscillator that puts out such a signal.

I found out the following project for driving high power LEDs http://forum.allaboutcircuits.com/showthread.php?t=32364.

I am now wondering whether I can actually switch the LEDs that quickly. And I furthermore wonder how should I incorporate the triggering?

2. ### DickCappels Moderator

Aug 21, 2008
2,591
610
Two steps:
1. Change the 555 circuit from astable to monostable.
2. Add a buffer to handle higher currents (you did not say how much current you need)

Step 1. Change from astable to monostable.
Starting with the circuit you have above,

A. Remove R2 and D1, disconnect pin 2 from pin 6 and C1.

B. connect R1 and Pin 7 to pin 6. The pulse width is determined by R1 and C1.

C. Connect a 47k resistor between pin 2 and pin 8.

D. Connect one end of a 470 pf capacitor to pin 2 and one end of the 47k resistor. The other end of the 470 pf capacitor is the negative-going trigger input.

A. Connect one end of a 470 ohm resistor to pin 3.

B. Connect the other end of the 470 ohm resistor to the base of an NPN transistor (select based on how much current with which you want to drive the LED.

C. Ground the emitter of the transistor.

D. Connect the LED in series with a current limiting resistor between the +12 volt power supply and the collector of the transistor. Be sure to observe polarity of the diode.

Last edited: Apr 2, 2013
3. ### sheldons Active Member

Oct 26, 2011
616
101
heres a strobe circuit i use....

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4. ### Mechanic Thread Starter New Member

Mar 26, 2013
3
0
Thanks for you help.

I am trying to understand how the schemes work.

DickCappels, how does your circuit produce two pulses? Monostable only produces one pulse, if I am correct.