Re: Suggestions please

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UKoncology wrote:
Gentlemen, I am trying to build, for hobbyist purposes, a circuit
which would meet the following requirements:
-It would drive a luxeon LED 3W continuously, with variable
brightness.
-It would also operate the same LED in a single flash mode, with
external triggering by a flash slave trigger. Ideally the flash
duration should be variable within a range of uSec to a few mSec, but
a fixed flash duration of 0.1 - 2mSec would be fine.
the idea is to use the LED as a microscope illuminator, and also allow
flash photography with the same LED to capture fast moving protists.
The LED in flash mode would be triggered by the camera flash via a
slave trigger, which I already have.
Unfortunately, I lack the expertise to design a suitable circuit - so
am asking for help, oh, and it should be simple enough for me to
build - I am an old codger from the thermionic era, and can't really
cope with PIC programming, which I guess would be a way of doing this.
If anyone can suggest a solution, or produce a schematic of such a
device, I'd really be very grateful, and am sure many of my fellow
microscopists would also be indebted. many thanks, HJ

I would approach this in the following way:
1) You need a controllable current source for the LED. I suggest using
the circuit from step 8 of
http://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/.

2) For the dimming I suggest you use a PWM (pulse width modulation)
circuit with a frequency above 50KHz. These are easy to make with a
NE555N chip. (Search PWM 555 on google)

3) For the pulse generation I suggest another 555 circuit in a different
arrangement called a "monostable". (Search monostable 555)

The idea is then to use the output of either of the 555 circuits to
trigger the current source circuit.

I hope this helps.

- --
Brendan Gillatt | GPG Key: 0xBF6A0D94
brendan {a} brendangillatt (dot) co (dot) uk
http://www.brendangillatt.co.uk
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