[David G4EBT]

My input to this project has largely been to design a PCB and to suggest elements of the circuit to be added. Initially I didn't know if it was to be powered from say a 'wallwart' or a battery, so I included a reverse polarity protection diode, but the current consumed by the project was so low - just a few mA, and given that the strobe would only be used occasionally, and for a few minutes, a PP3 battery made more sense, and a TL05 regulator.

It's quite possible that given that only one ultrabright LED was to be used, and would only be 'on' for 1/16th of the time at 300Hz, that the output of the 74HC08 would have been adequate to drive the LED. However, given that a transistor driver only needed two resistors and a transistor, it added little complexity to include one. I claim no credit for that - it was 'lifted' from the circuit provided by Tony Duell in post #3 of this thread. Tony had used four LEDs in his strobe, and the relevant part of his circuit is enclosed. The LED and transistor are powered from the unregulated 9V line.

It may also have been that IC2, which converts the 300Hz square wave from a symmetrical to asymmetrical square wave could have been eliminated, making the circuit simpler still. However, since it wasn't known whether LEDs possess 'persistence' rather like a filament bulb, and hence, would not go instantly one and off at 300Hz, so would not give a solid 'flash' for each cycle, again, Tony Duell's idea of 1/16 'on' and 15/16ths off for each cycle was incorporated.

I played no part in the design or it's concept, in which - as has been stated, David ('Radio Wrangler') and Tony Duell had the major input.

Pic 1 shows Tony Duell's LED driver circuit from his design in post #3.
Pic 2 is the final 'Donald Stott' circuit of the 300Hx strobe.
Pic 3 is the component overlay and 'X-Ray' of the PCB I designed.
Pic 4 is the positive artwork for anyone who still uses pre-sensitised UV PCB laminate.
Pic 5 is the negative artwork for use with the negative UV dry film process.

The artwork in pic 5 can also be used for the laser printer 'toner transfer' iron-on technique , which obviated the need for a UV light box and developer. The artwork is shown in reverse because if printed as a UV mask, the ink side of the acetate must be next to the laminate, and if used for the laser toner transfer method, it must be printed as a mirror image or when ironed on, will result in a back to front PCB.

I don't use a PCB design package - I find them not easy to use, and not geared to homebrew techniques. I use 'Paint' for drawing circuits and creating PCB layouts and artwork.

I built one myself to check that it worked. (Initially it didn't as a link was missing from the circuit to ground pin 12 of IC1). Anyone looking closely at the PCB layout might wonder why there's a connection from pin 11 of IC1 to pin 6 of the crystal oscillator socket and then on to pin 7 of IC2, when the oscillator only uses pins 7, 8 & 14. I just used a spare pad on the oscillator DIL socket to get a track from pin 11 IC1 to pin 7 of IC2. (Rather like the spare pin used by Bush as an anchor point on the DAC90A audio valve socket!).

I've been pleased to have played a part in this project, which I knew from the outset would be pursued with dogged persistence to a successful conclusion. My own strobe is housed is a small ABS box 8cms x 6cms x 4cms deep.

Hope that's of interest and use.