clocking start and stop times for runners

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Reaction time is a factor in this. I'd use a microcontroller to fire a piezoelectric beeper at the start (what do the real track and field guys use, something like beep-beep pause beep-beep pause beeeeeeeeep?)

A laser pointer to photo-transistor to trigger the stop. A modulated laser would have more immunity to false signals but if the receiver was in a shielded tube (paper towel tube, painted flat black on the inside) you could probably use a CW gizmo.

Radio Shack should still carry "logic level" beepers (built-in driver) and the photo-transistors. IIRC, their peak sensitivity is IR but a red laser pointer may be enough to turn one on.

Narrow beam flashlight would probably do it, too.

Something like a Basic Stamp

would do the trick if you don't have a drawer full of assorted microcontrollers.

Should be easy if the start and finish are reasonably close. If they're 26 miles and change apart, Hmmm ... have a cell phone on speaker set up at the start site to broadcast the starting beeps?

You neglected to say the limits of the timer. I would guess less than one hour should do.

Are you okay with purchasing a timer or do you prefer to build the device?

The photogate should always be a modulated light source so that external interference can be filtered out. This being the case, an incandescent lamp would be a poor choice.

An Ir sensor detects over too broad of an angle so this too is a poor choice. If you remove the fresnel lens, the detection angle would be narrower but it is still a passive sensor, meaning it would detect any heat source.

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Thank you for getting back to me. Yes, I am ok with purchasing a timer, but I am not sure how this would tie in. I not to smart!! Is there any other divice or sensor that may work for the stoping and starting the clock besides a manual push off and on swith. The distance is 40yrd. (40yrd Dash) Can it be accomplished without the use of a microcontroller?

By purchasing a timer, you eliminate any need to build with a microprocessor. You will need to find a timer, cooking timers usually count down rather than up, that you can hack. You will need to be able to solder wires to the timer trigger.

An optical gate will require electronic construction skills. A likely circuit will include a 555 timer IC to create a pulsing light beam for the transmitter and another to create a missing pulse detector for the receiver.

Perhaps the easiest approach is to get the optical beam sensors used on garage doors. Though this isn't the least expensive plus the operating voltage might not be DC.

I once found an all in one unit that used a mirror at the opposite side and provided a relay closure for the output. This you would normally connect to a bell to sense people crossing some area. I'd tell you the name but it is installed at an office a few miles from here. Perhaps I can go there this week and write further.

i want the design for a timer with a pulse delay of 1min and 1 usec at freq 1 Mhz