i need to create a system that has two gates. when the first gate is broken it starts the timer and when the second gate is broken it stops the timer. i was thinking about using something like this
http://www.electronic-kits-and-projects.com/3130.htm
or like this
http://www.maplin.co.uk/Module.aspx?...1800&doy=15m10
or like this
http://www.maplin.co.uk/Module.aspx?...7513&doy=15m10

oh and i need it to do it through the computer.
does anyone think its possible and quite cheap?

An old Apple computer with the 6502CPU works well for this application.
This computer has several 1 bit input ports that are addressed and can
be checked with a simple assembly language program. Bit location 1
on--start counter. Bit location 2 off--stop counter. Photo diodes or
Csd(?) will work for on/off bit switches--or of course you could use
simple wires or actual switches.

Good luck.

ok but im having diffuclty in finding a an apple comp like that. does anyone have any other ideas?
i know this is probably completely incorrect but i was thinking getting a USB connector and finding the red and the black wire and connecting that to the infra red gate. (que laughter)
basically i want create a timing system like i imagine they would have for something like the 100 metres where breaking the first gate starts the timer and breaking the second gate stops it.
Many thanks!

complementorylex wrote:

}basically i want create a timing system like i imagine they would have
}for something like the 100 metres where breaking the first gate starts
}the timer and breaking the second gate stops it.

Use an older Mac with modem & printer ports...first IR triggers
through modem port, 2nd thru printer port, assuming a Mac serial port
can communicate up to 100 meters from the PC. Programming the Mac
ought to be not difficult, assuming you can program.

Stan.