Externally triggerd timing/scoring system

I've been doing searches all over the net trying to find what I need to put together a cheap but effective timming unit using a laptop and timing software. I don't know what's needed to inteface the start/stop sensors to the serial port so that it starts the clock stops the clock and records the time to a data cell for logging. Does anyone know of any diagrams for wirring and hookup to the serial port ?

An IC such as the ST232 attached will do the job. It converts RS232 levels into CMOS/TTL levels. I think there are other versions also such as the MAX232.

ljcox said:

An IC such as the ST232 attached will do the job. It converts RS232 levels into CMOS/TTL levels. I think there are other versions also such as the MAX232.

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Thanks for the reply. I'll be working with 24vdc photo sensors and am pretty sure I don't want to put that voltage across any of the serial port pins so was going to use the output of the sensor to drive a relay. How would I go about using the relay input to tell the program to start the timer the second sensor/relay to stop the timer and load the timer reference into a cell in say excel.

Are you familiar with micro cotrollers? I would use a small PIC to read the output of the sensors. The PIC can meausure the time interval and send it to the computer. It can control the relay too.
As suggested, a MAX232 adapts the voltage levels.
You can use hyperterminal or similar tools to get the data and copy them into excel for following elaboration. If you require real-time calculations, you need to write a custom application with C or basic, though.