Woohoo! So here it is...in all it's unfinished glory.
List of Materials:
Laser Pointer -
$21.00
Phototransistor -
$1.50
AC Adapter -
$15.00
Software -
Free
Old 9pin or 25pin Serial Port - buried in the junk heap
Soldering Iron / Solder - if you mod you have this
Laptop or PC - I used a 486 DX2/50MHZ laptop with a bad LCD panel..I just knew it would be good for something. Oh yeah, you need Win9x or XP...you might get away with Linux and Wine
How it Works:
You put the phototransistor (light activated switch) on one side of your start/finish line, and then put the laser pointer on the other side and aim it at the transistor. When a car breaks the laser beam, a signal is sent through the serial cable to the PC. The software does the rest. I can see drag racing having one for each lane...the software supports 4 lanes I think, keeps track of laps, lap times, fastest lap, and speed.
The Bad News
It actually costs more than $4.00 because my original idea (flashlight) was a failure, and I had to upgrade to a laser pointer because of the distance I needed the light to travel without dispersing. So, a cheap laser pointer modified to plug into the wall will run you about $35.00, unless you can find a 3v AC adapter in your heap.
The Good News:
You don't have to attach any kind of transponder to your Zip.
More Bad News:
Because there's no transponder, any car that crosses the line is timed, if two cars cross at the same time...well you get the idea. I designed this mainly for drag racing and solo time trials around my track...forget about using this for multi-car racing purposes.
More Good News:
No more guessing about performance increases, track lines, or driver ability.
The Future:
Because the software supports more than one switch, adding a second spaced about a foot apart would give you a nice speed trap for testing high end and/or acceleration on the drag strip.
pics to come.