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"Propulsion Studies Database"

  No longer do we have to take a driver, stopwatch, pen and paper to record our lap times. Now we simply drive past the laser line light to start the timer and let the system record each lap as we pass, more accurately than I ever could eyeballing it.

How fast would a 14 inch long object have to travel, to pass between a laser, pulsing at 0.08 seconds with a 50% duty cycle?

If a pulse width of 0.08 seconds had a 25% duty cycle, how long would it be on for?

  At some point in time, even with the mirror design, the off pulses will line up to allow for an open straight shot. Yet that is the approach I was going with after doing the math on the single line having a 0.08 second pulse width.

  My idea used an old USB scroll mouse for powering the laser diode and taking the input from the sensor, to know when the beam is broken by the RC car. Which works great if I was always running at half speed, or wanted to monitor people walking past. The photocell is slow in response and likes any wavelength of light, so not a good choice for my purpose. Plus the mirror approach and my method of mounting, was more susceptible to vibration and false triggering. Also I decided against taking the extra hit on battery life powering the laser via USB.
  So now I've gone full circle and back to a single beam without the slow pulse and separate battery pack to power the laser. I'm using the photodiode in the scroll wheel circuit on the mouse for laser detection. This is much faster than the photocell and already has optical filtering to narrow the allowed wavelengths of light.

Old project image.
New project image.

  The device triggers the lap timer/stopwatch, a BASH script which takes input from the USB port and stores the lap times on my EeePC, in a format ready to import into the PSDB or a spreadsheet.

BASH script, for old project using input from scroll click paste function or the "Any-Key".

  This script could be used to track the time intervals of anything you like. I've even used it for a "lack of sleep" study and hit the spacebar every time I got up in the middle of the night for whatever reasons.
  The concept of using the USB mouse as an input device other than which it was designed, is an idea that hit me one night while thinking up an interface circuit of my own. You have a few micro switches and a couple of photodiode pickups for about ten bucks USD. I could not build a circuit for this cost, nor would it have all the testing and support which went into the mouse.

BASH script, for new project using input from scroll photodiode.
Use tar -xzvf eat.tar.gz to extract "Event Automated Timer" file.

Scientific Hypothesis Ignoring Testability in, equals Scientific Hypothesis Ignoring Testability out.

Project was reviewed and critiqued by the linux chat group found here, all are welcome to join us.