Simple PhotoCell Timing System
(S.P.T.S.)
LIGHT SOURCE
(c) Bryan Brown & Art McEwen 1997-1999
All rights reserved, not to be copied without permission.
Different computers require different intensities of light source to activate the PhotoCells. Initially, my trusty old 8088 required a 120 volt/60 watt light bulb about 4 inches away from the PhotoCell imbedded in the track. Ultimately, we ended up using a 120 volt/25 watt light bulb designed for use in a fish tank. (See picture of the Timing and Scoring Gantry on my web page). Art’s 386-20 worked initially on just ambient room light but when we moved the sensors to the back part of the track, the lighting wasn’t as good and he needed an overhear light (but at a distance of about 3 feet).
The net of this is that each track and computer are different. You will need to experiment and will learn from trial and error. Once you find the correct settings, you will never have to change them.
On my YMR track, I built a gantry which houses the light source. The advantage of the gantry is that the light can be fairly intense but exactly positioned and constant. Without a gantry, you run the risk of someone waving their hand or arm over the sensor and triggering a lap time/count. The gantry prevents this from happening. The other major advantage to the gantry is that you can dim the room lights for Enduro car night racing (thus killing ambient light) but still be able to have lap timing and scoring.
You may not need to build a gantry and you certainly don't need to build one right away. You can start by just using a desk lamp or table lamp. The building of the gantry (if required) can come later and you can integrate it into the scenery.
I did some experimenting with 12 volt lights and found, for my computer, that I couldn’t get enough light intensity. For a newer computer, this may work fine, but we decided to go with a simple 120 volt light. Simple is best!
Here is the YMR Timing Gantry with roof removed to reveal
120 volt/25 watt light bulb (as light source) and
PhotoCell installation demarked by orange line across track.
For LEMANS Enduro racing, you must stop your car over the PhotoCell (hence the orange markings) in order to register as a pit stop.
Last Updated April 21,2000
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