Does anyone have experience with gate sensing technology for cars? Right now I just use IR emitter / detector pair with the analog output directly into a microcontroller digital input. My concern is that the trip time would be too dependent on the front profile of the vehicle, i.e. vehicles with larger frontal profiles would trip first. Do the commercial units trip off the first derivative of the input signal or do they use a comparator / Schmitt trigger? What do your circuits do?
- Stan Pope
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"If it's not for the boys, it's for the birds!"
The standard sensor is a photodiode that is driven into saturation by an infrared LED beamed into it. The car causes a shadow, and the diode rapidly comes out of saturation. The system is immune to flash photography because a sudden increase in light would only drive the diode further into saturation, which is meaningless. It is immune to florescent light which contains very little IR. It is susceptable to strong IR environment such as outdoor light, or incandescent lamps.
Sunlight Max is my other system. This uses narrow band elliptical filtering to look for a special coded signal emitted by the IR LED. It is slower in operation, but immune to IR content in the environment. In fact, it will work in full sunlight. It is expensive, but some groups, especially in Florida and California, like to hold their derby outdoors.
Why on a multi lane track with only 1 car running does the time increase in the lanes closest to the recieving box of the timer. This happens when the timer is tripped by the car instead of the starting pin. It is about a .03 difference from one lane to the next closer one.
So , where is the best or correct palce to mount this style timer?
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Yes Yes and No, in that order. It is always better to have the movement of the gate start the timing instead of the cars themselves. The movement of the gate should be a more reliable event. Cars can have different nose profiles which could cause variations in the timing. If you are scoring by times you don't want that variation possibly influencing the results.Buckeye wrote:Should it be mounted so the tip of the starting pin breaks the beam? If you do that, wouldn't a simple switch on the starting mechanism, place properly do the same thing for alot less? Should it be mounted past the starting pins sweep so that the first car trips it?
Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.