infra red timers - why is the receiver on the bottom?

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madumi
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infra red timers - why is the receiver on the bottom?

Post by madumi » Thu Nov 09, 2017 3:17 pm

Just thought I'd throw this one out there, as I'm sure there must be a simple explanation... When I've been looking at many DIY timers, it seems that the transmitting LED is placed on top, the receiver on the bottom. Isn't that a recipe for interference from the ambient light?

Or is the flash of reflected light from cars finishing a worse situation to have to deal with if the receiver were to be placed on top? :scratching:



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gpraceman
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Re: infra red timers - why is the receiver on the bottom?

Post by gpraceman » Thu Nov 09, 2017 6:25 pm

It is less likely that the light will bounce off the track, then bounce off the underside of the car and then blind the sensor to the passing of the car over it.


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madumi
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Re: infra red timers - why is the receiver on the bottom?

Post by madumi » Thu Nov 09, 2017 10:05 pm

aaah, that makes sense... so, it would be one step better to paint that section of the track black also?



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Re: infra red timers - why is the receiver on the bottom?

Post by gpraceman » Thu Nov 09, 2017 10:23 pm

madumi wrote:aaah, that makes sense... so, it would be one step better to paint that section of the track black also?
Absolutely

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Randy Lisano
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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.

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MaxV
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Re: infra red timers - why is the receiver on the bottom?

Post by MaxV » Fri Nov 10, 2017 8:42 am

The Judge timer from newdirections does have the light source in the track and the sensors on the bridge. In my experience it has the least issue with light reflectivity.

Maybe better than flat black paint is to reduce the size of the aperture in the track. An 1/8 inch hole is big enough so sense the light, but too small to allow reflectivity.

Image


For more information:
http://www.maximum-velocity.com/pinewoo ... _v7_i2.htm



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