Needs to detect moving vehicles at night at a distance of 200 feet. Outputs
to a 555 Schmitt trigger. (No place to install a fixed reflector. LDR/photo-
diodes worked until the town put in street lights - the farmer put in a
flood light and the snow came.)
Just a detector is needed. (Ultimately it turns on exmas lights - a little
pleasure for the mill's night shift.)

 

You might try putting the photo-diodes inside a tube to shield it from ambient light then aim it toward expected traffic.

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