Fog detector?

[cornutt]

Here's a lighting question. I have some outside lights that I have my system (OPII) currently configured to bring up to 100% at sunset. Among other things, they light the driveway, the front yard, and the area in front of the garage doors. They are pretty bright on 100%, and after we get home from work I usually turn them down manually to 50%. I'd really rather the system just put them on 50% to begin with, but here's the problem: We live in an area that sometimes gets heavy fog. If there's fog, I want the lights to be on 100% so that the house (or at least the lights) can be seen from the road. If I could come up with some kind of fog sensor, I could program the system to turn the lights up to 50% at sunset, and then only put them on 100% if there is fog.

So: has anyone ever heard of a fog detector?

 

[mrhappy]

There are sensors used at airports called RVR sensors which measure the fog or visibility, they are'nt going to be cheap, but the principle generally is some sort of IR beam and photodetector arrangement a set distance apart, not sure how successful it would be if it was home built but may be worth an experiment?

 

[JeffCharger]

There are sensors used at airports called RVR sensors which measure the fog or visibility, they are'nt going to be cheap, but the principle generally is some sort of IR beam and photodetector arrangement a set distance apart, not sure how successful it would be if it was home built but may be worth an experiment?

could you just check a weather report to determine if it's supposed to be foggy? A script that scrapes your local weather site might help....

 

[pete_c]

You can also maybe utilize the HB 1-wire light/solar sensors or maybe a wireless X-10 light sensor(s) to accomplish the same for less money. I graph the HB light sensors and typically when cloudy/foggy the numbers are less. Also using a 1-Wire temperature sensor in a glass jar for sunlight measurements works.

The chart shows a 72 hour period. If its raining, cloudy or foggy the peaks are lower (numbers). A couple of "if then events" would turn on your lights when it was raining, cloudy or foggy. Setting up a sensor with the OPII would be some sort of graduated analogue to digital output sensor; not sure what I would utilize though (maybe UPB, X-10 or Z-Wave?). Maybe an HAI temperature module inside of a glass jar? The outside reading would be unique.

I utilize the airport visiblity readings and icons from a local airport (less than 15 miles or so away) in my WeatherUnderground webcam upload.

 

[mrhappy]

There are sensors used at airports called RVR sensors which measure the fog or visibility, they are'nt going to be cheap, but the principle generally is some sort of IR beam and photodetector arrangement a set distance apart, not sure how successful it would be if it was home built but may be worth an experiment?

could you just check a weather report to determine if it's supposed to be foggy? A script that scrapes your local weather site might help....

I did think of that but thought how often are they correct? Where I live the nearest official Met reporting station is over 30 miles from my house, I ain't a meteorologist (spelling?) but i'd imagine fog can change alot in that distance...but if you've got a met station on your doorstep then yep absolutely going to be easiest method..

 

[JeffCharger]

You can also maybe utilize the HB 1-wire light/solar sensors or maybe a wireless X-10 light sensor(s) to accomplish the same for less money. I graph the HB light sensors and typically when cloudy/foggy the numbers are less. Also using a 1-Wire temperature sensor in a glass jar for sunlight measurements works.

The chart shows a 72 hour period. If its raining, cloudy or foggy the peaks are lower (numbers). A couple of "if then events" would turn on your lights when it was raining, cloudy or foggy. Setting up a sensor with the OPII would be some sort of graduated analogue to digital output sensor; not sure what I would utilize though (maybe UPB, X-10 or Z-Wave?). Maybe an HAI temperature module inside of a glass jar? The outside reading would be unique.

I utilize the airport visiblity readings and icons from a local airport (less than 15 miles or so away) in my WeatherUnderground webcam upload.

I thought about the solar sensor, but it doesn't help if it's dark out. I guess you could predict the fog from the trend of the day's activity and sunlight......

 

[pete_c]

You could theoritically in addition utilize a humidity sensor and even a mapped out visual DVR zone of a nearby streetlamp at night doing the if then three variables then....I've had clouds or inclimate weather trip my DVR motion sensors. Getting the right combo though would be difficult; much like creating a logical event to turn on the alarm/run events to open and close your garage door. You could predict a lot creating an event variable but there will always be unique variable / combinations that you will miss; but then again my lights are already on at night.

 

[apostolakisl]

Here is a thought. Use the garage door opener gizmo that detects when the beam is broken to prevent the door from closing. I have noticed that a little dirt on the lens makes mine more sensitive, not unlike I would expect fog to do. You could put them relatively close together and cover the lens with increasing density filters until it is not quite triggered when the air is clear. Stacking a relatively weak filter material (clear colored plastic) with more and more layers until it trips, then back down one or two layers should do it. With a little fog in the air it pushes it over the limit. Wire that into your home automation system as an open/close circuit and have lights set to either foggy or not foggy based on that open/close status.

You could probably test this for free first by just using your garage door ones as they are, stacking filters until it blocks the garage from working, then back down one or two, then blow some smoke or dry ice fog across the beam and see if it stops the garage door from closing. It shouldn't take but 10 minutes to test the theory and if it works should be buildable on the cheap.

It won't measure the density of fog, just dense enough vs. not dense enough.

 

[judge_l]

What about some kind of light meter? It wouldn't matter what was making the light appear dimmer to the meter (smoke, fog) you would want the light to be brighter. I couldn't find anything that had any kind of output, they all just had an LCd display when I searched for them....

 

[apostolakisl]

What about some kind of light meter? It wouldn't matter what was making the light appear dimmer to the meter (smoke, fog) you would want the light to be brighter. I couldn't find anything that had any kind of output, they all just had an LCd display when I searched for them....

I think the garage door thing is working on that concept but using light in the infrared spectrum where it won't get confused by extraneous light sources, only the transmitter with its defined intensity and distance from the receiver.

 

[roussell]

Check this out, interesting concept that should be possible to replicate.

Terry

 

[opie]

How about a smoke detector (optical type) in a weatherproof housing? Power it and wire the relay to a zone. You would have to do some testing in a bathroom to see if fog triggers it or not.