Low cost - long-ish distance laser?

I was thinking cheap red. I got tired of not having a pointer in the conference room (the projector fires above the whiteboard, too high to reach) so I bought ten on ebay. $12 total, shipped from China.

"Driveway Alarm-Wireless Motion Sensor Alert System with Long Range Receiver & Transmitter. Home or Offic Security Protection-Front Doors, Entrways, Garages, Alleyways, Stockrooms, and Warehouses."

At amazon and most likely in a Hardware stort near you. ~20 bucks.

Make sure it is "LONG RANGE"

Put it in a tube, and blow compressed air out of it continuously. That's how folks do optical inspection of railroad tracks, and train undercarriages are _dirty_.

Another approach is to look obliquely through the free surface of a fluid that gets renewed continually.

Cheers

Phil Hobbs

Here's how Illinois does it: $1.3 million divided by 22 cameras is only $59,000 per camera. I don't think you'll have an ice problem where you're located so you can forget the heaters.

I have a similar problem. One of the weather stations that I help maintain has a camera on a tower at the 80ft level. It's currently in a proper heated environmental camera enclosure, but does need cleaning every few months. The insurance company requires a certified tower climber for this, which is not cheap or easily scheduled. So, I've been looking at alternatives: Probably overkill for your light sensor but still useful:

Personally, I think you need a quadcopter. Just fly over the lens, give it a squirt of cleaner, and blow off the excess with prop wash from the quadcopter. Not very efficient, but certainly more fun than other methods. If you have problems lifting the liquid cleaner, then build a catapult to deliver a water balloon full of cleaner to the light sensor, followed by quadcopter prop wash blow dry. Be sure to patent the system as the desert equivalent of the Illinois system.

Have a nice holiday.

But there's LOTS of laser pens on the market, and not all in the under-5mW range. The pilots are justified in worrying every time they get ranged.

I'm actually fairly proud of myself when I can come up with an answer that's almost as simple as possible. By nature I'm one of those guys who can answer any complicated question, and can make any simple question complicated in preparation to answering it.

infrared remote controls have the same problem. they solve it by modulating the signal at 37kHz or there-abouts and looking for the

infrared is more difficult to aim and focus than a visible laser but modulation should still work with a laser, you jusr need a moderately fast receiver (photodiode or phototransitor) instead of a "solar panel" for the receiver and a band-pass filter. optics at the home end focusing on the source would help too.

At least you did not offer a Spice listing that only the theoretical Gurus are set up to look at lol

Green laser is much easier to see than red. Subjectively a factor of five brighter for the same nominal power output.

In the case of pointing at stars the wavelength dependence of backscatter also helps. Although the 405nm violet was useless since the eyes sensitivity up there tails off badly even if backscatter is more.

Interesting idea. I like the motorized "film roll" plastic sheet. However, the situation is very different in a race car and on a tower. In a race car, one doesn't need to worry much about long term environmental issues, such as rain, dust, fog, UV, etc. However, on a tower, anything that moves will need to be protected from dirt, dust, water, birds, insects, and impact damage. An automatic film roll or protective plastic peeler is possible, but one that's rated for IP64 or better seems difficult and expensive. Compared to a windshield wiper, a motorized additional lens cover seems like an overly complex solution.

One of the potential problems I'm dealing are the effects of dust and wind storms. On mountain tops, they can easily reach some rather high speeds, which imbeds dust particles into plastic lens covers, and scratches common window glass. At this time, the window is made from the original version of what is now Corning Gorilla glass, which does a great job of resisting damage from airborne debris. If I were to add an additional plastic film in front of this window, it would be fatally pitted and sandblasted after the first storm. Film roll and

Incidentally, I'm now working on finding a windshield wiper blade that lasts 2 years, and a window cleaner formulation that won't evaporate in the tank, but will completely evaporate on glass. The wiper control electronics is trivial, except that it has to work reliably on a mountain top full of TV/FM transmitters.

Years ago, I was outside at night with one of the $1 lasers, I pointed it towards the auto dealership near my house. At over 100 yards the taillights lit up very brightly, I was impressed with the reflectors. Mikek

I think that stamped piece of aluminum is so simple, I don't know someone hasn't improved on it to make it a good design. (hmm, since you know what's wrong with it ;-) I hacked an N connector on to wifi dongle to connect directly to the MFJ1800. Then used usb down inside the boat. I used it on the boat for about 4 years. Even as bad as it is, it still got me internet on the boat. Good enough to watch youtube videos. Mikek

Retroreflecting film, especially the high efficiency stuff such as ScotchLite 3600X (corner cubes), ScotchLite 7610 (glass spheres) and some of the better Reflexite materials, can give you a detected signal increase of 70 dB. I've used them in instruments, and in the right situation they can make a seemingly impossible measurement easy.

Not bad for a bit of tape!

Some of the Reflexite materials are especially interesting, because they send the light back with a fixed offset angle, rather than directly back to the source.

Cheers

Phil Hobbs

A better question would be why MFJ hasn't bothered to fix theirs. It's still being sold: There's nothing wrong with the basic idea as shown by the simulation results. It should work, if it were built correctly. Since then, I've worked on a better way to build a sheet metal yagi, but don't want to discuss it here.

MFJ did get one thing right. They used a folded dipole driven element, which seems much better than the cheaper gamma match that gave me problems.

Full disclosure: Mike K (amdx) was instrumental in the above simulation. Here's part of the 2009 discussion:

A good start on a fix would be to remove the ferrite bead "balun" and replace it with a 4:1 balun. Something like this balun: I hacked an N connector on to wifi dongle to connect directly to the

Getting rid of the long exposed leads at the N connector was probably a big improvement. Same with adding an external antenna to the USB dongle. However, methinks that replacing the ferrite beads with a proper 4:1 balun would have had the most dramatic effect by properly matching the impedances (instead of just blocking the reflected RF with the chokes). The 4:1 VSWR is 36% power loss.

Most of the serious circuit designers on this list have LT Spice, and it's free and easy to get. So it's hardly something for just the "theoretical gurus".

Especially since theoretical gurus do their own math. ;)

Cheers

Phil Hobbs

LT Spice lets me *avoid* a lot of theory. I sometimes it to design dumb stuff like voltage dividers or Schmitt oscillators, just to save wear and tear on my calculator.

Reducing the dynamic pressure by using a *curved* piece of toughened glass might help that. Anything that helps shed the wind around the camera assembly will reduce the kinetic energy of incident particles. Perhaps even a wire grid; can you afford to "pixellate" the images through a grid? Just some random thoughts...

Enough time has passed that I believe Jeff has forgiven me. :-) Mikek