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Lightning Detectors

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GizmoWizard

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Does anyone know how the consumer hand-held lightning detectors work?
I assume that the strikes are detected using a VLF receiver of some sort. What I'd like to know is how do they go about getting the distance and direction from strike to user?
 
Several home brew designs are receivers that are tuned to about 300 kHz. None of the home brew designs I am familiar with provide any indication of distance or direction.
 
I have been toying with the same idea myself. Dr.Atomic, another contributor of this board has been giving me some ideas. I was originally looking at a detector circuit with a 300kHz tank circuit as the front end, which would flash an LED or sound a Piezo buzzer. He suggested an optical setup, namely a hemispherical photodetector, in conjunction with a microphone, to record the flash vs. thunder, and a program to (x/5) to determine mileage distance. The microphone would probably be a speaker, so that the large diaphragm would be more sensitive to the low frequencies. We would have to work out light filtering, to block the sun from overloading the sensor, but to look for discharges thru oxygen and nitrogen at a particular wavelength (777.4 nm for oxygen, 868.3 nm for nitrogen).

Here is some of my info references:
**broken link removed**

http://www.lightningsafety.com/nlsi_lhm/detectors.html

Hope that helps!! Otherwise, Google lightning detection methods/schematics
 
A couple of things -

A. When a thunderstorm approaches or isn't too intense one could expect that a flash/noise burst would be followed by the audible thunder. As the thunderstorm nears, it might be difficult to connect the flash with the resulting thunder. Multiple strikes could get confusing.

B. The filter idea is good - one might also tie some logic in that the visible flash should correlate with a noise burst - if not then the origin might not be lightning.
 
Just use an AM radio.
 
Electrode's 2nd link has a table that shows the hand-held detectors have about a 50 percent failure rate. stevez's suggestion that the F-B (flash-to-bang) would be more difficult to match during multiple strikes may account for that error rate.

Although the commerical detectors' ads do not mention sound as one of the detection elements, it just dawned on me that their ads do say that the detectors are more accurate outside than inside (a clue perhaps, since low frequency RF travels through buildings much easier than sound).

More thoughts/ideas?
 
I got a circuit somewhere for a lightning detector with a sensor from some copper wire like an areal , two germanium diodes and a µA meter.
The meter will show when lighning is nearby because of the magnetic flux created from the surge.
I see if i can find it.
OK the areal wire has to remain low because you don't want to get hit by a strike of course.

An AM radio is perfect for detection too.
 
I recall something about the potential between ground and sky building as a storm approaches - and that this could be measured. I understood that an increase in potential suggested an increase in strike probability - and that the local potential would drop as the result of a strike (as you'd expect).
 
I had seen a project on MatchRockets.com that utilized ionization to detect ambient charge in the air. It involved burning a camping lantern (Coleman) mantle to harvest the Thorium content, and mixing the ash into an epoxy. The epoxy is then applied to the sharp edge of a razor blade and then mounted on a tall dowel rod/ broom handle as an antenna above your roofline. A ammeter is connected between this and earth ground. Supposedly, you can see the charge build up just prior to a strike. Also, Americium 241 can be removed from a smoke detector and used as well.
 
Thanks for the links HiTech. I hadn't seen the second link before (the Sferic Detector), maybe I can get some more ideas from that schematic.
 
The absolute best lightning detector I've used is this one-shot type; they are easy to find and certainly disposable.

**broken link removed**
 
A few years back I was toying with the idea of using Hall Effect sensors at right angle to each other as the lightning detectors are really looking for a magnetic changes. Some detector aerials are wrapped in al-foil to keep radio waves out. If the Hall sensors weren't quite sensitive enough I was going to cut a slot in a ferrite ring(big ring) and position the sensor in the slot. This was the only solution I could think of to keep the device portable, the other lightning aerial was a metre(3') square.
 
Another (more expensive) method I've seen is the Stormscope by L-3 Avionics. There's also the Strikefinder? by Insight Avionics.

Both approachs use DSP processing to find range and bearing. If you search for patents on either product you can find some good information.

I think both devices use a pair of orthogonal coils of (60 turns) to receive the direction information.
 
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