Meteorological Sensors

Lightning sensor

The special feature of this detector is to provide a logarithmic response, approximately proportional to the distance. For a comparison, between linear and logarithmic scales scale, read This page.

In this new version (version 4) we have added R4 which limits the output voltage to 3.3 volts to prevent the Master from blocking the USB (it rarely happened but it could happen).

We're not competing at useful Lightning maps on the WEB. We are interested only in local lightning, within 50 Km or so. And we don't care about the direction and position, only the distance.

In this picture you can clearly see the difference between electrical impulses (ignition of appliances) and lightning from real. Lightning produce larger impulses.

The intent is to have an automated signal to protect sensitive equipment and in this our Measurer, works much better WEB maps. Web-based maps fail to see local lightning, especially if they're weak and low. Instead our Measurer, local lightning them all. And more are close and more accurately report them. Exactly what it takes to protect sensitive equipment.

Download the complete project Eagle and GCode for the cutter:
uploads/files/Theremino_LigtningDetector_V4.zip

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Achievable accuracy

Attention: The distance scale is highly approximate. The lightning are all different, Some are between cloud and cloud, others are vertical, Some are weak (and are considered farthest of reality), other stronger (and are treated as real's closest). There are lightning that last a very short time (then indistinguishable from electrical noise) and other lasting many seconds.

The maximum you can get is an order of magnitude type: 100 Km / 10 Km / 1 Km.

The accuracy is adequate for what we want to achieve, be warned of the danger. When you hear the Thunder the distance is less than 20 Km and receive very strong impulses. If the storm is very close, it triggers the relay which insulates the equipment, When you move you restore the relay. This is the purpose of this sensor, the rest leave it to maps on the web, they are made to do statistics and determining positions.

Everything that is beyond the 100 Km, We are interested only in the functional test. The chances that a thunderstorm you walking in the right direction for 100 Km, up to hit us, are virtually zero.

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Preliminary videos

These are videos made during the first tests, mind you:

• The position of the sensor is in the middle of the map, indicated with “Bollengo”
• The weather program was under construction and some boxes were not working yet
• The maps "blitzortung" delayed from 5 to 10 seconds
• The maps "blitzortung" do not indicate all lightning. Many local lightning are revealed by our sensor but in the maps on the Web do not appear.

https://www.theremino.com/files/Strikes_1.avi

https://www.theremino.com/files/Strikes_2.avi

In the first and second video you see lightning very close and making sure you also feel the Thunder (recorded from the microphone). In both videos the map on the web incorrectly identified them.

https://www.theremino.com/files/Strikes_2Km_not_25Km.avi

In this third video the time between pulse and Thunder indicates approximately 2 Km, but the map on the web incorrectly places the lightning to 25 Km from our laboratory.

Distances are always very rough, not all lightning have the same energy. Though we could check, with the time between pulse and Thunder, as for Lightning, our detector is more accurate maps Blitzortung.

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Directivity of the receiving coil

To obtain a uniform sensitivity in all directions, the receiving coil must have the vertical axis, as in the image below left. If you would like the image to the right, Lightning front and back would give stronger signals of reality. While the lightning bolts on the sides would give the weakest signals.

Vertical axis – Ok Horizontal axis – WRONG WELL
Directional sensitivity Bi-directional sensitivity

If there were no land, radiation lobes would have a more rounded shape and adjust. But the soil acts as a huge ground plane, that distorts the lobes and drives them upward.

May be natural to think of “improve” This sensor, by increasing the sensitivity. But this project aims to measure distances with great accuracy, not to reveal the lightning a thousand kilometers.

Another idea would be to put the spool directional standing and make it in one direction, with some metal shielding. There try, the only effect would be to screen the reel and unable to arrive at normal 300 Km. A structure able to modify directionality should be comparable in size to the wavelength. The frequencies we receive are approximately around the 100 KHz, then the wavelength is approximately 3000 meters. To get some effect on directionality, the elements (Spotlight and directors) should be enormous, and spaced hundreds of meters of each other.

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Construction of the receiving coil

The image on the left is a spool of elastic thread for jewellery (in the mercerie or on eBay). The image on the right shows a cropped from the center of one coil “Rolla” (big spools 16 ' ' that you wrap the SMD components). We recommend to buy “bobbins for costume jewellery” on eBay from francesina80 and specify that should be blank. Will make you a special price: 2 for 2.5 Euro, or ten per 4.5 Euro, shipping included.

The important thing is that the inner diameter is about 60 mm. The thread about from 0.18 or 0.22 mm and the number of turns around 500. The final impedance should be about 25 MH.

With a large coil just 60 mm, is measured with great accuracy the distance of lightning up to 300 km. Are unnecessary external antennas, because it picks up only the magnetic component, who walks through walls without attenuation.

Images of the coils used in rehearsal:
www.theremino.com/wp-content/uploads/files/Lightning_Sensor_Coils.zip

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Shield the coil by electric fields

The coil must be screened at the top and bottom with two large washers copper adhesive. Here is shown only the top washer and its connecting wire (in green) But even the lower washer must be equal, and also it grounded.

Not to decrease sensitivity the two washers must have a central hole is very large and should be cut, so as not to present one turn short. Enlarge the image by clicking it and look at the location indicated by the green arrow.

The coil outer pole must be connected to GND. Like this, the external coil windings are internal screen. This greatly reduces the interference by the electric system.

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Place the coil and amplifier circuit

The coil should be placed at least two metres away from any electrical wire. It is not recommended to place it in the attic (or even worse outdoors). We investigated this detector to be small and simple, a juxtaposition of the coil avoids complex plants and keep it all within a few meters from your computer.

Initially we suggested to place the coil circuit amplifier, connect to it with a short shielded and shield is the circuit that the coil. With this arrangement, between the receiver and the Master would use a three-conductor cable, as specified here.

We recently made new experiments and found a better solution. Closes the circuit amplifier in an aluminium box (or covered by copper adhesive), connected to GND. The box can stay close to your PC and to the Master. The box part a shielded cable that goes to the receiving coil. Not to lower the resonant frequency, the capacity of the cable should not exceed 200, 300 PF maximum. With a cable for TV, from 75 ohm resistor (Rg56 or RG59 from 53 pF per meter) you could get up to 3-5 meters. Or you could use the RG179 and RG187, they are very thin despite being only 65 pF per meter. With low-capacity cables It could be as much as 10 meters.

The receiving coil should be placed by trial so as to reduce as much as possible the noise. Very good if you can get below to 100, but it's still good, If you can stand under a 150 or 200.

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Functional check

In the application, you must configure the Pin as HAL: Adc_16, MinValue = 0, MaxValue = 1000, Response Speed = 100 and Response Speed button disabled (not Orange).

The left picture shows a scale of approximate distance and a bottom layer less than 80. The right image shows an electrical disturbance and lightning. Note that Lightning produces larger impulses. If the sensor is away from electrical wires, electrical noise should be quite weak, you don't get counted. The application Theremino Weather tight and weak pulses discards.

The baseline level indicates the proper operation of the detector circuit. You should not exceed the value of 200, better if you can stand under a 100. Changing position to the receiving coil, away from every object (even the wooden tables lead) and possibly by decreasing the sensitivity with the trimmer, You should be able to lower this level.

You could also shield the coil with two sheets of aluminium or copper, one above and one below, connected to GND. The two sheets should have a central hole and a radial cut, so as not to present one turn short, that would reduce the sensitivity. Check that the test generator is revealed, up to 100 – 120 cm away.

For a comparison, between linear and logarithmic scales scale, read This page.

In the future we will improve this project, with detailed instructions. For now we publish raw images, made during rehearsals. In these pictures you can see how they compare our sensor signal, with the distance shown by maps Blitzortung:
www.theremino.com/wp-content/uploads/files/Lightning_Distance_Scales.zip

If necessary write to Lello, to this address, for advice on building and functioning.

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Lightning test generator

Each time the button is pressed, the generator produces a pulse with a duration of 200 mS and with a frequency of approx 10 kHz, which is in the middle of the lightning detector passband (from 700 Hz to 30 KHz) gang where lightning produce the maximum energy.

With this generator you can make lightning sensor sensitivity. The lightning are simulated only as amplitude. The duration of these pulses is shorter than that of lightning from real.

The generator consists of:

• A stack from 9 Volts
• A connector for battery 9 Volts
• A resistor from 100 K
• A capacitor by 1 uF 16 Volts
• A button (in the pictures a microswitch)
• A coil from 220 UH wrapped up a small ferrite core open (must not be closed in a barrel) (about 50 coils on core from a dozen mm)

The battery keeps the load capacitor to 1 UF through a resistor from 100 K. When you press the button the capacitor is closed on the spool. The coil and the condenser swing for a brief moment and generate an electromagnetic wave, similar to that of lightning (but the shortest duration)

The coil should be similar to our, otherwise it could give much stronger or weaker magnetic pulses and distort the test. If with 58 you get very different impedance coils 220 UH, then the type of ferrite is not suitable.

• • Ferrite height = 11 mm
  • Width (outdoor) = 15 mm

• Width (inside) = 7 mm
• Turns = 58 (about)
• Wire diameter: 0.5 mm (about)
• Impedance: 220 UH

If necessary write to Lello, to this address, for advice on building and functioning.

The coil must be kept with the vertical axis (and also that of lightning detector must be vertical). A meter apart is approximately 300 Km. Approximately ten centimetres 30 Km. A centimeter is about 3 Km. With two coils close you should get the most signal (almost 1000 Thereminico value).