Lighting sensor based on low freq RF AM crystal radio, strike sound light sense

[eneuro]

Hello,
While massive lighting storms are very common in South Poland at summer I need for a few projects some kind of close lighting detection in the range of 10km.
I've noticed simply by tunning AM radio to its lowest band at  500KHz that when lighting strikes are around 30km there is "nice" cracking noise in the radio while listening to empty station 
I confirmed it with this online lighting maping webpage http://www.lightningmaps.org/realtime?lang=en .

There is nice correlation beetween this noise in radio and than this map shows a few seconds later lighting strike 

I know, that  it is available this AS3935 Franklin Lightning Sensor however opinion about its real lighting detection capabilities are divided https://www.eevblog.com/forum/projects/as3935-lightning-sensor/ and its efficiency graph in datasheet looks strange with 40% (less than coin flip probability) to closest hits (page 22 of its datasheet).

It looks like this Franklin lighting sensor has no sound or visible light irradiance feedback which, I think might help better estimate indyvidual lighting strikes distance and by averaging over last hits within lets say 1 hour storm distance estimation.
It only has something like storm front distance estimation what ever it means.

There is nice crystal radio intro with germanium diode  explained for AM radio sound demodulation.

Maybe such simple crystal radio could be usable to listen to for AM radio lighting cracking noise on MCU ADC pin, while transmiting low power white noise on tuned frequency on own transmiter close to this receiver  and when corelated with detected lighting outer air sound on other ADC pins for closer strikes try to estimate better this distance to indyvidual hits?

AS3935 needs external RLC and few more elements too, so it is quite interesting research try to do it in own DIY, while I read a few books about radio antenas design and now it is time experiment with RF transmiters & receivers 
I do not like this sensor has no sound or photodiode feedback for close lighting.

[Circuitous]

There's a chip for that.  I haven't used it, but it looks interesting.
http://www.digikey.com/product-detail/en/AS3935-BQFT/AS3935-BQFTCT-ND/3182215
I was thinking of trying it out, but hadn't gotten around to it.


There's a few items that might be helpful at stormwise.com
http://www.stormwise.com/page28.htm
They talk about detecting magnetic field changes from the strike, and there's a link to a simple detection circuit.

[eneuro]

There's a chip for that.

Yep, AS3935 Franklin Lightning Sensor I've mentioned in my first post with links to its datasheet, but when started analyze this data and related forum posts realized maybe it is worth try DIY it while it is like "black box" and only magic output provided 

They talk about detecting magnetic field changes from the strike, and there's a link to a simple detection circuit.

This detection circuit http://www.stormwise.com/7SR350KHz.pdf looks like all band detector without audio amplifier. However its 350 kHz low frequency lighting detection antena factory pre-tunned it is close to what I've observed at around 500kHz at AM radio during those storms.
I think I will try first this crystal radio circuit with amplifier, while trying tune this thing to 350kHz frequency.

This is outside my old AM radio receiver starting from around 500kHz AM, but If it worked I could test it during daily bike trips providing I'll be able to make this antena with RLC circuit smaller and more compact than in this video 

It seams it might work while piezo exchanged with amplifier audio earpiece gives some sounds from this simple crystal radio, so its time to make small PCB and try to tune this thing to thunder storms 

I haven't got 1N34 germanium diode for the moment, so will try available Schottky 1N5711 and see what happends 

[dannyf]

No need for a crystal radio. I'm sure an untuned circuit works too.

[vindoline]

There's quite a lot of info on Charles Wenzel's site at http://www.techlib.com/electronics/lightning.html

[eneuro]

Techlib has many interesting lightting detection tips 

However, around 300kHz RF receivers are used too.
For example in this "Basic low-power receiver" 330uH & 680pF LC resonant frequency is about: 340 kHz


I'm not sure why not to use for example: 20uH & 10 nF which gives about 350 kHz but we have 10 times smaller inductor?
Is it something with Q factor of this LC circuit, but while there is no pararell resistor R, so while this Q factor in RLC circuit is given by equation:

Qrlc(f,L,R):= (2*pi*f*L)/R;

can I assume that R goes to infinity and Q factor to 0?

It looks like that 10mH choke is antena support to help receive LF RF and to get similar resonant frequency in LC series circuit this tiny capacitor mentioned below  should have value around 22pF when 10mH choke is used-we get then around 340kHz 

These radio "crackles" are picked up by the antenna with the help of the 10 millihenry choke. Short antennas (short compared to the wavelength, that is) behave as though a very tiny capacitor is connected in series and this choke resonates with this capacitor allowing current to flow into the receiver.

While I'd like connect AM radio demodulated output from this basic receiver to ADC small MCU AVR pin and try to make post processing of these crack lighting strikes noise and make decision in software to qualify it to lighting strike or not depending on feedback from sound & light detection sensors too, maybe opamp amplifier with gain I do not know 50-100 could be better than this simple transistors based?

I think I need for the moment  understand better this Q factor influence on received signal in LC/RLC circuits while one can get the same resonant frequency

1/(2*3.1415*sqrt(L*C))  [Hz]

using smalller inductor & bigger capacitor and reverse.
Are there any issues when I use 22uH & 10nF (LC) in schematics above to get around 340kHz resonant frequency?
Maybe there are tolerance issues of this LC components, but I do not need tune to exactly to 340kHz in this project I guess.

Update: According to http://en.wikipedia.org/wiki/RLC_circuit#Q_factor

The Q factor is a widespread measure used to characterise resonators. It is defined as the peak energy stored in the circuit divided by the average energy dissipated in it per radian at resonance. Low Q circuits are therefore damped and lossy and high Q circuits are underdamped. Q is related to bandwidth; low Q circuits are wide band and high Q circuits are narrow band. In fact, it happens that Q is the inverse of fractional bandwidth

Maybe it could be good idea add pararell resistor to this 340kHz LC, but while I do not need narrow band, which Q factor choose?
For example with 22uH inductance and 100k resistor I have Q factor:

Qrlc(340*kHz,20*uH,100*1000)= 0.00047

when 330uH is used I have  15 times bigger 

Qrlc(340*kHz,330*uH,100*1000)= 0.00705

[eneuro]

For these whoe believe a modern car is a safe place during lighting 

Simply, it looks like lighting was looking his way to ground.
Hopefully, I think there is the hope that lighting hit this quite big vehicle, while its huge engine produced a lot of heat and hot air might attract lighting, so while driving electric car there is much lower chance to get hit by lighting I guess.
Additionaly this car worth a lot of money and passed many safety tests, but... after this lighting hit they were not able simply open the doors to escape while electronics failed 

It looks like vehicles antenas on top of the car is not the best idea too, while this truck driver had lighting inside just via antena and was lucky lighting found its ground but a lot of electronics were damaged and his shoulder was injured by lighting inside this huge truck.

I think, it is time to remove car radio antena and maybe mount on the bottom of vehicle some kind of metal wires/chains to get better contact with earth while there is  little electrical contact beetween wheels and ground?

DO NOt BELIEVE IN what TopGear showed in his BBC funny video about lighting simulation in the car while it looks power of nature is much bigger and this stupid video made 7 years ago may be very dangereus, while when you are hit by lighting in your car you do not expect this.

It was NOT REAL lighting strike, but high voltage from huge generators, so this video lies! 
There is NO ANTENA on car top in this simulation, while many car have one, so such stupid videos like this one are very dangerous 

Trying to figure out what kind of mobile antena might be best for lighting detection for a frequency of about 350kHz RF.
There will be POF (Plastic Optic Fibre) connection from antena resonator circuit with microcontroller controll unit to ensure huge voltage insulation levels and keep sensitive electronics safe in something like Faraday cage...

[Alex Eisenhut]

No need for a crystal radio. I'm sure an untuned circuit works too.

The crystal refers to the rectifier.

[eneuro]

No need for a crystal radio. I'm sure an untuned circuit works too.

The crystal refers to the rectifier.

TDA1083 chip based AM radio receiver with a few components should be fine as lighting radio sensor.
Something like this or other TDA1083 modified schematics with light output for POF will do the job.


However, while never before build crystal radio wanted to experiment with it and  try to... make full bridge rectifier to charge something using lighting energy (not by direct strike/avoid it    of course  ), but it will require big antena and good (safe) grounding, so this is not the best option for mobile lighting detector.


At 350kHz LF radio frequency wave length is 856m so vertical antena quarter-wave length is about 203m /667feet

There are some interesting Quarter-wave Tricks