Re: [Ee] Field mill

I suppose it depends how much resoluton you need but it's really easy to
find extremely cheap 'VU' meter kits using the ancient LM3914 and they can
be cascaded up to 100 LEDs as well as configured for 'centre zero',

On Sat, 7 Jun 2025 at 06:23, David VanHorn <[email protected]> wrote:

> I certainly could spin up a design for that, but I'd just rather buy
> something that already exists.
> Time on the bench vs time out doing what I'm wanting to do.. I'm getting
> old. :)
>
> Bob:  Thank you!!  I guess there are Hen's toothbrushes after all!!
>
> I checked, and the output impedance of the mill is 1k, so I have +/- 15mA
> to work with. I was thinking they wouldn't run such a low impedance, but I
> was wrong.
>
> On Fri, Jun 6, 2025 at 9:43 PM Allen Mulvey <[email protected]> wrote:
>
> > Could you use a microcontroller to send the data over a mesh or other
> > radio signal to a digital decoder. I use MQTT over both mesh and WiFi.
> > (In the past I have also used NRF24L01+ radios.)Single element data
> > makes for a very small packet and sending over very short intervals can
> > give almost real time visibility. Here is an example:
> > https://meshgauges.mulvey.us/
> >
> > Allen Mulvey
> >
> > On 6/6/2025 11:02 PM, David VanHorn wrote:
> > > Not worried in the slightest about fields around the output line. If I
> > were
> > > to use copper cable it would be shielded, and the output voltage is
> only
> > > +/-15V so the field that the detector sees would be uV/m at best.
> > >
> > > Imagine lightning striking the field mill, and I have a copper
> connection
> > > back to my car.....  Conversely a strike on my car, if I am holding a
> > cable
> > > that extends out from the car could also be fatal.
> > > Even the leader discharge (just before lightning strikes, and there are
> > > usually many leaders before a strike, only one usually makes contact)
> > could
> > > be fatal if I were holding or even nearby a cable connecting back to
> the
> > > mill.
> > >
> > > Fiber optic could work, but that seems expensive, and would of course
> > > require some sort of encoder/decoder system.
> > >
> > > A normal panel meter is going to be very hard to read at a distance,
> see
> > > above for concerns about lightning strikes on the mill.  That's why I'm
> > > thinking LED bargraph. Highly visible, and no cable to put me at risk.
> > >
> > > Lightning photography is a dangerous hobby. I've got significant
> > experience
> > > and training in severe weather observation under a PhD Meteorologist.
> > >
> > > The field mill will indicate about 200V/m on a nice day, then when
> > charged
> > > clouds are near the field will increase substantially. (2000..5000V/m
> > > typically, could be higher)  A strike will collapse the field for a few
> > > seconds, while it builds up again.
> > >
> > > Prior to this acquisition, my only available data was "Do I see leaders
> > > forming nearby?" (EASY to miss) and "Are the antennas on my car
> glowing?"
> > > (in which case I should already be somewhere else!!) and I've had that
> > > happen.
> > > I'm prepared to abandon the gear if necessary, but I'd REALLY rather
> not.
> > >
> > >
> > > I have no idea where to find one, but a LARGE analog meter, center
> zero,
> > of
> > > 10 to 100uA could work. It would have to be illuminated.  I know they
> > used
> > > to make such for classroom use, but probably hen's toothbrushes today.
> > > Visible at 50' or more, in the dark, is the key.
> > >
> > > When they launch rockets to trigger lightning, they are sitting in a
> > > grounded faraday cage building, all the electricals are at the pad, and
> > the
> > > "cable" is an air hose using pressure to close the remote switch.
> > > I am NOT trying to do this in the link below, rather I am trying to
> > enhance
> > > my safety in the field by knowing when strikes are likely to occur near
> > me.
> > > https://www.youtube.com/watch?v=9wlU6Typ9Y4  There was a much better
> > video
> > > on the weather channel, but apparently they've retired it.
> > > A field mill is used in these systems to determine the optimum launch
> > time.
> > >
> > >
> > >
> > > On Fri, Jun 6, 2025 at 7:17 PM Jason White <
> > > [email protected]> wrote:
> > >
> > >> Shielded differential pair? Coax with ground on outer and signal on
> > inner?
> > >> Fiber Optic?
> > >>
> > >> Why are you worried about the output line generating a field if you
> are
> > >> already running power to it? Do your power connections need to be
> > shielded?
> > >>
> > >> It seems like it would be straightforward to use a shielded cable and
> > read
> > >> it with a handheld meter with a backlight.
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