[TriEmbed] Electric Fence monitoring

Josh Wyatt dragojdw at gmail.com
Sat Jun 27 20:26:31 CDT 2020


So, a couple of folks emailed mentioning lightning strikes - and that's a
real risk, especially with a super-long antenna going almost directly into
your arduino. One presented solution was to implement some kind of
optocoupler, with the LED powered by harvested energy from the strike
(clever). Another idea is to use beefier diodes instead of a zener, for
your clamping circuit.

I've had a few lightning strikes on my property, within 100 feet of the
house. Each time, the nearby strike took out the shunt regulator circuit in
my garage door opener, which powers the safety optical beam and sensor, at
the bottom of the door. It was basically a 100 ohm resistor in series with
a .5 watt, 5.1v zener, to provide a cheap low-current 5.1v supply to the
remote sensors. Each time lightning struck nearby, the zener shorted. The
first time, I replaced it with the same zener... until the next strike. The
next time, I used a beefier (5 watt) 5.1v zener... until the next strike.
Finally, I replaced that zener with 8 series-connected 1n4007 diodes,
forward-biased. All strikes since then, no damage!

There are also various spark gaps that can shunt lightning strikes.

Your mileage may vary...
-j

On Sat, Jun 27, 2020 at 7:23 AM Josh Wyatt <dragojdw at gmail.com> wrote:

> Your solution looks pretty good to me; I might consider adding a couple of
> capacitors to clean the waveform up a bit if you're just looking to detect
> the pulse. Something like a .1uF between R2 and D2, and maybe a .01uF or
> .001uF from A0 to ground.
>
> Thanks,
> Josh
>
> On Fri, Jun 26, 2020 at 11:19 PM The MacDougals via TriEmbed <
> triembed at triembed.org> wrote:
>
>> My electric fence monitoring project is making progress.
>>
>>
>>
>> Attached is a scope shot of the signal I am trying to monitor.
>>
>> There are two issues I want to address before putting this signal on the
>> A0 pin of my ESP8266 development board (D1 mini).
>>
>> The spike to ~5 volts is concerning.  I think I can use a 3.3v Zener
>> diode to suppress this.  Installed between my signal and ground with the
>> banded end away from ground.
>>
>> The negative lobe of the signal is also concerning.  Can I just use a
>> diode in series here?  Banded end toward the A0 pin.  I can adjust the
>> voltage up a bit to compensate
>>
>> for voltage drop across the diode.
>>
>>
>>
>> I have drawn up a schematic of what I think is the solution.
>>
>>
>>
>> Thanks for any comments.
>>
>>
>>
>> ---> Paul
>>
>>
>>
>>
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