Cheap remote power indicator wanted

[Chris Green]

I want to know if something (an electric fence) is turned on and I don't particularly want to traipse out to the shed where the fence energiser is to check.

It gets turned on and off throughout the day as different people go in and out to check their horses so there is always a fair chance that it might not get turned back on, especially if visits overlap.

So I'm wondering how I might rig up some sort of remote indicator that will let me check whether it's on or not. Ideally it would be possible for a computer to monitor it as I could then have an alarm of some sort if it was off for, say, more than an hour.

The fence energiser is mains powered and in a building visible from the house, something very simple and mains powered would do the job as it can simply be powered from the same socket as the energiser, when off there would be a 'lack of signal'. However I'm not quite sure how to signal from there to the house (50 yards maybe). I don't really want a whole WiFi connection just for an on/off indication. Can one get a sort of WiFi 'beacon' that simply says "I'm here"? It's line of sight to one of my WiFi routers so that should be OK. What's the minimal sort of device for saying "I'm alive"?

[nothanks]

A cheap LED torch fixed to the shed and pointing at the house. Switched on with a relay whenever the supply to the fence is off. Add a timer to make the torch flash after an hour. Alternatively (and more expensively) there are several GSM-based "phone home" devices that can be configured to call your mobile. Search for <mains power failure alarm> or similar

[Tim Lamb]

In message [e-mail]>, Chris Green [e-mail] writes

Going sideways.... I assume the visitors have to crouch under the fence for access. Could you install a gate and have the fence wire routed across above head height.

>

[Peter Able]

Try using an AM radio. Most simple electric fences radiate "clicks".

PA

[Harry Bloomfield Esq]

Add some sort of wifi gadget, powered from the same power as the fence, then set up your laptop to ping the gadget at regular intervals. PingInfoView can do that, and sound an alarm, send you an email, when the pong fails.

The 'gadget', could be a Smart Plug, IP camera, old wifi router, old wifi capable phone - anything which has wifi capability.

[Pancho]

Does the shed mains power go via the house. If so, put a sonoff/tasmota WiFi power meter on the entire mains cable in/near the house.

A sonoff/tasmota style power meter isn't simple, but it is cheap.

[Theo]

If you had a wifi access point with enough range to reach the house (might need a directional antenna) you could write something on the computer to detect the presence of the 'Electric_Fence' wifi network?

eg on my Ubuntu machine:

$ nmcli device wifi list | grep Electric_Fence 11:22:33:44:55:66 Electric_Fence Infra 1 130 Mbit/s 30 WPA2 WPA3

You don't need to connect to the network, just detect its presence when scanning for available wifi networks.

Similar could be done with other kinds of RF (eg 433/868MHz) which would have longer range although you might need to disambiguate from other sources of those (eg car remote unlockers, tyre pressure sensors, etc). There is software 'rtl_433' to use a cheap TV dongle to decode them.

Theo

[N_Cook]

KISS indeed. A lamp in a tube directed to the house window you would view from. Works ok for Railtrack. Lamp on = fence powered and assumed working order

[Paul]

They make Wifi multimeters. But then you need power for it.

Apparently one way to detect run-state, is by measuring a current on the fencer. Rather than measuring voltage. You would need a 10:1 or

100:1 probe to handle voltages higher than the meter rating. Sometimes current can be handled on "low-side" to make safe monitoring readings.

A mains powered device could be measured with a Kill-O-Watt meter.

This Kill-O-Watt apparently has wireless, but there are many details which don't match your physical location, so this is merely a demo that such a thing exists. And Google is flat out refusing to help on this, returning a random spray of garbage.

Paul

[Chris Hogg]

Would a low-voltage LED with a diode in series, wired across a low-value resistor in the mains neutral return from the fence energiser work? When the fence energiser switches on, there'd be a small drop in AC voltage across said resistor, say a volt or two, rectified by the diode and enough to light the LED. Choice of resistor value would be important to develop a small voltage without stopping the fence energiser from working.

Or would there just be a bang and puff of smoke? :-)

[Chris Green]

Good point, annoying usually but this could be the answer!

[Chris Green]

Yes, I think this may be the best answer. I have a couple of WiFi enabled microcontrollers that should do the job. I'm just trying an ESP32 based one and it seems to be possible, I'm not quite sure about the range yet.

[Joe]

Do they have external antenna connections? There are antennas with several dB of gain available cheaply. Something like this:

|pcrid|426684131165|kword||match||plid||slid||product|AP03570|pgrid|100371159078|ptaid|pla-1766196707195|&CMP=KNC-GUK-CPC-SHOPPING-9262013734-100371159078-AP03570&s_kwcid=AL!5616!3!426684131165!!!network}!1766196707195!&gclid=EAIaIQobChMI_uGMy6vaggMVSfntCh19ogWZEAQYASABEgKFXfD_BwE is a bit more expensive.

My house wifi does about 100ft through one brick/glass wall to a laptop. An Xbee transceiver (433MHz) can do about 50ft through the same wall using very small antennas (about 1 inch).

Or to be more on-topic:

[nothanks]

Would it work - possibly, if you got the sums right, but it would be more reliable and easier to have a few back-back diodes in series. Having said that, I would simply use a relay (perhaps one with in-built adjustable delay such as

to switch a cheap LED torch. If you're concerned about battery life then use one of the many wall warts you probably have in a box somewhere) to replace the batteries.

[Chris Green]

The range is the issue, nothing like what I need even with line-of-sight between router and the ESP32 microcontroller. If the range was OK it would work perfectly, so maybe I need to find an ESP32 board (or similar) with an aerial.

[John Walliker]

There are some very low cost vhf and uhf radios that could be made to do what you want. For example,

are lots of other suppliers of similar products. The vhf versions are likely to have longer range than the uhf ones. John

[Chris Green]

They look useful, even if not for the present requirement, thank you.

[Animal]

+1. No tube needed.

[Thomas Prufer]

Two solutions:

Flashy light powered by the fence itself. So it shows the fence -- good because what good is power to the fence if it's shorted out? It's cheap, simple, measures th eimportant part, but you need to look at it.

Bunch of alarm devices, pricey, but send stuff to your phone via GSM, or measure fence voltage and upload it.

Prices disapper when set to UK, but this

is 189 € incl. 19% VAT.

Thomas Prufer

[Brian Gaff]

I was going to suggest a laser light pen customised to work off a psu, you could even have a photodiode receiver set up to look for the beam. A torch might not be bright enough to be seen on a sunny day. Many years ago they used to make intercoms that worked over the mains wiring and on some you could lock down the speak/call button. The other unit would be needed to receive the signal of course. I guess these are probably too low tech for today.

Brian