I was home for a couple weeks and my mother decided it was time to bust out the old electric fence we used back when the farm was a full-fledged hog farm and not a butterfly and wild kitten reserve. The raccoons will soon be edging their way up the hill and into my mother's sweet corn, but this year will find a surprise.

We joked about having a counter that either sounded a tone every time an intruder was deterred, or possibly a simple two-digit display or binary readout via LEDs. I've got CMOS binary counter/dividers and probably anything else I may need in the boneyard, but I'm wondering mostly how to interface the fence's driver, (a Red Snapper 64B) which is pulsing 110v at 60hz.

Thanks for any and all advice.

 

Couldn't find "Red Snapper 64B", but did find this: http://www.redsnapr.co.nz/

So, maybe you could place a low value resistor in series with the ground wire. Use the voltage drop across it to sense the current. No raccoon = no current = no voltage. Raccoon = pulsing (60Hz) current = pulsing voltage. Rectify and filter the voltage, and use that to trigger an alarm...or counter...or release the hounds. My experience as a sweet corn lovin' Iowa farm boy says the 'coons will find a way over, under, around, or through the electric fence. They are one clever critter. But, I'd give it a shot.

Ken

 

You could also try a missing pulse detector on the output. I imagine when an unfortunate racoon hits the fence the output drops considerably, you could use this to figure out when the fence was shorted...

 

Thanks guys. And I am also a sweet corn lovin' Iowa farm boy, now in Austin, but still.. I'll research these ideas and see where it leads. Even if it doesn't protect the corn completely, it'll surely be good for a giggle. A triggered camera would probably also be mildly hilarious for some surprised 'coon shots..

Would the series ground resistor idea be able to differentiate between say, a corn leaf fallen on the line vs. a full-on raccoon attack? You can hear the light (and memory-inducing) snapping of the pulse when something is barely touching it..

 

....Would the series ground resistor idea be able to differentiate between say, a corn leaf fallen on the line vs. a full-on raccoon attack? You can hear the light (and memory-inducing) snapping of the pulse when something is barely touching it..

That would be a problem.

Ken

 

Now I'm thinking that some sort of comparator set to rely on roughly the same voltage going around at each pulse would do the trick. A zapped critter showing a "disturbance in the force," so to speak?

I guess we shall see. Learning as I go..

Thanks y'all.

 

The missing pulse detector circuit commonly made from a simple 555 IC is a start but in my experience the output of fence chargers varies wildly. Some even have sufficient current such that a tree can be leaning against one yet there's still enough voltage present on the wire to give a shock.

For a sensor that will count actual hits I'm thinking a neon lamp and a phototransistor in a small box would work. Use a series resistor with the lamp to match your fence output but you may need to play around with values until you find one that just lights the bulb when there's absolutely no load on the fence wire, that way if something is putting a load on the fence the light won't. Separate the phototransistor from the neon lamp a bit inside the box to eliminate the possibility of arc over.