electric fence

[zotdoc]

I am installing an electric fence to keep some goats in place. My son is a big jurassic park fan. He and I think it would be cool to have flashing warning lights at intervals along the fence like they had in the movie. Any ideas on how to use the 7000 volts from the electric wire to run the lights/leds to show when the fence was activated?

[dyarker]

To make it non-lethal, the 7000V is limited to a VERY low current.<p>How about a separate 12V supply to run a yellow "gum ball" or LEDs on the posts?

[Externet]

Hi.
A separate string of lower voltage supply would have to run apart in the fence to power your lighting.
Do not believe everything you see at the movies. I did not pay attention to that scene, but for sure was not high voltage supplying the lamps.<p>I would say that connecting neon bulbs with several large resistors in series to limit the current, plus rectification into a capacitor to fire the neons in relaxation mode would take too much drain from the high voltage supply, as fences are usually long and may need many of the lights loading it.
The worse part is if you attempt to put together such contraption, will later find out that plain neon lamps under daylight would not be discernible. Leds from 7KV are out of the question and would not be visible either.<p>If you really, really want to play with the idea, using a few disposable cameras flash circuits will have a better chance, modified to self trigger repeatedly and carefully supplied by the 7KV.
Miguel

[Newz2000]

My first electronics kit was a simple blinking LED that ran off a simple LM3909 (discontinued) chip. I hooked it up to a D cell battery and it was still blinking 2+ years later.<p>I think your idea is cool, but I'd just make a few free-standing signs that use several high-intesity LEDs and some D cells or 9v batteries. Here's a simple, well-written project you can use as a base:
http://www.kpsec.freeuk.com/projects/flashl.htm<p>You could make a fancy looking sign out of painted wood and several bright red or yellow LEDs that blinked to draw attention. I'll bet you could make 3 or 4 such signs on a saturday and you'd just have to change the batteries every year or so (if you even cared to after that time).<p>That website has good tutorials for electronics projects aimed at school kids, so I'll bet you could adapt the "railroad crossing" or "heart shaped badge" projects listed there to get alternating blinking lights for a more interesting visual effect.<p>If you want an interesting box to contain those in, you can find the taillights for a '67 beetle on the internet for less than $9. You could build your project in one of those, seal it with caulk and attach it to your sign. Here's where I got the price for the tail light:
http://www.aircooled.net/new-bin/viewpr ... 03&cartid=
Choose "'62-'67 Beetle, Red" from the first drop down.

[bridgen]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Matt Nuzum:
[QB]My first electronics kit was a simple blinking LED that ran off a simple LM3909 (discontinued) chip. I hooked it up to a D cell battery and it was still blinking 2+ years later.<hr></blockquote>
Hi Matt.<p>I mounted a l.e.d. and an LM3909 with a 220uF capacitor directly on a D cell. Blink rate was around once every 3.5 seconds. It lasted almost 11 years.
I mounted it on another D cell last July. Strangely, the blink rate is now about once every 2.5 seconds.

[Will]

I have a use for this flashing LED but can't trace the function of an LM3909 - what was it ? Thanx

[Gorgon]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by David Bridgen:

I mounted it on another D cell last July. Strangely, the blink rate is now about once every 2.5 seconds.<hr></blockquote><p>If you used the same capacitor for 11 years I would suppose it dried up a bit and lost some capacitance on the road.<p>TOK <p>[ June 16, 2005: Message edited by: Gorgon ]</p>

[dacflyer]

rember also...more stuff you put on that fence wire,,,the more it will drag it down and then become non-effective.. how about this...get you some of them solar lights..modify them a little and use them as you like...might need to change the led to a hi brightness ones if need be.. like the red ones them you can still see fairly well inthe dark and daytime.
i found that the solar cell on top of these are easily able to power the led and charge the battery at same time..thats if i was using the red led , rather than the higher current yellow ones. good luck

[Newz2000]

The lm3909 are very hard to find. Now, you would probably use the very common 555 circuit. The link I posted above has some excellent explanations of the 555 and some example circuits.<p>Someone confirm... what is out these days that works well at 1.5 v?<p>I think the LMC555 is a lower power/voltage version of the 555, but if you're going to use high-intesity LEDs you may be talking about two batteries in series (for 3v) anyway, making it a moot point.<p>I'm not an expert in this, can anyone confirm?

[zotdoc]

Thanks for the good ideas. I like miguel's idea with the camera flashes and I remember a back issue of N&V on how to "hack" the flasher.

[jwax]

The LM3909 was a versatile chip! I have a few leftover from gifts I handed out- a D cell, a cap and a led flashing for years!
What were chip makers thinking when they discontinued that gem?

[philba]

the 3909 has/had integral charge pumps to get the voltage up to Vf of the LED. a plain 555 won't work for just 1.5V (i.e. 1 cell). You need to build a charge pump. Not impossible but a pain. You might want to start with discover circuits LED section. I had trouble getting several ones there working and finally built a hydrid that sort of worked though duration was less than I wanted. If there's interest, contact me...

[Chris Smith]

With 6KV or 7KV in the proximity of a neon or flourescent light, they will light up on their own. <p>No wires needed. Perhaps a small pick up plate like a cap, but no hard wire. <p>Will it be bright enough, I doubt it?