Is it possible to power a small LED an RF signal

[CADmancan]

I believe its possbile but wanted to ask if its possible to light a single LED light by and RF signal if its strong enough. I know there are LED's that are as low as 3 milliwatt that could work. Thanks in advance.

 

[vk6kro]

Yes, you can, but you have to be very close to the source of the RF.

Red LEDs require the lowest voltage to turn them on, but even they need about 1.3 volts.

RF signals that you might hear in a short wave radio are usually weaker than 50 microvolts at the receiver antenna, so they can't light a LED without amplification.

Near a transmitting antenna, even for a low powered transmitter, it is possible to pick up a volt or two of RF and this could be rectified with a suitable diode and the resulting DC used to light a LED.

 

[sophiecentaur]

About a hundred years ago, I was on an Radio Engineering induction course. We were shown model transmitting antennas with pea bulbs in various places and the brightness of the bulbs gave an indication of the different currents flowing. This also worked (but dimly) for parasitic elements (not actually connected to the driven element). LEDs need far less power than pea bulbs to make them work so I should imagine you should find no trouble in getting a result for demo purposes.

The question is what is "strong enough" and can you produce that sort of field easily and legally? Also, was the demo I was shown legal? It was in a very reputable Broadcasting Organisation.

 

[whocouldshebe]

I believe its possbile but wanted to ask if its possible to light a single LED light by and RF signal if its strong enough. I know there are LED's that are as low as 3 milliwatt that could work. Thanks in advance.

I have 2 antennas on my roof, 1 is 75 feet of phone cable suspended about 4 feet from the roof top, the other is 75 feet of triple shielded coaxial cable with a '2nd controller RF dish remote box antenna" on the end as a cap.

The cable wire run antenna is of one 50 foot strip joined by a gold plated connector to another 50 foot strip but at the 75ft mark I ran both cables down into my room through the window.

The cable wire gets between 300mV and 500mV. The telephone wire gets from 80mV to 160mV. Both flux up and down constantly. Today I'm off to buy a solar powered yard light for the trickle charge battery components inside.

This is the setup I have:

1. 75ft antenna of phone line & coaxial cable on roof putting out 380mV to 660mV.
2. Connected antenna wire the L tip of a spark plug.
3. Copper of coaxial cable connected to the metal screw portion on other end of spark plug
4. Other end of that coaxial cable run into a ignition coil, the connection in the middle.
5. 2 coaxial cable copper insides connected to the + and - side terminals of the ignition coil run both to the + end of a trickle charge solar yard lamp battery.
6. Negative end of solar yard lamp battery connected to metal pole in ground by coaxial cable.

Optional:
7. 1KV to 3KV capacitor or single direction diode running from ground to antenna to prevent overcharging of system and route to ground to keep large charges from collection on antenna.

If this doesn't work tonight I'm thinking of designing a better antenna, an aluminum fence mesh wire coated in polyurethane paint or a long strip of aluminum foil between 2 sheets of wax paper or saran-wrap elevated a few feet away from the ground should make a much better antenna. Other options include balloons suspended by a short length of thin copper wire.

I've even considered one of those spinning aluminum attic vents suspended over the roof with PVC pipe inside that has a copper run inside of it. Wool or fur can be wrapped around the PVC pipe and tied to the spinning vent by fishing line so that it spins around the pipe creating a static charge that will transfer to the copper line and run down to charge the battery inside my room.

I'm thinking maybe a lot of charge is lost back out into the air through the antenna though. A round antenna atop a pole would be best but it has to be metal coated in plastic, so I'm at a dead end on how to find one of those for free or how to make one for cheap?

I'll keep you up-to-date on my progress...
Any more wild and crazy but cheap ideas to charge this up?

(I had junk cables laying round and a metal pipe for ground, plus a spark plug only cost 40 cent and the ignition coil was $14 or less on Amazon, I'm thinking the batteries will cost less than $4 tonight, making this a truly green energy project.)

 

[Mike_In_Plano]

Yes,

you can get coupling over an inch or two using magnetic coupling. You might give this little oscillator a try.
For the inductor, it's best to use heavier wire, 16 gauge is good. Try making a pancake coil that starts about 1.5 inch and winds outward for 12 turns.
C2, C3, and C4 have cansiderable currents flowing through them, so they need to be film or ceramic. C3 is especially important, it's best a poly prop. Keep the path around the capacitors and through L1 fairly short and direct. If it's messy, than you'll loose energy.
R4 is a handy way to change the feedback. If it doesn't want to oscillate, decrease R4 to 10 or 22 ohms.

Usually, you can use a "sniffer coil" to tell if it's working (or an AM radio...) Just wind about four turns of 22-26 gauge wire in about 3/4 in diameter and use a small signal diode (1n914) in series. Run that to you milliamp setting of your volt ohm meter, and your ready to sniff when it's oscillating :)

The pick up coil should be about 20 turns of 26 or 28 gauge wire. A few hundred pF across it will "peak" it to help it pick up at a certain distance. Rectify it's signal with a 1n914, or even better, 1N34 (germanium diode).

It's fun project to play with, because it has many subtleties that even the "pros" fail to learn.

 

[whocouldshebe]

Yes, a loop antenna would be better, I'll just have to figure out how to build one to pick up all frequencies no matter how low or how high they are, probably some sort of multiple loop in loop design.

I really wanted to leave the oscillator out of it if at all possible. It seems many end up using a timer but don't want to do that unless it becomes unavoidable.

I'll try a pancake coil to see how that goes, I do have a few hundred winds around plastic tubing but I wasn't impressed with weak static signal it received.

I hate to order ceramic or film diodes at the internet's ridiculous prices. I've got some dead power supplies I'll open up to see what they have. I do have 1 germanium diode though in my crystal radio. All the diodes at radio-shack are silicon, and I was told they are not as good for projects like these, but I'll buy a pack of the assorted ones and try them out.

Another problem, it's hard to keep the path short being up on the roof on poles and all.

My mom has 3 classic crystal radios, one even lights up the tuner and is so loud that you can hear across the house. I remember the first time I saw it. I thought it was magic, no batteries! Maybe someday I'll be able to build a similar working radio. This old technology shouldn't be too hard to replicate I hope.

 

[Mike_In_Plano]

Wow,

That's extraordinary. I've built quite a few crystal sets, and I always had problems with the nearby station burying everything else, though I never thought it could supply enough energy to bring a lamp to glow.

If you have some switching supplies, the noise filter capacitors on the AC line are great. They tend to be in the ranges you need and are often film (rectangular plastic).

I got started pulling all of my parts from old equipment and then I joined with friends, and we would trade on junked parts, scavanged schematics, and meeting to show gadgets.

Amp-turns is the name of the game, and the cheapest way there is a parallel resonate circuit. You can use a timer to drive the resonance, but don't expect a timer to have the umpf to drive the current back and forth in the coil.

As to rectifiers, chances are that none that you will find in a power supply will help you. That's the job of small signal diodes.

In college, I finally broke down and spent a serious sum (maybe $50) on my parts kit. I ordered an assortment of resistors, capacitors, small signal devices (2n2222, 2n2907A, 2N3906, 2N3904, 1n914), and a few common chips. I sorted it all in bins and it was the best investment I ever made. From then on, ideas to reality often fell into hours instead of never, and with a solderless breadboard, you could tear it all down and build something else :)

Mike

 

[whocouldshebe]

I've been buried in work lately, but I got a AA battery to charge up with the coaxial cable enough to light an LED on a timer. It was a really cheap project. Here's what I did:

1. I bought a solar yard lamp from Wal-mart for $3, the cheapest one with the lowest mAh battery inside I could find.

2. I unhooked the solar panel, with no planel, the lamp will blink for days and run the battery completely dead, until no charge at all is left in the AA battery, you can test with volt meter.

3. Hooked up the 75ft of coaxial cable to the positive end of where the solar panel once was going from my chimney to the corner of my house and down into my window.

4. Hooked up another 25ft of coaxial cable to the negative end of where the solar panel once was going to a metal pole slammed deep into ground with a sledge hammer.

After about 12 hours the LED starts blinking, also when the air becomes moist or at night after a long hot dry day, also just before thunderstorms, it gets powered up quick!

I made the assumption that a solar panel uses a cheap very low power timer between the solar panel and the AA battery. The LED turns on whenever the charge from outside sky drops lower than the charge that has collected in the AA battery.

This would make an easy way to chain tons of little chargers together for multiple power sources of a very very low charge. I'd like to connect the solar panel back up and add a small 1 coke can wind generator also collecting static from the aluminum there chained together with coaxial. This provides a way for a charge to trickle in at night when there is no light.

Maybe I'll build 10 and put them on the roof and see how many volts/amps I can get out of it after 12 hours. I'll bet I have 12 volts easy by the end of the day.

I'm also currently building a dish covered in 1/2 inch mirrors, also called a mirror death ray, and plan to cook out with it this weekend, at half finished it already burns my skin scalding hot. The solar/wind/static array will power my laptop or a fan and a black water hose filled with water sitting on top of the black shingle roof will provide the hot water.

This will complete my super cheap completely green home project!

 

[Dmytry]

Keep in mind that antennas may be dangerous. Install a sparkgap to good ground. I'd actually do several sparkgaps.

 

[mheslep]

I believe its possbile but wanted to ask if its possible to light a single LED light by and RF signal if its strong enough. I know there are LED's that are as low as 3 milliwatt that could work. Thanks in advance.

It's possible to power much more than a single LED. The dependencies include the power of the transmitter, the gain on the transmitting antenna, distance between transmitter and receiver, and the gain of the receiving antenna. 148km link here:
[URL]http://img.cellular-news.com/story/33687/Wireless_Power_System_Transmits_Energy_Over_148km_1.jpg[/URL]
http://www.cellular-news.com/story/33687.php

If you intended to siphon some power off local, omni-directional broadcast AM-FM commercial transmission, that's being done too:
http://www.nytimes.com/2010/07/18/business/18novel.html

At Intel, Dr. Smith, working with the researcher Alanson Sample of the University of Washington, created an electronic “harvester” of ambient radio waves. It collects enough energy from a TV station broadcasting about 2.5 miles from the lab to run a temperature and humidity sensor.

The device collects enough power to produce about 50 microwatts of DC power, Dr. Smith said. That is enough for many sensing and computing jobs, said Professor Otis. The power consumption of a typical solar-powered calculator, for example, is only about 5 microwatts, he said, and that of a typical digital thermometer with a liquid crystal display is one microwatt.. ...

 

[mheslep]

Also see, e.g.,
http://www.powercastco.com/products/wireless-sensor-system/

 

[Studiot]

Bulbs glowing in RF have been used for a long time in the classic Physics experiment.

http://en.wikipedia.org/wiki/Lecher_lines

 

[whocouldshebe]

People keep warning about antennas like I'm going to get killed or something. Keep in mind this is only a 75ft strip of phone/cable wire. Most people have at least 3 times that in their homes already. Just imagine how many thousands of feet the 15 story building at work has in it, yet nobody ever says "Don't go in a building, you'll get shocked or killed by lightning."

We've got 150 foot trees all over the neighborhood too yet I've never got so much as a single static shock from a door nob after walking for years on my wooden carpet covered 4 foot suspended floors. The danger from this is practically ZERO, on the other hand, I've been painfully shocked countless times by inspected and approved devices and electronic wall plugs, metal plumbing, and wall plates in multiple houses. To warn about the dangers of tiny antennas just shows complete lack of experience using such small non-powered antennas.

I've hooked a spark gap up but the charge dissipates into the air easier than jumping the gap obviously. I don't see how anyone could ever make a spark from such a low trickle charge, in fact, I can just as easily ground out to an open ended piece of copper wire as I can to a grounded metal pole. I guess the resistance of the metal/dirt is greater than that of air itself.

If I were working with larger amps or thousands of volts, using a grounded pole would make sense, but for the tiny charge of only 350-500 millivolts, the only thing with enough pull that can eat that up is air or that tiny trickle charge timer inside the solar lamp housing after the solar panel is removed.

Walmart has 4th of July solar lamps on sale for $1.50 a piece. They come with a 2/3 AA battery inside that holds 250 mAh. I bought I couple to see how long it takes to charge up with my antenna. It should charge up a lot easier/faster than the 650 mAh batteries in the $3 ones.

I'd like get like 40 of them & hook them up to the antenna in a series to see if I can get a laptop to charge while it is turned off. I'm guessing that if I hook the DC to AC converter after the battery before LED, then when the light cuts on at a specific charge of 1.2v the charge will also travel to the converter eventually also to the charging cable.

It shouldn't matter that there is timer blinking it on/off since both the converter and the charging cable obviously have some kind of ultra capacitor to steady the charge as power flickers at practically any frequency.

Does the input frequency of a DC to AC $15 cigarette lighter even matter if the volts at least meet the operation range?

With 40 2/3 AA batteries, the amps should be there, the volts too obviously or the LED wouldn't blink, but some timers will blink while others stay off as each of the 2/3 AA batteries randomly reach full charge 3-4 times a day. Would the DC/AC plug even work at all? I'm thinking it will work, but only cut on at times when the DC charge is in the range it can work with.

It's odd to me since the DC being sent will turn on/off like AC, so I'm thinking 120 hz random spurts (or better) of DC will be needed to produce 60 hz AC. But how sporadic can those 120 hz of input be and still collect and power up the inverter?

 

[whocouldshebe]

Prices finally fell for the 4th of July solar lamps at Wal-Mart that nobody bought, down to $1 a piece. I bought 12 so I can hopefully get 12 volts out of it hook up in a series to trickle charge the battery pack for my laptop. I've got 12 strips of 100 foot telephone line I could run down to each solar power to pick up a charge at night.

There is no way to make the spark gap collect enough volts to work, probably due to the constant 98% humidity here nearly year round, but the trickle charge timers in the solar lamps prove to work just fine.

The only thing I worry about is the frequency. The LEDs on the solar lamps blink rapidly on/off I guess to drag the charge out all night. I'm thinking that it won't matter though since this is probably even better for charging up the battery, keeping it from overheating.

I know I could use the lamps to charge up a car battery then use that to run the laptop, but car batteries are more expensive than the solar lamps and free phone cables, and I'm trying to keep this as cheap and simple as possible.

I love the satellite dish example. I bet you could get lots of power off of that. Unfortunately I have already converted my 2 satellite dishes to a Death Rays using 1/4 & 1/2 inch square mirror tiles. I wonder if they can serve as tri-generator devices? Will the dish still get radio wave power even with mirrors on it? I know I'll still get heat and solar, add the radio and it could be even more efficient.

 

[sophiecentaur]

I love the satellite dish example. I bet you could get lots of power off of that. Unfortunately I have already converted my 2 satellite dishes to a Death Rays using 1/4 & 1/2 inch square mirror tiles.

Move over Dr. Fu Man Choo!
When do you intend to take over the world?

 

[whocouldshebe]

Update - I got another free satellite dish, I'll check the voltage on it before I convert it to a DIY usb Wifi extreme antenna booster using a tin vegetable can. I also bought some land down in Mexico, enough to run a 1 mile cable around the property, with no zoning laws or inspectors like we have in the US, if I can get 350mv off of 75 feet on my roof here I should be able to get 24.64 volts off a mile of scrap cable. Ideally it would be in the desert, lots of static electricity there, but the land I bought is in the mountains, around 2000-3000 feet with high humidity of 98% but maybe the height and frequent thunder storms will help. I got the 350mv at 250 feet elevation here, we have 98% humidity here too so for Mexico it should be no different, if anything, even better...