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Lighting a LED with ambient RF (was candle)

from ambient RF" I tried several different types of diodes and Ferrite rods and coils and could never get a measurable voltage across a .01 uf cap.

I don't see how you can make this work short of driving a micro Telsa transformer and prayer. There just isn't enough total power except very close to the transmitter or voltage available even in the tuned circuit tank and as soon as you try to draw any current the Q falls rapidly.

You have to get to about 80v for a neon lamp to break down and glow. By comparison getting 2-3v at 0.1uA or less for a white LED to just start glowing should be a lot easier but still a bit of a challenge.

A high long wire antenna isolated from ground will quite often have enough DC potential at very low current to light a neon screwdriver just from the atmospheric potential gradient. Uselessly low current except during thunderstorms when the LED would be at risk of damage.

My TV aerial is high enough up that on most winter days it will light a neon screwdriver at ground level! A book value atmospheric gradient of

100V/m is typical but some days it is much more and at high enough current to notice. If you try to measure it with an ordinary DVM rather than an ultrahigh impedance electrometer you tend to get much less.

I would expect it to be able to provide enough current to light one of the more sensitive LEDs provided it was protected from the overvoltage. Never tried it though.

You can drive electrostatic toys from the potential difference across two decent sized plates at different heights in the same way as with a Zamboni pile like the perpetual ringing clock in Oxford.

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A simple variant also serves as a thunderstorm alarm.

--
Regards, 
Martin Brown
Reply to
Martin Brown
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from ambient RF" I tried several different types of diodes and Ferrite rods and coils and could never get a measurable voltage across a .01 uf cap.

The issue is power. ...and impedance matching.

An LED will also leak off charge without lighting (visibly).

Yet above you express a problem getting enough voltage to light a neon?

Power. Impedance matching.

An AM receiver works better. A weather radio, even better.

Reply to
krw

scope

If a crystal set can pump milliwatts of electrical power into a headphone, something very similar should be able to light up an LED. No mixed fruits are involved.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
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Photonics and fiberoptic TTL data links 
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Reply to
John Larkin

from ambient RF" I tried several different types of diodes and Ferrite rods and coils and could never get a measurable voltage across a .01 uf cap.

I wasn't thinking electrostatics (hard to get DC from) but picking up energy from an AM station.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

ghting from ambient RF" I tried several different types of diodes and Ferri te rods and coils and could never get a measurable voltage across a .01 uf cap.

t which

ed.

's

apparently you can get ics for it,

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-overview.pdf though power levels and distances a quite far from you usual AM station

-Lasse

Reply to
langwadt 

--
So build one.
Reply to
John Fields

I might some day. I already have a lithium-battery night light that I built, glowing on the bookshelf near my bed. I figure it will last

20-30 years, always on. It has an interesting hands-free variable brightness feature, where I can find it by its glow, but crank it up as needed for finding my way around, after an earthquake or whatever.

Regular LED flashlights should do that, namely glow a little all the time, so you can find them in the dark.

Given the energy density of lithium batteries, "energy harvesting" rarely makes sense.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

The 30 to 100pF zero bias capacitance of an LED is going to look like a short circuit compared to the less than 1pF capacitance of a decent detector diode. However, if the capacitance is known, it can be resonated with a series inductor to light up the LED:

Here's an RF energy scavenger experiment that successfully lit up an LED (Fig 15) using a voltage multiplier: However, he cheated and used a nearby transmitter to power the device. Still, the use of a voltage multiplier might be useful.

I don't think a crystal radio does not deliver "milliwatts" to the headphones. See: which offers a table of minimal earphone power levels commonly used on crystal sets. Operating levels will be somewhat higher. Headphone Sennheiser Model HD433 9.6 pW Headphone Sennheiser Model HD330 0.78 pW 2x 2000 Ohm headphone Telefunken EH333 0.022 pW 2x 2000 Ohm headphone Omega 0.033 pW Crystal earplug "Taiwan" 0.13 pW Driver unit Adastra Model: 952-207 0.0078 pW Looks more like fractions of a pico watt, which is what I would expect from the signal levels found on a crude antenna.

Basic crystal radio calcs:

Here's the consensus on the original question: "Crystal radio to power an LED?" Accumulating the scavenged energy and using it to build an LED flasher might be a good way to make it work.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Well, let's do the math.

An LED will barely light at 1.4VDC and 2ma. 1.4V * 0.002A = 2.8mw That's how much power needs to be produced by this contrivance.

For the transmitter, I'll use KSCO, which is conveniently nearby. Daytime power is 10,000 watts. The three contours are 2.5, 0.5, and 0.15 mV/m field strength.

At the 2.5mV/m contour a fair size dipole antenna will pickup about

100uV into 75 ohms. Notes:
  1. Plenty of typo errors on this page, but the numbers seem correct.
  2. A simple dipole still has 0dBd gain down to about 1/10th wavelength. The impedance becomes small, but the gain remains at about 0dBd.

From the above calculator: Receive-Power = E^2/R = (100*10^-6)^2 / 75 = 133*10^-12 watts = 133 picowatts

That's not anywhere near enough power needed by the LED (2.8 milliwatts). However, it's more than enough for the

Reply to
Jeff Liebermann

Why not put the LED right across the crystal set LC tank? The tank needs capacitance anyhow. We have some high-efficiency LEDs in the low

10s of pF. The classic crystal set cap was a 365 pF variable.

Those are audibility threshold powers. They say nothing about how much power a crystal set can deliver.

Seems silly. A good 50 KW AM station might provide 100 uw/sq meter roughly five miles away. Collect some of that with a longwire antenna.

1 uw is enough to light a good led visibly in room light. 
--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

The Osram LEDs that we use are often too bright at 2 mA. They are clearly on in normal room lighting at 1 uA. Dark adapted, under optimal conditions, I could just barely make out light at about 800 picoamps.

My night light is an Avago green LED, a Tadiran lithium cell, and a 1 meg resistor. It should last 20 or 30 years.

According to my good'ol red Radiotron book, one might expect roughly

100 uW/sq meter a few miles from a 50KW AM station. You'd only need a couple of uW to light an LED. So it's just an impedance matching problem. It looks doable. 
--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

I used to drive past Sutro Tower every day in my ratty old Ford Fiesta. The speakers would make awful sounds, even with the radio off. I guess the output transistors were rectifying the RF picked up by the speaker wires.

--

John Larkin Highland Technology Inc

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jlarkin at highlandtechnology dot com

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators

Reply to
John Larkin

I need to try something like that up the road, where there are no houses, but feed from power station goes through. Three phase might screw it up.

Greg

Reply to
gregz

scope

blinked

So at 100 uw/sq meter (a few miles from a 50 KW AM station) that computes to 1 watt! Of course, that's a pretty big antenna.

Even the low end 10 m^2 times 100 uw/m^2 is a milliwatt! A good LED is visible at a couple of microwatts, so even a ferrite rod antenna should visibly light up a good LED a few miles from an AM station.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

I was just comparing results googling vs blekko. Google just returns me to here. I'm just trying to learn blekko. No ehow wiki on blekko.

Greg

Reply to
gregz

scope

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Greg

Reply to
gregz

Ok, let's use your numbers and see what happens.

I didn't know LED's would work at 1uA. Do you have the Osram part number handy? I found some "low current" LED's on the Osram web pile, but the spec sheets were for 2ma.

For the LED:

1.4VDC * 1uA = 1.4 microwatts 1.4VDC / 1uA = 1.4M load impedance

The ambient level in US metro areas is about 50 uWatts/sq-meter from a study that I can't seem to find.

For the antenna:

100 uWatts/sq-meter is the energy density. To convert into detected energy, the effective aperture of the receive antenna will be needed: For a 1Mhz dipole (143 meters long), that would be about 7000 sq-meters effective aperture. 100 uWatts/sq-meter * 7000 sq-meters = 0.7 watts

That will work, but who is going to install a 143 meter long half wave dipole just to light up an LED? Using a more reasonable 0.05 wavelength dipole, detected voltage will be 1/10th of the dipole, resulting in 1/100 the detected power as 0.007 watts = 7 milliwatts. That's considerably more than the 1.4 microwatts needed for the Osram LED, so it's quite possible that it will work.

Assuming I add loading coils to the 1/10th wavelength antenna to bring the dipole back up to 75 ohms, the input tank will need a turns ratio of: sqrt(1.4*10^6 ohms / 75 ohms) = 136:1 which is buildable but will probably need a big air core coil.

If an outdoor dipole antenna is too much, an indoor loop might work:

There are some additional losses, which haven't been considered. Balun loss at the antenna, half wave rectification only recovers half the power, decrease in antenna gain due to proximity to the ground, and resistive (Q) losses in the tank circuit.

The Tadiran batteries used in some SmartMeter applications have lasted

25 years. I'm fairly sure I won't live long enough to see such a battery die.

Incidentally, for finding things in the dark, I use phosphorescent paper and a UV LED flashlight. I paste various shapes cut from the paper to my calculator, cell phone, TV remote, door knob, light switches, etc. They're not self lighting, but when hit with a UV flashlight, they're VERY bright and easy to find.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Sounds about right. That 100 µW/m² is in good agreement with old CCIR (now ITU-R) field strength diagrams above average soil for a few kilometers at 1 MHz.

With an outdoor antenna, just tune out the capacitively reactance with some loading coil and use some 1:100 step up transformer and you might get some usable LED currents.

I remember seeing some articles (long before the Internet) about a transistorized tunable receiver powered by rectifying the signal from a strong local broadcast station :-)

For those not so familiar with the metric system 1 m² = 100 dm².

At the low end, the available power is only 1 µW.

Just googled around and found a measurements of a small (5 cm) loopstick with -80 dBi gain, thus, the available power would be 100 nW or 50 nA LED current. Perhaps an eye, well adapted to darkness for half an hour, might be able to see something :-).

Reply to
upsidedown

Your figures are over 3 decades out of date. The best modern white and some green LEDs are just about visibly lit on the die in normal room lighting at 1uA. When dark adapted you can drop that by a factor 100 or even more. ISTR the voltage drop is nearer 2v though and only green or white ones are worth trying since you need peak scotopic sensitivity.

Actual power requirement is about 2V * 0.01uA = 20nW in total darkness.

It is getting the 2v potential difference that is hard.

Selecting the brightest diode from a batch would be worthwhile...

Actually for a sensibly chosen modern high intensity LED suited to the task it is more like an impedance match to 2V/0.01uA = 200M.

Except it that should be sqrt(2x10^8/75) = 1700 turns

With 100uV on the antenna this gives 0.17V still not enough on its own, but a clever boost converter might be able to store enough energy on a low leakage capacitor for the occasional flash.

If you take the average current drawn down to below 1nA then it looks to me like you would be in the right ballpark for ordinary transistors. The 5000t resonant coil will be hard to make though.

--
Regards, 
Martin Brown
Reply to
Martin Brown

The resonant circuit impedance in a typical MW receiver is about 100 kOhms, while a LED circuit impedance is in the order of 100-1000 ohms.

Reply to
upsidedown

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