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/diy/ - Do It Yourself

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File: 31vS3v0NYhL._SX342_.jpg (7 KB, 342x342)
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I'm interested in making a device which will be contained inside a small glass dome and powered by an array of germanium diodes.
The concept is to create something which just operates and continues to operate for as long as possible. What does it actually do? Anything, just so long as it does SOMETHING, for a very long time.
Now germanium diodes aren't exactly a high power source of electricity as you know so whatever it is needs to have an extremely low power requirement. Any ideas?
Even lighting an LED is unfeasible but what if you could trickle-charge a small capacitor and have that light an LED periodically? Again it doesn't matter how long that would take, only that it is functioning.
you could keep a real time clock alive i guess
How do the diodes produce this power you intend to use?
if you were to try harvesting dark current of any form, you are completely fucked over.
I didn´t crunch numbers for germanium but LEDs them selfs also generate current.
but it would take bout 10000 of them for just 10mah.
Also cap leakage.
in other words: forget it

I assume he intends to use them to capture RF.

Realistically, there's not going to be anything you could do continuously with the EM energy hitting a "small" glass dome. You need a long-ass (like 10m) antenna just to keep a wristwatch fed with the dozen µA or so it requires.

Honestly, periodically lighting an LED is probably the best you're going to be able to do, at least relatively easily and frequently. Maybe make it flash out some message in morse code/ascii or some shit to make it more interesting, IDK.
Thanks for the input guys, it's just an idea I've had for a little while. I want to make something that will hopefully still function when I am gone and small enough to be passed down to my children. Obviously out of necessity it should have no moving parts and then obviously thinking about it that puts the capacitors out of the question too.
As you can probably tell I don't have a great amount of electrical knowledge, just from messing around with crystal sets about twenty years ago.
And to reiterate the problem isn't getting something to work, that's relatively easy (A crystal set itself for example), the problem is getting something that VISIBLY works.

I would really appreciate it if anyone could lend advice on this topic, is it really out of the question totally?
Could you use some of those memey tritium vials as a power source, or do you want it totally running off outside power?
The voltage is easy, but the amps is where you need tons of them.

Haven't read this fully but might be interesting:
>pic related
Why has nobody made a schottky-junction germanium diode?

From a cursory google search, it looks like there's disadvantages to germanium schottky diodes which means they're not produced anymore.

My interest in now piqued in this RF power collection concept. Looks like there's some semi-commercial products out there even (https://ca.mouser.com/applications/rf_energy_harvesting/). It's probably important to tune to the most powerful frequency in your area, but a circuit capable of on the fly tuning would probably draw too much power hmm...
Shit, never mind.
Energy harvesting through inductors works well without any tuning, at least that's what amplifying an inductor's output and listening to it tells me. I can hear all frequencies from mains hum to PSU whine so I think there shouldn't be a problem with having to get it in resonance, but I did have to increase the gain a lot to get much amplitude on the bass frequencies.

Getting energy from wifi shouldn't be too difficult, getting it from cell towers would be pretty good, and getting it from GPS satellites would be incredible.
5A at 0.07V? Pretty crazy, but the Pb junction diode did have particularly bad leakage current, namely 1A at 0.4V. But since the full 5A is mostly useless unless you're trying to build a spot-welder or something, the gold or copper junction diodes would work easily fine enough.
And that's from 1973!
Well that's when diode research was being done, not too surprising!
Well this blows all that out of the water.
>Low Average Forward Voltage (26 mV at 8 A)
I did a little research but I couldn't find a broad spectrum power density for the average city or something like that. I'm curious where the most power is. 60Hz probably I suppose.

That is beautiful. $5 a pop though.
>$5 a pop though
And nothing else comes close to it, at least nothing on Arrow, Octopart, Mouser, or Digikey. Might be missing one or two there though. The LX2400ILG is almost as good with 50mV, but it isn't stocked anywhere.
Thanks for all the feedback guys, this is very encouraging!
I'm afraid that my own paltry electrical experience and knowledge doesn't quite meet up with your own, I was hoping that whatever I made would just be a very simple and solid circuit.
I don't quite understand but would this SM74611 Smart Bypass Diode be of more use for this idea than a simple old germanium diode?
If you're using it to rectify radio waves coming from an antenna then definitely, but I've got no clue what difference forward or breakdown voltage makes on a diode photovoltaic setup like >>1291377, or why he's using zeners.

The advantage of a Ge diode for radio harvesting is that it has a lower forward voltage than a Si diode, and this SM74611 has a much lower drop again, meaning you're wasting less power when charging the filtration capacitor after rectifying the AC RF.

But since it looks like you're looking at the solar route, I don't have much of a clue at all.
How would you calculate the power from one "loop" of an rf rectification circuit? I suppose it depends on the input power almost entirely, with the loss from the rectifying element.
>If you're using it to rectify radio waves coming from an antenna then definitely

Well that's good because that is exactly what I wanted to do! Sorry if I made it seem like I was going the solar route due to my desire to house it in a glass dome but that was really just more for protection and aesthetics. I'd like it to look decent as well as function, a mantle decoration ideally.
Well you can easily calculate the maximum power available with some intensity and area calculations, and go from there with some efficiency estimates, and from there do some prototyping to figure out optimal coil/antenna geometry.

The power you'll be able to harvest will be pretty limited but available all the time, so your best bet is something that runs constantly and with very low power. A clock is about all I can think of under that category. But for the "leave charging and use occasionally" category, an electronic compass (using a 3-axis magnetometer), a flashlight, a lighter, or perhaps even a dosimeter would work.
>that puts the capacitors out of the question too

It doesn't. Electrolytics are notorious for having (relatively) short lifespans, especially when exposed to heat, but other kinds last an extremely long time. If you design your circuit to take into account the degradation of a more stable capacitor (that is to say, ensure it doesn't need a specific capacitance), there's no reason you can't use something other than electrolytics.
Oh, well that is nice information to have, thank you.
Do you think it would be feasible to use some sort of capacitor system which gradually charges up (It can take a very long time, that's fine) and then once a certain threshold is reached it lights an LED or does some other VISIBLE thing? If capacitors are back on the table then I suppose that actually opens the potential activities quite a lot, though I want to avoid any potential wear and tear.

In essence all I want is something that sits on the mantelpiece completely forgotten about but every now and then my kids would look at it and go "Hey, remember when dad made that?", it'll be almost like i'm still there, you know?
What about thermocouples? Im mean it like two metal objects of high thermal capacity. One in vacuum insulated dome, the other in ambient temperature. As the temperature shifts through a day, the insulated one would always lag behind, thus creating thermal difference, that can be used by peltier or other thermoelectric part (like simple thermocouple).
Bonus: if your descendant picks it up hundred of years later and warms it up with his hand, there will be enough power to display "HEY FUTURE FAG" message
Sauce ?
I've a sudden need of Al or Cu based diodes...
I'd quite like to know which capacitors are the best for low-leakage, for both low-power electronics and for stupidly long-period RC circuits.

Just a two-sided medallion that you hold in one hand would be enough for that to work, and it's a cool idea, but you'll need to design it with thermodynamics in mind if you want it to slowly charge up from ambient temperature changes. I think just making a standalone "thermal battery" like this that you can attach to anything low-power would be a worth project in itself. A watch is an obvious use for this, but you'd have to be creative with the heat-sinking.

It was an academic paper I have access to from being a student at my university, about schottky barrier diodes made with germanium as the semiconductor and a collection of different metals as the junction metal, I suspect you won't be able to buy them anywhere since they exhibit low reliability.
>broad spectrum power density
An SDR dongle will get you a reasonable estimate that excludes the mains hum and other low-frequency RF, but if I get my SDR working I can probably use my oscilloscope to compare amplitudes of signals with resonant antennae and establish a nice dataset of different energy densities at different frequencies.
That's very interesting
>What about thermocouples?
I came here to post this.
But since that's already been mentioned, how about air pressure changes?
>Do you think it would be feasible to use some sort of capacitor system which gradually charges up (It can take a very long time, that's fine) and then once a certain threshold is reached it lights an LED or does some other VISIBLE thing?


>I'd quite like to know which capacitors are the best for low-leakage, for both low-power electronics and for stupidly long-period RC circuits.

Off the top of my head, ceramic capacitors with a class 1 dielectric do not degrade over time. As a bonus, they have low losses. The downside is that they have much lower permittivity (and therefore capacitance) than other dielectrics. Getting enough of them to achieve decent total capacitance might cost a bit, since they're unusual to see above the nF range.

There may be some supercapacitors that work, however. I believe most of them have stable chemistries, but can be sensitive to moisture/humidity (which shouldn't be a problem in a sealed container). Never looked at them in enough detail to know what typical DC leakage and very long-term stability is like, though.
>or breakdown voltage makes on a diode photovoltaic setup like >>1291377, or why he's using zeners.
>That's very interesting

Those are random scrap pieces from random salvage projects. The images show it picking up EM from several sources, CLF, CRT, power cord, and concentrated sunlight. The box around it is to help rule out light as a false positive. It worked "okay" for finding wires and running electronics, but the inverse-square law means it needs to be very close already.
I was more concerned about leakage current than the dielectric decaying over time, since electrolytics tend to have more leakage current than ceramics. Are tantalums or some sort of polymer capacitors better for this purpose? If you're only powering a clock with microamps then you only need the capacitor to filter the high frequency radio received and rectified, and the leakage current would have to be significantly less than the current drawn by the clock. On the other hand, if you were making a burst-usage tool, like a flashlight or electronic compass, you would need a significant amount of energy storage, potentially upwards of 1 Joule, which is well and truly supercapacitor territory.

That thing can pick up low frequency RF as well as sunlight? I guess the photovoltaic effect explains the EMF for the sunlight, and the diodes themselves act as antennae for picking up RF? Unless you expect me to believe that the work function of a diode PV panel is that low.

For finding electronics I wonder how effective a hall effect sensor + battery + transistor + LED would be? Probably better than an inductor at least.
I really have no clue. I just slapped it together and took readings all over the place on different objects, powered and unpowered. It had continuity so just that alone would help pickup stuff as a wire antennae and the blocking aspect would get it going. As far as everything else, hell, maybe the metal difference being heated by the sun turned it into a weak thermoelectric Peltier module in addition to something else. There's really just too much going on with the cobbled together design to sort it out without lots and lots of testing. As a hall effect sensor, I think it'd be pretty random.
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I don't think you can get a thermoelectric effect from diodes, but I can't say that with certainty, since I think it does have something to do with electrons and holes. I suppose the way to see what causes what is to also make a diode device with cancelling antennae. You might have already made one of those, hence why the voltage dropped off so quickly away from the wire. A normal wire will have a magnetic field that decreases proportionally to R^2, but two wires next to each other carrying anti-phase current will have a magnetic field that drops off proportionally to R^3, and two cancelling antennae next to one another probably makes it drop off even quicker.

Perhaps I should buy a couple of those 0.25V diodes and mess about with energy harvesting myself, too bad I'm a little consumed with other projects at the moment.
Going to second the morse code suggestion, OP, especially given what you've said you want to make. Maybe make it display a message you want associated with you?
>I don't think you can get a thermoelectric effect from diodes, but I can't say that with certainty, since I think it does have something to do with electrons and holes.

It depends on the metal types that are soldered together; graphite works too. If they are different then heat will cause an electrical charge to be created.


All of those zenners are from all manner of different electronics.

>too bad I'm a little consumed with other projects at the moment.

Drink coffee at like 5pm and don't stop doing little projects until 3am. That's what I end up doing on rare occasions, though I use tea instead.
Forgot one of the links for zenner and solar,

But are zeners better than other diodes? And by how much?
>a lighter
Do you mean like an arc lighter?
Yep, it's probably more efficient than a resistive one. It is one of the more power-hungry options, but if you can get it to work of energy harvesting then you could probably make a killing off selling it on kickstarter or whatever.

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