An international parts order is too complex for such a small thing. I’m not in the USA or China. So no TP5000 for me, got to work with what I have.

I agree, no charging at 4.2 volts. The current charger I built seems to work well enough. I ran some tests and it charges within spec. The reason I turn off the charger to measure cell voltage is because otherwise I’ll mainly be measuring SMPS noise.

Anyway it beats the charger available in the local market, which is clearly unsafe, no matter how much they assure me that it’s ‘totally OK’.

No worries! I appreciate that you were just trying to assist!

Battery University is indeed a great resource!

However this is not a lithium polymer battery, and as it’s a 32700, it is not a prismatic or pouch cell either. It is a lithium iron phosphate (LiFePO4) cylindrical battery in metal housing. Battery University does have them listed in their table of chemistries (in case you’re curious), but they don’t seem to have much detailed information. Enough to build a charger though :)

https://batteryuniversity.com/article/bu-216-summary-table-of-lithium-based-batteries

Also some more detailed information here:

https://batteryuniversity.com/article/bu-205-types-of-lithium-ion

Anyway, thanks for your reference in any case! I’m not responding to criticize you, only to improve the utility of this conversation in case someone else finds it on search :)

Makes sense!

I’d order online if there was a LiFePO4 charger on the market. However, in my country I’ve been unable to find one, and importing (excise & duties, paperwork) is more work than building it myself. I’ll also likely need a design that I can cheaply include on custom PCBs for manufacture (not for sale to end-users, but for internal use by maintenance technicians).

I gave it a test on a cell today and it seems to charge fine and at a reasonable rate – but in a sudden flash of brilliance, I forgot to physically connect the ADC pin to the battery, so it couldn’t shut off. Well, that’s what testing is for I guess.

Anyway after fixing this, it looks like I can call this a win and move on. If it undergoes destructive optimization, I’ll report back here with a warning to others.

No, that won’t work.

A vibration switch will work.

If that’s not sensitive enough, another option is using a piezo element coupled to the case to detect vibration, with an op-amp or hex inverter to buffer + trigger the 555. However if you couple it too closely with e.g. the floor or furniture it will pick up nearby footsteps or cars. Might be good depending on the situation.

Wouldn’t that… just make me stop visiting YouTube instead of making me stop using Firefox?

I mean, my first reaction when a website is slow is not exactly “maybe I should change browsers”. It’s closer to “maybe I’ll visit a different website”.

That sounds even better!

Hm, that reminds me! If you’re designing your own PCB, some manufacturers will make the PCB out of aluminum for you instead of FR4. This is commonly used for high-intensity LED lights to help keep them cool.

Here’s some random info about them so you can see what I mean:

https://www.pcbgogo.com/Article/An_Introduction_to_Aluminum_PCBs_by_PCBGOGO.html

An alternative would be copper-clad polyimide adhered to the body. That also has better thermal properties than FR4.

In seconds? Wow. I think you’re right, you might need more than a small fan!

It might be worth exploring heat pipes or peltier effect coolers. The latter makes the problem worse (they are inefficient and generate a lot of heat) but your LED can be locally cooler if you can e.g. move all that extra heat into a big heatsink (also condensation can be problematic).

One cheap source of heat pipes for testing could be old graphics cards – they often outperform simple copper heat sinks. Use thermal epoxy to stick your LED to it and see if the performance is acceptable. On the exotic end of things, you could also water/oil cool it, or (carefully) make your own thermal grease from industrial diamond powder for a small boost in thermal conductivity.

Also even at 95% efficiency, it sounds like your boost converter has some heat to dump too!

Hah! I totally didn’t notice that. Good catch.

These are the smallest fans that I know of: https://www.mouser.com/new/sunon/sunon-mighty-mini-fan/

They go down to 9mm x 9mm x 3mm.

If this is to cool some component in the flashlight, have you considered a heatsink instead?

Bananas are not typically very high on the danger scale except in exotic (and universally embarrassing) circumstances.

In fact, that’s another thing we could use bananas for scale with. Probably driving to work is equivalent to several kilobananas worth of danger daily :)

Anyway, I think the positron should be about 44keV if that helps you calibrate your magnets. The typical banana should produce something on the order of a positron every 10 seconds (although I used much rounding for the sake of brevity). Most commercial positron sources e.g. used in hospital PET scanners, are many times stronger than that!

Nice – you wouldn’t happen to have any ideas on how to differentiate positron annihilation, from the continuous distribution of β− energies caused by the more common decay mode, using only a PIN photodiode? I’m a bit stumped on this point and suspect it’s not possible. I probably need to do gamma spectroscopy but would really rather not.

So, in the fine tradition of using bananas for scale…

Bananas are slightly more radioactive than the background, due to potassium-40 content. So an informal unit of radiation measure in educational settings is the ‘banana-equivalent-dose’, which is about 0.1 microsieverts.

My particle spectrometer saw first light today, and I figure that I could use a banana to calibrate it. Then I noticed that K-40 undergoes a rare (0.001%) decay to 40Ar, emitting a positron. So not only is a banana a decent around-the-house radioisotope source, it’s also an antimatter source.

Truly a remarkable and versatile fruit.

Well, if it’s annoying enough, we would just… stop using it, I guess. That does put some limit on how much advertising they can shove down our engagement holes. So the ad-blockers could force them to be so obnoxious that they ostracize their user base, at least in principle :D

The ads are already aggressive enough that I won’t use it to host video (I’d rather just pay more and host it myself), and only use it to view content when I have no other option (e.g. reviewing a colleague’s work that they posted there for some reason). The youtube ads we get in VN are also quite loud and obnoxious, to be fair :D

In principle, I’d be willing to pay them for ad-free content, but frankly I don’t find the content or suggestion algorithm are useful enough for me to spend any time there. Other activities are just more interesting to me.

As a mercenary science hermit, I approve.

I suppose wheeled boats are just… cars with sails? Sailcars? Wind chariots?

Hm, one thing I didn’t think about was magma, if the variations are not so small. Going to have more volcanic eruptions, as fluids get pressed out of high-gravity regions and into low-gravity ones (creating big mountains that grow and tumble into the high gravity wells like some sort of horizontal convection?). Earthquakes too, as the high gravity regions sink and the low gravity ones rise creating shear force. I bet the planet would be more “lumpy” than your run-of-the-mill oblong spheroid. I wonder what continental drift would be like?

With that much irregular magma flow, I bet the magnetic field would be weird if it could sustain one at all. Maybe as ‘cells’ where the eruptions occur in low gravity regions, then gets pulled into high gravity regions where it compresses, heats due to radioactive decay, melts and is pushed back out into low-gravity regions. So maybe you’d have ‘local north’ for the cell? Or a very weak magnetic field overall (yay radiation)? I don’t really know on this point.

Oh and exceptionally high-precision clocks won’t be useful except locally, because of the effect of gravity on spacetime, but that doesn’t seem so bad. Low precision clocks based on pendulums won’t be useful at all! Spring escapements should be fine though.

Maybe it would be better to live underwater?

Wow all of that, and home ownership still seems more accessible there than here. I bet real estate prices are a bargain!

Well if we are going for science…

Giant constructions will have a lot of wear and tear under varying gravity. On top of that, high winds and frequent storms are likely to weather geographical features a lot, making them more flat. In a fantasy world, you can just magic things away, so that’s fine :)

I don’t know about you, but I would find constant high winds fairly terrifying for air travel. Perhaps they are high enough to permit wheeled sailboats on land? That would be creative!

Instead of wind mills, you could have gravity mills. Pump water into a higher-altitude reservoir on low-gravity days, and let it flow down – turning a turbine – on high gravity days. At least electricity would be cheap.

Or if it varies by region, pump water horizontally (or let it flow slightly downward) from a high gravity region to a low one. Then pump the water upwards there, then horizontally again to the high gravity region. Then let it fall down to turn a turbine that runs all the pumps – perpetual motion (ish)!

Predicting tides becomes hard. Everything is going to be really windy all the time, as the atmosphere expands in low-gravity regions and contracts in high gravity ones. This makes tall buildings impractical, as they would also have to be built for some maximum gravity rating on top of the constant gravity storms.

The oceans would be weird, and violent. Hurricanes might get far more powerful than what we deal with, if the right gravity conditions occur.

For any sort of civilization to emerge, gravity would have to change/vary really slowly. I don’t even want to think of orbits. Kerbal Space Program would be like, really hard in that universe.

An Elitzur–Vaidman bomb-tester is a device that lets you test whether a light-sensitive bomb is a dud or not at arbitrary precision, without blowing it up. It is an example of interaction-free measurement.

The method does not really have any practical uses so far, although it has been demonstrated experimentally.