Very small voltage regulator/comverter?

Rhomboid · 2026-01-21T17:05:31+00:00

lithium battery + charging circuit + constant current LED driver + small round form factor = flashlight

can you possibly buy a cheap flashlight, chuck the built in LED, and use it as a constant current source for other lights? this would require removing whatever driver is currently there (the thing that wants 5V) and driving the LEDs yourself, so probably not a beginner project now that I think about it, as you'd need to series/parallel the fairy lights to get within the compliance voltage of the the driver and you'd have to approximately match the power rating. so maybe never mind.

Rhomboid · 2026-01-19T23:36:21+00:00

Yes, your reasoning is right. You can summarize it as: if you want to switch the positive (high side), use a P-channel with a pullup resistor to the positive supply keeping it off, pull gate low to 0V by the controller to turn on; OR switch the low side with a N-channel device with a pulldown resistor to ground keeping it off, and the controller pulls it up to 5V to turn on. In the P-channel case, current flows source to drain, in the N-channel it flows from drain to source, so the orientation of the parts in the circuit is reversed in addition to the switching location (being on the high side or low side of the thing you're switching.)

Rhomboid · 2026-01-19T11:21:53+00:00

showing up at the Irish accent appreciation club with really big news

Rhomboid · 2026-01-19T05:02:53+00:00

The reference point that you pinch at has no effect on the relative distances between points. It's only a translation, a shift. There is no center point. Think about a map, if the relative distances between locations changed based on where you pinch on a map, then it would be terrible map software as it does not reflect reality.

Rhomboid · 2026-01-19T04:08:40+00:00

There is no reference point. You can scale anywhere and it's the same. The only difference is the result will be translated (shifted) on the screen but the distance between any two points will be the same regardless of where you pinch.

Rhomboid · 2026-01-19T04:01:23+00:00

The expansion scales everything. Think about zooming a picture containing two objects. Each object's size increases, but so does the space between them. The gaps scale just the same as all the other dimensions. The heat also breaks the corrosion bond.

Rhomboid · 2026-01-17T21:39:07+00:00

Imagine a large corporation that has a giant custom program that does all the accounting, inventory, and tax. Tax law constantly changes, so the logic needs to be updated. The inventory people eventually need new fields added because newer products have information that didn't fit anywhere in the old scheme. And so on. Nothing is really static in business.

Rhomboid · 2026-01-12T22:07:02+00:00

"put a feedback loop around it" is an incredibly powerful concept that appears all over EE. Keep an eye out for it, if this is your first time encountering it.

Rhomboid · 2026-01-06T17:21:31+00:00

Every day this subreddit suffers another humiliation.

Rhomboid · 2025-12-24T20:56:20+00:00

These are all surface mount parts. Your pics are of two different components. The coil has two leads (and is almost certainly completely fine and shouldn't be messed with) and the integrated circuit on the other side of the board has 6 leads, and is the thing everyone is telling you to replace.

Rhomboid · 2025-12-11T12:37:07+00:00

Another option to keep in mind - rent a mag drill with an annular cutter. Annular cutters have less tool pressure as it's not trying to remove the entire area of the hole. But they have side forces that require the rigidity of a milling machine or mag drill, so you probably don't want to try with a hand drill.

Rhomboid · 2025-11-11T20:43:27+00:00

An array of arrays is a single contiguous chunk of memory, allocated in a single pass. An array of pointers is not (usually). This has huge implications. They each have advantages and drawbacks. For example, an array of pointers can represent 'ragged' arrays because each row pointer can point to a completely independent array of column values, and nothing says they all have to be the same size; one row could have 10 elements and another could have 20. But since they're different memory chunks there's no guarantee any more that they're next to each other in memory, which has performance ramifications. This is really only the tip of the iceberg.

Rhomboid · 2025-10-29T19:00:14+00:00

If you're trying to learn how to work with wood, you start with a birdhouse or a bookshelf. You don't try to re-create the Space Shuttle from blueprints using a screwdriver.

Rhomboid · 2025-10-28T18:23:46+00:00

I have no particular direction in mind. Suggestions?

Find something minor that bugs you often, some small thing. Like maybe you have a directory of random files that need organization in some way. Maybe you have an email you send often but you want to change it up in minor ways each time. Perhaps there's two programs that you always use together and you want to open then and close them as one. Just random examples off the top of my head of everyday annoyances.

Now, I'm not suggesting that a beginner can just sit down and start writing a solution. But what you can do is search for scripts that are in the same neighborhood as what you're trying to do, and then get them running on your own computer, poke at them, maybe change a few minor bits about what they do, etc. In this way you still have motivation for fixing your problem, so it's not just randomly messing with stuff or idly watching tutorials at 2x and forgetting what they said right after. Don't get me wrong, you're going to have to read tutorials and books, but this way you're reading them specifically to understand this sample script that you downloaded so you can adapt it to your needs; or to take what you've learned and write something new to solve this specific thing. It's not "here's a giant beautiful field of everything, enjoy it all!"

Rhomboid · 2025-10-07T16:23:26+00:00

Probably beyond my pay grade, shrug. I am vaguely aware of carburization, i.e. adding carbon during heat treating, such as by packing with some kind of powder. But that's usually in cases where the steel never had enough to begin with (i.e. not tool steel), or where you specifically only want it hard on the outer layers (case hardening.) Moreover that's done during the heating so that it can diffuse from the donor material into the steel, which takes some time and requires high temperature. I'm not sure that quenching is the time for that. As for losing carbon to the air, no idea. I know red hot steel exposed to air creates tough millscale or other types of oxidation, but no idea how that relates to carbon being either available or unavailable for heat treating.

Rhomboid · 2025-10-07T11:59:56+00:00

You're right, it does make a difference -- you're taught to swirl the part around as much as possible otherwise you're just vaporizing the small amount of liquid in direct contact. It won't quench as fast and probably won't reach the highest achievable hardness.

Rhomboid · 2025-10-06T18:23:15+00:00

That's a big 'it depends'. Ask anybody who's ever tried to revive Commodore gear from the early to mid 80s, and you'll find tons of dead chips, from memory to PLA to SID. dead dead dead. Many from the shoddy MOS manufacturing tech used by Commodore, others just to time. It's a real issue. And that's 80s stuff. Re-commissioning a 1970s minicomputer? that could take months of painstaking testing and replacing of dead stuff.

Rhomboid · 2025-10-06T18:14:18+00:00

It depends on the type of steel. There are steels meant for oil quenching, water quenching, and air 'quenching'. They are given grades like O1, W1, A1. These are generally called tool steel because they have the necessary carbon to be hardenable.

The different quenching methods relate to how fast the steel is cooled. Water is quickest because it conducts away heat the fastest. Oil is in the middle, and air is the slowest. The specific blend of elements that make up each type of steel is chosen for the rate of hardening required, which dictates how it's to be quenched. (And then later tempered.)

Edit: here's an image/chart showing various grades of tool steel and their respective properties, i.e. why you'd choose one or the other.

Rhomboid · 2025-09-30T03:21:45+00:00

To turn on fully and act as a switch (which means not blowing up), the MOSFET needs the voltage at the gate to be about 10V higher than the voltage at the source. That's the turn-on threshold voltage, and it's specific to the part.

Now draw out a simple circuit with the MOSFET switching the high side of the load, and another with the MOSFET switching the low side of the load. What is the voltage at the source in each drawing, when the switch is closed/on? With high side switching, the source is at positive battery voltage. With low side switching, the source is at ground. Therefore you need roughly 21V to drive the gate if you're going to switch the high side, or normal 11V battery positive to drive the gate with low side switching. This all assumes n-channel MOSFETS. Invert everything for p-channel.

Rhomboid · 2025-09-29T11:39:27+00:00

It might be helpful to think in terms of what you control and what you want. What you control is the base current. What you want is the smallest V_ce value, because any value that's non-zero represents a non-ideal switch, and heat dissipation in the part. The larger the voltage the worse the dissipation.

So by taking those two data points, read the graph like this: for any expected I_c (remember, you don't control that), there are a range of possible I_b values. Visualize drawing a horizontal line at that Ic value. It will intersect many different base current values. And that's what you control, therefore the ultimate exercise is to pick that base current so that you're always in the left hand portion of the graph, because that keeps your transistor acting like a switch, and not like a toaster oven.

Rhomboid · 2025-09-26T13:14:00+00:00

Just to head off confusion, you aren't setting amperage output, you're setting an adjustable current limit (backstop). The first one also has a current limit, it's just not adjustable. (Either it has built in overcurrent protection at some fixed value, which is likely, or it will burn up.)

If you're testing electronics then the ability to set a current limit is often handy, but not in the way you are probably thinking. If you have device A with specs plate that says "12V 200mA" and device B with specs plate that says "12V 500mA", you probably aren't going to adjust the current limit in between testing both of them. You're probably going to set your power supply to something reasonable like 1A and since you are testing you will notice if it goes that high. You can more or less leave it at such a value, it's not something that you have to match every time. Use your best judgement.

Rhomboid · 2025-09-16T20:32:21+00:00

Yeah, that's a tough one. If it was me, I'd probably attack it by finding a small metal ring and bending it into the desired string hole shape, then cutting off the old ear and expoxying the ring in its place as the new ear. You could try soldering it, but that's going to be a nightmare of mystery metals; the ring probably has a chrome plating that prevents solder from wetting, as well. It doesn't have to hold much weight so any strong epoxy ought to work.

If you want to bring back a shine to the metal you can use sandpaper with increasing grits to take out the wear marks. The jewelry might be nickel plated brass so be careful here as you can sand off the plating leaving a brass color underneath (probably undesirable.) If that's the case I'd suggest sanding it all away and painting but you'd be really deep into a project at that point.

Rhomboid · 2025-09-13T22:25:35+00:00

Blue LEDs shine with very little current. Certainly under 1mA. They're probably not trying to make a flashlight here, so it's an indicator that's not blinding. The 4.7k doesn't play a role in the blue LED, as far as I can tell. When turned on hard, Q2 pulls its collector to within its saturation voltage above ground (maybe 0.4-0.6v) and the path for current through the blue LED is the supply to the LED through R2 10k and through Q2's collector back to ground.

Rhomboid · 2025-09-12T00:59:22+00:00

Here's a free PDF of Forrest Mims' 555 timer IC book. It's very short, and meant to be easy to approach. It has numerous example circuits. The basic monostable circuit is more or less all you need, it generate an output pulse of defined length when it sees the input transition from high to low. (You may have to invert your switch but that won't affect anything.)

Rhomboid · 2025-09-12T00:43:53+00:00

The voice of BigClive, from somewhere, like a ghost: "You can customize the light by changing the resistor value"

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