Test Unknown Fuses Without Destroying Them

There’s a problem with fuses. On the face of it, testing would seem to be a one-shot deal — exceed the rated current and see if it blows. But once you know the answer, the device is useless. If only there were a way to test fuses without damaging them.

As it turns out there is, and [Kerry Wong] weaves quite a tale about his attempts to non-destructively test fuses. The fuses in question are nothing fancy — just the standard glass tube type, from a cheap assortment kit off Amazon. Therein lies the problem: can such cheap devices be trusted? Finding out requires diving much deeper into the technology of fuses than many people will have done, including understanding how the thermal and electrical characteristics of the fuse element behave.

[Kerry]’s test setup is simple, consisting of a constant current power supply and a voltmeter across the fuse to measure the voltage drop caused by the resistance of the fuse element. As he ramps up the current, the voltage drop increases linearly due to the increase in resistance of the alloy with increasing temperature. That only lasts up to a point, where the fuse resistance starts increasing exponentially. Pushing much past the point where the resistance has doubled would blow the fuse, so that’s the endpoint of his tests. Perhaps unsurprisingly, his no-name fuses all went significantly beyond their rated current, proving that you get what you pay for. See the video below for the tests and an analysis of the results.

It’s handy to know there’s a way to check fuses without popping them, and we’ll file this one away for future reference. Don’t forget that you should always check the fuse when troubleshooting, because you never know what the last person did to it.

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Salty? Tip Canister To Rage Quit Games

Do you long for a more pronounced way to rage quit video games? Smashing buttons comes naturally, of course, but this hurts the controller or keyboard. You can quit your longing, because [Insert Controller Here] has an elegant solution that’s worth its salt.

The Salty Rage Quit Controller is simple. The cup is filled with distilled water. When you pour salt in it, the two bolt terminals tell the Arduino Micro that the resistance in the water has decreased. The Micro sends whatever keystrokes you want, so you could call out your deadbeat medic before quitting, or just plain leave. [Insert Controller Here] has example code on his site to get you started. Click calmly past the break to watch the demo and build videos, or we’ll have to ban you for aggro.

With the right tools, you can turn anything into a game controller. Check out this car controller that uses Python and CAN bus sniffing.

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Circuit VR: Resistance Measurement With Four Wires

If you want to measure resistance and you know Ohm’s law, it seems like you have an easy answer, right? Feed a known current through the thing you want to measure and read the voltage required. A little math, and that’s it. Or is it? If you are measuring reasonably large resistance and you don’t mind small inaccuracies, sure. But for tiny measurements or highly accurate measurements, you’d be better off using the four-wire method. What’s more is, understanding why you want to use the four-wire method is a great example of using an understanding of electronics to find solutions to problems.
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Your Own Milliohm Meter

We like to pretend that wires are perfect all the time. For the most part that’s acceptable, but sometimes you really do care about those tiny fractional ohm quantities. Unfortunately though, most meters won’t read very low values. There are tricks you can use to achieve that aim, such as measuring low currents through a device with a known voltage applied. It is handier though to have an instrument to make the reading directly, and [Kasyan TV] did just that with a surprisingly low part count.

The whole thing is built from an LM317, a resistor, and a voltmeter module, that’s it. [Kasyan] mentions the meter’s accuracy means the lower digits are not meaningful, but it looks to us as though there are other sources of error — for example, there’s no way to zero out the probe’s resistance except during the initial calibration. Continue reading “Your Own Milliohm Meter”

Always Have A Square To Spare

Some aspects of humanity affect all of us at some point in our lives. Whether it’s getting caught in the rain without an umbrella, getting a flat tire on the way to work, or upgrading a Linux package which somehow breaks the entire installation, some experiences are truly universal. Among these is pulling a few squares of toilet paper off the roll, only to have the entire roll unravel with an overly aggressive pull. It’s possible to employ a little technology so that none of us have to go through this hassle again, though.

[William Holden] and [Eric Strebel] have decided to tackle this problem with an innovative bearing of sorts that replaces a typical toilet paper holder. Embedded in the mechanism is a set of magnetic discs which provide a higher resistance than a normal roll holder would. Slowly pulling out squares of paper is possible, but like a non-Newtonian fluid becomes solid when a higher force is applied, the magnets will provide enough resistance when a higher speed tug is performed on the toilet paper. This causes the paper to tear rather than unspool the whole roll, and also allows the user to operate the toilet paper one-handed.

This is a great solution to a problem we’ve all faced but probably forgot about a minute after we experienced it. And, it also holds your cell phone to keep it from falling in the toilet! If you’d like to check out their Kickstarter, they are trying to raise money to bring the product to market. And, if you want to upgrade your toilet paper dispenser even further, there’s also an IoT device for it as well, of course.

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Measure Resistance The Colourful Way

One of the first things anyone with an interest in electronics learns is the resistor colour code. The colour of the first band reveals the first figure, the second the subsequent figure, and the third a power-of-ten multiplier. At first you learn these colours, but eventually you just recognise the values through familiarity. You don’t have to think about multipliers when you see orange-orange-red, you just know that it’s a 3K3 resistor.

[Plusea] has come up with an entertaining interface for an ohmmeter, which instead of displaying the resistance on an LCD or a meter shows it as the colours of the code, via a set of addressable LEDs. The work is done by an ATtiny85 microcontroller, and the whole thing is mounted on a flexible PCB (fabrication of which is itself interesting, placing cut copper traces on a sheet of kapton and covering with a second kapton layer cut to be the solder mask). There is even a clever integration of a CR2032 battery holder from the PCB itself, though they admit that it could be made more compact with the use of SMD components instead of through-hole.

The write-up and associated photo album tells us a lot about the project, but is missing a crucial detail: a shot of it working. We’ll give them the benefit of the doubt on that front though, because we like the idea and its execution.

Strangely, this isn’t the first ohmmeter to use the resistor colour code in this way, we’ve previously brought you one featuring a light-up giant resistor.

Standard Resistor Teardowns

What do you do, when you want an ohm? What is an ohm, for that matter? Take a wander over to the textbook definitions, and you’re soon deep in a world of coulombs and parallel infinite planes one meter apart in a vacuum that you probably only half remember from your high school physics class. It’s hard work, this metrology lark.

Of course, you can just order a resistor. A few cents each when you’re buying small quantities or much less when you’re buying a reel of five thousand, and there you have it. An ohm. Only it’s not really an ohm, more like nearly an ohm. Within 1% of an ohm is pretty good, but Vishay or Bourns or whoever don’t have the margins to get philosophical about those infinite planes when you’re only giving them a few cents.

When you REALLY want an ohm, you buy a standard resistor, and you pay a more significant sum. You’re never going to wire one of these up to bias a transistor or drive an LED, instead it’s about as close as it’s possible to get on your bench to the value it says on the box and you can use it for calibration purposes. PPM figures well in excess of the resolution of even superior DMMs sound pretty good to us!

[Zlymex] was curious about standard resistors, so performed a teardown of a few to see what they contain. And after a pithy explanation of the terms involved he’s managed to look inside quite a few of them.

Inside he finds hermetically sealed wire-wound resistors, some oil-filled wire-wound resistors, and the occasional hefty piece of manganin. He also tears down some of the hermetically sealed resistors themselves, finding both wire-wound and foil resistance elements within.

It is a curious obsession that permeates hacker culture, that of standard measurements, and it’s one we’ve covered quite a few times here. Time enthusiasts with atomic clocks like this rather beautiful discrete logic build, or voltage enthusiasts with their temperature compensated references or programmable standards. Surprisingly though, this appears to be the first time we’ve looked at standard resistors.

Thanks [David Gustafik] for the tip.