Regular Old Diodes Can Be More Photosensitive Than You Think

November 3, 2025 by Lewin Day 26 Comments

[Dhananjay Gadre] happened across a useful little trick the other day. Take any old 1N4148 or 1N914 glass-package signal diode and wire it up right, and you’ve got yourself a nifty little IR detector.

The trick is to treat the diode just like you would a proper IR photodiode. The part should be reverse biased with a resistor inline, and the signal taken from the anode side. Point an IR remote at your little diode and you’ll readily see the modulated signal pop up on a scope, clear as day.

The phenomenon is discussed at length over on Stack Exchange. Indeed, it’s a simple fact that most semiconductor devices are subject to some sort of photoelectric effect or another. It’s just that we stick the majority of them in opaque black packages so it never comes up in practice. In reality, things like photodiodes and phototransistors aren’t especially different from the regular parts—they’re just put in transparent packages and engineered and calibrated to give predictable responses when used in such a way.

Is this the way you’d go if your project needed an IR detector? Probably not—you’d be better served buying the specific parts you need from the outset. But, if you find yourself in a pinch, and you really need to detect some IR signals and all you’ve got on hand is glass-package signal diodes? Yeah, you can probably get it to work.

While this trick is well known to many oldheads, it’s often a lightbulb moment for many up-and-coming engineers and makers to realize this. Glass-packaged diodes aren’t the only light-sensitive parts out there, either. As we’ve explored previously, certain revisions of Raspberry Pi would reboot if exposed to a camera flash, while you can even use regular old LEDs as sensors if you’re so inclined. If you’ve got your own secret knowledge about how to repurpose regular components in weird ways, don’t hesitate to notify the tipsline!

Microscopic view of chiral magnetic material

Twisting Magnetism To Control Electron Flow

March 22, 2025 by Heidi Ulrich 11 Comments

If you ever wished electrons would just behave, this one’s for you. A team from Tohoku, Osaka, and Manchester Universities has cracked open an interesting phenomenon in the chiral helimagnet α-EuP₃: they’ve induced one-way electron flow without bringing diodes into play. Their findings are published in the Proceedings of the National Academy of Sciences.

The twist in this is quite literal. By coaxing europium atoms into a chiral magnetic spiral, the researchers found they could generate rectification: current that prefers one direction over another. Think of it as adding a one-way street in your circuit, but based on magnetic chirality rather than semiconductors. When the material flips to an achiral (ferromagnetic) state, the one-way effect vanishes. No asymmetry, no preferential flow. They’ve essentially toggled the electron highway signs with an external magnetic field. This elegant control over band asymmetry might lead to low-power, high-speed data storage based on magnetic chirality.

If you are curious how all this ties back to quantum theory, you can trace the roots of chiral electron flow back to the early days of quantum electrodynamics – when physicists first started untangling how particles and fields really interact.

There’s a whole world of weird physics waiting for us. In the field of chemistry, chirality has been covered by Hackaday, foreshadowing the lesser favorable ways of use. Read up on the article and share with us what you think.

Turning Down The Noise On SMPS

March 17, 2025 by Bryan Cockfield 13 Comments

On paper, electricity behaves in easy-to-understand, predictable ways. That’s mostly because the wires on the page have zero resistance and the switching times are actually zero, whereas in real life neither of these things are true. That’s what makes things like switch-mode power supplies (SMPS) difficult to build and troubleshoot. Switching inductors and capacitors tens or hundreds of thousands of times a second (or more) causes some these difficulties to arise when these devices are built in the real world. [FesZ Electronis] takes a deep dive into some of the reasons these difficulties come up in this video.

The first piece of electronics that can generate noise in an SMPS are the rectifier diodes. These have a certain amount of non-ideal capacitance as well as which causes a phenomenon called reverse current, but this can be managed by proper component choice to somewhat to limit noise.

The other major piece of silicon in power supplies like this that drives noise are the switching transistors. Since the noise is generally caused by the switching itself, there is a lot that can be done here to help limit it. One thing is to slow down the amount of time it takes to transition between states, limiting the transients that form as a result of making and breaking connections rapidly. The other, similar to selecting diodes, is to select transistors that have properties (specifically relating to inherent capacitances) that will limit noise generation in applications like this.

Of course there is a lot more information as well as charts and graphs in [FesZ]’s video. He’s become well-known for deep dives into practical electrical engineering topics like these for a while now. We especially like his videos about impedance matching as well as a more recent video where he models a photovoltaic solar panel in SPICE.

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Line Power With No Transformer

February 24, 2025 by Al Williams 43 Comments

Normally, when you want a low DC voltage from the AC line, you think about using a transformer of some kind. [RCD66] noticed that an AC monitor meter must have some sort of power supply but had no transformers in sight. That led to an exploration of how those work and how you can use them, too. You can watch the work in the video below.

Sensibly, there is a transformer in the test setup — an isolation transformer to make it safe to probe the circuit. But there’s no transformer providing voltage changes. Isolation is important even if you are taking apart something commercial that might be trasformerless.

The circuit is simple enough: it uses a capacitor, a resistor, and a pair of diodes (one of them a zener diode). He uses this basic circuit to drive simple regulators with input and output filter capacitors. We’ve seen many variations on this design over the years.

You can’t draw a lot of power through this arrangement. But sometimes it is all you need. However, this is pretty dangerous, as we’ve discussed before. Be sure you understand exactly what the risks are before you decide to build something like this.

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Ideal Diodes And How To Build Them

October 19, 2024 by Al Williams 17 Comments

[Julian] knows that real diodes you can buy don’t work exactly like we say they do. That’s actually pretty common. We routinely ignore things like wire resistance and source resistance in batteries. Diodes have problems that are harder to ignore, such as the forward voltage drop. So, while a real diode will only pass current in one direction, it will also drop some of the voltage. [Julian] shows you how you can get simulated ideal diodes and why you might want them in a recent video you can see below.

The video starts with a simple demonstration and enumerates some of the practical limitations. Then, he pulls out some ideal diode modules. These typically don’t solve every problem, so they aren’t really ideal in the theoretical sense. But they typically appear to have no forward voltage drop.

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How Do You Fill The 1N34 Void?

May 26, 2024 by Jenny List 31 Comments

The germanium point contact diode, and almost every semiconductor device using germanium, is now obsolete. There was a time when almost every television or radio would have contained one or two of them, but the world has moved on from both analogue broadcasting and discrete analogue electronics in its lower-frequency RF circuitry. [TSBrownie] is taking a look at alternatives to the venerable 1N34A point-contact diode in one of the few places a point-contact diode makes sense, the crystal radio.

In the video below the break, he settles on a slightly more plentiful Eastern European D9K as a substitute after trying a silicon rectifier (awful) and a Schottky diode (great in theory, not so good in practice). We’ve trodden this path in the past and settled on a DC bias to reduce the extra forward voltage needed for a 1N4148 silicon diode to conduct because, like him, we found a Schottky disappointing.

The 1N34 is an interesting component, and we profiled its inventor a few years ago. Meanwhile, it’s worth remembering that sometimes, we just have to let old parts go.

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MOSFET Heater Is Its Own Thermostat

March 29, 2023 by Bryan Cockfield 16 Comments

While we might all be quick to grab a microcontroller and an appropriate sensor to solve some problem, gather data about a system, or control another piece of technology, there are some downsides with this method. Software has a lot of failure modes, and relying on it without any backups or redundancy can lead to problems. Often, a much more reliable way to solve a simple problem is with hardware. This heating circuit, for example, uses a MOSFET as a heating element and as its own temperature control.

The function of the circuit relies on a parasitic diode formed within the transistor itself, inherent in its construction. This diode is found in most power MOSFETs and conducts from the source to the drain. The key is that it conducts at a rate proportional to its temperature, so if the circuit is fed with AC, during the negative half of the voltage cycle this diode can be probed and used as a thermostat. In this build, it is controlled by a set of resistors attached to a voltage regulator, which turn the heater on if it hasn’t reached its threshold temperature yet.

In theory, these resistors could be replaced with potentiometers to allow for adjustable heat for certain applications, with plastic cutting and welding, temperature control for small biological systems, or heating other circuits as target applications for this type of analog circuitry. For more analog circuit design inspiration, though, you’ll want to take a look at some classic pieces of electronics literature.