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A graph of current versus time for circuits with and without inductors

A Deep Dive Into Inductors

February 5, 2026 by 5 Comments

[Prof MAD] runs us through The Hidden Power of Inductors — Why Coils Resist Change.

The less often used of the passive components, the humble and mysterious inductor is the subject of this video. The essence of inductance is a conductor’s tendency to resist changes in current. When the current is steady it is invisible, but when current changes an inductor pushes back. The good old waterwheel analogy is given to explain what an inductor’s effect is like.

There are three things to notice about the effect of an inductor: increases in current are delayed, decreases in current are delayed, and when there is no change in current there is no noticeable effect. The inductor doesn’t resist current flow, but it does resist changes in current flow. This resistive effect only occurs when current is changing, and it is known as “inductive reactance”.

After explaining an inductor’s behavior the video digs into how a typical inductor coil actually achieves this. The basic idea is that the inductor stores energy in a magnetic field, and it takes some time to charge up or discharge this field, accounting for the delay in current that is seen.

There’s a warning about high voltages which can be seen when power to an inductor is suddenly cut off. Typically a circuit will include snubber circuits or flyback diodes to help manage such effects which can otherwise damage components or lead to electric shock.

[Prof MAD] spends the rest of the video with some math that explains how voltage across an inductor is proportional to the rate of change of current over time (the first derivative of current against time). The inductance can then be defined as a constant of proportionality (L). This is the voltage that appears across a coil when current changes by 1 ampere per second, opposing the change. The unit is the volt-second-per-ampere (VsA-1) which is known as the Henry, named in honor of the American physicist Joseph Henry.

Inductance can sometimes be put to good use in circuits, but just as often it is unwanted parasitic induction whose effects need to be mitigated, for more info see: Inductance In PCB Layout: The Good, The Bad, And The Fugly.

Continue reading “A Deep Dive Into Inductors” →

Toybox Tractor: Plywood, Lathe Hacks, And 350W Of Fun

February 5, 2026 by 14 Comments

When you think of a toy tractor, what probably comes to mind is something with fairly simple lines, maybe the iconic yellow and green, big rear tires, small front ones. Well, that’s exactly what [James] built, with simple, clean lines and a sturdy build that will hold up to driving around off-road in the garden. This Tractor is a great build, combining CAD, metal and wood work, some 3D printing, and electronics.

Starting at the power plant for the build, [James] went with a 350W DC motor powered by a 36V Li-ion battery from an e-bike. The motor turns a solid rear axle he made on a mini-lathe, connected to a set of riding lawn mower wheels. The mini-lathe spindle bore was too small to accommodate the shaft, and the lathe was not long enough to use the tailstock, so [James] had to get creative, using a vice and a piece of wood to make a stand–in tailstock, allowing him to turn this custom rear axle. The signature smoothly curved bonnet was made possible with plywood and body filler, rather than the sheet metal found on full-sized tractors. In fact, most of the build’s frame used plywood, giving it plenty of strength and, once painted, helping give it the appearance of a toy pulled out of a toybox.

This build had a bit of many domains in it, and all combined into a fantastic final result that no doubt will bring a smile to any face that gets to take the Tractor for a ride. Thanks [James] for documenting your build process, the hacks needed to pull off the tough bits along the way in making this fun toy. If you found this fun, be sure to check out another tractor related project.

Simulating Pots With LTSpice

January 21, 2026 by 9 Comments

One of the good things about simulating circuits is that you can easily change component values trivially. In the real world, you might use a potentiometer or a pot to provide an adjustable value. However, as [Ralph] discovered, there’s no pot component in LTSpice. At first, he cobbled up a fake pot with two resistors, one representing the top terminal to the wiper, and the other one representing the wiper to the bottom terminal. Check it out in the video below.

At first, [Ralph] just set values for the two halves manually, making sure not to set either resistor to zero so as not to merge the nets. However, as you might guess, you can make the values parameters and then step them.  Continue reading “Simulating Pots With LTSpice” →

TV Remote Uses Floppy Disks

January 19, 2026 by 9 Comments

Famously, the save icon on most computer user interfaces references a fairly obsolete piece of technology: the venerable floppy disk. It’s likely that most people below the age of about 30 have never interacted with one of these once-ubiquitous storage devices, so much so that many don’t recognize the object within the save icon itself anymore. [Mads Chr. Olesen]’s kids might be an exception here, though, as he’s built a remote control for them that uses real floppy disks to select the programming on the TV.

This project partially began as a way to keep the children from turning into zombies as a result of the modern auto-play brainrot-based economies common in modern media. He wanted his kids to be able to make meaningful choices and then not get sucked into these types of systems. The floppy disk presents a perfect solution here. They’re tangible media and can actually store data, so he got to work interfacing a real floppy disk drive with a microcontroller. When a disk is inserted the microcontroller wakes up, reads the data, and then sends out a command to stream the relevant media to the Chromecast on the TV. When the disk is removed, the microcontroller stops play.

Like any remote, this one is battery powered as well, but running a microcontroller and floppy disk drive came with a few challenges. This one is powered by 18650 lithium cells to help with current peaks from the drive, and after working out a few kinks it works perfectly for [Mads] children. We’ve seen a few other floppy disk-based remote controls like this one which replaces the data stored on the magnetic disc with an RFID tag instead.

A hand holding the Zoyi ZT-QB9 Smart Clamp meter

Review And Demo Of The Zoyi ZT-QB9 Smart Clamp Meter

January 18, 2026 by 14 Comments

Over on YouTube [Kiss Analog] reviews the New Zoyi ZT-QB9 Smart Clamp meter.

If you’re putting together an electronics lab from scratch you absolutely must get a multimeter to start. A typical multimeter will be able to do current measurements but it will require you to break the circuit you’re measuring and interface it to your meter using its mechanical probes.

A good choice for your second, or third, multimeter is a clamp-based one. Many of the clamp meters have the clamp probe available for current measurements while still allowing you to use the standard 4mm banana jack probes for other measurements, particularly voltage and resistance.

If you’re curious to know more about how clamp meters work the answer is that they rely on some physics called the Hall Effect, as explained by the good people at Fluke.

In the video the following clamp meters are seen: Zoyi ZT-QB9, PROVA 11, and Hioki CM4375. If you’re in the market for a clamp meter you might also like to consider the EEVblog BM036 or a clamp meter from Fluke.

We have of course posted about clamp meters before. Check out Frnisi DMC-100: A Clamp Meter Worth Cracking Open or ESP32 Powers DIY Smart Energy Meter if you’d like to know more. Have your own trusty clamp meter? Don’t need no stinkin’ clamp meter? Let us know in the comments!

Continue reading “Review And Demo Of The Zoyi ZT-QB9 Smart Clamp Meter” →

A Guide To Using Triacs For Switching AC

January 18, 2026 by 14 Comments

For switching high-powered loads from a microcontroller, or for switching AC loads in general, most of us will reach into the parts bin and pull out a generic relay of some sort. Relays are fundamental, proven technologies to safely switch all kinds of loads. They do have their downsides, though, so if you need silent operation, precise timing, or the ability to operate orders of magnitude more times you might want to look at a triac instead. These solid state devices can switch AC loads unlike other transistor-based devices and [Ray] at OpenSprinkler is here to give us an overview on how to use them.

The key to switching an AC load is bi-directional conductivity. A normal transistor or diode can only conduct in one direction, so if you try to switch an AC load with one of these you’ll end up with what essentially amounts to a bad rectifier. Triacs do have a “gate” analogous to the base of a bipolar junction transistor, but the gate will trigger the triac when current flows in either direction as well. The amount of current needed to trigger the triac does depend on the state of the switched waveform, so it can be more complex to configure than a relay or transistor in some situations.

After going through some of the theory around these devices, [Ray] demonstrates how to use them with an irrigation system, which are almost always operating on a 24VAC system thanks to various historical quirks. This involves providing the triacs with a low voltage source to provide gate current as well as a few other steps. But with that out of the way, switching AC loads with triacs can become second nature. If you prefer a DC setup for your sprinklers, though, [vinthewrench] has demonstrated how to convert these sprinkler systems instead.

[Dr Ali Shirsavar] drawing schematics and equations on the whiteboard

Calculating The Capacitance And ESR Specifications For The Output Capacitor In Your Switching-Mode Power Supply

January 18, 2026 by 13 Comments

[Dr Ali Shirsavar] from Biricha Digital runs us through How to Select the Perfect Output Capacitor for Your Power Supply. Your switching-mode power supply (SMPS) will require an output capacitor both to iron out voltage swings due to loading and to attenuate ripple caused by switching. In this video we learn how to calculate the required capacitance, and when necessary the ESR, for your output capacitor.

To begin [Dr Ali] shows us that in order to calculate the minimum capacitance to mitigate voltage swings we need values for Δi, Δv, and Ts. Using these we can calculate the minimum output capacitance. We then need to calculate another minimum capacitance for our circuit given that we need to attenuate ripple. To calculate this second minimum we need to change our approach depending on the type of capacitor we are using, such as ceramic, or electrolytic, or something else.

When our circuit calls for an electrolytic capacitor the equivalent series resistance (ESR) becomes relevant and we need to take it into account. The ESR is so predominant that in our calculations for the minimum capacitance to mitigate ripple we can ignore the capacitance and use the ESR only as it is the feature which dominates. [Dr Ali] goes into detail for both examples using ceramic capacitors and electrolytic capacitors. Armed with the minimum capacitance (in Farads) and maximum ESR (in Ohms) you can then go shopping to find a capacitor which meets the requirements.

If you’re interested in capacitors and capacitance you might enjoy reading about Measuring Capacitance Against Voltage and Getting A Handle On ESR With A Couple Of DIY Meters.