ESP32: When Is A P4 A P4, But Not The P4 You Thought It Was

March 21, 2026 by Jenny List 30 Comments

We’re used to electronic parts of the same type staying predictably the same, sometimes over many years. An early Z80 from the mid 1970s can be exchanged with one from the end of production a few years ago, for example. This week, we’ve had DMs from several readers who’ve found that this is not always the case, and the culprit is surprising. Espressif has released a new revision of their P4 application processor, and though it’s ostensibly the same, there are a couple of changes that have been catching people out.

The changes lie in both hardware and software, in that there’s a pin that’s changed from NC to a power rail, a few extra passives are needed, and firmware must be compiled separately for either revision. The problem is that they are being sold as the same device and appear in some places under the same SKU! This is leading to uncertainty as to which P4 revision is in stock at wholesalers. We’ve been told about boards designed for the old revision being assembled with the new one, a situation difficult to rework your way out of. Designers are also left uncertain as to which firmware build is needed for boards assembled in remote factories.

The ESP32-P4 is an impressive part for its price, and we’re sure that we’ll be seeing plenty of projects using this new revision over the coming years. We’re surprised that it doesn’t have a different enough part number and that the wholesalers have seemingly been caught napping by the change. We’re told that some of the well-known Chinese assembly houses are now carrying the two chips as separate SKUs, but that’s scant consolation for a designer with a pile of boards carrying the wrong part. If you’re working with the P4, watch out, make sure your board is designed for the latest revision, and ask your supplier to check which chips you’ll get.

If the P4 is new to you, we’ve already seen a few projects using it.

Hackaday Podcast Episode 362: Compression Molding, IPv4x, And Wired Headphones

March 20, 2026 by Jenny List 7 Comments

As the sun goes down on a glorious spring evening on the western edge of Europe, Elliot Williams is joined by Jenny List for a look at the week in all things Hackaday.

First up: Hackaday Europe tickets are on sale! Bad luck folks, the early bird tickets disappeared in an instant, but regular ones are still available for now. We’re really looking forward to making our way to Lecco for a weekend of hacks, and it would be great to see you there too.

Then we have a new feature for the podcast, the Hackaday Mailbag. This week’s contribution comes from [Kenny], a longtime friend of Hackaday and probably our most regular conference attendee.

To the hacks, and we have some good ones. An air hockey robot might not seem like a challenge, but the engineering which went into [BasementBuilds’] one proves it’s not a job for the faint hearted. Then we look at compression molding of recycled plastic using 3D-printed molds, something that seems surprisingly accessible and we’d like to try, too. We’ve got a new DOS, a 3D-printed zipper repair, the IPv4 replacement we didn’t get, and the mind-bending logic of ternary computing. It’s one of those weeks where the quick hacks could all deserve their own in-depth look, but perhaps the stand-outs are and Arduino style compiler that includes the source code compressed within the binary, and a beautifully-done revival of a 1980s brick cellphone as a modern 5G unit.

Finally in the longer reads we’ve got an examination of wired versus Bluetooth headphones — we’re both in the wired camp — and a look back at the age of free dialup. As is so often the case, the experience there differed between Brits and Americans. Anyway, enjoy the episode, and we have another week to look forward to.

Download your own personal copy of the Podcast in glorious 192 kB MP3.

Continue reading “Hackaday Podcast Episode 362: Compression Molding, IPv4x, And Wired Headphones” →

Reading The World’s Smallest Hard Drive

March 19, 2026 by Jenny List 20 Comments

You have a tiny twenty-year-old hard drive with a weird interface. How do you read it? If you’re [Will Whang], by reverse engineering, and building an interface board.

In many of our portable, mobile, and desktop computers, we’re used to solid-state storage. It’s fast and low power, and current supply-chain price hikes notwithstanding, affordable in the grand scheme of things. It wasn’t always this way though, a couple of decades ago a large flash drive was prohibitively expensive. Hard drive manufacturers did their best to fill the gap with tiny spinning-rust storage devices which led to the smallest of them all: the Toshiba MK4001MTD. It crammed 4 GB onto a 0.85″ platter, and could be found in a few devices such as high-end Nokia phones.

Breaking out the Nokia’s hard drive interface.

The drive’s connector is a pattern of pads on a flexible PCB, one he couldn’t help noticing had a striking resemblance to an obscure SD card variant. Hooking it up to an SD reader didn’t work unfortunately, so a battered Nokia was called into service. It was found to be using something electrically similar to the SD cards, but with the ATA protocol familiar from the world of full-size hard drives.

The interface uses the PIO capability of the RP2040, and the board makes a tidy peripheral in itself. We’re guessing not many of you have one of these drives, but perhaps if you do, those early 2000s phone pics aren’t lost for good after all.

These drives are rare enough that this is the first time we’ve featured one here at Hackaday, but we’ve certainly ventured into hard drive technology before.

Modular 18650 Packs, No Spot Welding Required

March 19, 2026 by Jenny List 48 Comments

Building a battery pack from 18650 cells traditionally requires patience, a spot welder, and a supply of nickel strip. But what if there was another way? [Ben] is here with Cell-Lock, a modular battery assembly system.

At the system’s heart are a set of interlocking end caps and connection pieces that function as locking cams as well as the electrical connections where needed. They were inspired by the cam systems used for furniture assembly, and are activated by rotation with a screwdriver. The result is a mechanically stable battery system in which different configurations can easily be assembled.

We like that it doesn’t involve any heat near those cells; in part because we’ve seen our share of dodgy connections overheating. But we do have a few concerns. These include how reliable a connection those cams would make, as well as how much current they could safely take without overheating. If both of those could be addressed, we can see that this is an idea with a future.

You can see plenty of examples on the linked project, including an e-bike pack which seems to return no problems. Meanwhile this is by no means the first modular battery pack system we’ve seen.

Hacking The System In A Moral Panic: We Need To Talk

March 17, 2026 by Jenny List 95 Comments

It seems that for as long as there have been readily available 3D printers, there have been moral panics about their being used to print firearms. The latest surrounds a Washington State Legislature bill, HB2320, which criminalises the printing of unregistered guns. Perhaps most controversially, it seeks so impose a requirement on printers sold in the state to phone home and check a database of known firearms and refuse to print them when asked.

This has drawn a wave of protest from the 3D printing community, and seems from where we are sitting to be a spectacularly ill-conceived piece of legislation. It’s simply not clear how it could be implemented, given the way 3D printers and slicing software actually work.

Oddly This Isn’t About Firearms

The root of the problem with this bill and others like it lies in ignorance, and a misplaced belief in the power of legislation. Firearms are just the example here, but we can think of others and we’re sure you can too. Legislators aren’t stupid, but by and large they don’t come from technology or engineering backgrounds.

Meanwhile they have voters to keep happy, and therefore when a moral panic like this one arises their priority is to be seen to be doing something about it. They dream up a technically infeasible solution, push to get it written into law, and their job is done. Let the engineers figure out how to make it work. Continue reading “Hacking The System In A Moral Panic: We Need To Talk” →

A Voltage Regulator Before Electronics

March 16, 2026 by Jenny List 40 Comments

Did you ever wonder how the mechanical voltage regulator — that big black box wired up to the generator on a car from the ’60s or before — worked? [Jonelsonster] has some answers.

For most people in 2026 an old car perhaps means one from the 20th century, now that vehicles from the 1990s and 2000s have become the beloved jalopies of sallow youths with a liking for older cars and a low budget. But even a 1990s vehicle is modern in terms of its technology, because a computer controls the show. It has electronic fuel injection (EFI), anti-lock braking system (ABS), closed loop emissions control, and the like.

Go back in time to the 1970s, and you’ll find minimal electronics in the average car. The ABS is gone, and the closest thing you might find to EFI is an electronic ignition where the points in the distributor have been replaced with a simple transistor. Perhaps an electronic voltage regulator on the alternator. Much earlier than that and everything was mechanical, be that the ignition, or that regulator.

The video below the break has a pair of units, it seems from 1940s tractors. They would have had a DC generator, a spinning coil with a commutator and brushes, in a magnetic field provided by another coil. These things weren’t particularly powerful by today’s standards and sometimes their charging could be a little lackluster, but they did work. We get to see how, as he lifts the lid off to reveal what look like a set of relays.

We’re shown the functions of each of the three coils with the aid of a lab power supply; we have a reverse current relay that disconnects the generator if the battery tries to power it, an over-current relay that disconnects the field coil if the current is too high, and an over-voltage relay that does the same for voltage. The regulating comes down to the magnetic characteristics, and while it’s crude, it does the job.

We remember European devices with two coils and no field terminal, but the principle is the same. There is never a dull moment when you own an all mechanical car.

Continue reading “A Voltage Regulator Before Electronics” →

The Shockley 4-Layer Diode In 2026

March 14, 2026 by Jenny List 10 Comments

The physicist William Shockley is perhaps today best known for three things: his role in the invention of the transistor, his calamitous management of Shockley Semiconductor which led to a mass defection of employees and precipitated the birth of the Silicon Valley we know, and his later descent into promoting eugenics. This was not the sum of his work though, and [David Prutchi] has been experimenting with a now-mostly-forgotten device that bears the Shockley name (PDF), after finding one used in an early heart pacemaker circuit. His findings are both comprehensive and fascinating.

The Shockley diode, or 4-layer diode as it later became known, is as its name suggests a two terminal device with a 4-layer NPNP structure. It can be modeled as a pair of complementary transistors in parallel with a reverse biased diode, and the avalanche breakdown characteristics of that diode when a particular voltage is applied to it provide the impetus to turn on the two transistors. This makes it a voltage controlled switch, that activates when the voltage across it reaches that value.

The PDF linked above goes into the Shockley diode applications, and in them we find a range of relaxation oscillators, switches, and logic circuits. The oscillators in particular could be made with the barest minimum of components, important in a time when each semiconductor device could be very expensive. It may have faded into obscurity as it was superseded by more versatile 4-layer devices such as the PUJT or silicon-controlled switch and then integrated circuits, but he makes the point that its thyristor cousin is still very much with us.

This appears to be the first time we’ve featured a 4-layer diode, but we’ve certainly covered the genesis of the transistor in the past.