Category: DIY

Repurposing Components from a Broken Air Purifier | May 03 2026, 15:00

The air purifier broke down, so I bought a used one with a new cartridge for the price of a replacement cartridge plus $40. I completely disassembled the old one, extracted the reusable components, and figured out how it works. Just like in school 🙂

Inside, it comprises:

– an ESP32-WROOM-32D controller. But a part of the board responsible for voltage burned out, so it’s trash now.

– a CO sensor MQ-7 (unfortunately soldered to the board, but can be desoldered). Though, it needs a heating cycle for correct operation. First 5V (60 sec) for sensor cleaning, then 1.5V (90 sec) for measurement. But, it can also be used elsewhere.

– Plantower PMS9103M — a high-precision laser sensor for measuring airborne particulate matter concentrations (PM1.0, PM2.5, PM10). Can be connected to Arduino, specification available.

– a microwave motion sensor (radar), model RCWL-0516. Can be connected to Arduino, very simple interface. Detects motion up to 5-7 meters around within 360 degrees.

– 200W Snowfan YY225H310B motor. Also quite simple to connect, but it requires 310V DC plus 15V for speed control. But that’s all.

– a Hall sensor (magnet)

The motor is the most valuable part. It’s priced at $100 on eBay. Though, it should probably be tested first to see if it hasn’t burned out.

Unlocking the Mystery: Dual Voltage Needs in Smart Locks | March 07 2026, 22:43

Update: figured it out, looks like the lock needs 6v + 6v for different purposes. Maybe the power part and electronics.

Anyone who knows electronics, help me understand. Red wires are connected to contacts that respond to the tester. A total of 8 batteries. I can’t see a classic snake configuration here. Can’t understand why the lower right ones are responding. I want to connect an external adapter

Decoding Leather Products: From Genuine to Synthetic | February 23 2026, 18:11

Today I learned how the hierarchy of leather products is actually structured. Everyone knows that faux leather is completely synthetic; it’s a layer of polymer on a fabric base. There is also cheap leather, often labeled as Genuine Leather, which technically remains an animal-derived product. It turns out to be the lower, looser layer of the hide, which on its own lacks strength or aesthetics, so it’s turned into a sort of sandwich, encased in a thick layer of plastic (polyurethane) with embossing. Essentially, cheap leather is split or compressed leather scraps (Bonded leather or bi-cast/tri-cast), glued together with plastic. It’s essentially akin to plywood or particle board.

How such leather is produced: 1) Leather scraps and waste are taken 2) they are shredded into small fibers 3) mixed with a binder – polyurethane or latex – resulting in a mass similar to pulp 4) this mixture is evenly distributed on a substrate, which typically serves as fabric or paper material 5) a roller or plate with a pattern mimicking natural leather is then pressed onto the surface of the mixture, creating a texture reminiscent of real leather. 6) After drying, a protective coating is applied to enhance the strength, wear resistance, and appearance of the material.

Expensive leather is called Aniline or Full Grain. Essentially, it is made from the top part of the hide (which is exposed to air on the animal). It is dyed with transparent dyes, and contains no plastic. Nubuck or suede is part of the hide which, excuse me, comes in contact with the flesh.

Many also judge the quality of leather by its smell, thinking that a distinctive aroma is the main sign of authenticity and high class. This is easily mistaken. The scent we associate with expensive leather is often the result of chemists’ work. Manufacturers of cheap bonded leather products use special fragrance sprays that mimic the smell of expensive tanning. Real high-quality leather, such as vegetable-tanned leather, smells more like wood, oak bark, or mimosa, because these substances are used in its processing.

Another professional secret concerns the edges of the product. If you see that the edge of a bag or belt is neatly filled with a thick layer of “rubber” or paint so that the structure of the layers is not visible, this is often not done for design’s sake. Such a technique helps to conceal that very plastic sandwich which makes up the material. Craftsmen working with truly high-quality Full Grain leather often leave the cuts open or just slightly polish them with wax, because they have nothing to hide — the fiber structure of such leather is equally dense throughout its thickness.

Building a Plotter from Scratch: My DIY Journey | January 30 2026, 05:43

I assembled a plotter from a kit. It’s practically a Lego set – you spill out the parts from the box and then read the manual. It worked right away. I have some ideas about what to do with this thing, I’ll tell you sometime.

From Freezer to Fridge: A DIY Cooling Hack | December 19 2025, 00:56

Today I sold a refrigerator. It has a story. The essence of it is that it’s not a refrigerator, although it looks like one. It’s a freezer. And it freezes on average to minus 18 degrees. I bought it second-hand, thinking it was a refrigerator. The buyer also came today thinking it was a refrigerator.

And here I realize that minus 18 degrees is not at all what I need.

Well, I am a Solution Architect. I didn’t want to dig into it, I just drove to Lowe’s and bought a simple blinker. It turns on and off according to schedule whatever is plugged into it. I stuck a radio thermometer inside (I had one) and adjusted the blinking frequency (20 minutes) so that the internal temperature was on average +4 degrees Celsius. The radio thermometer showed that the temperature fluctuations were very small – nominally plus or minus 0.5 degrees from +4, even less. And so it worked for me for some months until I realized that I just didn’t need it.

Sold it today with the adapter. It’s gone to the people.

The Ingenious Spy Device Gifted in Friendship: Unveiling The Thing | September 01 2025, 01:03

Today in the museum I saw The Thing in person – simply a brilliant espionage device. In 1945, a group of Soviet schoolchildren presented a large wooden Great Seal of the United States to the U.S. Ambassador in Moscow, Averell Harriman, as a “gesture of friendship”. The seal was beautifully hand-carved and hung in the ambassador’s office for a whole 7 years. And it leaked secrets!

No batteries involved! It was all very clever, especially for 1945.

Essentially, it was a passive radio relay or “parasitic resonator”. Inside the wooden seal was a small metal cylinder with a membrane and an antenna-rod.

Soviet operators directed a specific frequency radio wave (about 330 MHz) into the ambassador’s office.

Inside the device was a cavity resonator, tuned to the same frequency. It “responded” to the radio signal and began to retransmit it back.

On one side of the cylinder was a thin flexible membrane. It vibrated from the sound in the room (voices, footsteps).

The vibrations of the membrane altered the capacity and resonance parameters of the device, slightly shifting the reflected radio signal by frequency and phase. This was the modulation of speech onto the external signal.

Outside the building (like in a KGB car nearby), the retransmitted signal was received and the sound modulation was extracted – effectively capturing the overheard conversation.

Why was this almost impossible to detect? The device had no battery and emitted nothing by itself. It “came to life” only when irradiated with an external radio signal. In standard radio monitoring checks, it remained “dead”. Essentially, it was akin to an ancestor of the RFID tag – a passive device that operates only on external request.

But most interestingly, the inventor was Leon Theremin, the same person behind the musical instrument “thereminvox” (played with hands in the air).

His biography reads like a novel. In the early 1920s, Theremin went to the U.S., patented his thereminvox instrument, and collaborated with RCA; his New York studio was visited by Charlie Chaplin, Albert Einstein, Gershwin, and other notable personalities. It is written that he visited the USSR – Already in 1926, he demonstrated television at the Kremlin.

At that time, televisions with screens the size of a matchbox were being created, but his television had a huge screen (1.5 x 1.5 m) and a resolution of 100 lines. In 1927, the scientist demonstrated his installation to Soviet military leaders K.E. Voroshilov, I.V. Tukhachevsky, and S.M. Budyonny:

state minds watched in horror as Stalin walked through the Kremlin courtyard on the screen.

This sight so frightened them that the invention was immediately classified and quietly buried in the archives, and television was soon invented by the Americans.

Eventually, in 1938, he secretly returned to the USSR, but was soon arrested as a “non-returnee” and sent to the camps, but his talent was still used in the so-called “sharashka” – on projects together with Sergei Korolev, including the development of radio-controlled apparatuses and listening systems, including the aforementioned “Great Seal bug”.

DIY Wireless Reaction Game: Building Interactive Button-Based Activities | July 28 2025, 22:26

Who knows their way around electronics? Any recommendations?

I want to make a thing some weekend. A big bulbous button. It lights up – you smash it. The app records the time from when it lights up to when it’s smashed. There might be several buttons and they could be scattered – on walls or the floor. WIRELESS. They might light up randomly – this is controlled by the app (phone or computer). Metrics like average reaction time are calculated on the fly for different understandings of the word ‘average’. For instance, you could place buttons on the ground a few meters apart and invent a moving game for the kids. Or attach them to a wall and smash them with a ball. Basically, it’s a technical question.

How would you do it – dumb buttons on an nRF24L01+ chip or smart buttons on an esp32 microcontroller?

In the first case, every such module listens to the radio: as soon as a command with its ID arrives from the central node, it turns on the light. After the button is pressed, it sends back a “pressed” message. The timer is on the side of the central node. Each button has an Arduino Pro Mini + nRF24L01+, but there will also be a central hub with either nRF24L01+ and Arduino Uno, Mega or ESP32, which collects the data and is connected to the computer (Bluetooth or WiFi).

In the second case, the buttons are connected via Bluetooth (BLE) or WiFi. The brains of the button is the ESP32, which needs to be programmed through a programmer.

Cost-wise, both approaches are roughly the same minus the cost of arcade buttons and 3D printing, somewhere around $10-15 per button.