Low Cost Oscilloscope Gets Low Cost Upgrades

April 20, 2025 by Bryan Cockfield 51 Comments

Entry-level oscilloscopes are a great way to get some low-cost instrumentation on a test bench, whether it’s for a garage lab or a schoolroom. But the cheapest ones are often cheap for a reason, and even though they work well for the price they won’t stand up to more advanced equipment. But missing features don’t have to stay missing forever, as it’s possible to augment them to get some of these features. [Tommy’s] project shows you one way to make a silk purse from a sow’s ear, at least as it relates to oscilloscopes.

Most of the problem with these lower-cost tools is their low precision due to fewer bits of analog-digital conversion. They also tend to be quite noisy, further lowering the quality of the oscilloscope. [Tommy] is focusing his efforts on the DSO138-mini, an oscilloscope with a bandwidth of 100 kHz and an effective resolution of 10 bits. The first step is to add an anti-aliasing filter to the input, which is essentially a low-pass filter that removes high frequency components of the signal, which could cause a problem due to the lower resolution of the device. After that, digital post-processing is done on the output, which removes noise caused by the system’s power supply, among other things, and essentially acts as a second low-pass filter.

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Homemade VNA Delivers High-Frequency Performance On A Budget

April 16, 2025 by Dan Maloney 7 Comments

With vector network analyzers, the commercial offerings seem to come in two flavors: relatively inexpensive but limited capabilities, and full-featured but scary expensive. There doesn’t seem to be much middle ground, especially if you want something that performs well in the microwave bands.

Unless, of course, you build your own vector network analyzer (VNA). That’s what [Henrik Forsten] did, and we’ve got to say we’re even more impressed by the results than we were with his earlier effort. That version was not without its problems, and fixing them was very much on the list of goals for this build. Keeping the build affordable was also key, which resulted in some design compromises while still meeting [Henrik]’s measurement requirements.

The Bill of Materials includes dual-channel broadband RF mixer chips, high-speed 12-bit ADCs, and a fast FPGA to handle the torrent of data and run the digital signal processing functions. The custom six-layer PCB is on the large side and includes large cutouts for the directional couplers, which use short lengths of stripped coaxial cable lined with ferrite rings. To properly isolate signals between stages, [Henrik] sandwiched the PCB between a two-piece aluminum enclosure. Wisely, he printed a prototype enclosure and lined it with aluminum foil to test for fit and function before committing to milling the final version. He did note some leakage around the SMA connectors, but a few RF gaskets made from scraps of foil and solder braid did the trick.

This is a pretty slick build, especially considering he managed to keep the price tag at a very reasonable $300. It’s more expensive than the popular NanoVNA or its clones, but it seems like quite a bargain considering its capabilities.

Homebrew Phosphorescence Detector Looks For The Glow In Everyday Objects

November 28, 2024 by Dan Maloney 8 Comments

Spoiler alert: almond butter isn’t phosphorescent. But powdered milk is, at least to the limit of detection of this homebrew phosphorescence detector.

Why spend a bunch of time and money on such a thing? The obvious answer is “Why not?”, but more specifically, when [lcamtuf]’s son took a shine (lol) to making phosphorescent compounds, it just seemed natural for dad to tag along in his own way. The basic concept of the detector is to build a light-tight test chamber that can be periodically and briefly flooded with UV light, charging up the putatively phosphorescent compounds within. A high-speed photodiode is then used to detect the afterglow, which can be quantified and displayed.

The analog end of the circuit was the far fussier end of the design, with a high-speed transimpedance amplifier to provide the needed current gain. Another scaling amp and a low-pass filter boosts and cleans up the signal for a 14-bit ADC. [lcamtuf] went to great lengths to make the front end as low-noise as possible, including ferrite beads and short leads to prevent picking up RF interference. The digital side has an AVR microcontroller that talks to the ADC and runs an LCD panel, plus switches the 340 nm LEDs on and off rapidly via a low gate capacitance MOSFET.

Unfortunately, not many things found randomly around the average home are all that phosphorescent. We’re not sure what [lcamtuf] tried other than the aforementioned foodstuffs, but we’d have thought something like table salt would do the trick, at least the iodized stuff. But no matter, the lessons learned along the way were worth the trip.

A Homebrew Gas Chromatograph That Won’t Bust Your Budget

October 13, 2024 by Dan Maloney 19 Comments

Chances are good that most of us will go through life without ever having to perform gas chromatography, and if we do have the occasion to do so, it’ll likely be on a professional basis using a somewhat expensive commercial instrument. That doesn’t mean you can’t roll your own gas chromatograph, though, and if you make a few compromises, it’s not even all that expensive.

At its heart, gas chromatography is pretty simple; it’s just selectively retarding the movement of a gas phase using a solid matrix and measuring the physical or chemical properties of the separated components of the gas as they pass through the system. That’s exactly what [Markus Bindhammer] has accomplished here, in about the simplest way possible. Gas chromatographs generally use a carrier gas such as helium to move the sample through the system. However, since that’s expensive stuff, [Markus] decided to use room air as the carrier.

The column itself is just a meter or so of silicone tubing packed with chromatography-grade silica gel, which is probably the most expensive thing on the BOM. It also includes an injection port homebrewed from brass compression fittings and some machined acrylic blocks. Those hold the detectors, an MQ-2 gas sensor module, and a thermal conductivity sensor fashioned from the filament of a grain-of-wheat incandescent lamp. To read the sensors and control the air pump, [Markus] employs an Arduino Uno, which unfortunately doesn’t have great resolution on its analog-to-digital converter. To fix that, he used the ubiquitous HX7111 load cell amplifier to read the output from the thermal conductivity sensor.

After purging the column and warming up the sensors, [Markus] injected a sample of lighter fuel and exported the data to Excel. The MQ-2 clearly shows two fractions coming off the column, which makes sense for the mix of propane and butane in the lighter fuel. You can also see two peaks in the thermal conductivity data from a different fuel containing only butane, corresponding to the two different isomers of the four-carbon alkane.

[Markus] has been on a bit of a tear lately; just last week, we featured his photochromic memristor and, before that, his all-in-one electrochemistry lab.

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A Brief Look Inside A Homebrew Digital Sampler From 1979

June 17, 2024 by Dan Maloney 12 Comments

While we generally prefer to bring our readers as much information about a project as possible, sometimes we just have to go with what we see. That generally happens with new projects and work in progress, but it can also happen with old projects. Sometimes very old indeed, as is the case with this digital sampling unit for analog oscilloscopes, circa 1979.

We’ve got precious little to go on with this one other than the bit of eye candy in the video tour below and its description. Luckily, we’ve had a few private conversations with its maker, [Mitsuru Yamada], over the years, enough to piece together a little of the back story here — with apologies for any wrong assumptions, of course.

Built when he was only 19, this sampler was an attempt to build something that couldn’t be bought, at least not for a reasonable price. With no inexpensive monolithic analog-to-digital converters on the market, he decided to roll his own. A few years back he recreated the core of that with his all-discrete successive approximation ADC.

The sampler shown below has an 8-bit SAR ADC using discrete CMOS logic and enough NMOS memory to store 256 samples. You can see the ADC and memory cards in the homebrew card cage made from aluminum angle stock. The front panel has a ton of controls and sports a wide-range attenuator, DC offset, and trigger circuit with both manual and automatic settings.

It’s an impressive build, especially for a 19-year-old with presumably limited resources. We’ve reached out to [Yamada-san] in the hope that he’ll be able to provide more details on what’s under the hood and if this still works after all these years. We’ll pass along whatever we get, but in the meantime, enjoy.

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Arduino Measures Remaining Battery Power With Zero Components, No I/O Pin

December 21, 2023 by Donald Papp 22 Comments

[Trent M. Wyatt]’s CPUVolt library provides a fast way to measure voltage using no external components, and no I/O pin. It only applies to certain microcontrollers, but he provides example Arduino code showing how handy this can be for battery-powered projects.

The usual way to measure VCC is simple, but has shortcomings.

The classical way to measure a system’s voltage is to connect one of your MCU’s ADC pins to a voltage divider made from a couple resistors. A simple calculation yields a reading of the system’s voltage, but this approach has two disadvantages: one is that it constantly consumes power, and the other is that it ties up a pin that you might want to use for something else.

There are ways to mitigate these issues, but it would be best to avoid them entirely. Microchip application note 2447 describes a method of doing exactly that, and that’s precisely what [Trent]’s Arduino library implements.

What happens in this method is one selects Vbg (a fixed internal voltage reference that is temperature-independent) as Vin, and selects Vcc as the ADC’s voltage reference. This is essentially backwards from how the ADC is normally used, but it requires no external hookup and is only a bit of calculation away from determining Vcc in millivolts. There is some non-linearity in the results, but for the purposes of measuring battery power in a system or deciding when to send a “low battery” signal, it’s an attractive solution.

Being an Arduino library, CPUVolt makes this idea very easy to use, but the concept and method is actually something we have seen before. If you’re interested in the low-level details, then check out our earlier coverage which goes into some detail on exactly what is going on, using an ATtiny84.

Upgraded Toy Guitar Plays Music

October 25, 2023 by Bryan Cockfield 1 Comment

Getting the finishing details on a Halloween costume completed is the key to impressing friends and strangers alike on the trick-or-treat rounds. Especially when it comes to things like props, these details can push a good Halloween costume to great with the right touches. [Jonathan]’s friend’s daughter will be well ahead of the game thanks to these additions to a toy guitar which is part of her costume this year.

The toy guitar as it was when it arrived had the capability to play a few lackluster sound effects. The goal here was to get it to play a much more impressive set of songs instead, and to make a couple upgrades along the way as well. To that end, [Jonathan] started by dismantling the toy and investigating the PCBs for potential reuse. He decided to keep the buttons in the neck of the guitar despite their non-standard wiring configuration, but toss out the main board in favor of an ESP32. The ESP32 is tasked with reading the buttons, playing a corresponding song loaded on an SD card, and handling the digital to analog conversion when sending it out to be played on the speaker.

The project doesn’t stop there, though. [Jonathan] also did some custom mixing for the songs to account for the lack of stereo sound and a working volume knob, plus he used the ESP32’s wireless capabilities to set the guitar up as a local file server so that songs can be sent to and from the device without any wires. He also released the source code on the project’s GitHub page for anyone looking to use any parts of this project. Don’t forget there’s a Halloween contest going on right now, so be sure to submit the final version of projects like these there!

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