adc

98 Articles

How Bad Can A Cheap Knockoff ADS1115 ADC Be?

October 15, 2025 by 29 Comments

Although the saying of caveat emptor rings loudly in the mind of any purveyor of electronic components, the lure of Very Cheap Stuff is almost impossible to resist. Sure, that $0.60 Ti ADS1115 ADC on LCSC feels like it almost has to be a knock-off since the same part on Digikey is $4 a pop, and that’s when you buy a pack of 1,000. Yet what if it’s a really good knockoff that provides similar performance for a fraction of the price, such as with those cheap ADC boards you can get from Amazon? Cue [James Bowman] letting curiosity getting the better of him and ordering a stash of four boards presumably equipped with at least some kind of cheapo knockoff part, mostly on account of getting all boards for a mere $2.97.

The goal was of course to subject these four purported ADS1115s to some testing and comparison with the listed performance in the Ti datasheet. Telling was that each of the ADCs on the boards showed different characteristics, noticeably with the Data Rate. This is supposed to be ±10% of the nominal, so 7.2 – 8.8 times per second in 8 samples per second mode, but three boards lagged at 6.5 – 7 SPS and the fourth did an astounding 300 SPS, which would give you pretty noisy results.

Using a calibrated 2.5 voltage source the accuracy of the measurements were also validated, which showed them to be too low by 12 mV. The good news was that a linear correction on the MCU can correct for this, but it shows that despite these parts being ADS1115 compatible and having features like the PGA working, you’re definitely getting dinged on performance and accuracy.

[James] said that he’s going to run the same tests on an ADS1115 board obtained from Adafruit, which likely will have the genuine part.  We would also love to see someone test the $0.60 version from LCSC to see whether they can match the datasheet. Either way, if you are eyeing this ADC for your own projects, it pays to consider whether the compromises and potential broken-ness of the knockoffs are worth it over coughing up a bit more cash. As they say, caveat emptor.

ASIC physical layout

The Entire Process Of Building An Open Source Analog ASIC

October 8, 2025 by 6 Comments

Our hacker [Pat Deegan] of Psychogenic Technologies shows us the entire process of designing an analog ASIC. An ASIC is of course an Application-Specific Integrated Circuit, which is basically just custom hardware. That’s right, “just” custom hardware.

Services such as those from Tiny Tapeout make it possible to get your hardware designs built. And tools such as those found in Tiny Tapeout Analog Design VM with Skywater 130 PDK make it possible to get your hardware designs… designed.

In the video [Pat] takes you through using xschem (for schematic capture) and magic (for physical layout) to design a custom ADC. We learn that when it comes to hardware you have the choice of many different types of FETs, and not much else. Capacitors are expensive and to be avoided. Inductors are verboten. Getting specific values for things (such as resistors) is pretty much impossible so you generally just have to hope that things come out in relative proportions.

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A High Resolution ADC From Scratch

October 4, 2025 by 6 Comments

It’s a well-known conundrum that while most computers these days are digital in nature, almost nothing in nature is. Most things we encounter in the real world, whether it’s temperature, time, sound, pressure, or any other measurable phenomenon comes to us in analog form. To convert these signals to something understandable by a digital converter we need an analog-to-digital converter or ADC, and [Igor] has built a unique one from scratch called a delta sigma converter.

What separates delta sigma converters apart is their high sampling rate combined with a clever way of averaging the measurements to get a very precise final value. In [Igor]’s version this average is provided by an op-amp that integrates the input signal and a feedback signal, allowing for an extremely precise digital value to be outputted at the end of the conversion process. [Igor] has built this one from scratch as well, and is using it to interface a magnetic rotary encoder to control digital audio playback.

Although he has this set up with specific hardware, he has enough detail in his video (including timing diagrams and explanations of all of the theory behind these circuits) for anyone else to build one of these for other means, and it should be easily adaptable for plenty of uses. There are plenty of different ADC topologies too, and we saw many different ones a few years ago during our op-amp challenge.

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Pi Pico Powers Parts-Bin Audio Interface

June 20, 2025 by 10 Comments

USB audio is great, but what if you needed to use it and had no budget? Well, depending on the contents of your parts bin, you might be able to use [Veyniac]’s Pico-Audio-Interface as a free (and libre! It’s GPL3.0) sound capture device.

In the project’s Reddit thread, [Veyniac] describes needing audio input for his homemade synth, but having no budget. Necessity being the mother of invention, rather than beg borrow or steal a device with a working sound card, he hacked together this lovely device. It shows up as a USB Audio Class 2.0 device so should work with just about anything, and offers 12-bit resolution and 4x oversampling to try and deal with USB noise with its 2-channel, 44.1 kHz sample rate.

Aside from the Pico, all you need is an LM324 op-amp IC and a handful of resistors and capacitors — [Veyniac] estimates about $10 to purchase the whole BOM. He claims that the captured audio sounds okay in his use, but can’t guarantee it will  be for anyone else, noise being the fickle beast that it is. We figure that sounding “Okay” has got to be pretty good, given that you usually get what you pay for — and again, [Veyniac] did build this in a cave with a box of scraps. Well, except for the cave part. Probably.

While the goal here was not to rival a commercial USB sound card, we have seen projects to do that. We’re quite grateful to [Omadeira] for the tip, because this really is a hack. If you, too, want a share of our undying gratitude (which is still worth its weight in gold, despite fluctuations in the spot price of precious metals), send in a tip of your own.

Low Cost Oscilloscope Gets Low Cost Upgrades

April 20, 2025 by 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 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 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.