How bad can a $2.97 ADC be?

It may not even be a clone. As the author said, it could just as easily be production line items that were tested and found to be outside of spec tolerances and resold off-label.

I have done this a bunch of different times, mostly to resolve sourcing disputes. Dissolving in boiling sulphuric acid/nitric acid will make quick work of most epoxy packaging

IMO, I have mostly seen mislabeling, rebinning, and passing off obvious QC rejects.

example from many years ago: https://www.youtube.com/watch?v=e6DfBuPwAAA

I don't know if we can ping people here, but this looks like something that would be right up Ken Shirriff's alley.

1. https://righto.com

I think you might both be right- the author may be thinking of lower cost MCUs only aiming for tolerable ADC performance, while you might be thinking of all MCUs, even higher cost.

The RP2350 has 9.2 ENOB on a 12 bit ADC. Sure, you might be able to decimate multiple samples to get more bits out of them, but the spec sheet supports the author's claim (https://www.raspberrypi.com/documentation/pico-sdk/hardware....). There are even lower cost MCUs like the CH32V003 that have even worse ADC performance.

On the other hand, some MCUs can definitely do 10+ bits, such as the STM32H7 line which gets 13+ ENOB from a 16 bit ADC. This is impressive, but the H7 MCUs are literally an order of magnitude more expensive than the RP2350, so they might not be something the author tinkers with much. https://www.st.com/resource/en/application_note/dm00628458-g...

I tested a few STM32F103 dev boards, using a Siglent SDM3055 multimeter and Siglent SPD330X power supply.

The chip has a 12bit SAR ADC. Layout and board design mattered a lot, but even the worst ones had 10 bits worth, and the best one had nearly 12 bits effective.

That was without doing too much on the software side, meaning the other modules weren't running, besides a single serial output. On the bad boards the serial affected it, but on the good board very little.

> To get something faster we switched to ADS7953. It has 16 channels and runs 10 times faster.

I recall reading about a project at CERN to design a 12bit ADC chip that could sample at tens of GHz, maybe 50 or more.

I was perplexed at how they could achieve this.

Turned out it was the same we programmers do. Parallel processing.

They had taken a 12bit SAR unit which ran at like MHz rates, and just cloned it many times. They then had a large analog multiplexer in front to route the signal to the active ADC unit in a round-robin fashion.

That takes a lot of chip real-estate, and the analog muxer had to be carefully designed.

For a simpler approach to speed there is Flash ADCs[1], which kinda brute-force it.

For precision I know multi-slope ADCs[2] are often used.

Sadly I don't know much about the history, and would also love to learn more about it. Bound to be some fascinating stories there.

[1]: https://en.wikipedia.org/wiki/Flash_ADC

[2]: https://www.analog.com/media/en/training-seminars/tutorials/...

> The ADS7953 is somewhat of a ferrari, whereas the MCP3208 feels like a Toyota, simple to use, unimpressive performance.

What about the AD9226? It only has a single channel but can do up to 65 MSa/s at 12 bits. I bought one as a module for around $12 on AliExpress to experiment with software decoding of analog video. I only run it at 20 MSa/s and only use 8 bits because, funnily enough, the limiting factor is the speed at which I could get the data into my laptop. I connected it to a Raspberry Pi Zero and use the SMI peripheral as described here: https://iosoft.blog/2020/07/16/raspberry-pi-smi/

Ultra high-speed ADCs are extremely ugly to handle with microcontrollers. That's mostly FPGA territory: toggle its pins, suck the data from the ADC and offer them on a friendly parallel bus for a microcontroller (USBC->Parallel interface from FTDI).

They need a lot of pins to be toggled. Otherwise they spit out no data.

And a lot of manual stuff means it's super DMA unfriendly. And you need DMA for high-speed stuff.

Interesting, most of the counterfeits that affect me (eg. FTDI, STM32 clones) have been just straight up clones developed from scratch, not excess inventory / ghost shifts / packaged rejects. I guess it might be a digital/mixed-signal split, with the two worlds having different issues?

(also interestingly the STM32 clones I've seen had stacked die flash because they didn't fab them in a technology that could also do flash, so you can easily tell the counterfeit from sanding down the package and looking for an extra set of bonding wires; it's also a cool place to access the internal flash bus if you wanna bypass some readout protection :) )

Author here. I did consider this, as others have reported getting ADS1015 marked as ADS1115. If it were an ADS1015 the readout would be truncated at 12 bits. These parts definitely delivered 16 bits of readout.

Never had bigger issues ordering from LCSC. And I buy a lot of stuff from them.

OP is using the chip with the data rate set to 8 samples per second.

Natively/internally, it runs at 860 samples per second, and you can configure it to provide that data at a lower sample rate at lower noise levels by averaging multiple readings together internally.

These numbers add up fast when you have dozens or hundreds of components on your board. A $3 part is often one of the most expensive items on a board! If you're trying to get something shipped to consumers for $20 each, with an enclosure, packaging, shipping, retail markup, and profit...that's a huge price disparity.

Also, and perhaps more importantly, the test rig is a lot simpler and a lot cheaper if you can generally trust manufacturer data. Sure, send off a few samples (likely prototypes with parts from Digikey instead of LCSC) to run extended testing in an environmental chamber with thermal imaging, build an endurance test rig that pushes the button once a second for four weeks to simulate once-daily use for years, whatever you want to do...but after that, if TI says it's good from -40 to +125, you're going to trust them on a lot of the edge cases.

Do 100% testing of the things you can test in-circuit if you can - power it up at room temperature and make sure it works once - but that doesn't mean you get the actual rated performance across all published environmental conditions.

> Why don't they integrate good ADCs?

There are a bunch of reasons but the primary reason is that good ADCs are made using a different mixed signal process than microcontrollers. MCU ADCs are capacitive charge-balancing successive-approximation type which limits their sensitivity and precision.

Standalone ADCs also eliminate significant sources of noise like temperature fluctuations and electronic noise (the digital logic on the chip often runs at less than 1Mhz for example)

If hate the esp32 adc, let me introduce you to its "fpu." Or its external flash and memory...

I thought they were talking about League of Legends players, whoops