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 ADC on LCSC that swears it’s a Ti ADS1115 may 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? Cue [James Bowman] letting curiosity getting the better of him and ordering a stash of four boards presumably equipped with said 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. 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.
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This articles is written by : Nermeen Nabil Khear Abdelmalak
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