Strange Case of Adafruit ADS1115 and QIFEI ADS1115

[kevinjwalters]

I've been testing ADCs recently, just comparing them with the output of the SAMD21 DAC on a Feather M0 Bluefruit. I was buying some other items from a vendor on eBay (UK) and thought I'd get an ADS1115 board. I hadn't really done any research on this and perhaps the 4 USD equivalent price should have raised an alarm but I wasn't aware of the pricing at the time.

It turns out the QIFEI ADS1115 board is probably using a clone of the 12-bit ADS1015 but also displays some undesirable characteristics: the top 4 bits are missing, it doesn't seem to supply data reliabily (i2c dropped to 75000 baud seemed to improve it slightly) and it may be less reliable when powered at 5V - I tested powered at 3.87V from batteries.

I don't have a real TI ADS1115 like the one on the ADS1115 16-Bit ADC - 4 Channel with Programmable Gain Amplifier for comparison, but the QIFEI's bizarre performance can be clearly seen below:

Comparison of ADC on Feather M0 vs fake ADS1115

adc-analaysis-run1-20210205-v5-g1.png (222.1 KiB) Viewed 524 times

For anyone else who gets tempted by one of these, this is what the board looks like so you can avoid it.

QIFEI fake ADS1115 board top side

qifei-fakeads1115-second-top.JPG (563.91 KiB) Viewed 524 times

QIFEI fake ADS1115 board under side

qifei-fakeads1115-second-underside.JPG (501.21 KiB) Viewed 524 times

[kevinjwalters]

And I took a close-up photo of the chip:

QIFEI fake ADS1115 - chip close-up

qifei-fakeads1115-second-iccloseup.JPG (334.31 KiB) Viewed 523 times

[lbarhai]

We found the same thing on the QIFEI ADS1115. We ordered from the same seller on Amazon 3 different times, and luckily the first time we ordered, the ADS1115 was not fake so we can easily compare the two boards and we found some interesting and noticeable differences that can help you avoid the fake boards.

Front of ADS1115

IMG_4779.jpeg (140.55 KiB) Viewed 431 times

[lbarhai]

Here is the image of the backside of both boards.

IMG_4781.png (695.39 KiB) Viewed 431 times

[kevinjwalters]

Good sleuthing!

I ended up buying some Seeedstudio Grove bits and picked up one of their ADS1115 boards. Feels more comfortable having a trusted brand of some sort rather than an anonymous board.