high res ADC with internal Vref, MUX, gain

Projects General Guidance
1

Hi there!

I made two similar projects (voltage logger, battery cycler) that required high resolution voltage measurements on 4 differential channels. Measurements go from 0-5V, I sample at arount 4Hz.

So far I am using

  • MCP3551 as my ADC
  • TL431 as my external voltage reference
  • DG409 as my multiplexer

I am somewhat happy with the result. Noise is low enough to measure into the microvolt range and long term stability over weeks is also quite good. But my solution is a lot of "stuff", both in hardware and software. Is there a simpler device that can be used? I have looked for some time but cannot find a chip or shield with similar properties and library support. An inbuilt amplifier with ~50x gain would also be nice.

cheers

2

You have created a quite respective device. Mount it securely, use soldered connections, in a box hiding it for all eyes. Be satisfied! Why optimize something that's working?
I make "working things", not beauty boxes, and I'm satisfied with that.

3

The simplest improvement would be to use an A/D with a built in multiplexer.

4

I built this setup twice for my previous projects and it really takes time and effort to get it right. When I build similar projects in the future, my hope is to spend less time on getting the voltage measurement part done. Then my brain has more time to think about what it is that I should measure :slight_smile:

Assuming there is no single chip that meets my wish list, does anyone have recommendations for ADCs with

  • =18bit

  • =4 differential channels

  • a good arduino library

?

I stress the library part because I have no clue about spi/i2c and setting registers or whatever else is needed on these chips.

On a side note: It seems to me there is not much development of new ADCs with mux/gain/Vref. Or is it "just" the arduino libraries that are missing? All my search results are several years old and I am surprised by that.
The only real product I regularly find is the Iowa Scaled Engineering ARD-LTC2499 shield. I am sure it is a nice shield but the price tag + potential shipping to europe make it quite expensive for my hobbyist projects.

5

I'm pretty happy with the ADS1115. Native resolution is 16 bits, but with oversampling and averaging it can easily be pushed to 18.

Adafruit has a well designed breakout board, so it is wire up and go (in a shielded , grounded box obviously). Their library does everything I want.

6

I decided to give a shield built around the ADS1256 a try. Should arrive on the weekend. It promises 24bit resolution, 4 differential inputs, a reference voltage source (+2,5V, usable up to +5V measurements) and a PGA. I found a few libraries and even some current development for use with ESP or Teensy. Hopefully this will make life easier in future projects.
The ADS1115 is also interesting but for the moment I want at least 18bit without oversampling.