Scullcom/Barbouri LTC2400 "Millivoltmeter" Software

[WillTurner]

Many moons ago, Louis Scully ("Scullcom") started a LTC2400 based "millivoltmeter" project  with a 0-40VDC input range.   He produced a number of supporting videos describing the project, see http://www.scullcom.uk/millivolt-meter-mk2/. In May 2016, Greg "Barbouri" updated the project, and produced a nice board  https://www.barbouri.com/2016/05/26/millivolt-meter/ which he made available through OSHPark https://oshpark.com/shared_projects/qgv0fpKN. The Scullcom/Barbouri design evolved into using  a Caddock precision /10 resistive divider, AD8626 op amp front end, ADR4540B 4.096V reference, I2C LCD display, and Arduino Pro Mini host. There appear to have been few comments about the project here, but see https://www.eevblog.com/forum/metrology/7-5digit-diy-voltmeter/msg1390898/#msg1390898, and the following posts for a couple of comments.
  Earlier in the year, I decided to build up four boards. I had a friend that I knew could do an excellent job with the surface mount components, and an 80yo neighbour who still dabbles in electronics; so I promised them a board each for Christmas. The software for the project was pretty raw, and about six months ago I incorporated integer offset and gain calibration. I've been sitting on it since then, and have just pulled it out again to fulfill my Xmas promises. Although I can see much work remaining (both software, and hardware) the latest code is attached. 

[Doctorandus_P]

As an alternative, building this with an ADS1220 might be an interesting option to keep the price down.
The ADS1220 has an internal voltage reference and PGA upto 128x.
As a bonus you also get an integrated temperature sensor.