The magic’s pretty much in the Mozzi library, the code is pretty simple and is just adapted from a Mozzi example. Not to denigrate @HAGIWO’s work!
@fredrik said elsewhere an MCP6002 ($0.36 at Mouser) should work in place of the NJM2732D ($2.58). It’d be even nicer if something from Tayda would work, but I don’t see any that are rail-to-rail input/output.