I have bought a couple of cheap digital sound pressure level meters and tried to hack them to provide a linear dB output, since they pretty all have ATMELS inside as well. They are all astonishly complex.
I am not a rookie in electronics, but I did not succeed to find any usable DC signal in any of them.
The main problem is that the signals are floating, and they are NOT linear. Nowhere. Not even close to be DC.
Even a device, that provided a DC jack, turned out to supply a linear signal until a certain level that "geared down" several times without notice when the sound pressure increased, even when selecting fixed range.
A real linear output seems to be provided only by expensive devices, or by exotic devices that are not easy to get on the market. Currently the best deal is using old SPLs that have a linear galvanometer-display (not just a logarithmic scale).
Those are easy to hack but are not easy to find on the market in quantities.
Has someone succeded and can recommend a cheap SPL that will do?