What is needed to create dwg from drawing?
It's not an easy task and according to my knowledge there is no way to do it fully automatic (I might be wrong of course).

You have options as follows:
Read scans and


recreate it manually in CAD application
recreate it using digitizer (in the old days they had puck - kinda magnifier with crosslines to digitize from printouts/blueprints)
create 3D object omitting 2D drawings
convert bitmap to vectors in 2D app
use scannig service like this (would be expensive)


Depending on complexity of your schemas, the easiest way, would be option 1 or 3. Option 4 is very doubtful (even if it's the most automatic way, it won't create useful data)

The most of CAD apps have option to import bitmap and then work on such "background". For example in AutoCAD use command Imageattach