Surprisingly, scanning the fingerprint image was not an easy task. I’ve spent several days trying to retrieve any data from the sensor except the hardware id but without any success. Apparently the task of processing raw images from the capacitive scanner is not a very common task and it was hard to find any code examples or documentation online.
However, some search could help me to solve this problem. I have discovered that some branches of Android kernel have a special driver for the FPC1020A scanners written by the company Fingerprints. And, working with these sources could help me to find out that documentation I have is incomplete.
First of all, the FPC1020A chip has at least four revisions requiring different setup procedures. Many of the setup values are real “magic numbers” as they are not described in the documentation and look like 64bit integer values. Probably the full and proper documentation could bring some light on this topic but I don’t have it at the moment.
I did not write the code to detect which revision I have but just tried out one setup sequence by one. Suddenly, the revision A3 enabled finger detection and scanning functions.
So, at the moment, I have a code for ESP IDF to work with both types of the FPC1020A scanners I have, detect the presence of the finger and receive a huge array of 8-bit values representing the fingerprint image. Not a big step, but a very important milestone - now the biometric part of the project moves from the hardware to software section - I need to find/build algorithms for recognition and matching fingerprints