Sure thing! I am actually using the TH3D Unified Firmware Package (https://www.th3dstudio.com/knowledge-base/th3d-unified-firmware/). They basically took Marlin and have presets that work for a bunch of popular printers (Creality, Wanhao, etc) and the latest version supports the i3.
First thing to do with the firmware is to find this line and uncomment it to set the firmware up for the i3:
Then from there I just added the following lines to the configuration.h:
#define X_PROBE_OFFSET_FROM_EXTRUDER 47 //Your BLTouch X_PROBE_OFFSET_FROM_EXTRUDE
#define Y_PROBE_OFFSET_FROM_EXTRUDER -47 //Your BLTouch Y_PROBE_OFFSET_FROM_EXTRUDE
#define Z_PROBE_OFFSET_FROM_EXTRUDER -1.9 //Your BLTouch Z_PROBE_OFFSET_FROM_EXTRUDE
#define Z_CLEARANCE_DEPLOY_PROBE 15 // set up at least 15
#define Z_CLEARANCE_BETWEEN_PROBES 10 // set up at least 10
// Home z axis in middle of the bed since we are using probe as z end stop now
#define Z_MIN_POS = 0
#define Z_MAX_POS = 180
#define GRID_MAX_POINTS_X 5
#define GRID_MAX_POINTS_Y GRID_MAX_POINTS_X
#define LEFT_PROBE_BED_POSITION 50
#define RIGHT_PROBE_BED_POSITION 150
#define FRONT_PROBE_BED_POSITION 50
#define BACK_PROBE_BED_POSITION 150
#define SERVO0_PIN 27 //BLTouch orange wire
#define CONFIGURATION_H_VERSION 010110
In addition, like I mentioned previously I commented out SD card support in configuration_backend.h:
The offsets and probe bed positions you will have to adjust based on whatever mount you have for the BLTouch, I'm not super happy with the one I am using since it puts the probe so far away from the nozzle in 2 directions, might have to design my own.
This video has a lot of good information you can follow but since his is machine is the i3 plus the wiring has to be done as I described and not how he does it. Also he starts from a marlin fork for the i3 plus but the configuration is largely the same if you start from TH3D firmware.
Perhaps if I get some free time soon and there is enough interest I could do a write up with pictures and stuff.
Hope that helps!