This hand held throttle is very well supported in Rocrail.
For the fimware, I have to refer to the original FREDI site.
A few remarks have to be made to help you being succesfull with the production of this FredI.
Fix the empty PCB with screws in it's future housing, and use it to drill the exact positions of the pushbuttons, SW2 and leds.
All other parts can be mounted after that.
The pushbuttons and leds are mounted at the backside of the PCB.
Please take care not to use the center hole of the leds, because that one is only a drilling mould.
After a serious check, connect the pcb , without IC1, to LocoNet. Check if 3,3 volt is correct between pt 7 and 8 in IC1 socket.
As far as my experience has gone, R11 can be omitted.
Should you have any misfunctioning, the resistor might help.
Then refer to installation instructions at http://fremodcc.sourceforge.net/diy/fred2/fredi_d.html