We found that the firmware for the VFD clock does not compile well with the latest Arduino Core for ESP32 files from GitHub. As result we experienced several crashes of the software on the ESP32 and it is impossible to save the settings as the command for writing the settings causes a crash too. When we use an older version of the Arduino Core for ESP32 software from October 2017, everything works as expected. We will investigate this further, but in the meantime you can use the older version as a workaround. You can download the October 2017 version here: http://www.axiris.eu/download/arduino-esp32-master-2017-10-06.zip If you don't want to compile the firmware yourself or still have problems, you can use the binaries attached with this update. We are currently working on an assembly manual for this product where everything is described including compiling the software and sending it to the ESP32. We expect the manual to be ready by the end of next week.

I did the simulations with the TL70 series, in the final PCBs I used the LMs because I have more lying there.They are excellent opamps and it does not matter for the print layout.I think you can use many types if their GB product is high enough.I chose DIP8 / 14 because that is easier for DIY, therefore the PCB is also single-sided.the TL72 / -74 are still available in DIP as is the LM833 but the 837 is apparently no longer available in DIP.You may be able to use an adapter, but I would try the TL074 first.  

Nice project, do you have any more information of the  linear encoder used Regards Alfred

Dear Steve, thank you for the clarification.

I noticed the difference between the schematics and the PCB too. They don't match.