The old school circuit uses a LM1881 to do the sync separation. The sync pulses are counted by a 4040 and compared with a 74688. I compared my circuit with a commercial trigger generator, and it works the same.
The new version uses the ATmega328PB's internal analog comparator to separate the sync pulses. The internal counters are used to check the field (odd/even), count the lines and compare the selected line.
The software part takes care of the user interface. It debounces the push button switches and drives the OLED display. I used a modified font for this project. More on this later.