Prototyping:

I built the prototype on a protoboard so I could easily substitute components and make changes. I did not build the entire circuit at once and "swing for the fences", e.g. powering it on and hoping I didn't release any smoke. I built it up in stages, testing as it was built.

1. I built the resistor divider/Zener circuit and tested the resulting voltage level.

2. I added the unity gain amplifier which provides isolation and the voltage reference to the 2nd op-amp.

3. I added the output stage with the voltage divider feedback circuit.