simple cheap (power-wasting) voltage step-down regulator from 3.3V to 1.2V using zener & led

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Instead could use two 7660 ICs two divide a 5.0 V supply twice to produce a 2.5 V supply and a 1.25 V supply. Note that 1.25 V is within the ice40's 1.2 V core supply tolerance range of 1.14 V to 1.26 V.

And a similar really cheap way to get 3.3V from 5V using red (-1.7V) LED into 3.3 V zener:

regarding the very first image, turns out 1.2V zeners don't really exist...seems lower limit is 2.0V zeners. So an alternative could be to use a 2.1V zener to subtract 2.0V from 3.3V:

assuming that don't already have a stable high voltage to start with, then could drop down to the lowest zener (lowest I can find cheaply are 2.0V) and then from that 2.0V do a simple resistor-divider:

Takes about 5us for the 1.2V level to get close enough to be considered "on", since just needs to charge up the 1nF and 10nF capacitors through the somewhat low-valued resistors:

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