You can do it with an R-2R ladder. At 1Hz the sine wave
will be a little chunky, but you could smooth it by using an
op-amp that has its slew rate slowed down with a capacitor
in the feedback path.

If you aren't terribly fussy, a 4-bit R-2R DAC would give
fairly reasonable results with just an RC filter on the output
rather than the op-amp idea. It's only 1Hz after all

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