Shouldn't really need a DAC, just use the PWM output. Any $5 microcontroller should be able to do this with some reliability. Heck, the PiPico has programmable

Shouldn't really need a DAC, just use the PWM output. Any $5 microcontroller should be able to do this with some reliability. Heck, the PiPico has programmable IO which could do this without the processor. Or hey, a 555 timer with the right resistors and capacitors would do the same thing.