how can'i get 5 V AC output 230 V AC: input? for a measurement unit bases on DSP?
closed as too broad by PeterJ, Dmitry Grigoryev, uint128_t, PlasmaHH, Daniel Grillo Apr 27 '16 at 11:29
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Stepping down or up AC voltages is precisely what transformers do.
Alternately, if you only need to measure the voltage, and not draw significant current from it, you could use a voltage divider. A voltage divider would be much cheaper and simpler.
However, keep in mind that there are safety codes that require that the low voltage components are isolated from the mains components. You would not want to accidentally electrocute the user of your device when there's some fault in your device. A transformer may meet these isolation requirements. A voltage divider certainly will not.