I was reading [Hack Into a Timer AC Socket][1] and when I got to this paragraph:

> The design firstly have a RC buck? (not sure how to call correctly in English) circuit to step down the voltage from 220V AC to 5V AC, a 0.33uf safety capacitor (yellow one) used here, accompanying with a 1M discharge resistor. And after these two there is another current limited big resistor to prevent pulse and shock.

I was curious - I didn't even realize you could change AC voltage levels without a transformer (or at least not cheaper than with a transformer).

I understand that a resistor will lower voltage for a given current, but I would have expected AC mains to be too much power for a cheap resistor. And I don't get what the capacitor does - even if it is helpful here to get smoother DC power, wouldn't it interfere with anything else on the same AC line?

WARNING - **ALL** PARTS OF THIS CIRCUIT SHOULD BE CONSIDERED TO BE AT AC MAINS POTENTIAL AT ALL TIMES.

Capacitor C1 **MUST** be an [**"X RATED" capacitor**](http://electrosome.com/x-and-y-rated-capacitors/) specified by its manufacturer   
for "across mains" use. NB NOT 'Y' rated.  
[Examples of X & Y rated capacitors](http://www.vishay.com/capacitors/rfi-safety-rated-xy/)
  



![Schematic][2]


  [1]: http://blog.electrodragon.com/hack-into-a-timer-ac-socket/
  [2]: https://i.sstatic.net/qIvsP.png