Sync clock derived from AC power source
AC power supplies convert voltage from mains power, which is 50/60Hz depending on where you live.  If you can use any clock between 10 and 400Hz, then you can produce a clock by feeding it into a comparator/Schmitt Trigger with a ground reference:







simulate this circuit &ndash; Schematic created using CircuitLab

If you need a specific frequency other than 50/60Hz that is a multiple of 50/60Hz, you can multiply/divide the frequency.  If you need adjustable frequency, you could use any sort of RC-controlled oscillator or a programmable timer/counter on a microcontroller.