The development of alternative energy sources and energy storage devices makes the problem of synchronization with the AC power grids, more relevant. To realize synchronization necessary detect zero crossing of signal. To detect zero crossing exist hardware approach and software approach. Hardware approach is simple but it has low precision. Software approach has high precision but it is complicated and expansive. In this paper is presented simple approach with high precision. It combines precision of software approach and simplicity of hardware approach. Precision of experimental measurement is 20µs. At the moment this system is quite expensive, reason of using of laboratory tools. This solution might be make chipper and with higher precision.