audio electrical signal used as a switch tool with an electricall audio signal coming from the pc (3,5mm,"headphones")is somehow posible built a "switch system" that switch-on two differents and independents circuits as the signal frecuencie reach some level?...one is switched at 4khz the other at 8khz.As long as the frecuencie is going on the circuit is connected,the two circuits never workby peter61 - Controllers