The invention relates to a method for providing a trigger signal in response to the commutation of a mechanically commutated electric motor (1). The method comprising the steps of providing a mechanically commutated electric motor (1), providing a power supply for said mechanically commutated electric motor via electrical supply leads (10, 11) from power supply circuitry, providing a filter (15) connected to said electrical supply leads (10, 11), detecting with said filter (15) a voltage spike occurring at commutation, outputting from said filter (15) said trigger signal.