yes.. i am trying to think about that, but is to possible to "home-make" a cheap hall effect sensor? or the only option is to buy the ready one? because as far as i understand. it's simply a pickup-coil and an amplifier.. right?
Alternatively, would it be possible to detect a "peak" at the instant that the curents starts/stops flowing? (this, sure could be done using a 555 or any microcontroller, but my question is: is a single transition alternative enough to generate emf and be detected?)