Well the chip has built in 2 op amps as preamplefiers.So sure there not realy sesitive becose these not ment to be sensitive.To bad i dont have any op amps laying around.
I also put an trasnfromers iron core in the coil (The coil it self was riped out of an litle mains transformer) and it works good
By the way timing an electric field wod recuire a more suficent circuit.Becose of the input cap.It may dicharge slowly (Holding the led bar high) or the negative spike cod dicharge it intantly (Puling the LED bar low)
I think the AC filter works by discharging the cap thru the chip.
I tryed to put an 555 timer on and the piezo speaker.But the freqency tricked the AC filter.And the capacitense was mesing whith the timer chip.
If i wod conect an coil to a batery i wod only get the on and off spike (my device can only sense AC felds)I wod need to conected to AC.And the results wod be difrent from coil to coil (curent,inductance,size...)
But the bigest problem is its picking up radio waves and there fore limiting its sesetivety