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My latest iterations use BJT circuits on the input stages and then an op-amp for the final stage. So far this seems to work better to achieve the sensitivity I need. I use a dual op-amp and the second one conditions the signal to feed into the PIC's ADC.Opamps with a low frequency response can pick up a cell phone at 900MHz or at 1.8GHz.
I think it is because the input transistor of the opamp is overloaded and becomes an AM detector diode then the opamp amplifies the low frequency modulation.
I don't know if an opamp can pickup a signal from a ghost.
Opamps with a low frequency response can pick up a cell phone at 900MHz or at 1.8GHz.
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I don't know if an opamp can pickup a signal from a ghost.
Maybe the ghost will be using a cell phone?
." I don't see a coil at all" It's probably because they use a hall detector
Hi folks... I've been developing a homemade EMF meter with LED bargraph display, and am looking for some tips on tweaking the EMF sensing circuit.
I don't have a schematic for my actual circuit handy (circuit's at home, I'm at work), but it's based on this one:
**broken link removed**
But, if I disconnect the side of the coil going to the + input on the op amp in the schematic, leaving it free floating, then I can pick up fields. So, in essence, it's acting more as an antenna than an inductor. Any thoughts on this? Maybe I need a better coil?
My 2nd question: the circuit is a LOT more sensitive if I connect it to an earth ground, such as when I connect the grounding clip on my oscilloscope when taking readings. Any thoughts on this? Since I intend this device to be portable, I can't be earthing it all the time.
I'll post a more complete schematic this weekend when time permits, but thought I'd post what I have in case anyone has suggestions for making it better!
Thanks,
KJP