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[on:]

Hi!

I'm a little embarrassed to ask this because I study electrical engineering but here it goes.... I'm building electric field detector as a school project and I would like to read it with arduino and log/plot the results. I've got the circuit set-up with 5V from arduino. I would like to know to which point in circuit (and how: cap, resistor,...?) do I connect arduino (analog pin)? I tried connecting at various points in the circuit (instead of LED&220R, on last transistor emitter,...), even tried an op-amp,.... and I don't seem to get consistent readings. Any help/suggestions would be really helpful.

Circuit from http://talkingelectronics.com/projects/200TrCcts/200TrCcts.html#8
 

[Reply #1 on:]

Connect Gnd of arduino to emitter and analog input to collector of last transistor (powering a led).
It's not clear, what kind of electrical field you want to sense, DC, RF? Circuits posted above doesn't have any filtering, so I suggest it would likely sense 50/60 Hz electrical field from AC grid most of the time

[Reply #2 on:]

I'm trying to detect E-filed beneath 110kV power lines for a school project. I tried connecting it the way you said and now I get readings from 700 up. I probably need some sort of filtering, does anyone have any suggestions? I really appreciate your help!

[Reply #3 on:]

Voltage you are reading is "inverse", it goes down with higher electric fields.
Btw, to sense kV you don't need transistors, arduino pin is sensitive enough to pick up a signal w/o amplification. Just attach a piece of wire to a pin. I think, a capacitor between input and Gnd would be necessary to adjust sensitivity and filter out RF. Try to experiment with cap value, 100 pF and up. As Electrical Field  of the AC, you need to calculate RMS in software to get better accuracy, and some software LPF also help increase precision of results.   

[Reply #4 on:]

I just wanted to say thank you for your help! I got it working and it gives me very nice results.

[Reply #5 on:]

I got it working and it gives me very nice results.

Please post the final schematic and values for those to come 

[Reply #6 on:]

OK, the time has come 

I was really busy with college and everything so I allmost forgot to post the circuit. But here it is.
Final circuit:


Assembled device:


As Magician said this circuit is too sensitive to measure EF under a power line (35kV). So I connected the antenna directly to analog input pin and got the results, I tried 100pF and some other value of capacitors but the readings were "strange", no capacitor it is .

And here are the results:
Directly under the wires from first to the second pillar:


At the pillar, perpendicular to the wires:


Once again thanks for all your help!