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I need to make this electronic electroscope, http://amasci.com/emotor/chargdet.html#13 , but i dont get it , how can i connect an antenna to the gate lead and where the resistance would be connected , in series to FET or to the antenna , if it was to be connected to the gate lead , how?

Mario
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  • Follow the link in the text ["about the circuit"](http://amasci.com/electrom/e-field2.html) – MikeJ-UK Mar 20 '13 at 09:19
  • I built something like that when FETs first became available, over 30 years ago. – Leon Heller Mar 20 '13 at 10:22
  • @Leon Heller - I remember making something similar (possibly from an article by R A Penfold or F G Rayer). Electronics used to be such fun ;) – MikeJ-UK Mar 20 '13 at 11:30
  • @MikeJ-UK - I think I just found the [circuit](http://www.transkommunikation.ch/dateien/schaltungen/diverse_tbs_schaltungen/Static%20Field%20Detector.pdf) (or one of them, I imagine he did a few versions) by R.Penfold ;-) I think I have a couple of the little green project books he wrote round here somewhere. – Oli Glaser Mar 20 '13 at 13:25

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Build it exactly as shown - you have one end of the resistor connected to the gate, then the other end connected to an antenna. The resistor is not required as noted in the text, but it should help protect the FET gate from damage. The length of the antenna is not so important, even without one you should see some sensitivity.

You can also use a MOSFET or CMOS gate to make this kind of circuit - basically, anything with a very high input impedance will do.

See this question I recently answered about someone accidentally making one by leaving a microcontroller input floating (it actually has a link to the same circuit)

Also see this FET input opamp based version by Robert Penfold mentioned in the comments. An another here which shows a breadboard layout.

Community
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Oli Glaser
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