M
mike
- Jan 1, 1970
- 0
I built a crude electrometer.
Poke the gate of a jfet in the air and read the
drain current.
Uses a neon bulb as input protection and gate bias.
Problem is that it's WAY too sensitive for what I want.
100M resistor to ground kills the sensitivity.
Looks like I need something on the order of a few Gigahoms.
Anybody experienced with DIY BIG resistors?
About an inch of pencil line on card stock is about right.
But that's gonna be very unstable.
Best I've come up with so far is sheet magnetic material
used for stick-up business cards.
It's dimensionally stable enough to bolt on a contact.
Two parallel strips shunted by another strip
makes a variable resistor. I expect it's gonna
be unstable too, but at least it's adjustable.
Better ideas?
NO, I'm not gonna buy a resistor. I'll be done with
this thing before tomorrow's mail.
Thanks, mike
Poke the gate of a jfet in the air and read the
drain current.
Uses a neon bulb as input protection and gate bias.
Problem is that it's WAY too sensitive for what I want.
100M resistor to ground kills the sensitivity.
Looks like I need something on the order of a few Gigahoms.
Anybody experienced with DIY BIG resistors?
About an inch of pencil line on card stock is about right.
But that's gonna be very unstable.
Best I've come up with so far is sheet magnetic material
used for stick-up business cards.
It's dimensionally stable enough to bolt on a contact.
Two parallel strips shunted by another strip
makes a variable resistor. I expect it's gonna
be unstable too, but at least it's adjustable.
Better ideas?
NO, I'm not gonna buy a resistor. I'll be done with
this thing before tomorrow's mail.
Thanks, mike