Static electricity detector
StaticBuildup, Fri Feb 23 2018, 11:50PMStatic charge detector. The lights are red for positive charge and green for negative. It is meant to be directional, but the lights can be uneven. Detects charged materials such as clothing, blankets and furniture.
Re: Static electricity detector
DerAlbi, Sun Feb 25 2018, 11:49PM
Cool thingy
My first reaction was "WTF, how.. 
."
Floating mosfet gates, i guess?
Effectfull. You could even sell it to the strange people that believe in field harmony magic and stuff.
DerAlbi, Sun Feb 25 2018, 11:49PM
Cool thingy
My first reaction was "WTF, how.. ."Floating mosfet gates, i guess?
Effectfull. You could even sell it to the strange people that believe in field harmony magic and stuff.
Re: Static electricity detector
Bjørn, Mon Feb 26 2018, 06:21AM
Very nice!
Did you use floating inputs on a microcontroller or transistors?
Bjørn, Mon Feb 26 2018, 06:21AM
Very nice!
Did you use floating inputs on a microcontroller or transistors?
Re: Static electricity detector
StaticBuildup, Tue Feb 27 2018, 10:50AM
Glad you like it.
I used floating JFET gates.
StaticBuildup, Tue Feb 27 2018, 10:50AM
Glad you like it.
I used floating JFET gates.
Re: Static electricity detector
DerAlbi, Tue Feb 27 2018, 06:25PM
How do you zero it ?
DerAlbi, Tue Feb 27 2018, 06:25PM
How do you zero it ?
Re: Static electricity detector
StaticBuildup, Tue Feb 27 2018, 11:39PM
That is a problem. The lights sometimes stay on and I have to dissipate the charge on the gates by touching something grounded and then touching the inputs. I might try to add high value resistors from gate to drain to bleed off the charge.
I have also noticed that when moving away from a charged object, it detects opposite charge. This is noticeable in the video. The pink blanket on the left is positively charged (red), but moving away from it creates a negative charge (green).
StaticBuildup, Tue Feb 27 2018, 11:39PM
That is a problem. The lights sometimes stay on and I have to dissipate the charge on the gates by touching something grounded and then touching the inputs. I might try to add high value resistors from gate to drain to bleed off the charge.
I have also noticed that when moving away from a charged object, it detects opposite charge. This is noticeable in the video. The pink blanket on the left is positively charged (red), but moving away from it creates a negative charge (green).
Re: Static electricity detector
DerAlbi, Wed Feb 28 2018, 12:21AM
Hmmh, what you describe sounds like leakage current is already influencing stuff, so adding resistors will only make the problem worse.
Against leakage current, you could try to
a) use way bigger antennas, so there is more charge overall thus longer leakage time
b) maybe using a reverse polarized mosfet. Imagine the gate drains allways to the soruce, therefore the gate discharges to gnd. connect an other mosfet (inactive) with soruce to VCC and connect the gates together. This should result in the charge draining to GND be resupplied by the other mosfet leaking VDD to Gate.
Anyhow, no need to be extra fancy here, the effect works
DerAlbi, Wed Feb 28 2018, 12:21AM
Hmmh, what you describe sounds like leakage current is already influencing stuff, so adding resistors will only make the problem worse.
Against leakage current, you could try to
a) use way bigger antennas, so there is more charge overall thus longer leakage time
b) maybe using a reverse polarized mosfet. Imagine the gate drains allways to the soruce, therefore the gate discharges to gnd. connect an other mosfet (inactive) with soruce to VCC and connect the gates together. This should result in the charge draining to GND be resupplied by the other mosfet leaking VDD to Gate.
Anyhow, no need to be extra fancy here, the effect works
Re: Static electricity detector
Sulaiman, Wed Feb 28 2018, 09:56PM
In the late '70's I was trying to measure photodiode currents in the sub-pA range using a parametric amplifier, fA leakage currents.
I could not get it stable, then one day standing about 1yd away I moved my hand, and the meter needle flew across the dial.
The plethora of charges on me, my clothes, anything, everything, was enough to induce fA currents in the circuitry... I never managed to make it viable.
I'm not expert in this are but I would not use insulators (plastic box etc.) too near to the electrostatic probe electrode as accumulated charge causes drift.
But
The probe is perfect - it does what it is meant to do - nice.
P.S. I suspect that it would sell better as a ghost/ufo/cosmic-rift detector.
Sulaiman, Wed Feb 28 2018, 09:56PM
In the late '70's I was trying to measure photodiode currents in the sub-pA range using a parametric amplifier, fA leakage currents.
I could not get it stable, then one day standing about 1yd away I moved my hand, and the meter needle flew across the dial.
The plethora of charges on me, my clothes, anything, everything, was enough to induce fA currents in the circuitry... I never managed to make it viable.
I'm not expert in this are but I would not use insulators (plastic box etc.) too near to the electrostatic probe electrode as accumulated charge causes drift.
But
The probe is perfect - it does what it is meant to do - nice.
P.S. I suspect that it would sell better as a ghost/ufo/cosmic-rift detector.
Re: Static electricity detector
Dr. Slack, Thu Mar 01 2018, 07:11AM
I'd second Sulaiman's concerns.
I read an article by Bob Pease (RIP) a while ago (if you don't know his stuff, get googling. If I called him 'the Feynman of analogue electronics', I'd be exaggerating, but not by much) that talked about measuring fA leakage on an electrometer amplifier input. To do this, he used it as a fed-back integrator, with a low leakage capacitor, and measured the drift.
Problem one was the physical volume of the capacitor, the bigger the cap the more frequently cosmic ray strikes generaterd charge pairs in the volume, causing the integrator output to jump.
Problem two was that everything had been built on PTFE, and charge stored on the surfaces took minutes and hours to move around, disturbing the readings while they did. Covering as much of the unnecessary insulator surface with alli foil mitigated that.
Dr. Slack, Thu Mar 01 2018, 07:11AM
I'd second Sulaiman's concerns.
I read an article by Bob Pease (RIP) a while ago (if you don't know his stuff, get googling. If I called him 'the Feynman of analogue electronics', I'd be exaggerating, but not by much) that talked about measuring fA leakage on an electrometer amplifier input. To do this, he used it as a fed-back integrator, with a low leakage capacitor, and measured the drift.
Problem one was the physical volume of the capacitor, the bigger the cap the more frequently cosmic ray strikes generaterd charge pairs in the volume, causing the integrator output to jump.
Problem two was that everything had been built on PTFE, and charge stored on the surfaces took minutes and hours to move around, disturbing the readings while they did. Covering as much of the unnecessary insulator surface with alli foil mitigated that.
Re: Static electricity detector
StaticBuildup, Thu Mar 01 2018, 12:46PM
I think the lights stay on because of gate-source capacitance.
JFETs
I will try to add a resistor to discharge that and see what happens.
StaticBuildup, Thu Mar 01 2018, 12:46PM
I think the lights stay on because of gate-source capacitance.
JFETs
I will try to add a resistor to discharge that and see what happens.
Re: Static electricity detector
Sulaiman, Thu Mar 01 2018, 12:57PM
I agree with adding gate-source resistors, start with the highest value that you can find, e.g. 33 MOhm.
Lower resistance = greater stability
Higher resistance = greater sensitivity
Don't make it too stable or it will not detect the smaller ghosts or higher flying UFOs
.
P.S. gate-ground is more common and useful than gate-source,
as it allows more stable source-ground voltage - hence stable bias, assuming that you are using a source resistor,
if you do not use a source resistor (typ 100R to 1kR) the drain current will drift a lot with temperature..
Sulaiman, Thu Mar 01 2018, 12:57PM
I agree with adding gate-source resistors, start with the highest value that you can find, e.g. 33 MOhm.
Lower resistance = greater stability
Higher resistance = greater sensitivity
Don't make it too stable or it will not detect the smaller ghosts or higher flying UFOs
.P.S. gate-ground is more common and useful than gate-source,
as it allows more stable source-ground voltage - hence stable bias, assuming that you are using a source resistor,
if you do not use a source resistor (typ 100R to 1kR) the drain current will drift a lot with temperature..
Re: Static electricity detector
Hazmatt_(The Underdog), Sat Mar 03 2018, 04:44PM
I can't see your vid, but I was working on this years ago and the main problem I had was the gates stayed charged too.
I think I got around this by using a square wave to power the JFET, I say that because I never committed to a design, but give that a try too and see if that will work, I can't remember if it did.
Hazmatt_(The Underdog), Sat Mar 03 2018, 04:44PM
I can't see your vid, but I was working on this years ago and the main problem I had was the gates stayed charged too.
I think I got around this by using a square wave to power the JFET, I say that because I never committed to a design, but give that a try too and see if that will work, I can't remember if it did.
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