ESD Detector for $2!

Cyparagon said:

Why not? You could also get a plug ($2 at the hardware store) and just add the ground wire to it.

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Just something about it seemed unsettling. I'm fully aware that having the ground would be fine, but there'd be the hot still stripped, and a nub of it would be visible. I just play it too safe I guess.

No. Buy a DIY repair plug then just attach a wire to the ground. Their wont be any other wire exposed or otherwise then

Tw15t3r said:

Also, technically speaking, any large enough metal object, whether connected with the Earth or not, is good to use as earthing. But it must be really huge, e.g. The railing of a stairwell that runs continuously from the bottom to the top floor (of a several storey building). Nothing beats Earth of course. It's the biggest known mass we have that's easily accessible.

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No, technically speaking all you have is a large capacitor where one plate is your large metal object, the dielectric is whatever is between it and the earth, and the other plate is the earth! Some very high frequency AC signals may see it as a current path due to capacitive coupling, but it is NOT a ground. It only appears to ground you out because the static charge stored on you causes you to be at a different potential than the capacitor plate and touching it neutralizes the potential difference via transfering current to the capacitor. At best you are brought "down" to a potential lower than what you were at which may be imperceptible, but you are NOT DISCHARGED or GROUNDED.

Tw15t3r said:

Anyway, Cube777, you said you have managed to make it really really sensitive now. Can it detect a fully charged battery if brought near to it? There should be small electric fields present, and it'd look really cool if it does that!

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Electric fields are only present where there is a current flow. Ideally there is no current flowing in a disconnected battery, but in a real battery there is a minute current due to the internal resistance of the battery. This internal resistance only causes currents on the orders of microamps to flow - at worst, and the resulting microwatts of EM fields are nearly undetectable from even the most sensitive devices.

That being said; I have been waiting a LONG TIME to post this image:

:crackup:
That's great, +1


Also though, Is there something special about the transistor used in this or will any one do?

Sigurthr said:

No, technically speaking all you have is a large capacitor where one plate is your large metal object, the dielectric is whatever is between it and the earth, and the other plate is the earth! Some very high frequency AC signals may see it as a current path due to capacitive coupling, but it is NOT a ground. It only appears to ground you out because the static charge stored on you causes you to be at a different potential than the capacitor plate and touching it neutralizes the potential difference via transfering current to the capacitor. At best you are brought "down" to a potential lower than what you were at which may be imperceptible, but you are NOT DISCHARGED or GROUNDED.

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It's definitely not a true earthing, yes, but for practical purposes, it will "charge up the capcitor" formed between that object and the Earth, and then, due to high surface area, leak the charge back into the atmosphere, effectively getting rid of almost all if not all the charge one might have built up. That's why it has to be huge. I would say this method's sufficient enough to prevent ESD to components, or at the very least, better than nothing.

Sigurthr said:

Electric fields are only present where there is a current flow. Ideally there is no current flowing in a disconnected battery, but in a real battery there is a minute current due to the internal resistance of the battery. This internal resistance only causes currents on the orders of microamps to flow - at worst, and the resulting microwatts of EM fields are nearly undetectable from even the most sensitive devices.

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You're probably referring to magnetic fields. Magnetic fields are formed when charges move. Electric fields are caused by static charges. That's why the study of Electrostatics involves electric fields only.

The device that is constructed here can detect all three: electric field, magnetic field (only when moving), and electromagnetic field. It's basically an antenna which is on one side of a picofarad capacitor that acts as a gate. An EM field generates a voltage, hence it works. A moving magnetic field generates a voltage in the conductor, also working it. An electric field with a high potential causes a repelling of charges into the gate of the transistor, charging it and turning it on, hence it works as well.

Yeah, meant to type magnetic fields there. I had to copy / paste things over as the page crashed mid way through typing up my post and I didn't realize I hadn't the Ctrl-C'd recently. The sentence I initially wrote about the electric field in a battery being orders of magnitude weaker than those observed in electrostatics got entirely left out as well. Apologies for the confusion.

Many water pipes are now PVC or PEX plastic. However,
the water in them is likely conductive enough to bleed
off a charge in a couple seconds.
HMike

Sigurthr said:

Yeah, meant to type magnetic fields there. I had to copy / paste things over as the page crashed mid way through typing up my post and I didn't realize I hadn't the Ctrl-C'd recently. The sentence I initially wrote about the electric field in a battery being orders of magnitude weaker than those observed in electrostatics got entirely left out as well. Apologies for the confusion.

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Ah, ok, yea I did get confused there. That clears it up.

Nice pic btw. I'll definitely be using it when talking about earthing issues in the future!

Heh, yeah when I saw it I had to save it. It popped up a few years ago in an engineering thread about RF grounding principles.

On the link I posted in the OP they say when you connect 10X 9V batteries in series (90V in total) the detector can detect it.

So does that mean if shove a metal stake into the ground and attach a wire I can ground myself?

JollyKillBill said:

So does that mean if shove a metal stake into the ground and attach a wire I can ground myself?

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Yes you can. Although ideally you should shove in several metal stakes into the ground to conduct electricity to the ground better. This is especially so if the ground is quite dry.

Tw15t3r said:

Yes you can. Although ideally you should shove in several metal stakes into the ground to conduct electricity to the ground better. This is especially so if the ground is quite dry.

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Thanks, I have been holding off on a few builds because I didn't want to stuff it up with static

MPF102 was once a very popular JFET for anything from DC up to VHF bands. other parts like BF245 will also work.
the irony here is that the static this cct registers can easily kill it. also, temperature and impurities around the gate terminal such as sweat and flux will cause leakage and drastically degrade sensitivity.
as esd protection i have an esd mat (earthed) and also a wrist strap that i never actually wear. at work the floor is tiled with some conductive material under which lies an earthed copper mesh. All shoes, furniture and clothes are somewhat conductive, too. in the fabric of those clothes is woven thin wire and in a way we wear faraday cages....
I have a portable static field meter, basically a pimped up version of the circuit discussed here. it shows the measured value on a lcd display in kilovolts with resolution of 10V.I noticed that non-dissipative surfaces can easily charge up to 1kV just by sitting there doing nothing but interacting with air currents in the room

phenol said:

I noticed that non-dissipative surfaces can easily charge up to 1kV just by sitting there doing nothing but interacting with air currents in the room

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Woah...
Sounds like we're all in the ESD Danger zone :crackup:

In theory I think if you built this into a small box with an extendable antenna, such as an RC toy controller would have, you could help protect the device from the static that would harm it.

Also, I believe the 1meg resistor does not decrease sensitivity (although I could be wrong, the paper didn't mention it decreasing) but protects it from static. so if you placed that between the circuit and the larger antenna you should be golden.


On another train of thought, what if you replaced the LED with a meter, like from an analogue multimeter.
Say this is the meter [ ]
say these lines are the range [\ /]
say you set the meter to have
the needle centered when there
was 0 charge in the area [ | ]

then you could read the + or -
charges by wether the needle goes [\ ] or [ /]

You would have to use an n channel and a p channel if you wanted to measure the positive and negative. Also the response wouldn't be linear so the meter reading would be basically worthless. Id use two different color leds, one for pos, one for neg.