This video will describe how to build a static electricity detector using an active Wheatstone bridge. RF Field Strength Meter Video: • Wheatstone Bridge / R...
Thank you for this excellent tutorial. I couldn't find 2N3819 jFETs locally so I have used BF246B instead. I'm powering this unit from one Li-Ion 18650 cell because I need it to be portable so I can use it in my workshop. Power consumption when idle is around 1mA, it should work around 3 months on a 2500mAh cell. I have also added a piezzo buzzer by utilizing LMV321 op amp in comparator mode. Detection distance in my case is 1 to 1.5 meters. Make sure to completely REMOVE FLUX RESIDUE from the board because it greatly affects the distance - on a dirty board, distance was reduced to a few centimeters.
Hi, thanks so much for the excellent video. The JFET you are using on the breadboard was NTE312. I thought they were 2n3819 in which the gate is the middle pin.
@@0033mer Hi again, Thks for yr prompt reply. I just tried the circuit as shown in your diagram using 2N3819. The circuit worked as expected. But when I unplug the 20m damper I did not have the sensibility as you did. The ammeter simply shoots beyond 50uA and that's it. Anyway it's not very important. I was just playing around. Currently I am walking thru all the videos you had published. I learnt a hell lot of things from you. Encore bravo et merci
Thank you for the great video and schematic diagram. Can you tell the polarity of the charge induced to the detector? Wether it is positive or negative? Also can you list the components used. Thank you. ❤️
To detect the polarity of charge you would need a electroscope. If you look at the triboelectric series list you will find that my plastic cup would have a negative charge. The FET in the circuit responds to a negative charge. All components to build the circuit are listed on the schematic.
If the voltage induced on the JFET gate is negative, it causes current through drain to source to reduce. This causes the voltage drop across the 3.3k source resistor to reduce, so the voltage at the JFET Source terminal is increasing. Meanwhile, this causes the JFET on the left to do the opposite - voltage across its 3.3k resistor increases, causing the voltage at that Source to decrease. So for a negative charge induced on the sense antenna, the left side of the meter will go more positive than the right side. If you connect the meter + terminal to the right and - terminal to the left, it will now correctly indicate if the charge is positive or negative. Be aware, however, that there is a difference between charge induced, and charge transferred. Especially if you have not grounded the instrument, you can get spurious readings.
To connect the meter polarity correctly to show charge polarity, first understand how this responds to charge: If the voltage induced on the JFET gate is negative, it causes current through drain to source to reduce. This causes the voltage drop across the 3.3k source resistor to reduce, so the voltage at the JFET Source terminal is increasing. Meanwhile, this causes the JFET on the left to do the opposite - voltage across its 3.3k resistor increases, causing the voltage at that Source to decrease. So for a negative charge induced on the sense antenna, the left side of the meter will go more positive than the right side. If you connect the meter + terminal to the right and - terminal to the left, it will now correctly indicate if the charge is positive or negative. Be aware, however, that there is a difference between charge induced, and charge transferred. Especially if you have not grounded the instrument, you can get spurious readings.
Surgical mask using for protecting against COVID-19 usually include 3-layers, the middle layer is made of melt-blown polymer which is electrostatic charged for capturing and holding virus. Many poor quality mask has no electrostatic charged or very weak. I have some different surgical masks and I want to compare their static strength in order to find out which provide better protection. However, I could not afford to buy a electrometer. I want to make use of your circuit to build a eletrometer with a DMM which can give me a figure for comparison. Do you have any suggestion how to find electrostatic unit from the reading. Also, I find many schematics not using bridge curcuit. What is the advantage and disadvantage on using bridge curcuit like the one you presented.
The Wheatstone bridge uses null deflection measurement which cancels out errors and can detect minute input changes that will unbalance the bridge giving a meter deflection. Power supply variation will not affect the null point. Check out this video on the subject: ua-cam.com/video/WaFBUnep7T0/v-deo.html
So I tried recreating this for a school project but when I hook voltage to the circuit I’m getting 2.4 milliamperes of current through the meter. That’s before I have any static electricity near it. I bought the transistors online and the resistors exactly like you have but I’m not sure why it’s measuring so much current. I’m using resistors instead of potentiometers but the ohms are correct. So I can’t zero out my meter. I’m just wondering why it’s not reading at 0 like yours is in the circuit until you apply static electricity near it. I’ve double checked my circuit and wiring as it’s not a hard one to build. Just unsure why it’s reading so much current I bought a 500 ua meter. But it maxed it out so I measured with a digital one
You need a potentiometer to zero the circuit, its hard to do otherwise. Check out this video around the 7 min mark that shows how to zero the circuit: ua-cam.com/video/WaFBUnep7T0/v-deo.html
@@0033mer ok. But I’m not seeing two 1k ohm resistors. Just one and the potentiometer. Did you replace one of these with the potentiometer and is that how you dialed it in. If the sensitivity pot (100k resistor) is not in the circuit
There is one 1k ohm resistor and one 1k ohm potentiometer as shown in the schematic. A potentiometer has three leads. The 1k ohm resistor is in series with the wiper lead.
@@0033mer OK so if I put a potentiometer in place of the 1k resistor that I have, will it reduce the current going through my circuit so it doesn’t max out my meter when I apply voltage. I double checked my wiring earlier and everything seems correct . And I have a 500uA meter I just don’t understand why current is so high and maxed my meter out if everything is the same
An electroscope uses electrostatic induction to detect static electricity. Two pieces of metal foil hanging side by side will repel each other when a charged object comes close.
Thanks for the answer, your videos are valuable!
Outstanding work.
Thank you !! And thanks for the great informative scientific description of the circuit!
You're welcome!
Thank you for this excellent tutorial. I couldn't find 2N3819 jFETs locally so I have used BF246B instead. I'm powering this unit from one Li-Ion 18650 cell because I need it to be portable so I can use it in my workshop. Power consumption when idle is around 1mA, it should work around 3 months on a 2500mAh cell. I have also added a piezzo buzzer by utilizing LMV321 op amp in comparator mode. Detection distance in my case is 1 to 1.5 meters. Make sure to completely REMOVE FLUX RESIDUE from the board because it greatly affects the distance - on a dirty board, distance was reduced to a few centimeters.
Glad it worked out for you. Thanks for sharing!
Nice video
Awesome
Nice
Interesting
Hi, thanks so much for the excellent video. The JFET you are using on the breadboard was NTE312. I thought they were 2n3819 in which the gate is the middle pin.
The NTE312 and 2N3819 are electrically equivalent Either can be used in the circuit. Pinouts will vary, connect as per data sheet.
@@0033mer Hi again, Thks for yr prompt reply. I just tried the circuit as shown in your diagram using 2N3819. The circuit worked as expected. But when I unplug the 20m damper I did not have the sensibility as you did. The ammeter simply shoots beyond 50uA and that's it. Anyway it's not very important. I was just playing around. Currently I am walking thru all the videos you had published. I learnt a hell lot of things from you. Encore bravo et merci
Thank you for the great video and schematic diagram. Can you tell the polarity of the charge induced to the detector? Wether it is positive or negative? Also can you list the components used. Thank you. ❤️
To detect the polarity of charge you would need a electroscope. If you look at the triboelectric series list you will find that my plastic cup would have a negative charge. The FET in the circuit responds to a negative charge. All components to build the circuit are listed on the schematic.
0033mer, will the FET respond to a Positive charge? If not, how is it possible for it to detect positive charge? Thank you.
If the voltage induced on the JFET gate is negative, it causes current through drain to source to reduce. This causes the voltage drop across the 3.3k source resistor to reduce, so the voltage at the JFET Source terminal is increasing.
Meanwhile, this causes the JFET on the left to do the opposite - voltage across its 3.3k resistor increases, causing the voltage at that Source to decrease.
So for a negative charge induced on the sense antenna, the left side of the meter will go more positive than the right side.
If you connect the meter + terminal to the right and - terminal to the left, it will now correctly indicate if the charge is positive or negative.
Be aware, however, that there is a difference between charge induced, and charge transferred. Especially if you have not grounded the instrument, you can get spurious readings.
To connect the meter polarity correctly to show charge polarity, first understand how this responds to charge:
If the voltage induced on the JFET gate is negative, it causes current through drain to source to reduce. This causes the voltage drop across the 3.3k source resistor to reduce, so the voltage at the JFET Source terminal is increasing.
Meanwhile, this causes the JFET on the left to do the opposite - voltage across its 3.3k resistor increases, causing the voltage at that Source to decrease.
So for a negative charge induced on the sense antenna, the left side of the meter will go more positive than the right side.
If you connect the meter + terminal to the right and - terminal to the left, it will now correctly indicate if the charge is positive or negative.
Be aware, however, that there is a difference between charge induced, and charge transferred. Especially if you have not grounded the instrument, you can get spurious readings.
I will be using this +-50uA center zero meter with this circuit:
amzn.to/3b76hG6
ua-cam.com/video/WaFBUnep7T0/v-deo.html
Can I directly add a buzzer on the place of ammeter?
Can I use 22 meg ohm resistor instead of 20 meg ohm you used?
For a micrometer, can a dmm be used? For example a Fluke 179?
Yes .. a DMM can be used with DC ammeter selected. The bar graph display is handy to see peak readings.
What component did you use/what is it called, to adjust/center the panel meter?
Potentiometer.
Surgical mask using for protecting against COVID-19 usually include 3-layers, the middle layer is made of melt-blown polymer which is electrostatic charged for capturing and holding virus. Many poor quality mask has no electrostatic charged or very weak. I have some different surgical masks and I want to compare their static strength in order to find out which provide better protection. However, I could not afford to buy a electrometer. I want to make use of your circuit to build a eletrometer with a DMM which can give me a figure for comparison. Do you have any suggestion how to find electrostatic unit from the reading. Also, I find many schematics not using bridge curcuit. What is the advantage and disadvantage on using bridge curcuit like the one you presented.
The Wheatstone bridge uses null deflection measurement which cancels out errors and can detect minute input changes that will unbalance the bridge giving a meter deflection. Power supply variation will not affect the null point. Check out this video on the subject: ua-cam.com/video/WaFBUnep7T0/v-deo.html
Interesting. Does it have an application for preventing ESD?
Not preventing ESD but can measure ESD quantity in your situation.
@@0033mer Yes, I meant that as a tool to double check if you've accumulated electric charge before you touch something.
Thanks for sharing
does this work with IRFZ44N
No ..An N channel JFET works in depletion mode and a IRFZ44N is an enhancement device.
OK thanks @@0033mer
So I tried recreating this for a school project but when I hook voltage to the circuit I’m getting 2.4 milliamperes of current through the meter. That’s before I have any static electricity near it. I bought the transistors online and the resistors exactly like you have but I’m not sure why it’s measuring so much current. I’m using resistors instead of potentiometers but the ohms are correct. So I can’t zero out my meter. I’m just wondering why it’s not reading at 0 like yours is in the circuit until you apply static electricity near it. I’ve double checked my circuit and wiring as it’s not a hard one to build. Just unsure why it’s reading so much current I bought a 500 ua meter. But it maxed it out so I measured with a digital one
You need a potentiometer to zero the circuit, its hard to do otherwise. Check out this video around the 7 min mark that shows how to zero the circuit:
ua-cam.com/video/WaFBUnep7T0/v-deo.html
@@0033mer ok. But I’m not seeing two 1k ohm resistors. Just one and the potentiometer. Did you replace one of these with the potentiometer and is that how you dialed it in. If the sensitivity pot (100k resistor) is not in the circuit
There is one 1k ohm resistor and one 1k ohm potentiometer as shown in the schematic. A potentiometer has three leads. The 1k ohm resistor is in series with the wiper lead.
@@0033mer OK so if I put a potentiometer in place of the 1k resistor that I have, will it reduce the current going through my circuit so it doesn’t max out my meter when I apply voltage. I double checked my wiring earlier and everything seems correct . And I have a 500uA meter I just don’t understand why current is so high and maxed my meter out if everything is the same
Do you have an email I can contact you through ?
¿Could this be modified to work as a crude electroscope?
It is basically a Electroscope but more as a Electrometer as it indicates a quantity value.
JFET? Is he related to Bobba Fett? lol but good circuit
How to the non moving detectors work?
An electroscope uses electrostatic induction to detect static electricity. Two pieces of metal foil hanging side by side will repel each other when a charged object comes close.
Yea, 69th like!
I dont know 100k-ohm and 1k-ohm potentiometer specification MODEL NUMBER.......PLEASE ANYBODY HELP ME IN THIS REGARD
www.mouser.ca/datasheet/2/54/3329-776941.pdf