Sunday, June 16, 2024

How can I teach my self about electronics and electrical engineering?

How can I teach my self about electronics and electrical engineering?

Good for you! You will have a better attitude than 95% of students.

You need a decent understanding of physics first. Do you have that? If there is still time, enroll in physics classes in high school. It really helps with understanding electricity and electronics.

You can also watch this series of lectures by Prof Richard Muller:
https://www.youtube.com/playlist?list=PLUdYlQf0_sSsfcNOPSNPQKHDhSjTJATPu

Grob "Basic Electronics" is a very good book to start with. You do not need the latest edition. The 2003 version is under $20 used on Amazon.
http://www.amazon.com/gp/product/0078247160

Malvino's "Electronic Principles" is, in my opinion, an even better textbook. Again, you do not need the latest edition. The 6th Edition is also under $20 used on Amazon.
http://www.amazon.com/Electronic-Principles-Albert-Malvino/dp/0028028333/ref=pd_sim_14_3

"The Art of Electronics" by Horowitz and Hill is NOT a beginner's book. It assumes that you already have a basic knowledge of electricity, Ohm's Law, Kirchoff's Laws, and dives right in with RC circuits and semiconductors. It is an excellent book once you have that knowledge, going in very deep. The latest 3rd edition is about $90, but worth it. The older 2nd edition is still selling for as much or more, so I strongly recommend just getting the 3rd edition when you are ready for it.
http://www.amazon.com/The-Art-Electronics-Paul-Horowitz/dp/0521809266/ref=pd_sim_sbs_14_6

The US NAVY has its book on electricity and electronics available online as a PDF.
http://compatt.com/Tutorials/NEETS/NEETS.html

When you get to Op Amps (operational amplifiers), I strongly recommend Bruce Carter's "Op Amps for Everyone". The 4th edition is the latest, and well worth the money. $65 new on Amazon, or $40 used. The 2nd and 3rd editions are available online as PDFs.
http://www.amazon.com/Amps-Everyone-Fourth-Bruce-Carter/dp/0123914957/ref=sr_1_1

Is it possible to self-study Electronics Engineering?

Is it possible to self-study Electronics Engineering?

 Absolutely yes! I did and do (never stop learning). I know quite a few others who have and do. The most successful people I've known in EE were already teaching themselves electronics long before going to college, or never got a degree. A friend of mine was building experiments for NASA when he was 19, with nothing but a high school diploma and studying on his own. Did you see the story about the NASA satellite launched in 1978 that returned in 2014, the ISEE-3, and was discovered to be still working? He built or took part in building about half of the equipment on board.

This Satellite Just Returned From Circling the Sun, But NASA’s Lost the Ability to Talk to It

Fortunately, a coalition of ham radio operators got the necessary information from NASA and put up the equipment and antennas to talk to it with the help of crowdfunding, finding only one of the 13 pieces of sensing equipment had failed. Later reports said that only 5 were working, I don't know why that number changed. The intention was to send the ISEE-3 to another comet. Sadly, the rockets failed to work correctly, possibly due to age, possibly due to poor decisions based on flawed knowledge. Contact was subsequently lost.

International Cometary Explorer

He has had a long career repairing and designing electronic equipment, sometimes designing modifications, sometimes designing entirely new things. He has been building temperature logging electronics for decades that is lowered into drill holes. They must stay together at temperatures that melt solder, and keep accurate time and temperature. He is currently working on a newer version. Researchers and companies all over the world ask him to build these sensors, sometimes he must first get permission from the US government depending on the country.

I will point you to my answer here, I suggest reading other answers to this question:

Steven J Greenfield's answer to How can I teach my self about electronics and electrical engineering?

Even if you go to college, the majority of study in your life will be self-study.

Saturday, June 15, 2024

How do I make soldering flux?

How do I make soldering flux?

If it is for lead-tin electronic soldering, the rosin flux inside the solder is mostly colophony (pine rosin). The same stuff used on violin bows, and that pitchers have it powdered in a bag.
https://amzn.to/3Vqe8V9

Mix it with half 99% isopropyl alcohol, half denatured alcohol to make a liquid. It will take several days to completely dissolve, just be patient. I bought a box of a dozen empty fingernail polish bottles. 
https://amzn.to/4bcxV0c

Put the powdered pine rosin in first, then top it off with the alcohol mixture.

Colophony is sold in drug stores, and on Amazon. It comes from pine sap and has quite a few uses.

What are the disadvantages of lead-free solder vs. lead solder?

What are the disadvantages of lead-free solder vs. lead solder?

The major disadvantages in no particular order are:

A "good" lead-free solder joint is grainy and rough.

Please note that both of these solder balls are cold, yet look how shiny the leaded solder is next to the rough lead-free solder:


I have found that lead-free solder often requires tight temperature regulation on your soldering iron, depending on the exact mix of metals. For many years, I and others have used unregulated irons or those with interchangeable tips that are at 600F, 700F, or 800F with 63/37 and 60/40 solder without problems. When I switched to lead-free, I had to get a digital adjustable iron because many lead-free solders have only a 10 or 15F working range.

The flux in lead-free solder is much more active than the rosin (literally pine sap) flux in leaded solder. In addition, you -must- use a lot of added flux when soldering lead-free solder. You should not be breathing in smoke from any kind of soldering, but the lead-free flux is much more irritating to your eyes and respiratory tract. And unless you use no-clean flux, the flux must be cleaned from the board or it will corrode the metal.

Tin whiskers! Lead was originally added to solder because of tin whiskers. No one is really sure why they grow, but they can grow at prodigious rates and cause failures. There is no clear, repeatable correlation, but elevated temperature, humidity, and voltage seem to have some correlation. Tin whiskers have been known to grow right through conformal coatings. This is especially a risk in modern high density, low current circuit boards.

Page on nasa.gov

The major concern from solder smoke is the flux, not lead. Lead does not tend go into vapor at soldering temperatures. For that, lead mining and smelting are the main pathways, and leaded gasoline for countries that still allow it. Leaded paint being an ingestion risk for children and amateur home renovators. Keeping in mind, of course, that lead absorption is cumulative as it is slow to leave the body.

As a side effect of lead-free solder, much more aggressive fluxes must be used, and in much greater quantities. In my many years of soldering, I've rarely added flux when using leaded solder, but -always- end up adding flux for lead-free joints. In either case, the smoke is very bad for you and should be aggressively removed. I've found the common tabletop smoke fan is a huge waste of money. I have a 200mm fan that is in a flex arm lamp in place of the magnifying lens. It is like a mini fume hood.

As for skin absorption, I've commonly used empty solder wick rolls to hold the solder I'm using. And wash my hands before doing anything else.

Lead (Pb) Toxicity: How Are People Exposed to Lead?

The Problem with Solder Smoke

Coal burning releases a lot more lead into the environment and has been cited as the major source of lead found in children's blood.
Lead in Children’s Blood Is Mainly Caused by Coal-Fired Ash after Phasing out of Leaded Gasoline in Shanghai

What are the best types of solders for beginners?

 What are the best types of solders for beginners?

In my opinion, tin-lead solder, specifically 63/37, with rosin flux core.

63/37 is called a eutectic alloy of tin and lead. That means that there is no paste phase. It goes from solid to liquid, and liquid to solid with no soft paste phase between. At 183C.

60/40 solder has a narrow temperature range where it is not solid, but not liquid. If you move or otherwise disturb the joint while cooling in this phase, you’ll end up with a lumpy joint, a type of cold solder joint or dry solder joint. It will probably work electrically now, but fail later by cracking.

A lead-tin solder joint, properly done, looks shiny.

Lead-free solder is difficult to use. Even on a new, clean PCB and new components, you’ll need lots of extra flux. And a lead-free solder joint done correctly, still looks grainy.

Steven J Greenfield's answer to What are the disadvantages of lead-free solder vs. lead solder?

In my experience, lead free solder also seems to require much tighter control of soldering iron temperature.

Am I the only one who finds conical soldering tips stupid?

 Am I the only one who finds conical soldering tips stupid?

No, you are not. I do not like them. Screwdriver aka chisel tips give you a flat surface to make better contact, causing better heat transfer.

Also the slant-cut cone tips are good for soldering surface mount ICs.

These are employed in a method of soldering called drag soldering, used on SMD IC pins.

https://youtu.be/hoLf8gvvXXU?t=6m41s

I hate that every soldering iron these days seems to come with a tiny conical tip. The really pointy ones do a terrible job transferring heat, and the solder wants to pull away from the very end.

I’ve been soldering since I was preteen, professionally since I was 19.

What is the main aim of soldering?

 What is the main aim of soldering?

For electrical/electronic use, the main aim is to prevent movement and prevent corrosion between two conductors.

A lot of people mistakenly think solder is primarily to provide a conductive path, but that is not the main purpose. And it does end up partly fulfilling that purpose. Like heat sink paste is meant only to fill the microscopic voids as it is more heat conductive than air, solder is meant only to fill the voids as it is more electrically conductive than air. In both cases of heat and electricity, the best conduction is to have the metals in contact.

With surface mount, the ideal situation is with the metal of the part sitting on the copper PCB pad, with just enough solder to mechanically hold the part and seal the contact surfaces in. Although this image from Example analytical investigations is meant as an example of a cracked ceramic capacitor, please note that the bottom of the metal on the end of the capacitor is in contact with the PCB pad, and there is just enough of a solder meniscus to hold the part in place:

For high reliability electronics and PTH components, clinched leads are much more reliable than merely poking the component wire through the PCB hole and soldering it in place. Clinching is when the leads are bent over partly or fully so as to come into contact with the copper PCB trace. Thanks to Electronic Techniques--PCB HARDWARE AND COMPONENT ASSEMBLY (part 1) for the image:

Please note that NASA uses the Western Union Splice aka Lineman’s Splice, which was originally done without soldering. NASA includes soldering. This makes a very secure mechanical and electrical connection.

Image from How-To: Splice Wire to NASA Standards | Make:

More on NASA’s soldering standards, see chapter 8:

https://nepp.nasa.gov/docuploads/06AA01BA-FC7E-4094-AE829CE371A7B05D/NASA-STD-8739.3.pdf

Also note that when crimped connections are used, the proper crimping tool will completely crush the wire so as to drive all air out, and the wire must NOT be tinned with solder. Image from Crimp Photo Gallery

There are exceptions. There is a type of surface mount IC called a Ball Grid Array or BGA that relies on uniform balls of solder to connect a grid of connections on the bottom of the IC with a matching grid of contacts on the PCB. BGAs are a bit of a problem. Remember all those XBoxes with the Red Ring of Death? BGA problems exacerbated by inadequate cooling.

Thanks to BGA - O que é isso ? for the image of a cross section of BGA solder balls:

Solder isn’t that great a conductor. It is much better to have two pieces of copper in intimate contact. However, copper corrodes. Moisture in the air will get on and between the copper pieces (component leads, wires, PCB traces) and cause corrosion accelerated by current flowing between them. And any vibration has the risk of making the connection intermittent. Oils and dust can work their way in and also cause problems.

Solder fills the gaps, keeping the copper in contact, and preventing contaminants and corrosion out. The surface of leaded solder rather quickly develops a film of corrosion, but it has no appreciable effect on the resistance of the connection.

I have seen this illustrated as I’ve worked on a lot of electronics over the decades. ICs in even very high quality sockets will eventually develop problems and the IC must be “reseated”, ie, pulled out and reinserted. This physically wipes corrosion and contaminants away and restores the copper to copper connection.

The only time I’ve had to resolder a soldered connection is when some outside force like heat causes the solder to partly melt and become granular (a type of “cold solder joint”), or fracture due to a lot of vibration. Even then, I suspect the vibration was at work on an already somewhat faulty solder joint.

What is the fastest clock speed a 555 timer can go?

 What is the fastest clock speed a 555 timer can go?

It depends. There are or have been about 20 different variations of 555 compatible chips. Bipolar transistor (aka TTL) and MOSFET being the biggest distinction, but some are optimized for speed, some for low voltage, some for low quiescent and running current.

So which one? Choose the one you wish to use, then look up the specific datasheet for that specific part number from that particular manufacturer.

NE555
SE555
TLC555
ICM7555
etc.

The original NE555 timer and NE556 dual timer from Signetics was only rated to work up to 100kHz. That is a very conservative number, as you’d expect from a datasheet, as I commonly used them up to 500kHz. Texas Instruments now makes a nearly identical chip that continues to use the NE555 designation.

Other varieties can go much higher in frequency. Here is a list on Wikipedia that shows just about every variation, with frequency up to 5MHz and supply voltage as low as 0.9V, although not in the same chip.

555 timer IC derivatives - Wikipedia

Note that no minimum frequency is given. This is going to depend on factors like leakage currents in the timing capacitor. Long times require a very high charge/discharge resistance and a large capacitor, however, larger capacitors tend to have more leakage.

Tantalum capacitors have a lot less leakage current than aluminum electrolytic capacitors. Modern ceramic capacitors have very low leakage and come in types with much more capacitance than possible in the past, on the order of 10 to 20uF.

However, those high value, low ESR, low leakage capacitors tend to be very voltage sensitive, losing capacitance at relatively modest voltages. Resulting in rather unpredictable timing.

A company in Australia is or was programming 8 pin microcontollers to act like an enhanced 555 chip in several varieties.

The CSS555 is a programmable 555 timer with internal EEPROM. The Control Voltage pin 5 must be kept above 1V to avoid triggering programming mode, so it is not fully compatible with all circuits. But then, you can’t just drop a CMOS 555 into a circuit designed for a TTL 555 or vice versa and expect zero changes.

http://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555_App_Note1_Serial_Interface.pdf

Are Ohm's law and Kirchhoff's law applicable to AC circuits?

 Are Ohm's law and Kirchhoff's law applicable to AC circuits?

Yes, if you properly examine all the resistances and reactances, taking into account phase of currents and voltages. Not just of the components, but parasitic and distributed parameters. Electrons can’t just disappear and reappear, therefore Kirchoff’s Current Law must be true; energy can’t just disappear and reappear and that is current times voltage, therefore Kirchoff’s Voltage Law must be true.

Steven J Greenfield's answer to Kirchoff's laws are invalid for AC. So why do books use Kirchoff's laws for an alternating current?

You must analyze the circuit correctly. It is not enough to simply take peak or RMS values and try to analyze it. Kirchoff's laws apply for a given instant in time. So the voltages at a given moment around a loop will all sum to zero, or currents in a node sum to zero if you look at the instantaneous voltage and current.

But they will be out of phase. So merely seeing 9Vrms on an inductor, 3Vrms on a capacitor, 5Vrms on a resistor, all connected in series to a 10Vrms AC source does not tell you the whole story.

It is simpler in a simulation program like Spice to measure the current individually in a parallel circuit, than the voltage in a series circuit. So here I have three components, a resistor, capacitor, and inductor in parallel. You can see the mess of currents out of phase. Yet the purple line, which is the sum of all currents, adds to zero at all times, within the limits of finite calculations.

You can click on that to see a larger image. Created in LTSpiceIV, thanks to Linear Technology for making their Spice front-end free for all.

You might notice that I(L) is greater than the total supply current. Watch what I(C) is doing and think about what happens when the reactance of the inductor and the capacitor are equal. This is a condition called resonance, and it only happens at one frequency for a given inductance and capacitance.

How do I use concept of Wheatstone bridge in solving circuit of capacitance?

 How do I use concept of Wheatstone bridge in solving circuit of capacitance?

A Wheatstone Bridge is used to measure small changes in a much larger signal, either a voltage or a resistance ratio. It can also be used to measure small changes in capacitance, such as for a sensor that changes capacitance to indicate the quantity it is measuring.

A garden variety Wheatstone Bridge from Electronics-Tutorials dot com:

Or R3 may be fixed, and R2 made a variable resistor.

To measure capacitance, you must use an AC voltage source. Then you use resistors on the left, and the other a reference capacitor and the capacitance you are measuring. On the left side, there is no phase shift because it is pure resistance, on the right, there is no phase shift because it is pure capacitance. Assuming a very low impedance AC driving source.

Thanks to Play-Hookey dot com for the image:

Or both along the top are resistors, and the bottom elements are the reference capacitor and the capacitance you are measuring.

Thanks again to Play-Hookey dot com:

Here, C1 is a variable, but it could be a fixed reference and make R2 a variable resistor. Don’t make R1 the variable. With fixedR1, R1C1 and R2Cx make a shift in phase, and by making R2 variable, you are making the phase shift equal when the voltages are equal.

If you make R1 variable, then except for the special case of R1 and R2 being equal and C1 and Cx being equal, you’ll never get both phase and voltage equal at the same time and so the null will be shallow and inaccurate.

Although to be pedantic, a Wheatstone Bridge is DC current and resistive only. A Shering Bridge is the name given for a particular configuration used to measure capacitance and the dissipation factor.

Schering Bridge Measurement of Capacitance using Schering Bridge | Electrical4U

C1 is the capacitor being measured. C4 is variable, and R4 is variable.

Heathkit sold several different varieties of RLC bridges, which are just Wheatstone Bridges using AC as the driving voltage. When measuring a capacitor, a reference capacitor is switched into the circuit. When measuring an inductor, a reference inductor is switched in the circuit. Here is a simplified diagram from the Heathkit IG-5281 solid state RLC bridge:

Different frequencies are used to suit the ranges:

In the case of Heathkit’s RLC bridges, they do not include any reference inductors, instead they must be supplied by the user.

Although it isn’t strictly correct to call all of these Wheatstone Bridges, we do anyway.

Another device that uses the same principle to measure antenna impedance is called a Noise Bridge. A wideband noise is used as the signal source. A receiver tuned to the frequency of interest will hear a null in the noise when the variable resistor and capacitor balance the bridge. It is a bit difficult to see how this is a modified Wheatstone Bridge. The secondary is centertapped, often wound as a trifilar transformer. When the reactance and resistance of VR1//VC1 = C2//Unknown, the centertap has zero signal and so the receiver has a null (the noise gets quiet).

C2 is an offset value to allow inductive impedance to be measured, too. When the unknown impedance is purely resistive, the bridge is balanced when VR1 is equal to the load, and VC1 = C2. If there is some capacitance in the load, then VC1 will be set to a higher value to match C2 + the load capacitance.

When the load is partly inductive, VC1 will be set to less than C2. The two dials are then calibrated in ohms on VR1, and reactance for VC1.

A series connection may also be used.

Build this circuit, it adapts your VOM or DMM into a capacitance measuring device.

Build this circuit, it adapts your VOM or DMM into a capacitance measuring device. 

The parts values you see are intended to display 1pF per mV on the lowest scale, so on a 2V reading you’d have 2000pF or 2nF. The highest range is 20uF at 2V. You MUST use a regulated voltage. A 9V battery and a 7805 will work just fine, as will four AA or AAA and a modern low dropout regulator.

That is my circuit, I designed it and was selling capacitance meters starting in high school in the late ‘70s. The first ones just used a 50uA meter or your own VOM analog multimeter as the display, this particular circuit was designed for use with a DMM on the 200mV scale. But it is good to 2V output.

I still have the prototype that I build for DMMs from this circuit. I recently found out it is good to 10fF on a meter that can read down to 10uV!

Are people with Asperger’s excellent in data mining because of their pattern recognition?

 Are people with Asperger’s excellent in data mining because of their pattern recognition?

I can’t speak for you or anyone else, only myself.

I think that characteristics that seem to be part of my Asperger’s have made me very good at troubleshooting and repairing electronics and electromechanical devices.

You must have seen the Tshirt that says:

There are two kinds of people in the world

  1. Those who can extrapolate from incomplete data

I’m definitely in category 1. I’ve worked on a lot of different kinds of electronics, and I’ve noticed that many techs will overly-generalize symptoms. It seems to follow the 90/10 rule. 90% of the jobs, they’ll be right, but then spend 90% of their time and parts on 10% of the repairs trying to figure out what is actually wrong after replacing the wrong parts. They often “shotgun” the repair.

When someone “shotguns” a repair, it means they just keeps replacing parts willy-nilly in an ever expanding pattern around the affected circuits. It is a waste of time and parts.

Whereas I’ll see slight differences and treat those 10% repairs differently, spending a little more time looking for the real cause and a LOT less time repairing.

Often, all I have to go on is a mental visual model (I have a vivid imagination) and subtle clues. In the repair world, you can’t build up a vast array of data and then process it. You must pay attention to little squeaks, pops, even smells, make up some hypothesis about what is going wrong, make predictions and test them, and see if it responds how it should if you are correct.

I will also consider what other parts may have been stressed when the obviously defective parts went bad, or what else may have caused those parts to go bad but not be obviously defective. As a result, it is very unusual for me to have a repair come back.


Remember when email spam really started taking off? I got really good at determining which emails were spam just from the subject line. There were no email filters at that time, or they were primitive and prone to failure. I can’t tell you exactly what I’d look for. Naturally many spam subject lines are very obvious, but not always, and I was very good at picking those out.


I worked for decades without a degree, but HR departments won’t even schedule an interview without one. So when I had an opportunity to get a 2yr EET degree tuition-free, I jumped at it.

Just a couple of weeks after I started, one of the other students brought in the controller for an in-floor heating system he and his father had installed. It had apparently burned up. He said this was the second time this had happened.

He brought it in to see if any of the electronics instructors could figure out why this had happened twice. They all clucked over it like brooding hens, and after a couple of hours of consulting with different instructors, they announced “it has a short in it.”

I was floored. That is what people who know nothing about electronics (no offense) say is wrong when their remote control buttons don’t work correctly, or the TV picture is rolling.

I got a look at it, finally. I asked this gentleman a series of questions and determined:

  1. The heating element has a positive temperature co-efficient and so even if you connect it without a thermostat, it will only get to around 90 to 100F in the room running full out.
  2. Both times this happened, the room temperature seemed normal, not warm.
  3. He and his father save and reuse old wire nuts.

This tells me first of all that the controller did NOT short, because the room would have become very warm, and under normal current limited by the heating element, the controller should not have gotten more than slightly warm.

Looking at the controller, wiring, and remains of the wire nuts, I determined that the heat and burning started at the wire nuts and proceeded down the wire. All of the burning and melting was on the outside of the plastic box, none came from inside. The controller board looked perfect.

Clearly, the old, previously used wire nuts had failed. A little heat, the plastic gets soft. The metal loses its spring and doesn’t hold the wires as tight, causing more resistance. This causes more heat. As the copper gets hot, it oxidizes, further increasing resistance and heat.

The insulation begins melting. The excess wire had just been left in a partly coiled heap on top of the control box. Eventually, two wires contacted enough to really get the insulation burning. Only then did the breaker finally blow, because up until this point, it had been drawing normal amounts of current.

This took me less than 5 minutes to suss out. And most of that was asking questions.


A year later, my instructor brought in a winch controller with burned wires and a button stuck down. See the little box with two buttons? Thanks to Zoro dot com:

It had two red and two black wires. He said he’d hooked it up to a car battery, hit one button and it let out cable, hit the other button and nothing happened. So he pressed and held the button, then the wires started smoking and the button stayed down when he let go. At that point he yanked the wires off the battery.

He offered a day off to anyone or any group who could tell him what went wrong. I said that I would not compete, as I felt it would be unfair of me and because I figured I’d give it away just asking questions and looking at it. So I did not even look at the winch controller.

After nearly an hour of students in groups working on this, he had everyone write down what they thought went wrong and he went through them.

I was gobsmacked - he chose two that simply said “It has a short in it”!

I couldn’t let this pass. I said “Now do you want to know what actually happened?”

I drew two DPDT symbols on the whiteboard with appropriate wires to show how one switch connects the motor B+ to M+ and B- to M- for Forward, and B+ to M- and B- to M+ for Reverse. And that what the instructor had done was mix up the wires so he had one motor wire on the battery, and one battery wire on the motor. Then when pressed one way, it would connect the motor to the battery but would actually run in the opposite direction to the marking on the button, and the other button would short across the battery. This would melt the plastic inside the housing and so the button stuck down.

I had still not looked at the winch controller. I said “If you go look at it, you’ll find that there will be some small way to tell which are for the battery, and which are for the motor, and that one battery wire and one motor wire will be burnt.”

That is exactly what they found.

Can one apply the Wheatstone Bridge formula with inductors or capacitors as impedances?

 Can one apply the Wheatstone Bridge formula with inductors or capacitors as impedances?

The Wheatstone Bridge is an old circuit topology that continues to be very useful where small changes exist in a much larger, constant signal. In this circuit from Hackaday dot com, the resistor R2 is adjusted until there is a null measured on the meter G:

When a null is reached, the ratio of R1/R2 = R3/Rx and so Rx can be calculated. If R1 and R3 are equal, then it can be reduced to simply Rx = R2 at null. This same configuration is used still in things like strain gauges and in circuits where a very small signal is riding on a much larger, constant signal. Thanks to AllAboutCircuits dot com for this schematic of one possible strain gauge Wheatstone Bridge configuration:

To measure reactance and impedance, an AC signal source of a frequency appropriate for the devices being measured is used rather than a DC source. R1 and R2 above would remain resistors, R3 will be replaced with a reference capacitor for measuring capacitors, or reference inductor for measuring inductance. Thanks to Play-Hookey dot com for the image:

AC Applications of the Wheatstone Bridge

The output will be AC so it must be rectified to show on a meter or magic eye tube. Minor circuit changes may be made to change the balanced, floating Null signal into a single-ended signal that is easier to amplify and display.

In this old tube based Heathkit IT-28 capacitor analyzer, it uses 60Hz AC to drive it and a magic eye tube as a null indicator. It can also take an external reference inductor. Thanks to the California Historical Radio dot com page:

Later transistorized version Heathkit IB-5281 has internal reference inductors, thanks to EEVBlog for the image:

An RX Noise Bridge is a device used to analyze antennas and other complex impedances. It uses your radio receiver as the device used to measure the null, and a broadband white noise source as the AC signal source. A variable resistor and variable capacitor are adjusted for a null in noise volume. It is just a Wheatstone bridge. Thanks to RFCafe dot com for this schematic of the Palomar RX Noise Bridge, everything to the left of T-1 is just a noise source and amplifier:

Thanks to Palomar-Engineers dot com for this picture of the device itself, note the markings in Ohms of Xc, Xl, and R:

Another device used for measuring frequency curves and impedance is called a Return Loss Bridge or RLB. It is again just a Wheatstone Bridge, used with a signal source and a radio receiver. It can also be used with a broadband noise source and one of those RTL SDR $15 wideband radio receivers to make a simple network analyzer/spectrum analyzer.

Thanks to RTL-SDR dot com for these sample screenshots of an RTL SDR receiver being used to measure the pass characteristics of filters using a RLB and noise source:

Tuning an HF Antenna with an Airspy, SWR-Bridge and Noise Source

Using the Airspy as a Network Analyzer for Characterizing Antennas

Thanks to K8IQY dot com for the schematic of a RLB:

A slightly different version that is functionally the same from VK2ZAY dot com:

These are well-suited to measuring SWR of an antenna or load. The transformers are there only to change the balanced Null signal into a single-ended signal for easier measurement.

What everyday items causes static electricity on an object?

 What everyday items causes static electricity on an object?

Almost everything. The triboelectric effect causes charges to transfer merely from two surfaces coming into contact and being pulled away again. They don’t really need to be rubbed, it isn’t from friction. Rubbing is just a fast way to make and break contact many times.

If you have one of these noncontact AC voltage testers:

Just rub or tap it on your shirt and it will beep momentarily as static charge is built-up and discharges. It will go crazy if you rub your cat with it, or your hair if you’ve just washed it. That is due to the Triboelectric effect between the plastic on the tip and whatever you’ve touched or rubbed it on.

Then those charged surfaces can transfer charge to another object by contact or even by something called electrostatic induction. A charged object brought near a neutral object causes charges to flow on the surface of the neutral object. Some other object may draw some of that charge away, so that when the original charged object is moved away, the initially neutral object is now charged.