Detect current on Raspberry pi

[tlfong01]

Pre-requisites for guessing how the weird buzzer oscillates
https://www.electronics-tutorials.ws/os ... ators.html

Buzzer schematic 70% sure, brain storming guessing welcome

I think my background knowledge in inductance and feedback is far from adequate to understand what is going on. I don't even know where to start a wild guess.

Perhaps I can start looking at time period d-a

1. Time interval d-a: Q1 fully saturated, Ic = Ice(sat), Vc ~= 0.
2. Time point a, base suddenly drops from 0V to -10V (why not say, 2V to 0V?) Q1 suddenly cut off, connected inductor L2 has back EMF 25V (fives times of Vcc = 5V is what I usually read, though I don't know how to calculate).
3.

/ to continue, ...
...

[tlfong01]

Pre-requisites for guessing how the weird buzzer oscillates
https://www.electronics-tutorials.ws/os ... ators.html

Buzzer schematic 70% sure, brain storming guessing welcome
I think my background knowledge in inductance and feedback is far from adequate to understand what is going on. I don't even know where to start a wild guess.

Rpi/Esp8266/Mcp23S17 GPIO Controlled Smart Buzzer Newbie Design Notes

/ to continue, ...

Appendices - Prerequisites - Mutual Inductance

Oliver Heaviside - Wikipedia
Oliver Heaviside FRS (1850 – 1925) was an English self-taught electrical engineer, mathematician, and physicist who adapted complex numbers to the study of electrical circuits, invented mathematical techniques for the solution of differential equations (equivalent to Laplace transforms), reformulated Maxwell's field equations in terms of electric and magnetic forces and energy flux, and independently co-formulated vector analysis. Although at odds with the scientific establishment for most of his life, Heaviside changed the face of telecommunications, mathematics, and science for years to come.

Inductance -Wikipedia
In electromagnetism and electronics, inductance is the property of an electrical conductor by which a change in electric current through it induces an electromotive force (voltage) in the conductor. It is more accurately called self-inductance.

The same property causes a current in one conductor to induce an electromotive force in nearby conductors; this is called mutual inductance.

The term inductance was coined by Oliver Heaviside in 1886. It is customary to use the symbol L for inductance, in honour of the physicist Heinrich Lenz. In the SI system, the unit of inductance is the henry (H), which is the amount of inductance which causes a voltage of 1 volt when the current is changing at a rate of one ampere per second. It is named for Joseph Henry, who discovered inductance independently of Faraday.

Electric circuits which are located close together, so the magnetic field created by the current in one passes through the other, are said to be inductively coupled.

A change in current in one circuit will cause the magnetic flux through the other circuit to vary, which will induce a voltage in the other circuit, by Faraday's law.

The ratio of the voltage induced in the second circuit to the rate of change of current in the first circuit is called the mutual inductance M between the circuits. It is also measured in henries.

Dot Convention and Mutal Inductance Polarity - Wikipedia
https://en.wikipedia.org/wiki/Polarity_ ... nductance)

In electrical engineering, dot marking convention, or alphanumeric marking convention, or both, can be used to denote the same relative instantaneous polarity of two mutually inductive components such as between transformer windings. These markings may be found on transformer cases beside terminals, winding leads, nameplates, schematic and wiring diagrams.

The convention is that current entering a transformer at the end of a winding marked with a dot, will tend to produce current exiting other windings at their dotted ends.

Maintaining proper polarity is important in power system protection, measurement and control systems. A reversed instrument transformer winding may defeat protective relays, give inaccurate power and energy measurements, or result in display of negative power factor. Reversed connections of paralleled transformer windings will cause circulating currents or an effective short circuit. In signal circuits, reversed connections of transformer windings can result in incorrect operation of amplifiers and speaker systems, or cancellation of signals that are meant to add.

Polarity
Leads of primary and secondary windings are said to be of the same polarity when instantaneous current entering the primary winding lead results in instantaneous current leaving the secondary winding lead as though the two leads were a continuous circuit.[1][2] In the case of two windings wound around the same core in parallel, for example, the polarity will be the same on the same ends: A sudden (instantaneous) current in the first coil will induce a voltage opposing the sudden increase (Lenz's law) in the first and also in the second coil, because the inductive magnetic field produced by the current in the first coil traverses the two coils in the same manner. The second coil will, therefore, show an induced current opposite in direction to the inducing current in the first coil. Both leads behave like a continuous circuit, one current entering into the first lead and another current leaving the second lead.

Transformer windings
Two methods are commonly used to denote which terminals present the same relative polarity. A dot may be used, or an alphanumeric designation. Alphanumeric designations are typically in the form H1 for primaries, and for secondaries, X1, (and Y1, Z1, if more windings present).

Terminal layout conventions
Transformers are said to have "additive" or "subtractive" polarity based on their physical arrangement of terminals and the polarity of windings connected to the terminals.

The convention used for North American transformers is that, facing the high voltage side of the transformer, the H1 terminal is on the observer's right. A transformer is called "additive" if, conceptually, connecting the high-voltage terminal to the adjacent low-voltage terminal gives a total voltage between the other two terminals that is the sum of the high voltage and low voltage ratings, when the high-voltage winding is excited at rated voltage. The H1 and X2 terminals are physically adjacent.

In the "subtractive" arrangement, the H1 and X1 terminals are adjacent, and the voltage measured between H2 and X2 would be the difference of the high voltage and low voltage windings. Pole mounted distribution transformers are manufactured with additive polarity, while instrument transformers are made with subtractive polarity. Where markings have been obscured or are suspect, a test can be made by interconnecting the windings and exciting the transformer, and measuring the voltages.

Dollars Trilogy (Themes) 2,904,371 views
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The Good, the Bad and the Ugly - The Danish National Symphony Orchestra (Live) 11,701,452 views
https://www.youtube.com/watch?v=enuOArEfqGo
...

[tlfong01]

Pre-requisites for guessing how the weird buzzer oscillates
https://www.electronics-tutorials.ws/os ... ators.html
Perhaps I can start looking at time period d-a
1. Time interval d-a: Q1 fully saturated, Ic = Ice(sat), Vc ~= 0.
2. Time point a, base suddenly drops from 0V to -10V (why not say, 2V to 0V?) Q1 suddenly cut off, connected inductor L2 has back EMF 25V (fives times of Vcc = 5V is what I usually read, though I don't know how to calculate).
3.

Electronics Tutorials on Inductance

Now I am reading yet one more time the Electronics Tutorials on inductance. The following picture showing an inductor's voltage and current when a switch is open and closed is very useful when studying the buzzer circuit where the transistor is switching on and off during oscillation. The description on aiding and opposing inductors is also useful.
...

[tlfong01]

Electronics Tutorials on Inductance
Now I am reading yet one more time the Electronics Tutorials on inductance. The following picture showing an inductor's voltage and current when a switch is open and closed is very useful when studying the buzzer circuit where the transistor is switching on and off during oscillation. The description on aiding and opposing inductors is also useful.

Yet another drawing, 80% sure, brainstorming oscillator circuit analysis welcome

Now I guess the diode is a 2.5V Zener diode, but only 50% sure. Perhaps I should remove it and check it out.

Update - 2018dec18hkt2043

I removed the diode and found the marking looks like 1Nxx48. I guess it is 80% likely that it is 1N4148. Now I think it is unlikely a Zener, because that is many times more expensive, and the Zener voltage is usually not that defined or constant, so there is a design problem, ...

1N4148 Small Signal Fast Switching Diode
https://www.vishay.com/docs/81857/1n4148.pdf


...

[tlfong01]

Electronics Tutorials on Inductance
Now I am reading yet one more time the Electronics Tutorials on inductance.

Heavyside and Imaginary Numbers

I was surprised to read that Heavyside invented many things in electrical engineering, including vector analysis and using imaginary numbers to represent phasors. I always found imaginary number mysterious. Perhaps I need to try hard to understand this weird thing, which I now think is a prerequisite to understand AC circuits, inductance, and of course buzzer oscillations.

Complex Numbers and Phasors - Electronics Tutorials
https://www.electronics-tutorials.ws/ac ... mbers.html

Imaginary Numbers - BBC In Our Time
https://www.bbc.co.uk/programmes/b00tt6b2

Melvyn Bragg and his guests discuss imaginary numbers.

In the sixteenth century, a group of mathematicians in Bologna found a solution to a problem that had puzzled generations before them: a completely new kind of number.

For more than a century this discovery was greeted with such scepticism that the great French thinker Rene Descartes dismissed it as an "imaginary" number.The name stuck - but so did the numbers.

Long dismissed as useless or even fictitious, the imaginary number i and its properties were first explored seriously in the eighteenth century.

Today the imaginary numbers are in daily use by engineers, and are vital to our understanding of phenomena including electricity and radio waves.

With Marcus du Sautoy Professor of Mathematics at Oxford University, Ian Stewart Emeritus Professor of Mathematics at the University of Warwick, Caroline Series Professor of Mathematics at the University of Warwick. Producer: Thomas Morris.

[Burngate]

Complex and imaginary numbers: you have to be carefull!
If you don't watch out, you'll start down that slippery road, taking in sets and groups towards vector spaces.

The first symptom is that you start thinking about what infinity is (if it exists) and why electrons going round in circles don't radiate, whilst black holes do.
Then you come across Einstein's General Relativity, and why it doesn't agree with Quntum mechanics.

You may be able to stop at that stage, and just call yourself a Physicist, just like Hawking, but many a poor soul has ended up being labeled a Mathematician.

That way lies Madness.

[tlfong01]

Complex and imaginary numbers: you have to be carefull!
That way lies Madness.

Ah, I agree imagining imaginary stuff drives you mad. Heaviside is an example.

The Problem with Oliver Heaviside - Providentia 2017sept29
https://drvitelli.typepad.com/provident ... iside.html

Oliver Heavyside: Rags to Recognition, to Madness - Dan Maloney 2018oct30
https://hackaday.com/2018/10/30/oliver- ... o-madness/

Top 10 Mad Scientists - 390,617 views
https://www.youtube.com/watch?v=OFdVrJHnqHE

[tlfong01]

Complex and imaginary numbers: you have to be carefull!
If you don't watch out, you'll start down that slippery road, taking in sets and groups towards vector spaces.
The first symptom is that you start thinking about what infinity is (if it exists) and why electrons going round in circles don't radiate, whilst black holes do.
Then you come across Einstein's General Relativity, and why it doesn't agree with Quntum mechanics.
You may be able to stop at that stage, and just call yourself a Physicist, just like Hawking, but many a poor soul has ended up being labeled a Mathematician.
That way lies Madness.

j and e

Well, actually I have no problem with middle school physics and algebra, though I don't like trigonometry and geometry. Elementary electronics maths like Boolean Algebra, Truth Table, Karnaugh Map, Set Theory are OK with me.

I only want to learn AC circuits and oscillators, which I think are prerequisites of making cheap smart wireless door bell, ... The problem is even tutorials for AC circuit newbies start with the scary imaginary number j!

Complex Numbers and Phasors - Electronics Tutorials
https://www.electronics-tutorials.ws/ac ... mbers.html

And along side j, comes another scary number e. It is these two scary numbers that might drive me mad.

Anyway, I googled and found the BBC In Our Time guys talking about e. I guess I will go listen those not yet mad professors talking about this weird number.

e - BBC In Our Time (43 minutes)
https://www.bbc.co.uk/programmes/b04hz49f

Melvyn Bragg and his guests discuss Euler's number, also known as e. First discovered in the seventeenth century by the Swiss mathematician Jacob Bernoulli when he was studying compound interest, e is now recognised as one of the most important and interesting numbers in mathematics. Roughly equal to 2.718, e is useful in studying many everyday situations, from personal savings to epidemics. It also features in Euler's Identity, sometimes described as the most beautiful equation ever written.

With:
Colva Roney-Dougal, University of St Andrews
June Barrow-Green, Open University
Vicky Neale, University of Oxford
...

[tlfong01]

Complex and imaginary numbers: you have to be carefull!
The first symptom is that you start thinking about what infinity is, ...
That way lies Madness, ...

j and e
Anyway, I googled and found the BBC In Our Time guys talking about e. I guess I will go listen those not yet mad professors talking about this weird number.

The first symptom is that you start thinking about what infinity is, ..

Well, the BBC In Our Time talk on the number e starts with an imagination of an Infinitively small unit of time, ... so I cannot avoid thinking of infinity if I wan to know what is the number e, ...

So I went checking out what is infinity, but then another thing comes with it, a paradox, ... I need to stop thinking for now, otherwise I would go mad, ...

Zeno's Paradoxes In Our Time - 42 minutes
https://www.bbc.co.uk/programmes/b07vs3v1

Melvyn Bragg and guests discuss Zeno of Elea, a pre-Socratic philosopher from c490-430 BC whose paradoxes were described by Bertrand Russell as "immeasurably subtle and profound." The best known argue against motion, such as that of an arrow in flight which is at a series of different points but moving at none of them, or that of Achilles who, despite being the faster runner, will never catch up with a tortoise with a head start. Aristotle and Aquinas engaged with these, as did Russell, yet it is still debatable whether Zeno's Paradoxes have been resolved.

With
Marcus du Sautoy
Professor of Mathematics and Simonyi Professor for the Public Understanding of Science at the University of Oxford
Barbara Sattler
Lecturer in Philosophy. University of St Andrews
James Warren
Reader in Ancient Philosophy at the University of Cambridge

...

[tlfong01]

3. I found a couple of buzzers in my junk box, some broken, some not, and I mixed up all of them. Now I took a group picture, as displayed below.

Buzzer Spec
...

[tlfong01]

Buzzer Spec

Buzzer Mark II Notes

1. All SMD components
2. NPN BJT = FairChild KST1623L6
3. Schematic same as Mark 1
4. Waveforms also similar
5. Frequency = 420Hz
5. Vcc = 5V, I = 17mA
6. Collector peak = 30V, Base = -10V, Andoe = -5V

...

[tlfong01]

Complex and imaginary numbers: you have to be carefull!
If you don't watch out, you'll start down that slippery road, taking in sets and groups towards vector spaces. ...
That way lies Madness.

Vector spaces > Tensor spaces > Tensor flow > Rpi Python Cat Detector

Well, I am not at all interested in vector spaces, but I read that Heaviside introduced vector analysis to electromagnetic inductors etc, and later vector analysis changed to tensor analysis. So I think I need to know a little bit of vector thing, before the tensor thing, then finally my goal, a cat detector!

Raspberry Pi Pet Detector Camera Using Python, TensorFlow, and Twilio - Edje Electronics 2018dec18
https://www.youtube.com/watch?time_cont ... GqVNuYol6o

I used TensorFlow and a Raspberry Pi to create a pet detector camera that watches the door and texts me when my cat wants to be let inside! This video explains how the code works, so you can use it as an example for your own object detection application.

Over-Engineered Raspberry Pi Outdoor Cat Feeder - Jeremy S Cook 2018dec20
https://blog.hackster.io/over-engineere ... 532162c7fe

Feline Feeder Station - krakenabyss 2018dec20
https://imgur.com/a/wmLsGkd#vWhZsQW

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(youtube) https://www.youtube.com/watch?v=6Yt3mMBmm3M
...

[tlfong01]

DIY Raspberry Pi face recognition system - Julian Horsey

I am thinking trying the above.

https://www.geeky-gadgets.com/diy-raspb ... 0-01-2019/

https://www.hackster.io/SeeedStudio/fac ... hat-abcec9

[tlfong01]

Motion Activated Security Camera with the Raspberry Pi Zero

Building a Motion Activated Security Camera with the Raspberry Pi Zero - Mark West 2018aug12
https://www.bouvet.no/bouvet-deler/utbr ... ry-pi-zero