texts: Solving a transistor circuit and determine the base current

texts:
I need to determine the base current of the circuit I have attached below.
Given:

current amplification \$B = 500\$
\$U_{CC} = 12V\$
\$U_{BE} = 0.7V\$
\$R_C = 3.2k \Omega\$
\$R_E = 9k \Omega\$
\$R_1 = 47 \Omega\$
\$R_2 = 19 \Omega\$

What we need to get:
base current \$I_B\$ in $\mu A$ (2 decimals)

My attempt: (feel free to correct me if I use the wrong vocabulary to describe my attempt, thank you!)

At first I introduced a new current \$I_q\$ which flows through \$R_2\$. Having that done I know that \$I_q = \frac {U_{BE}}{R_2}\$. Since \$U_{BE} = 0.7V\$ and \$R_2 = 19 \Omega\$ are given I calculated the value for \$I_q \approx 0.03684210526A\$.
Now I looked at the top left part of the circuit. We know that \$R_1\$ must be \$R_1 = \frac {U_{CC} - U_{BE}}{I_q + I_b}\$. Well solve the equation for \$I_b\$. We then receive \$I_b = \frac {U_{CC} - U_{BE}}{R1} - I_q\$. If we fill the equation with the given values and \$I_q\$ we get: \$I_b = \frac {12V - 0.7V}{47} - 0.03684210526 = 0.2035834267A\$. Now we need to convert \$I_B\$ to \$\mu A\$ which should be \$203583,43 \mu A\$ (rounded).


texts: What exactly is a diode and how do I use it to step down voltage?

texts:
So last year I did a Christmas lights project and learned that cutting off a couple christmas bulbs off a $2 string of 100 bulbs is not so straightforward, it's practically rocket science. Maybe not "rocket science" per se but it takes some serious knowledge of things like ohms and voltage and resistors and diodes etc - which if you don't have a formal engineering education may be challenging to grasp without learning the fundamentals first.

You can't cut even a few bulbs off because if you do it will increase the load on all the remaining bulbs which will significantly shorten their lifespan, and potentially increase fire risk due to overloading voltage on each bulb. This is because each bulb effectively functions as a resistor and the whole string is designed with the bulbs as resistors, specially made so the string works. But it isn't so easy to shorten or lengthen.

I learned about using resistors and successfully used some, however resistors get extremely hot and for that reason I decided to take down the shortened strings.

It was suggested that I could use diodes to step down the voltage rather than use resistors to "soak up" (my term) the excess heat and voltage from the missing bulbs.

However I still didn't really understand what diodes are or why they don't get hot or how I can actually use these, in for example a string of christmas lights to remove say 15 bulbs from a string of 100.

I previous asked this question last year: Is a diode an effective way to replace a resistor in an application where heat should be avoided? for which I accepted an answer however I still don't fully understand diodes and if and how to use a diode in such a project.

For example, the answer given was:

  Using the diode however switches off the voltage and power by 50% If this reduced power is acceptable consider reversing the diode in one string to balance the load current.

However, I don't really understand this. So here are my questions:

======= Questions ========

How does the diode reduce the voltage without getting hot while the resistor gets extremely hot?
In what way can I use a diode in such a project? It still isn't clear to me how to use a diode in this kind of project.
What are some other practical usages for small projects in which a diode can be used (for a beginner)?

Christmas is over again but for purely educational reasons I would really like to have a comprehensive grasp of the best solutions for such a project. I would like to try more projects in the future.

Update:

I understand it more now (although not entirely). With the answer below and the following two youtube video I just watched now I understand a little better.

Basically, a resistor is more like a sponge whereas a diode is more like a wall. While a resistor absorbs current and releases it as heat, a diode on the other hand will simply reject all the current going in one direction (up to the capacity of the diode).

If you use a diode too small, it is like driving a car into a wall made of 2x4. The car will go through because it has more power than the wall (actual diodes will explode when the current is too high for it, as can be seen in various youtube videos). Likewise, a diode that is big enough is like a large brick wall. A car hitting it will be stopped and the wall will be pretty much unaffected.

This isn't a perfect analogy but it's helpful to me (I just made up this analogy).

Here are the two videos on diodes I watched which helped:

https://www.youtube.com/watch?v=6lep5e3KMdY

https://www.youtube.com/watch?v=TFgWDcBp-uY

These don't answer all my questions but they do mostly answer why a resistor heats up but a diode does not. A diode doesn't absorb the energy it simply blocks it. A resistor absorbs the energy which is then released as heat.


texts:
This will be my first time trying to power my Arduino from an external source rather than an USB port.

I will need to power my Arduino Nano (Rev 3.0) with an external 24V DC power supply (from a 24V, 36Ah lead acid battery), so I was wondering what I could do.

I have three possible solutions:

Connect the 24V power supply to a 24V-to-12V DC buck converter, and supply the 12V voltage to the Vin pin on Arduino Nano to power my Arduino Nano.
Connect the 24V power supply to a 24V-to-12V DC buck converter, and supply the 12V voltage to a voltage regulator (LM7805), and supply the 5V voltage to the 5V pin on Arduino Nano to power my Arduino Nano.
Connect the 24V power supply to a voltage regulator (LM7805) directly, and supply the 5V output voltage to the 5V pin on Arduino Nano to power my Arduino Nano.

Do all of the 3 solutions work theoretically? Will all of them successfully power the Arduino Nano? Which one is better?

EDIT

I will get my 24V DC supply from a 24V, 36Ah lead acid battery, and I will use my Arduino Nano to power a DC motor via L293D and buttons. I am not sure how much output current I will need, but I think it wouldn't be a lot. Will the 24V, 36Ah lead acid battery affect my choice?


texts:
Please excuse what may be a stupid question, since I don't have access to test gear. I'm obviously no expert, and trying to learn the behavior of op amps.
What happens to an op amp (in my case, TL072) if the output is directly shorted to the input? (The red line in the attached diagram.) And does the behavior change whether it is inverting or non-inverting? I'm assuming that in both cases they reach saturation without damage to the chip.
This got me wondering how the amp would behave with a capacitor between input and output rather than a direct short. Can anyone advise? Thanks.


texts: Exotic semiconductors for fast digital ASIC

texts:
I am researching exotic semiconductors for a digital ASIC with a few million logic gates which should run as fast as possible within a $30 million budget. (Specifically, I need to do a single fully-parallel 4096-bit multiplication repeatedly. For more context, I am building an ASIC to compute this Verifiable Delay Function.)

It seems there are semiconductors that perform better than silicon in terms of speed of logic operations, including gallium arsenide, gallium nitride and indium phosphide. My research suggests that these semiconductors are generally used for analogue ASICs as opposed to digital logic, so it is hard to tell which semiconductors are viable for my use case.

Which semiconductor is viable for a digital ASIC with millions of logic gates (say, ~20 million gates) and can provide the fastest performance in terms of speed of logical gates?

Edits in response to comments

Budget: Our maximum budget is in the tens of millions of dollars, ~$30 million.
Speed: To quantify the speed, we ideally need someone spending $1 billion to be at most 2x faster than us. Notice the Verifiable Delay Function (VDF) is inherently sequential, so lots of parallelism does not help.
SiGe process technology: I understood GaAs can give a significant speed bump with respect to SiGe. If 100nm GaAs is faster than 7nm SiGe then size of SiGe is not relevant. As for GaAs, we're only looking to use existing process technology.
Pins: We do not need a large number of pins. The reason is there is a single 4096-bit input and a single 4096-bit output per VDF run with 10 minutes of intermediary repeated multiplications spanning 10 minutes. The I/O speed is marginal compared to the multiplication speed.
Power and cooling: The ASIC should be runnable by individuals without power supply and cooling that is much more sophisticated than a top-of-the-range GPU.
Graphics technology: As I understand, graphics technology is optimised for massively parallel computation. The ASIC we want needs to be optimised for speed of sequential computation, i.e. latency.
Obfuscation/reverse engineering: The ASIC will be developed for an open-source project (namely, Ethereum). The ASIC will itself have an open-source circuit design.
More context: See these slides that explain the use of the ASIC for a blockchain random number generator.


texts: Finding Optimal Resistor Combination for Desired Equivalent Resistance

texts: My question is simple, though I'm not sure how to succinctly word it in the title. Often times when working with circuits (as a student) we need a specific resistor value, but only have resistors of other values, so we build an equivalent resistor from parallel and series combinations. I was wondering if there is any good method for choosing the optimal configuration (minimizing the number of resistors required) for creating an equivalent resistor from a fixed set of resistors. I'm not so much looking for an exact algorithm but rather a general heuristic for choosing the configuration.


texts: EEG amplifier circuit low and high pass filters. Oscillations, noise, etc

texts:
I designed a EEG amplifier circuit for for EEG signal amplification and filtering.

Because I never had any experience in filters, It would be highly appreciated if someone could check my design.

In general circuit looks like this: AD620->Driven Leg->DC-restoration(offset correction)->two passive filters(low and high pass) before amplification->regulated amplifier, gain 1..25->2nd order active high-pass, gain 1.5->4th order active low-pass, gain 30->passive high pass->to ADC

50 hgz hum cancellation done with Driven Leg.
Offset correction schematic, DLR block and AD620 are not shown.

The first my concern is oscillation.

I am going to use TL084CN op-amps. And their oscillation can be a problem.

The second my concern is filter design. I used online tools for filters design:

http://www.analog.com/designtools/en/filterwizard
http://sim.okawa-denshi.jp/en/OPttool.php

According to okawa-densh tool some of the filters will oscillate. For e.g. Oscillation frequency for 1-st stage of low-pass second order filter:

f = 71 [Hz]

For High-pass filter:

f=0.16 [Hz]

Is it normal?

I simulated circuit in LTspice, images below. Graph is frequency response. Lines on graph marked with dots on the schematic.

Thank you.


texts:
I've been trying to get a Colpitts oscillator to work with multisim, following this schematic, which I found in a book (I just copied it):

Yet, it does not work, all I get is a 0 voltage signal from the oscilloscope.

The same circuit, simulated in LTSpice, worked fine:

So, does anyone with experience in multisim know how to get this simulation to work? A similar oscillator in the "examples -> miscellaneus circuits -> claposcillator" works great, adn the book where I found it also simulated it in Multisim and according to it, simulation works fine as well (book is Electronic devices eighth edition, by Floyd, page 84X)

Here are some of the things I've tried:

Add a AC voltage source with low voltage to simulate noise
Change the values of the capacitors to the ones in the LTSpice figure
Try different transistors and components


texts: Is there a safety issue with halogen bulbs if the outer glass envelope comes off leaving exposed wires

texts: If the bulb fails and outer glass envelope becomes detached is there a safety issue with the inner exposed wires between the small inner bulb and the bayonet cap?


texts: decreasing base current on saturated npn transistor

texts:
I would like to know if decreasing the current at the base on a saturated transistor(as in the attached photo) will cause the transistor gain to increase and by that, to maintain the collector current.
For example: in the saturated NPN transistor at the pictured, the gain is x10.So the Ib=2mA,Ic=20mA and the Vce=0.2V.
Let's say that the gain of the transistor in the active state is x100.
If I decrease the Ib current, will the gain of the transistor rise and keep the same Ic current(20mA)?
Also, can the Ib be decreased  more and more while maintaining the Ic(20mA)until it reaches its maximum gain(x100)?
If, for example, the Ib will decrease to 1mA and the Ic in result will fall to 10mA, the voltage drop on the transistor(Vce)should be 3.6V(9V-2V-(340ΩX0.01A).
So, doesn't the gain of the transistor be increase by X20 and cause the 1mA to be 20mA again, while keeping that behavior(maintains the same Ic, while the Ib gradually decreases) until it reaches its maximum possible gain?
Thanks in advance.
UPDATE!

I meant that when i find the working point of the transistor by cross line the Vce and the Ic(red dot)at the active area,i can find the Ib current in the graph(150uA)and also calculate by this the Hfe at this point(16mA/0.150mA),but when i find the working point of the transistor by cross line the Vce and the Ic(blue dot)at the saturated area(the area on the right of the diagnol common line/the brown arrows)the graph can't tell me nothing about the Ib current or its Hfe as the other case,does it?it seems that it only shows me that it is in saturation state without any values that i can determine by the graph at that point.Am i right?.


texts: MMA8452 high quiescent current consumption

texts:
I have designed a PCB where I am using the MMA8452Q accelerometer.
Because it is a battery powered device, we want to ensure that we are using the lowest sleep current states of all the components on board.
However, while testing we noted that the accelerometer is still consuming ~30 uA of current in system sleep state, even though firmware has put it in low power mode with ODR of 12.5 Hz. In our application, we just use INT1 to identify any interrupt and convey it to the MCU whenever set orientation threshold is crossed.

I have a couple of queries:

I have decoupled VDD (pin 14) with 0.1 uF and VDDIO (pin 1) with 4.7 uF. Datasheet suggests the opposite. Can that be a reason for the heightened current in low power mode?

SA0 (pin 7) is hard-wired to GND. Is this affecting the quiescent current in low power state? Maybe there's an internal connection in the chip to some power rail which is creating a current flow path.

Any help would be appreciated.


texts: Are all electricians qualified to work with simple relay logic?

texts:
I hope I'm asking this question in the right place. I have an idea for a product that would be installed at certain types of businesses. It's a very simple relay logic system that would be connected to A/C power.

I drew up the schematic for the circuit and it runs properly in a simulator. However, not being an electrician or electrical engineer, I'm well aware that there are too many practical concerns related to implementation for me to hope to get it right, and I wouldn't be able to install these systems regardless because I'm not certified to do so.

Which means I need to find an electrician to partner with.

My question is this: although I know that there are those who specialize in relay logic, would I need someone with that specialization for my relatively simple case? Or is relay logic something that some electricians can (or should) work with, and others not?


texts: I had some problems setting up a Opto Coupler today. The data sheet is here. I set it up putting a 470 ohm resistor to ground from the cathode (pin 2). I am understand the selection of this resistor as it is used to set the current through the LED to about 10mA when he ANODE(pin 1) is given 5 Volts. What I don't understand is why a 270 Ohm resistor(as shown in the test circuit) is needed between pin 4 and 6. From testing I know that with the 270 resistor I get a range of about .2 to 5 volts on the output, and without the outputs range is 0.08 to 1.4 volts. I know its something to do with the biasing the circuit and the gains from the internal transistor... Wondering if someone could point me towards a source that actually explains how to bias a opto coupler... its been a few years since I played with transistors.


texts: Why is there a resistor in a cmos X-OR gate?

texts:
While reading up on logic gates i came across this image on Wikipedia:

According to the article, the resistor on the supply voltage for the inverter is necessary to ensure that no current is leaked from the inputs to the output but i don't see how that would be possible regardless of the resistor being there or not.

From what i've read, one of the benefits of mosfets is that the input impedance is high and thus any current leakage would be insignificant.

The statement in the article is marked with a [citation needed] so i suspect it might be false but i can't find any information to confirm or disprove the statements validity.


texts: Use a power bank instead of batteries for a LEGO train

texts:
I'm tired of charging and charging batteries for my LEGO train. It takes 6 AAA batteries. I have several questions:

6xAAA means the motor needs 9V, right?
When using rechargeables they only supply something like 1.2V, so the motor is slower? Or are the batteries empty more rapidly? How does that work?
I want to use a power bank that has fast charge ability (ie supply 9V) and hook that up. How do the AMPs play into this? And will that automatically switch to fast charge (9V, 2A) when the motor needs that?


texts:
I'm a total beginner with programming ARM microcontrollers, but I do have experience with AVR and PIC microcontrollers.

A few days back I have purchased a STM32F103VET6 development board from eBay. I'm now trying to program this board but I don't know where to start. I have also received a CD which contains some datasheets and some documents (all in Chinese).

Could someone tell me how to start? Or does someone have some source samples?

I have already installed Keil uVision4. I also have a J-link debugger.


texts: Proper way to route high-voltage tracks near THT components

texts:
I think this is not a duplicate of this question.
My design has the following constraints:

type and position of connectors
pinout assignments
260 VDC / 2A for high-voltage tracks
12V / 200 mA for low-voltage tracks

Here a part of my layout. It's repeated identically for every sector of the circular PCB:

Let's call the square pad of the connector pin 1:

Pin 1 and 2: high-voltage tracks (260 VDC / 2A)
Pin 3 and 4: low-voltage tracks (12V / 200 mA)
pin 5 and 6: low-voltage (signals) tracks (5V / 1 mA)

The connector pitch is 3,5 mm in X and 3 mm in Y. They are Molex 172316-1206 and can withstand 400V / 11A.
For pins 3..6 I have no problems.

My concerns are about pins 1..2, in particular how to properly route the tracks between pin 2 and the middle pad above. I'm afraid about the isolation between bottom track (blue) and the nearby pads.

The track is 32 mil width (to maximise isolation) and the distance to the left and right pads (one is the capacitor, the other pin 1 of the connector) is 2.2 mm from center-to-center. The real creepage between the track and the outer ring of the pad is about 1 mm.

I checked here the needed spacing for 300 VDC isolation:

IPC-2221B:
    external   1.25 mm
    internal   0.2 mm
    coated     0.4 mm

I'm not sure (even reading the description in the page) what does "coated" actually mean.

I'm working on a standard PCB with 2-layers and solder mask on both sides. I have to consider my tracks as "external" or "coated"?


texts: Why are modern telephone lightning arrestors less prone to (rectification) RFI problems than old ones?

texts:
I was reading about telephone lightning arrestors in my ARRL RFI Book (first edition, copyright 1998), in chapter 9 "Telephone RFI" (by Pete Krieger, previously WA8KZH, now K8COM) and on page 9.6, the following is stated (emphasis mine):

  The Lightning Arrestor

  Telephone service enters a house at a grounded,  fused lightning
  arrestor located outside at the house end of the telephone company
  drop. Years of exposure to weather or moisture can cause corrosion or
  discoloration (onset of corrosion) of wires, junction boxes or
  components inside the lightning protector housing. If the arrestor is
  accessible, a good visual inspection may reveal  potential problems.
  Lightning arrestors, especially those that have done their job a few
  times, can become nonlinear, acting like a diode, rectifying any RF
  energy present on the phone lines (just like the crystal radios many
  hams built in their early years).  If you discover that a lightning
  arrestor is creating RFI, the fact that it's rectifying RF is one
  indication that it needed to be replaced anyway!  Modern arrestors
  are less prone to RFI problems than older ones.

Just a few notes about this quote... This is the entire (small) section, so this is likely all the information that I have behind my question.  Also, the context does indicate that the lightning arrestor is standard telephone service equipment, and therefore part of a standard land-line telephone installation; therefore, this question may be limited to only standard telephone company equipment. Quite possibly, it may be a broader generalization -- I just don't know.

So, it's that last sentence that piqued my interest.  Why, exactly, are modern lightning arrestors less prone to RFI problems?  Is it more even "wearing" so it doesn't become a diode? Is it a better design, so it lasts longer and fails more gracefully?

EDIT:

I emphasized the "diode" aspects of the quote from the book a little more in preparation for making the following request:

I would like to argue that for me to accept an answer, your answer has to show either how semiconducting happened more frequently with the old style, or alternately show how semiconducting happens less frequently with the new style.  This is because I can't really decide between the two really great answers already given.  How did a lightning hit (or moisture, or time) cause carbon blocks (the old style) to semiconduct?


texts:
OK so the car manual says not to stick items into the car's USB port while starting the car. Like any good engineer(ing student) I tried to see what will happen if I did so, and am now the proud owner of a few dead USB sticks. So yes, the manual wasn't kidding.

Without going through the hassle of sticking an oscilloscope into the USB car ports, I presume that some kind of voltage spike must be going through the USB port when the car engine is started. What causes it? The current surge in the starter motor circuit causing an inductive current pulse in adjacent wiring from the 12V battery to the USB port?

It is somewhat tedious to remember to remove items from the USB port before starting the car, so I was wondering if we could design some kind of surge protector for the USB port to prevent it frying sensitive electronics.

Any comments on my attached circuit diagram? What capacitances and inductances would you suggest, absent any tests with an oscilloscope to quantify the surge size and times? (It is OK to over-engineer it)

Would you also recommend similarly protecting the data in/out ports of the USB output, just in case?

Regarding the question about the car model, see a similar warning from a Youtube video on another model of car. Kia USB port video


texts:
I was reading about the radio telescope - Murchison Widefield Array (MWA) situated in western Australia. Antennas of this telescope are quite unique and different from usual dish radio telescope. In MWA a four by four regular grid of dual-polarisation dipole elements arranged on a 4m x 4m steel mesh. So, I was wondering why these dipole elements would have been placed over the mesh, on searching over internet I found out that this mesh is called as counterpoise (though I am not sure if I am correct or not) further I read about it and partially understand that these mesh and ground (Earth) act as two plates of capacitor but I didn't get why it is done and what's use of it?

MWA antenna - image courtesy: SKA


texts: Why is only one out of 2 batteries is discharging when connected in series?

texts:
I am using 2 Lead-acid batteries to run a DC motor. (Say battery A and /battery B). Both had potential of 12V before starting the motor. After two hours of running the motor, battery A still had potential of 12V, but the battery B showed 0V. Does this mean only one of the batteries is discharging?
If yes, why?

Battery spec is 24V, 350 watt.


texts: Explanation of the result of a solved exercise concerning the unit step response of a system

texts:
I came across a solved exercise regarding Signals and Systems in which there is a system with impulse response \$h(n)=u(n)\$ and input \$x(n)=u(n)\$. The goal was to find the output of that system (unit step response).

(Note that \$u(n)\$ is the unit step)

So the solution begins saying that the output is the convolution between the input and the impulse response which is:

$$y(n)=x(n)\ast h(n)=\sum_{m=-\infty}^{\infty}x(m)\cdot h(n-m)=\sum_{m=0}^{n}1=n+1$$

After that the solution concludes that the output is:

$$y(n)=(n+1)\cdot u(n)$$

Everything is really elementary and I probably miss something here but how does the term \$u(n)\$ appeared in the output? Wasn't proved that the output is \$n+1\$?

Exectly the same happens in another one concerning a system with \$x(n)=h(n)=a^{n}
\cdot u(n)\$ where although \$y(n)=a^{n}\cdot (n+1)\$ the result eventually is said to be \$y(n)=a^{n}\cdot (n+1)\cdot u(n)\$.


texts: ARM: Read the value of an Alternate Function pin

texts:
I have an ARM STM32 where each GPIO pin can be configured as "input", "output", "analogue" or "alternate function". In "alternate function" mode, the ARM drives a lot of the logic for basic communication protocols, removing some of the grunt work for the programmer.

While I have been able to "read" the value of input and output GPIO pins using the standard library functions GPIO_ReadInputDataBit and GPIO_ReadOutputDataBit, I cannot seem to be able to read the value of alternate function pins without using a scope.

Is there a way to query the ARM about the value of its alternate function pins?


texts: Maximum Bluetooth LE devices near each other

texts:
I am planning to put 100+ Ruuvitag beacons(Bluetooth LE tranmistters) in a ~120m2 area. There will be approximately 1 meter distance between devices. I need to get their advertisements at once(each beacon will send data every X minutes) using Raspberry Pi Zero.

Something like this:

Any idea how many Bluetooth LE devices can transmit advertisements at once without interefering with each other?
How many advertisements do you think a single receiver could receive at once without problems?


texts: Would 5.5 x 2.1 mm male plug work inside a 5.5 x 2.5 mm female jack for DC power?

texts:
General Question

I am wondering, is it possible to use a 5.5 x 2.1 mm male plug inside a 5.5 x 2.5 mm jack for transferring 12 Vdc?

My thoughts are just that it may just be a tight fit on the inner conductor.  It may also just not fit.  I figured before spending money and waiting a few days to try it out, it was worth asking here.

My Use Case

I have an Intel NUC, which can be powered off 12 Vdc via a 5.5 mm x 2.5 mm jack:

  The back panel DC connector is compatible with a 5.5 mm/OD (outer diameter)
  and 2.5 mm/ID (inner diameter) plug, where the inner contact is +12-19 (±10%) V DC and the
  shell is GND.

Source

And it seems the 5.5 x 2.1 mm plugs are much more common, so I would like to use that.


texts:
I've got SN74LS93N chip that I am trying to get to work.
I connected it as per datasheet but instead of counting, all outputs are flashing with clock signal...

Video to circuit

I read online and found advice to connected all unused pins to ground (not on this video) but the result is the same... Am I doing something wrong?

Thanks
pete

EDIT:

Posting how I connected the circuit. I used Falstad - Hope it's okay..

Circuit

EDIT2:

I built the clock as per Ben Eater's instructions from YT.
Schematics below

Clock Schematics


texts: Sizing a trace on a PCB to carry 50 amps

texts:
Currently working on a 4 layer pcb-card where I need to trace for 50 amps, any ideas how I can design it?

Any tips would be appreciated. Thanks!


texts: What is the current path when you touch the 230 V outlet?

texts: The outlet's potential is 230 V, the earth's potential is 0 V. The person touching the outlet will get shocked, but why? What is the path that completes this circuit so current will flow?


texts: Can I replace D cell with AA cell in an electric train?

texts:
I have an electric train powered by 2 D cells. But they are quite cumbersome and I have only AA charger and a bunch of good quality AA rechargeable batteries. So I want to tweak my electric train and make it run on some amount (to be calculated) of AA cells. Is it possible?

(will current given by AA cells be enough, maybe there are some other factors why producers put D cells and not AA cells)


texts: using sig generator and scope as TDR for troubleshooting ethernet

texts:
I had some problems with a new run of cat5e. I have already established it's definitely a damaged cable using a cheap network continuity tester and double checking my wiring and crimps.

I saw on YouTube there are people using a signal gen and scope as a DIY TDR.
However I don't have a signal generator and my scope is a cheap tenma(farnell brand) scope with a 40MHZ bandwidth I believe.

Is it possible for me to build an oscillator that's within the bandwidth of my scope and use it as a tdr to locate where the fault is? This is just for fun really.


texts: Smartest way to charge 18650 batteries when they are used in series

texts:
I'm wondering how I could/should charge the 18650 batteries used in the following circuit. I want to charge them via USB in a power bank case like this.
But I probably won't be able to use the existing charging circuit because I'm using the batteries in series to get more voltage.

simulate this circuit – Schematic created using CircuitLab


texts:
I am loading the following code into ATmega32A PU 1535 to flash the LED on pin 40, PORTA 0:

#include <avr/io.h>
#include <util/delay.h>

#define __DELAY_BACKWARD_COMPATIBLE__

#ifndef F_CPU
#define F_CPU 16000000UL    /* 16 MHz clock speed */
#endif

int
main(void)
{
    DDRA |= (1<<PA0);              /* Nakes PORTA as output */

    while (1)
    {
        PORTA |= (1<<PA0);         /* turn 1st led on */
        _delay_ms(150);            /* 0.15s delay, but is on by 10ms actually */
        PORTA &= ~(1<<PA0);        /* turn led off */
        _delay_ms(10);             /* delay 0.01s, but is off by 150ms actually*/
    }
}

LED blinks but as pointed in the comments LED is on 10ms and off 150ms. How it is so? The only way I can get this result is that delays are actually called before IO, like this:

        _delay_ms(150)
        PORTA |= (1<<PA0);         /* turn 1st led on */
        _delay_ms(10);
        PORTA &= ~(1<<PA0);        /* turn led off */

Since _delay_ms doesn't warn against compiler optimizations nor it gives any special hints in that direction I must be doing something wrong.


texts: What are the correct ways of connecting a long distance analog sensor?

texts:
I'm hugely new to electronics. I'm about to place some outdoor sensors around the house and those should be accessed by a Raspberry-Pi which is in middle of the house. I'm aware about setting those analog sensors with RPI with ADC modules.

However, my concern is that all of the sensors are around 30m radius from the RPI. What are some good methods of connecting those sensors to RPI?

WIFI/Bluetooth: I would need to place a wifi/bluetooth capable module with every sensor.

Radio: This sounds complicated.

Cables: 30m cable could generate lot of noise level. But I'm open to use this method with proper knowledge, if someone like to offer.


texts: Why are servo motors geting weaker in a few minutes?

texts:
What I am experianceing is very weird but I will try to explane it as best as I can.

I have a simple robot arm with 4 Degrees Of Freedom (DOF). This is not a robotics problem but thought it would be better to write what I am doing. I am using a Turnigy TGY-S901D servo motor at each DOF. Each motor has an encoder that you send a command (via RS-485).

So look what happened a few days ago. I plugged it in my computer and send a command to the base motor (first DOF) one time and it worked find. Then did the same thing to the second DOF, again everything was fine. I did this for all the motors (all the DOF).

Then tried to move the first DOF again but it moved slower and not to the correct position, it needed a few degrees more. Send the same command (after I put the motor to its origin position) and it moved even slower and was even more far from the end goal. After 3-4 commands, it ended up not being able to move at all. I can hear it trying to move but with no success.

The same thing happened, after, with all the other motors. With each new command they moved slower and with a bigger error.

After that, I left the robot arm for a few days. Today I tried again to use and the first DOF does not work at all but all the others acted they way I discribed above. The first time everything worked fine and every new command made them slower.

Important NOTE: In the past I was able to use it just fine. Never had this problem. This problem appeared last week for the first time.

It is like it gets tired. Does anybody know why this is happening?


texts:
Looking to use a relay with ardiuno but having a hard time trying to figure out what transistor I need to use, all the tutorials I can find always use an example transistor (usually 2N2222) to figure out what resistor to use, but not how to select a proper transistor in the first place. Once I have a transistor that is properly suited then I should be able to use those previous guides to figure out what resistor I need for arduino.

Can anyone enlighten me on how I should go about selecting the proper one for my needs? You're more than welcome to tell me what would work (properly suited not overkill) but I'd also like to know how to figure this out for future projects.

Note: The relay will be powered by a separate power source and not from arduino. Relay is not going to be located on or near the circuit board (remotely mounted) hence choosing a relay with a built in flyback diode.

Relay: 301-1A-S-D1-12VDC

Coil resistance: 123 Ohms, Coil Current: 97.5 mA
https://www.mouser.com/datasheet/2/378/301-2555.pdf


texts: 50 hertz sine wave in oscilloscope when I touch it

texts: I bought a new PicoScope USB oscilloscope and noticed that when I touch the tip of the probe with my hand I see a 50 Hz signal of 2 volts on the screen. What is causing this? (Or rather, how is the mains 50 Hz sine wave getting through me to the scope?)


texts: How do I test a circuit without an oscilloscope?

texts: Just what the title says; I'm playing with simple beginner circuits, signal amplifiers and stuff. Without fancy laboratory equipment such as an oscilloscope, how should I test the output signal is amplified ?


texts: How to model charge leakage in N-Channel MOSFET?

texts: What a square wave voltage is applied to the gate of the MOSFET, there seems to be a voltage leak between the gate and the drain. Can I model this voltage leak using resistors and capacitors? Also, is there an equation that describes this voltage leak?


texts:
I would like to force my STM32F4 to reset on fault, I tried to copy NVIC_SystemReset in assembly as :

    .section  .text.Default_Handler,"ax",%progbits
    Default_Handler:
        dsb
        ldr     r0, =0xE000ED0C
        ldr     r1, =0x05FA0007
        str     r1, [r0, #0]
        dsb
    Infinite_Loop:
        b  Infinite_Loop
    .size  Default_Handler, .-Default_Handler

But it does not reset, the program simply hangs. Is it because Default_Handler is an interrupt ? Did I miss the obvious ?

NVIC_SystemReset works fine in user space.


texts: How to design 125Khz Antenna for 1 meter RFID reader

texts:
Firstly, I'm not from electronics background so my knowledge is limited in this area.

Target System - I am looking to build/ extend the range of 125khz RFID reader upto 1 meter (~ 3ft) to be captured while walking through a gate detector (kind of like two pillar antenna in pic below).

Reason: Commercial gate readers are way too costlier to implement so am looking to build my own.

Current State - The below current 10x10cm loop antenna provides me a range upto (~1 ft).

Question: How do i design an Antenna in such a way it has a read range of 5 - 6 feet (throughout the height of pillar) and having read distance up to 3 feet (distance where the tag is presented)? Here the read range is as important as the read distance.

Considerations:

Going for a RF Gate Antenna (the ones you find in clothing store) and plug & play with RFID reader?
Increasing the size/ length of the antenna coil but maintaining
the same inductance.
Adding multiple small antennas (like an Array) across the length of the pillar.
Making a dual loop antenna to cover the broader range.

Any help would be appreciated towards moving from my current state to target? I prefer to stick with 125 Khz LF frequency range.

Many thanks!


texts: Why 10Log(p1/p2) and 20Log(v1/v2)? Why not just 10Log(x1/x2)?

texts:
Based on my very basic current understanding of decibels in electronics, it is said that I should use the db = 10Log(p1/p2) formula if I want to calculate the power ratio in db between two values and the db = 20Log(v1/v2) formula if I want to calculate the voltage (or current) db ration between two values.

Although I understand how these formulas are derived, I don't understand why we need two formulas (one for power and one for voltage), are two formulas really necessary? I am asking this because as far as I understand, the calculated db value by itself is just a ratio between two values and if that is the case, isn't a ratio just a ratio and nothing more?

In other words, in my head, a doubling of power or doubling of voltage is the exact same thing! Both values are being doubled so I would expect the same db ratio result from both comparison (power and voltage). Below are two examples:

Example for power:

P1 = 200;
p2 = 100;

db = 10Log(p1/p2) = 3 db.

Example for voltage:

v1 = 200;
v2 = 100;

db = 10Log(v1/v2) = 3 db ... (notice not using 20Log(v1/v2) formula here)

The logic above makes sense to me because I see doubling as doubling, it does not matter to me if we are doubling power or doubling voltage, both measurements are being doubled so why should't they have the same db value? Specially since we already specify watts or volts on the db units result (dBm, dBv dBu, dBc, etc)?

What am I missing?

Thanks.


texts: I need to create a circuit that sends out a signal only if the input it on for longer than a specified time. Lets say 20 seconds for this example. So if the input to the circuit was pulled high for 10 seconds no output would be sent, but if the input was pulled high for 21 seconds an output would be sent and it would be held until reboot or a reset button is pressed. I looked into 555 timer circuits, but I couldn't figure out how to achieve this without building a lot of discrete logic. I am also not allowed to use a microcontroller for this, but could potentially use an FPGA or PLC.


texts: I'm trying to design and build a simple ac/dc smps that outputs 5v dc and capable of 2 amps. I currently have it mostly designed using a nmos but the problem I'm running into now is how to get a pwm signal with 18V. Is there any advantage to using a PMOS or a NMOS or vice versa? I need to build this soon to stay on track for my project so any input is helpful! I was thinking of using a microcontroller to do the feedback but I understand that I will need a gate driver for it also. I'm not the strongest at programming so I am interested in seeing if there's any ic's or circuitry that I can design that will do the feedback for the pwm input for the gate of the mosfet. I imagine I would still need a gate driver for that option too. I appreciate the help.


texts:
Is there any Phase difference between the current in primary and secondary coils of a transformer?

If I draw the diagram of a transformer, and try to find-out the direction of current using Lenz's law; if I keep the coiling-pattern of primary and secondary coils Same (Say both as righthand-screw, or both as Lefthand-screw); I'm getting an 'opposite', i.e. 180-degrees phase-shifted currents in the 2 coils.

is it the case indeed?

However I do-not know, in which-way Lenz's law acts in transformer; because the law states the induced current will try to hinder the cause. but when the secondary circuit of a step-up transformer turned On (closed) , so-far I've know , the current in primary-coil goes-up

P.S.

However, since
Amount of Induced-current depends upon CHANGE-rate of magnetic field (Faraday's law),
=> Amount of current induced in a secondary coil (at a moment), is proportionate with  CHANGE RATE of current of the Primary coil;

&

NOT on the  CURRENT in primary coil directly (though it apparently seems from the graph).
So, same phase-state of primary coil and secondary coil means, in AC, the Graph for Current, and the graph for Change-rate of current, is same.  I want to know also, am I right? because, if it was not, then surely a phase difference would found.


texts: Paralleling power supplies for higher current

texts:
I am looking at using two Cincon (CFM80S240 and CFM60S240) power supplies in parallel to achieve a higher current output. Is this possible? If so, can I just hook them up in parallel, or is there some specific way of doing this to prevent one from "fighting" the other?

Both power supplies are rated for 24V with 1% ripple and noise, +/- 1% voltage accuracy, +/- .5% line regulation, and +/- 1% load regulation.

Ideally, this would be possible since they would both be the same voltage. But, due to tolerances in manufacturing, there is no guarantee that they would be identical voltage outputs.

I wasn't sure if I should also hook up a capacitor in parallel with them to help stabilize the output voltage.


texts: Is ferrite correct material to use for a DC current sensing application

texts:
I am trying to build a non-invasive current sensor using a hall effect sensor and ferrite core.

I am using a hall effect sensor sandwiched between 2 halves of a ferrite core like this: ferrite core - digi-key
I grooved out the core with a dremmel so that the hall effect sensor can sit inside and allow the flux lines to pass through it.

It works well until the ferrite core magnetizes after the wire being sensed has current flowing through it long enough..

Is there a better material to use other than ferrite that will allow flux lines to pass, but not become magnetized?


texts: I am not very sure about how to completely solve this question. I tried to calculate the equivalent impedance by C and R and got R/(1+jwRC). Then I calculated the transmittance by using the voltage divider rule and got G(w) = (1+jwRC)/(2+jwRC). Which shows me that at w=0, g = 1/2 and as w goes to infinity g approaches 1. Am I right? Is this enough for the solution? What about the characteristic frequence and magnitude/phase responses? Which type of filter is it?


texts: Figuring out a substitute for an old amp capacitor #2

texts: What type are the yellow caps in the picture and what do I substitute them with?


texts:
There are some vias in my layout which I can't move after having selected them and holding left click. It displays a white cross after selection.
I have checked that those vias are not locked and they are not.
Any idea what I can do ?


texts:
I have a microcontroller which needs to communicate over a cable, which will be approx. 5m long, with another very small microcontroller. The devices will be used outdoors in various conditions. The data rate will not be very high. When you connect the small uC with the cable to the big uC, a identification string and periodic (each minute) battery updates are sent from the small uC.

I thought about I2C but I'm not sure if it is designed for such needs? CAN is also possible but I think it´s a little bit overkill for my needs. Does anyone have good ideas?

EDIT:
I want to use as few pins as possible for the cable.


texts: I’m working wth a closed system (black box), and try to figure out what it consists of. When introducing a current below 400 mA, the current stays constant. When the current exceeds 400mA it drops to 80 mA where it stays constant. What might be hiding inside? Some arrangment of capicators? Or would that stop the entre flow of current?


texts: on a network analyzer's measurement what's the meaning of a negative PF?

texts:
on a 1 MVA transfomer, process in the place is plastics injection machinery. On the plotted data from an analyzer results in PF jumping from 0.998 to -0.997 (roughly) for all the measurement period but staying at positive when power consumption decreased, going deeper i could see kVAR value being negative. I just don't understand the meaning of that. or maybe the analizer was poorly connected?
Could you share your ideas o this?


texts:
Can someone help me understand the working of this circuit:

My questions :

Please explain me how this circuit will work in its entire operation range.
I am not able to understand the purpose of the Zener diode and the 10K parallel combination. What purpose do they actually serve in this circuit?
The Q2101 transistor does not have a base resistor to limit its current. Isn't this circuit wrong?


texts: What's a conceptual way to understand ohm-cm?

texts:
Resistivity is defined in units of \$\Omega \times \textrm{cm}\$. I don't conceptually understand what is meant by the unit.

If it was \$\Omega / \textrm{cm}\$, that would be easy to understand - a certain number of ohms for every centimeter. How can one understand \$\Omega \times \textrm{cm}\$?


texts: Pull-up resistor I2C value; R(min) formula approximation

texts:
For pull-up resistor of I2C, I have found formula to determine R(min).

For a device with; 0,4 VOL(MAX) at 3mA IOL
The calculation can be done for VDD = 5V:

R(min) = (5V - 0,4) / 3mA = 1533 ohm.

The thing i cannot understand. Here we assume that over the transtor; there will fall 0,4V and 3mA, when using this resistor. But we do not know exactly if we use 1533 ohm, that 3 mA will flow so 0,4V will fall.

It could also be that there will fall much lower voltage; lets say 0,2V at 1,5mA (or higher voltage and current)

Then R(min) = (5V - 0,2) / 1,5mA = 3200 ohm.

So the question is; how do we know that there will fall exactly 0,4V when we use 1533 ohm, so 3mA will flow. Is this an approximation we do? because we truly need loadline and characterics to do this exactly?


texts: When the Gain Margin is negative, for what range of frequencies is will the output resonate out of control?

texts:
If your system/transfer function has greater than zero gain for the frequency associated with -180 degrees phase, the system is said to be unstable. What does this mean for other input frequencies?

Does this mean that any input frequency would result in an unstably growing output? Or just a certain range of frequencies?

Bode plot for use as reference:


texts:
I have ADXL345 digital accelerometer by Analog Devices. I use Beaglebone ADXL345 library that exist here: http://inspire.logicsupply.com/2014/08/beaglebone-3-axis-accelerometer.html

So I can read the accelerations at X,Y,Z axis. However, when I placed the board at plate surface, it reads X and Y accelerations as -0.728G and -0.788G. They should be zero. How to calibrate this accelerometer?

In addition, it reads stable z axis accelaration as 2.044G. It only changes If I reverse the board. I dont understand. What does it mean?

my ADXL345 board:


texts: INPUT 100-240VAC - will it only work with Voltage Rating within 100-240 ?

texts: Written on my Smartphone Charger is: INPUT 100-240VAC. Does that mean it will only work with Voltage Rating within 100-240, not higher than 240, and lower than 100 ?


texts: Why would using full buffers cause problems?

texts:
When reading docs on Smbus2, a Python i2c library, I found this statement:

It is possible to write 32 bytes at the time, but I have found that
error-prone. Write less and add a delay in between if you run into
trouble.

I thought alright, I'll use less. But then I thought maybe I should not use the full buffer on the microcontrollers i2cs and other networks I work with. But that's inconvenient. Does anyone know why using a full buffer might cause errors? Would it be a good practice to always use a part of a buffer and not the entire buffer for i2c?
Edit: I just realized the smbus2 doc doesn't mention the buffer size explicitly. It occurred to me maybe there are chips with buffers less than 32 bytes. I started working with i2c recently have only seen 32 and 64 byte buffers.


texts: I understand the point of an LC circuit in a Tesla Coil: add an increasing amount of energy to the circuit with each cycle in resonance, but how does the Primary Coil complete this? Specifically, I was wondering about the Spark Gap. I understand that the Spark Gap, once it fires, will complete the Primary LC circuit so it can resonate. But does resonance occur after the spark gap has fired, or while it's firing? Because with resonance, electricity would have to flow back and forth. So is that what's happening in the spark?


texts: How can I make a toggle switch for two LEDs?

texts:
Please see this following link.

That's exactly I want to make but with little change, In place of a single LED I want to place 2 LEDs (not combined). I mean let's say we have 2 LEDs - one red, one green

When I press switch once, red LED should glow and green LED should be off again.

When I press switch again, green LED should glow and red LED should be off.

I'm new to electronics so please don't suggest me any complex circuit designs, just keep it simple ;] friends


texts: How do modern CPUs treat memory operations?

texts:
How does a modern CPU treat memory reads and writes on the hardware level?
With old 8-bit architectures all memory locations are read and written to one byte at a time, but how do modern CPUs that have much wider data buses treat 8-bit memory?
What would a modern CPU like an x86 or ARM based CPU do if it needs to read and write a value in memory which width is less than it's data bus width? AFAIK modern architectures read and write memory in chunks, so would it read and write several memory locations at a time then?


texts:
I am trying to figure out how long my project will last on a single battery. It's powered by a single AA battery with an NCP1402 3.3 volt boost converter. I've determined that the target circuit draws around 75 µA at rest and around 250 µA for 35 ms per second. I could just run that number, assume the boost converter is 80% efficient and go with the result (which is around 2 years or so), but I would like, if possible, to validate that experimentally.

I have a µCurrent Gold, and hooked it up to my Rigol DS1052 scope to get the numbers above (with a bench 3.3 volt supply and the circuit on a breadboard). But when I repeat the experiment with the boost converter, what I see is a complex waveform with peaks at around 1 mA which decays down to 0. Not only that, but it's quite irregular. I can't make any sense out of it.

I've discovered my scope does have an averaging function, but it doesn't help - it can't gather enough samples into the average to make a difference.

My big concern is that the boost converter efficiency may be way, way lower than 80% at such a low draw, but I can't really verify that.

I did try just using a multimeter (still with the µCurrent Gold), and I get an answer of 450 µA. That would last around 9 months - still acceptable, but is it correct?


texts:
I am attempting to do a Monte Carlo simulation of a basic current measurement circuit using SiMetrix.  The current goes through a sense resistor, amplified by an op-amp and then to an ADC.  I'm trying to include the error of the ADC in my simulation, but I can't figure out how to randomize it.  I found that the total error contribution of the ADC is +/- 5mV.  How can I add that error to the output of my op-amp for use in a Monte Carlo simulation?  I would like to make it a Gaussian distribution, similar to what you do with resistor tolerances.  The problem with gauss is that it is a multiplier, and therefore would not give me any results centered about 0 (0 * multiplier = 0).  Here is the sim schematic:

Option 1: Sine wave voltage source in series with output

This option will add or subtract 5mV from the output signal in a transient analysis, but it is not random.

Option 2: Current source in parallel with a resistor with gauss tolerance

This option would give me the distribution I want, but I don't know how to get the current to randomly switch directions or magnitude (to give me +/- 5mV max).

Option 3: DC voltage source in series with the output

This option would give me a static 5mV offset, but this is not useful in Monte Carlo sims.

Option 4:  Noise source?

Could a noise source accomplish this random behavior?  I was ultimately trying to get a gauss distribution, but I would be happy with pseudo-random.

Option 5: Voltage controlled voltage source

I could use a voltage controlled voltage source with a gain set to 1 and some distribution about 1.  The problem with this method is that it would have less effect at lower voltages since it is ratiometric.


texts: How can I model the LC output filter for this BTL audio IC using SPICE?

texts:
I am using a Texas Instruments TAS5717 in a design. It is a 10W audio class-D amplifier.

For my design, I have copied the schematic from the evaluation board, shown on pg. 17 of this PDF. I used the values for the inductor and capacitors as shown, and things "work" on a prototype spin of my board. I would like to characterize and fine tune the circuit now. The current inductors are quite bit and my board size limited. I would like to know how switching to smaller inductors will impact the circuit.

Here is my schematic of the output filter:

While looking for more material on this subject, I came across this TI document on class-D LC filter design. Inside, it explains the differences between "AD" and "BD" modulation. It also shows some nice plots of impedance vs. frequency and gain vs. frequency for selected components.

One of my issues is that the evaluation schematic does not match up exactly with the schematic shown in the LC filter design guide. (C7/C10 and R55/R56 are not present. What do they do? - Edit: I learned C7/R55 and C10/R56 are RC snubber circuits to aid in EMI suppression.)

I will be using this device in "BD" mode, unless there is a compelling reason to use "AD" mode. (ie C9 not placed).

I would like to be able to characterize the evaluation schematic filter and experiment with different parameters to see the effect, and create plots similar to those shown in the LC filter design guide. Is there a way to model this "BD" filter in PSPICE/LTSPICE?


texts: How to get a simplified circuit out of three smaller circuits?

texts:
I completed the three basic tasks in three independent circuits; however, the optional part is a bit confusing for me; how could I simplify them in one single circuit? Should I find inspiration in the truth tables or in the logical formulas of the 3 circuits?

I tried using boolean algebra manipulation to split them in a general circuit, but failed. How could I approach this? I need to implement it in a diagram, posteriorly build it on a breadboard and I can only use OR AND NOT gates.


texts: Battery holder for protected 18650 battery

texts:
When placing a 18650 Li-Ion rechargeable battery in its battery holder, everything is fine. The problem is with protected 18650 Li-Ion battery. There are protection circuits attached into them and they are longer in size. Hardly can they go into the battery holder or come out and in most of case they are damaged.

What battery holders should I use for protected 18650 Li-Ion rechargeable batteries?


texts: Is the Current of A Full Wave Bridge Rectifier Roughly Constant?

texts: If I have a full wave bridge rectifier that produces pulsed DC output (without any type of filtering) is the current constant from the AC side to the DC side? In other words: if the input is .5A AC input will the output be .5A DC output?


texts: How do I read capacitor data sheets to best evaluate a replacement capacitor?

texts:
I'm looking at two capacitor data sheets for some blow caps in my KBNBX-LA motherboard. Here is a pictures of the caps on the mobo.

The caps read Rubycon 6.3v3300uF MBZ. I was able to find these exact caps on eBay, and and Amazon. But, they were pretty expensive. I couldn't find them on Digikey (which was sort of a red flag to me). I went to Rubycon direct and I was able to find the datasheet on the MBZ series. The MBZ series is titled, "105 deg C Ultra Low ESR for PC mother board." However, they no longer sell the MBZ series. There is no mention of what they replaced it with, but it seems like it was replaced with the ZLJ series which is titled, "105℃ Long Life, Low Impedance, High Ripple Current."

It's also kind of interesting the the MBZ series has a higher ripple current at 6.3v 3300uF at 3230, than the LZJ at 2250.

My question is using the two spec sheets above, is the ZLJ series the replacement to the MBZ series? What's the difference? Long Life sounds like an upgrade? Is there any downside?

I don't understand much of what ripple current even is. I'm pretty new to this.

Search the Rubycon site?

Got a second and think I picked the wrong alternative, here is the Rubycon product search. Maybe I didn't even do that right.


texts: Creating a PCB - Electrical Schematic for AMIS 30543

texts:
I'm working on a project and I'm at the phase of combining the components into one PCB. Right now I'm stuck trying to understand some inconsistencies with a stepper motor drivers' documentation. The stepper motor driver is the Pololu AMIS-30543.
Here is the schematic available on the product's web page.

Here is the schematic available on the product's datasheet.

Here is what I have so far for my electrical schematic. What I'm wanting to know is if I'm on the right track and how to address the inconsistencies between the prior two images. Thank you for your time!


texts: Where is the best source on the web to find authorized excess and end-of-life components?


texts: I am designing a heater and i want to hold the nichrome wire inside a frame, what can be used?

texts: Can i use cement for holding the wire ? Or some other material is required.


texts: Why is the RESET pin set up like this in this Z80 schematic?

texts:
I've found the following schematic:

Which after a lot of datasheet reading I mostly understand.

The main thing I don't understand, however, is what's going on with the RESET pin. First of all, I understand that the RESET pin is active-low. In this case, why is it pulled high to +5V? Surely I wouldn't want the CPU to reset. I assume the answer to this part is something to do with resetting on boot.

My main question is why there's a capacitor from RESET to (what seems to be) ground.

Is that even ground? If so, why is there a capacitor before it? If not, what is it, and what does it do?


texts: Terminology question: does the term "bit-banging" implies not using external signal edge interrupts for timing?

texts:
Assuming I realize some communication protocol (e.g. SPI or I2C) just with GPIOs (no dedicated HW). In order to handle timing, I can either:

set interrupt on the CLK edge
set timer interrupt and test the DATA line periodically

Option 1 uses external interrupt (the CLK signal comes from the outer world), while option 2 does not rely on external signals (if CLK line disconnects from whatever reason, it still works - it doesn't depend on it)

Finally, the question: can both options 1 and 2 be referred to as "bit-banging", or just the second?

(as the term "banging" can be interpreted as "knock with constant pace". I hope my question is clear...)


texts:
In class AB amplifier, we introduce two 0.7V sources to avoid cross over distortion.

To do this, we use diodes, all of the circuits employing diodes look like,

My question is, why aren't they like this (down)

In the original circuit, doesn't a voltage of 1.4 drop across the two diodes, biasing the base-emitter of NPN alone, leaving PNP unbiased? If \$ \,v_{in} \, \$ is at 0, then the base-emitter junction is not forward biased (until, we get down to 0.7V), hence effectively, we have not avoided the cross over distortion.
I'm missing something obvious, someone kindly help.


texts: does a broken or blown ac adapter conduct electricity?

texts:
I had this question in my mind for many days.
The main question came to my mind from times ago when I was working on some electronic devices and at that time I had an ac adapter that it had some keys on it which let me to choose voltages from 1.5 to 12 (It was not advanced like those power sources that are used on electronics labs, it was at the size of a laptops power adapter) it had open wires at the end and I used to twist the wire ends of my circuits to the adapter's ones.
In the middle of my work and when I was building the circuit to connect and test with the adapter, suddenly the adapter blown (boom!) I had no idea of what caused this, why would an adapter blow? I had no idea, I just plugged it out of wall fast to prevent further mess.
I now have made my own power source, I had an old samsung phone (which is dead now - rip) it had a charger which had an output of 4.2V and 650mA and I cut the end that connects to the phone and that gave me two open wire for using in my projects.
What Im saying is that:
1. If I unconciously touched the open wires of the old adapter (which blown) could I have got out alive or I was going to R.I.P like my samsung phone?
Im saying that does a blown ac adapter conduct out electricity or they have machanism for these situations (they stop conducting out electricity)
If they dont, Is it true to say that every mobile phone charger that we carry is a killing machine???
2. Is what Im doing right? (working with open ends of ac adapters and just twist them to every circuit I make?)


texts:
I'm trying to make a small module that has 2 rotary encoders (both have build-in push buttons), hardware debouncing circuit and have to be compatible with both 5.0V and 3.3V microcontroller logic inputs.

What I've found, that most typical schematic involves the inverting Schmitt trigger (74HC14 or 74LS14) and should be looks like:

simulate this circuit – Schematic created using CircuitLab

The D1 could be omitted since it is just for decreasing charging time of capacitor C1.

Could you help me with questions:

1) Will 74HC14 (74LS14) work with 3.3V input?

2) Could 74HC14 (74LS14) use the 3.3V as power supply?

3) Could 74HC14 (74LS14) produce the 3.3V output to be connected with STM32F103**** (or other 3.3V logic level microcontoller)

Or should I use the SN74LV14A instead of 74HC14 (74LS14)? Looks like SN74LV14A is more suitable for lower voltages.


texts:
I got to measure inductance of circuit with two loops connected like this:

simulate this circuit – Schematic created using CircuitLab

simulate this circuit

The box measures \$L\$. I have this formula $$M=\frac{L_1-L_2}{4}$$ and when I compute \$M\$, it's negative. Is that ok? What does it mean? Should I make the result absolute?

In one measurement, I got \$L_1=-1394~ \mu H\$ and \$L_2=-1392~ \mu H\$. That seems wierd. I measured like 10m long cables. Isn't that suspicious? What could make the result wrong like this?

Additional information:

I was measuring with frequency \$200 kHz\$ and cables are flat. PNLY and Twist. One loop was made by connecting two nearest wires in the cable.


texts:
I've been trying to figure out the inductance in Henries from a schematic of a Rabbit Microprocessor development board, however, instead of finding an inductance value over the components in question, theres an ohm/amp value, I thought maybe it was the inductive reactance, but theres only DC in this circuit and most of the inductors are probably being used as filter elements. However , to add more confusion, in this same schematic, some inductors are stated in Henries while others are stated in Ohms/Amps.

*So how should I interpret an inductor whose value is in ohms, It cant be inductive reactance can it? *

I dont understand how is it related or is it simply a ferrite bead with a certain dc resistance? Here are pictures of the schematic im analyzing:

Here you can see one of the inductors in ohms

This second pic is also from the same schematic, while there is an inductor stated in Henries (nH to be precise) the other inductor is in ohms


texts: Reference ground for Vgs on the source pin of an N-channel MOSFET

texts:
Hey fellas,
So I'm trying to take advantage of n-channel mosfet's inherent low RdsOn, but also want a high-side configuration. I've got the following circuit here and it seems to work in this simulator. But I have a few questions.

Upon having Vds(12V) and Vgs(15V in the link) equal, my voltage across my MOSFET shoots way up, indicating that I'd be dropping a ton of current on it and blowing it up. Is this accurate?

In my mind, the 1K resistor on the output gives a reference to ground. The reason I have this is that if I want to maintain signal even if the load (30ohm) is disconnected. The 30 ohm is really a placeholder. The real loads this thing could be driving could be anywhere from 2 ohms to sub-ohm loads.

Is this a standard configuration that people use for MOSFETs? I know most people will just say to use a P type here, but I'm stubborn and really want to figure out a way to use an N-channel to avoid heatsinks as much as possible. I've never really seen a configuration like this online, but with so many tutorials out there they never really cover this concept.

Does Vgs need to be higher than Vds? I figured they could be the same, as I know mosfets can be used to control high-voltage devices with low signal levels. Is this a limitation of the simulator or am I incorrect?

Edit: The reason this is happening is because my Vgs is being referenced to the output of the SOURCE pin, not directly to ground. My voltage is across my load and my "pull-down" resistor, meaning I'm still at Vd at Vs. therefore Vgs MUST be higher than that to drive the MOSFET properly. If a mod wants to lock this that's fine, I answered my own question. Apologies for writing this whole thing but I can't figure out how to delete my own post.
Here is the link to my circuit. Any comments and advice are appreciated, thank you!


texts:
I have torodial transformer output of 25 0 25 V AC.
After rectification i get +-37 V AC dual rail.
That is total of 74V DC 37+37
How can I step down this voltage to +-45


texts: What is the function of a MOSFET driver in an H-bridge?

texts: What would happen if I didn't use MOSFET gate a driver, and simply connected the MOSFET gates directly to the logic outputs of a microcontroller? I am quite confused about the need of a MOSFET driver.


texts:
What is the difference between a latch and a flip-flop?

What I am thinking is that a latch is equivalent to a flip-flop since it is used to store bits and is also equivalent to a register which is also used to store data. But after reading some articles on the internet I found differences between latches and flip-flops based on edge triggered and level sensitive functionality?

What does that mean? Is a flip-flop the same as a latch or not?


texts: Initialize IWDG with two difference handles

texts:
I am implementing a watchdog in my project, where i am using a IWDG in STM32F4 series controller. I am trying to initialize the watchdog twice with different handles, since it is implemented in two different tasks. As per functionality wise it is working with no problems, but when i reviewed my code, I found that I have initailized the IWDG twice with same instance but different handles passed.
My initialization is as follows,

IWDG_HandleTypeDef rIWDG;
IWDG_HandleTypeDef rIWDG1;
void IWDG_vInit(void)
{

   rIWDG.Instance = IWDG;
   rIWDG.Init.Prescaler = IWDG_PRESCALER;
   rIWDG.Init.Reload = IWDG_RELOAD_VALUE;
   if (HAL_IWDG_Init(&rIWDG) != HAL_OK)
   {
      //Error Handler
   }

   rIWDG1.Instance = IWDG;
   rIWDG1.Init.Prescaler = IWDG_PRESCALER_256;
   rIWDG1.Init.Reload = IWDG_WINDOW_VALUE1;
   if (HAL_IWDG_Init(&rIWDG1) != HAL_OK)
   {
      // Error Handler
   }

}

Is this a problem? Am i allowed to initialize this way? If its wrong how is it working fine with proper window values.

Thank You.


texts: Is it safe and feasible to use a "damaged" transformer?

texts:
I want to make my own DIY spot welder, so I'm trying the instructions I found on several places (for instance, here, here or here) about using an old microwave transformer. I salvaged it from a broken machine and the recipe says to replace the secondary winding by two or three turns of a heavy, thick insulated cable (I got a 16mm2 one).

The problem is that removing the original winding wasn't exactly a walk in the park; after cutting it with a radial jigsaw I had to smash it hard with a chisel until it finally came off. This produced noticeable physical damage to the transformer itself, namely in the core sheets: some of the insulating varnish came off, some of the first sheets got a bit deformed and separated from the rest and finally and what looks more severe, these "separations" also happened in two or three places in the laminated core, opening it in three different blocks that I managed to more or less put back to their original position by, again, heavily smashing them together. Currently there is minimal space between those cracks, I would say less than a mm, but you can still put your nail between the layers by applying some force and, of course, the insulation there (in case it was any, something I'm not sure about) is gone.

I know little about the physics and theory behind transformers, and I'm wondering if I can still attempt to use the damaged transformer and/or if it is a bad idea/hazardous/simply won't work. As far as I understand, the purpose is to get a low voltage but a high current, capable of melting steel, so I don't think "precission" is a concern, but I read about why the core is laminated and, as far as I know, there is a risk that it will overheat due to eddy currents, although I don't know if those couple of cracks and deformations will be THAT significant. Also, I found at least one source (sorry, forgot to bookmark) where they state to be very careful with the core sheets and not to bend or even slightly separate them in any way.

What's your recommendation? One friend, who studied technical secondary school to become an electrician, simple said me to "try it and see what happens", but I don't want to burn my house, destroy all the household appliance or even fry myself.

Two secondary, final questions:

Are sheets also isolated between them or just covered on top with varnish
after "physically" joining them together "by force"? Should I paint the separated
lamines with some epoxy or glue before joining them if I'm going to
try the transformer? In that case, would it be dangerous if a little
metal part is still in contact with another sheet of metal from the
core? Because I cannot assure 100% of the sheet will get covered with the stuff...
Is it hazardous and/or could it significantly affect reliability if
two turns of the primary coil short between them? I closely inspected
it and looks like it was "scratched" in a small area (see 4th picture) and there is a risk
it lost its insulation there; I think that chance is very low and
I'll try to assure by covering it with epoxy or another type of
insulation/varnish, but just in case...

I'm attaching some pictures of how does the transformer currently look; I hope they are useful for making a judgement...

Thanks a lot for helping!


texts: can a power mosfet driver be used 'standalone'?

texts:
TI has the UCCx732x series power mosfet driver. It's capable of 4A, with obvious thermal caveats.

If my power needs are below 4A, can I use this driver chip directly? Is there a downside of doing so?


texts: Transfer function for Sallen-Key Low-pass Filter

texts:
How can I find the transfer function H(s) of the following circuit by using the nodal analysis?

My thoughts woulb be:

the equation for the node
\$ i_1 = i_1 + i_3 \$

\$ i_1 = \frac{U_e - U_1}{R_1} \$

\$ i_2 =  \frac{U_1-U_2}{X_{c1}}\$

\$ i_3 = \frac{U_1 - U_a}{X_{c2}} \$

I expressed \$ U_2 \$ using the voltage divider

\$ U_2 = U_1\cdot\frac{X_{c1}}{X_{c1}R_2} \$

My idea was to express \$U_1\$ and \$U_1\$ set it all in the initial node equation \$ i_1 = i_1 + i_3 \$ and from that i might be able to derive the transfer function \$ \frac{U_a}{U_e} \$. But I don't know how to express \$ U_1 \$.

Accroding to some websites this is what the transfer function looks like for that typs of filters:

\$ \frac{U_{out}}{U_{in}} =  \frac{\frac{1}{R_1C_1R_2C_2}}{s^2 + s(\frac{1}{R_2C_2} + \frac{1}{R_1C_2}) + \frac{1}{R_1C_1R_2C_2} } \$


texts: STM32: Running many peripherals at the same time

texts:
I need to do EMC testing for a board controlled by an STM32F2. Ideally, I want to activate, full-speed, every peripheral on the board.

That is, I want to be reading/writing as fast as possible to the memories (SD, Flash, RAM) and putting/receiving as much as possible through the communication channels (Ethernet, USART). All of this, at the same time.

At the moment I have individual drivers for each peripheral, but the drivers are "blocking", meaning that when one driver operates, all the others are idle.

How can I have all my peripherals churn full-speed at the same time?

Note: I don't really care what the peripherals do, just that they be very active.


texts:
I was going through radio transmission, and looking at a handout from Analog Devices on Heterodyne structure. Here is layout from this handout.

What I understand that in "MOD" (refer the layout above) level the actual signal is mixed with the carrier frequency, so that my baseband signal is moved to carrier frequency  on which we will do the transmission. In that case why we need two mixers after the "MOD" level to further upconvert the frequency.

Example: to transmit at 200 MHz, my carrier frequency would already be 200MHz inside the "MOD" stage. Then why need to further upconvert this frequency via these mixers.

I have thought on it a lot, but still could not figure a satisfactory answer.

Your guidance will be greatly appreciated.

ADDITION:

During "MOD" stage, we do add the signal with some sort of sine function, say $$sin(2\pi f_ct)$$.

In that case is this $$f_c$$ the carrier frequency (200 MHz for my example), clearly it can't be, it has to be much much lower than that, and then we use the mixer to move it to 200MHz. Then during modulation stage, why do we call the $$f_c$$ as carrier frequency, aren't we suuposed to transmit the signal at this frequency??


texts: Conversion of 12 bit ADC/DAC data to floating point for PID operation

texts:
I am working with PIDs for temperature control.  I have implemented the PID using floating point numbers. I am using 8051 for PID implementation.I have two queries:
I have to apply the PID output to a 12 bit DAC. How do i convert 32 bit float to 12 bit.
How to convert a 12 bit ADC data so that i can feed to PID input
Both ADC and DAC work with 5 V reference. So LSB size is 5V/4096= 1.22mV
thanks.


texts: How to drop 5v regular phone charger voltage to 3.7v to run a device, which use 3.7v output battery before

texts:
I have Motorola Moto 360 2st edition smartwatch and watch original battery is dead. I have converted smartwatch into table watch in DIY wooden block and added 18650 3.7v battery instead and now its works fine for 2 to 3 days but then battery dies and I have to remove 18650 and charge with its charge.

Dead Smartwatch original battery photo.

Can I convert regular phone charger with 5V output to 3.8V output to run my smartwatch continually? If yes what I have to do ?


texts:
I have actually a solution based on a multiplexer (CD4051) which drives 8 outputs, either at 0V or 3.3V (the input is at 3.3V). Each output of the multiplexer drive a NMOS and the goal is to have a signal behind the NMOS driven to 0V or floating. In an another words I drive 7 signals at 0V and one signal is not driven (floating).
The multiplexer is used to extend the gpio of my microcontroller (3 to 8 and could be more by adding more cascading multiplexers).
My question is could I do the same without the NMOS? I mean, is it possible to have a component (multiplexer) which has an output either at 0V or floating? To be more accurate, could it be possible to have 7 outputs at 0V and one floating?

I guess it is not feasible but I prefer to ask, in case of :)

Thanks in advance


texts: PCB clearance/keepout area surrounding wireless antenna

texts:
Suppose a PCB antenna or chip antenna is integrated onto a board design with a wireless IC, e.g. a Zigbee or Bluetooth module.

What are some guidelines regarding clearance/keepout area on the PCB that one should allocate surrounding the anteanna, so as to ensure effective transmission and reception?

Example: In the following image of a PCB (pulled from Google images), there is a USB connector situated fairly close to the PCB antenna:

I presume since RF design is a very significant field, there must be both theory- and practice-based rules of thumb regarding this (I understand there are a lot of case-based factors that play a role, so this question is only to scout for some generic helpful suggestions).

In particular:

How far should the clearance be maintained? E.g., is it critical to maintain more than 10 mm of clearance area horizontally out from each end of the antenna?
In which axial/angular directions is the clearance most important? E.g., I presume the Fresnel Zone plays a role here, so is there a cone or certain maximum angle within which the clearance is most pertinent?
Which of the following are most critical to "keep out" in the keepout area?

large metallic objects such as header pins or USB connectors, etc.
ground copper pour
any copper traces whatsoever
all of the above?


texts: How to overcome current drop in circuit with high inductance value?

texts:
I have a very simple circuit that uses a switch to switch between a resistive loop and inductive + resistive loop.
Whenever I switch from resistive load to inductive load, the current of the source current measured over the R2 drops to almost 19A.

How can I make the current stay stable even when I switch the switch?

The current drop happens when I turn off the switch as shown on picture below:


texts: A proper way to determine correct voltage of unmarked components?

texts:
My kids have been tearing apart a number of different gadgets, from RC cars, to toys, to coffee makers.

There are a variety of cool little motors and lights in these devices that we would like to use on oddball projects.  (For serious projects, I prefer to spec out the component and purchase it directly)

So far, I've been using a variable voltage DC power supply to guess the right voltage based on what seems to be the correct speed, brightness, etc... without burning the item out.

Is there any scientific or mathematical technique that can be used to know when you are at a correct level of current or voltage for a given device, or does it simply depend on the specifications of the device?


texts: Understanding an unknown digital encoding

texts:
I'm trying to understand a certain undocumented digital protocol. It looks similar to Miller or coded mark inversion (CMI) encoding. So far I managed to decode the encoded data and get the expected results. However I can't figure out one detail that prevents me from encoding data in a way identical to the black box encoder.

The symbols of the protocol are 00, 01, 10, 11 (0 and 1 in my case are certain voltage levels after clock recovery, but I think physical layer details aren't relevant to decode). 00 and 11 symbols both decode to binary 0. 01 and 10 symbols decode to binary 1.

For example, 00 11 01 00 10 11 00 decodes to 0010100. This is the result I am expecting and I'm fairly certain it is correct. This interpretation also makes sense since I know the protocol should be inversion-invariant (swapping 0 and 1 in the symbols should decode to the same bits).

This is how the state diagram looks like (based on a fairly large sample of encoded data):

For example, if last symbol was 00 and next bit to encode is 0, then the next symbol is always 11.

The problem is that some transitions are ambiguous. In particular, if last symbol was 00 and next bit is 1, sometimes the encoder produces 01 and sometimes 10. Similarly, if last symbol was 10 and next bit is 1, sometimes another 10 is produced and sometimes it goes to 01.

Here are how some sequences of bits get encoded to different symbol sequences:

1010 -> 01 00 01 00
1010 -> 01 00 10 11
1010 -> 10 11 01 00

0110 -> 00 01 01 00
0110 -> 00 10 01 00
0110 -> 00 10 10 11
0110 -> 11 01 01 00

Some transitions are never observed: there's never a 11 to 10 and 01 to 10 (this should be present if this was Miller encoding). A consequence of this is that in the symbol stream there's sometimes three consecutive 0s (which wouldn't occur in differential Manchester), but never three consecutive 1s. This goes somewhat contrary to the symmetrical nature I would expect from the protocol.

What I'm trying to understand is how these ambiguous transitions are determined. So far I've found out:

It's deterministic. Resetting the encoder and encoding the same stream of bits always results in the same stream of symbols.
It's not linked to certain positions in the stream. The bits 01 at the same  position in a stream can sometimes be encoded either 00 01 or 00 10 sequence of symbols (depending on surrounding bits). Encoding is also not determined by odd or even bits.
It seems locally dependent on a few previous symbols, but not in a simple way. It seems if some bits are changed it only affects encoding about 4-5 symbols around the change, but for the rest of the stream encoding choices don't change.

I found that the smallest number of preceding bits that unambiguously predicts 00 to 01/10 transition is 5 bits. For 10 to 10/01 it is 4 bits. Unfortunately my ability to feed data to the encoder is somewhat limited so I wasn't able to fill a complete look up table.

Here is an example of a partial look-up table I came up with:

If preceded by:
 0, 1, 1, 0
 0, 0, 1, 0
 0, 1, 0, 1
Then
 bit 1 after symbol 10 is encoded as 10

If preceded by:
 1, 1, 0, 1
 1, 0, 0, 0
 1, 0, 1, 1
Then
 bit 1 after symbol 10 is encoded as 01

So my question is, is there a purpose for encoding bits like this? It seems deterministic enough that it looks like an intentional feature rather than a bug or undefined behavior. On the other hand, using a lookup table seems needlessly complicated when something simple like a differential Manchester encoding would suffice.

My gut feeling is that I'm missing something obvious here. I would welcome any suggestions on what the actual algorithm behind choosing the ambiguous symbol transitions in encoding could be.


texts: Circuits for two way data transfer from iPhone to Arduino via headphone jack

texts:
What I'm trying to do:

I recently bought an iPhone 3GS (yes iPhone...) and I am going to install Android on it so I can make apps myself for it and incorporate it in a bigger project, using the WiFi and the touchscreen capabilities to interface with my Arduino.

The iPhone is soon to be jailbroken and it is not connected to a 3G network.

Technology behind it:

Like I said earlier, I am going to jailbreak it so I can install Android on it. Then, I'm going to connect this cable that will split the headphone and  microphone signal to it and then connect it to my Arduino. This is where I get stuck. I want the Arduino to generate signals to the "iDroid App" and it to also send signals back.

What circuits should I implement for the microphone and speaker?

I have seen this question, but it doesn't cover microphones, and I can't find out how to actually do anything with the information. I've seen this also, and although it has awesome code samples, it doesn't explain the circuits. These aren't really duplicates, they are related, but I need further explanation and help.


texts: common circuit to turn on/off ac motor of 110V AC or 230V AC using MOC3041 and BTA16 Resistor calculation

texts:
I am building a common circuit to turn on/off ac motor of 110V AC or 230V AC using MOC3041 and BTA16.
How do i calculate both resistor value R and Rg ( With Wattage ). For accurate control of TRIC.
Motor maximum load current is 3A.


texts: How to tell if the switch is open or closed on a mains line?

texts:
Imagine a circuit that may or may not be connected to mains voltage.

If mains is connected, it is trivial to determine if the switch is closed, by using a zero-cross detector circuit.

If mains is not connected, it is necessary to power the switch.
How can it be powered in an isolated way, from a 5V/12V source, such that the state of the switch can be determined?

The circuit should not be affected by whether mains is connected or not.

Is this possible?

My question is strictly for this circuit. Nothing can be changed. The monitoring circuit can only be connected with the two wires as illustrated in the diagram.

I've voted to close my original question because it ended up off-topic and unrelated to what my actual question was.

simulate this circuit – Schematic created using CircuitLab


texts: How does a battery balance and protection circuit work?

texts:
I am building a 4S LiPo battery pack that I would like to incorporate in a portable speaker project and I need to make sure the batteries will never require maintenance beside replacing them completely in 5 years or so. The batteries I am using are NCR18650B so they should be pretty decent.

I am using the following BMS board that is using a Seiko charging IC:

In order to test that this works properly I intentionally unbalanced a cell by having it charged up to 4V and I left the other 3 cells at the same voltage of 3.85V.

The bench power supply is set to 16.8V for charging and the following things can be observed:

As soon as the first battery is charged to 4.25V the pack is disconnected from the power supply. In this particular case, the total energy in the pack is pretty low because the batteries where significantly unbalanced. Why not disconnect only the most charged cell?
I am unable to detect balancing with the power supply on or off, after the BMS decides charging is done. No current is flowing from the most charged cell.
I tried an alternative balancing board and this behavior seems to be consistent. All the commercial balancing PCBs "work" the same way?

How does all this balancing actually work? What would be the best option for my scenario where I need a 4S pack from which the load will draw peaks of ~1A for short periods of time?


texts:
I have an input power source that fades an LED on and off smoothly, from 0 volts to 7.5 volts. I would like to use a 12 volt LED. I have been looking at step up regulators which look suitable for handling the constant input, but ideally I would like the new 12 volt LED to retain the fade on/off effect.
Is there such thing as a step up regulator that will fade to the fixed output voltage?


texts:
A current of 1A flows in a wire carried by electrons. How many electrons pass through the a cross-section of the wire each second?

This is a quite simple but really difficult question to me right now, and I put this as the heading because it is one of the most basics of questions.

So the charge of an electron is -1.6 x 10^(-19) C. If we look at the definition of what current is, it is the rate at which charge is moving.

But how are we supposed to find the number of electrons, without any other information?


texts: TFP401: 24-bit TFP401 to drive an 18-bit LCD panel, possible?

texts:
We would like to use this LCD panel as it matches customer dimensions perfectly:
https://www.digikey.com/product-detail/en/sharp-microelectronics/LS037V7DW03A/425-2871-ND/4862435

This display has 6-bits per colour so 18-bits RGB.

TFP401 has 24-bits RGB or 8-bits per colour.

1) Can we still use TFP401 to drive the panel? this means some pins won't be connected.

2) video signal input is from HDMI

Please help, thanks!


texts:
I am new to the PCB world and currenctly I am using NI ULTIBOARD program.

So lets say I have this part cre2512-r001:

Does that mean that C=2.2 mm or 2 mm or 1.8 mm? becouse I am a bit counfused what is the size of the pads.

The same goes for A. Is A=6.65 mm or 6.45 mm or 6.25?


texts: Capacitor in parallel with battery for high current output

texts:
I have a long-term application with very low quiescent current and infrequent pulses. I've spec'ed high capacity, low pulse current batteries that will give me the lifetime I need, and I want to charge a capacitor to handle the infrequent high current (regulated) loads.

Can I put the cap directly in parallel with my batteries? Will the voltage drop from the current pulse have a negative effect on the battery? Or would I have to regulate before as well as after the cap?


texts: Can a PC motherboard be used as an uber microcontroller?

texts:
I'm aware of the differences between a common microcontroller and a full blown motherboard from a computer server.  But consider what happens when the PC memory testing tool memtest86 is run:-

Here the tool can be seen running on a largish core i7, accessing 16GB of   RAM.  Clearly it also has access to the hard disk from which it booted, loaded and ran.  Access to the network, usb and serial interfaces is probably possible then too. And it's running with no operating system, just itself.

So instead of running memory tests, could some application be written that would do what I wanted it to do and control things via the available interfaces?  Or are there on board devices and components that need a full blown OS?

I'm not asking if this is particularly useful, but whether it's possible?


texts: Current-sense for NES/SNES gamepad detection - getting a voltage spike

texts:
I'm in the process of designing a wireless controller receiver for the NES/SNES game consoles.  My wireless receiver consists of a bluetooth module and an AVR microcontroller, with the microcontroller connected to the controller's control lines.  It's designed to be installed inside the console itself, but I don't want to break support for normal controllers, so I need some way of detecting when a controller is plugged in.
The controllers themselves aren't designed with this in mind, so I've been looking into a couple of options.  The NES/SNES controllers are basically nothing more than a parallel-to-serial shift register (the NES controller just uses an off-the-shelf CD4021, the SNES has a custom chip that is basically just a 12-bit version of the same thing) with pull-up resistors and membrane switches to ground on each of the parallel inputs, and the latch, clock, and data (bit 8) signals connected to the cable between the console and the controller.
Monitoring the data line doesn't do any good, because there is no way to discern between having a controller plugged in with no buttons pressed vs. no controller plugged in, so the controller isn't detected until after a button has been pressed, and there's no way to detect that the controller has been disconnected, because it appears just the same as if the controller was connected but idle.
My next option is a high-side current sense circuit, using the controller as the load.  With the controller disconnected, no current flows through the sense resistor, so no voltage is dropped across it.  When the controller is connected, current flows, voltage drops, current sense amp outputs a voltage.  This is working fine with one exception.  When I first apply voltage to the circuit, or when I connect the controller, there's a momentary voltage spike on the monitor's output line that hits roughly double the supply voltage, so that's no good.  I'm not even sure how exactly that's possible, since the spike goes above the supply rail, but it's pretty clear on the multimeter.
Analog really isn't my thing so I have a feeling I'm doing something wrong.  I've attached my current schematic, can anybody suggest a good way of suppressing this voltage spike?  I'm not sure if a zener diode would be fast enough to handle it, and adding an RC low-pass filter onto the output doesn't help either, and just ends up lowering the output voltage.  I need something, I'm pretty sure 10V will blow the ADC pin on the microcontroller. Any thoughts?
Looking at the schematic, I realize I forgot to add decoupling caps on the INA282 supply line as per the datasheet.  I have them in the circuit, but I still get the spike.


texts: Can a 74HC595 independently enable or disable output pin without interrupting other active pins?

texts:
I am doing a project for which I need to expand the IO pins available on NodeMCU. I  plan to use 74HC595 for the same, I have a question regarding that as given below.

Is it possible to independently enable or disable output without interrupting the loads which are already active?


texts: How to redesign the circuit such that the switching threshold is VDD/2.

texts: he switching threshold is the input voltage where the output crosses VDD/2. I want to redesign the circuit such that the witching threshold is VDD/2.


texts:
i have a several devices which are usually powered by  external power supplies, and i want to be able to switch these on and off. i looked into mosfets before and they worked like a charm for other projects but this time it doesnt really work out yet.

As soon as i connect Q2 to GND my arduino shuts down. Which usually indicates something's going wrong somewhere. I checked all contacts on my board and everything seems to be fine. I also just connected just one power supply at the second element so far, so there shouldnt be any interference between several power supplies yet...

If i add an additional resistor of the same value as the pull-downs, between Q2 and GND its fine but the Mosfet isnt working, using a smaller value and i'm back at the arduino shut down.

thx!


texts: JFET transconductance vs. MOSFET transconductance

texts:
JFET's n-channel highest transconductance (from datasheets) is marked as

In theory, the same value is defined as that applies for n-channel JFET.

I haven't found equation which defines MOSFET's highest transconductance yet, so I'm wondering if the same equation can be applied except Up is switched with Ut - threshold voltage?

All I want is to somehow get "K" (conduction parameter) for MOSFET. Usually values like electron mobility parameter, oxide capacitance and W/L-ratio aren't given in datasheets so you have to calculate K in different way. For example, how would you calculate drain current in saturation mode, if K is unknown? Maybe through transconductance, but how if for calculating gm you need either drain current or conduction parameter?

Things are easier with JFET, where K is defined as K = Idss/Up squared. Both values here are given in all datasheets.


texts: powering led strip from 2 alternating power sources

texts: I am building out an enclosed trailer for work that I am adding interior LED strips to for lighting as winter is arriving and it gets dark pretty early. I would like to be able to power the lights in 2 separate ways. One way will be to tap off the existing switch & incandescent light (light will be eliminated) that came with the trailer that operates while connected to my truck when its hooked up; that's the easy one. I am a builder so the trailer is dropped at a customer location 99% of the time. I am adding an AC plug on the exterior that will power receptacles in the trailer and an inverter that will power the LED strip lighting. My question is do I need to do anything special with relays, or as long as both power sources (truck or AC power) aren't connected at the same time will I be fine? Please excuse my offensively crude drawing. To summarize: LED strips powered by 12v truck power OR ac inverted power, never powered by both at the same time. Both ways are fuse protected. Can I just wire this up straight forward or will I need any kind of relay? Thanks so much!


texts:
I was reading the spec for a patch cable (Ponoma B-36-02) and when came across the following:

"Operating Voltage:
     Hand-held Testing: 30VAC/60 VDC Max.
     Hands free testing in Controlled Voltage Environment: 5000 WVDC"

I was puzzled by the extreme difference between the two operating voltage ratings. What is a controlled voltage environment? Also, is there a specific regulatory body that has defined "Hand-held" and "Hands free" and "Controlled Voltage Environment"?


texts: Power supply circuit for powering SG90 servo. How to handle high current requirements?

texts:
I need to power a small SG90 servo motor. I could easily use a 5V battery but why bother? :) Aside from this not funny joke, I'd like to put to good use my little knowledge of electronics gained at University.

The datasheet of the servo does not mention any current draw (max, min, average, etc., ...). However I know that my USB port can barely handle Arduino with some sensor and a servo moving around so I guess it could easily be 100 mA. This figure is nothing I know, but it's a start at least. Furthermore the servo does not do any "heavy lifting" it just rotates a small aluminium bar which is super light. There should not be any "stuck" positions.

Since my main PS is a 12 V battery I thought I could step down the voltage using some resistors and then use an op amp (LM741) and a NPN transistor (2N3904) to set voltage and current, respectively. See the schematics below.

By using this circuit I should be able to output 100 mA while keeping the heat dissipation of the 2N3904 NPN within the admissible range of max 0.5 W. I guess I could even go up to 200 mA if I work around the circuit a bit more, however, before going on I ask myself and you, is this circuit able to handle such high current loads such a servo motor (i.e. do you see any flaw in this)?