texts:
An instruction from the instruction set of intel 8085 that is SBI data (Subtract immediate with borrow) . This instruction says "The contents of the second byte of the instruction and the contents of the CY flag are both subtracted from the accumulator. The result is placed in the accumulator."

Or

(A) <-- (A) -(byte 2) - (CY)

In this what does second byte or byte mean ?

Also in the instruction STA addr (Store immediate address) which says "The content of the accumulator is moved to the memory location whose address is specified in byte 2 and byte 3 of the instruction." What does byte 2 and byte 3 mean ?


texts:
I've skimmed through several sparse articles online about hysteresis in a MOSFET's I-V characteristics. What I found was sparse, but some articles attribute uneven-ness in the gate structure, causing some charge to move slower.

As for my limited knowledge of Physics, it's still reasonable to think that pulling or pushing out charge carriers would instantaneously collapse/build-up electric field. Not only that, the current must have something similar to a "momentum", even though electrons have extremely low mass.

I really don't have the time to read through all these articles and even if I did, my Physics is lacking. So can anybody just summarize this for me, or point to a shortened article?

Has there been any design of a MOSFET Gate Driver that deals with this issue?

EDIT:

Perhaps what I should've said is "Hysteresis in MOSFET's response time" (or maybe this is still incorrect?). I don't know what's wrong with me tonight. I'm shifting my sleeping schedule, so I already feel groggy.


texts: LC circuit of buck converter in nRF8001 datasheet

texts:
In the datasheet of the nRF8001, they specify in the reference schematic (page 51) the LC circuit to use with the integrated DC/DC converter (see below).

Why is there a small inductor L5 in series with L4?

Is it related to the self resonant frequency of the inductors? That was my first thought, but the 10nF inductor specified in their integration note (Taiyo Yuden LBMF1608T100K) has a minimum self resonant frequency of 32MHz. The exact frequency of the nRF8001 buck converter is not specified, but it seems to be well above the frequency of any buck converters.


texts:
I have recently acquired a 3D printer and have been experiencing all kinds of trouble with the fans used to cool the printer head, the parts and the controller board.

The controller is a smoothie-compatible custom board with a 24V PSU.

Some fans simply won't spin, some will spin only reluctantly ("wobbling" between two speeds for certain command values, spinning only when commanded at 75% or above), and all are far noisier when used in the printer than when plugged into a 12V PSU.

All this leads me to think these fans are rated for 12V and used with a pulsed 24V power supply.

I could not get the customer support to tell me the voltage these fans are supposed to be rated for. The fans have no label or visible identification. I finally sacrificed the one that would not spin anyway to try and get a clue about its rated voltage, but even the Hall sensor chip has no marking :

My knowledge of electronics is sketchy at best, I have nothing but a basic multimeter at hand and don't intend to buy an oscilloscope just to debug this pesky fan problem, but still I would be glad to understand what is happening there.

As far as I understand it, the controller board uses a PWM signal to achieve variable speed for the fans. The PWMs are generated using a sigma-delta algorithm with a 1ms base period. It means the fan power suppply is a 24v signal consisting of 1ms power pulses followed by the necessary number of 1ms no-power cycles to achieve an average power-up time matching the set value.

For some reason they added a 22µF capacitor between ground and the fan control signal (in the fan connectors located on the printer head), so I suppose the PWM must be somewhat smoothed.

According to the controller configuration, the PWM is limited to the 0-50% range, meaning the "average" voltage fed to a given fan never exceeds 12V (in reality, 1ms 24V pulses followed by 1ms power off, possibly smoothed by the capacitor).

Aapparently the smoothie designers explicitely warn about using 12V-rated fans on a 24V PSU, even using the PWM limitation trick to reduce the "average" voltage to 12V or less.

I've been scouring the Internet to try and understand what consequences overvolting these fans could have (on the fans themselves and possibly on the power supply), but my electronics skills are not sufficient to figure that out by myself.

So my questions are :

are these symptoms consistent with the use of 12V fans on a 24V PSU?
what are the consequences for the fans and the PSU?
what is the role of these mysterious capacitors? (the manufacturer claims they are just there to filter some noise, but I don't see what could need noise protection in a printer head consisting only of 3 fans and a heating resistor)
is there a way of getting these fans to work (e.g. by boosting the PWM signal above 50%) without damaging the fans and/or the PSU, or shall I replace them with proper 24V-rated components?
in case I put 24V-rated fans in my printer, shall I leave the capacitors in place or unsolder them (i.e. are these capacitors likely to hinder the fans, for instance making the spin-off more difficult) ?


texts:
In Logisim I created a circuit containing RAM module with separate input and output lines

I want to build this circuit from real items. However I could not find any SRAM chips that have separate I/O pins.

Does this kind of RAM chips exist? Or I have to find a way to somehow separate them?


texts: Closing loops or not? - supply lines on a PCB

texts:
When routing a Gnd line, I wonder if it's best to keep loops open, like so:

or to close the loop, like so:

I could think of some arguments in favor of closing the loop:

PRO Looping arguments:

Coupled magnetic fields try to create current (by inducing voltage). If the loop is open, the current cannot flow. So it's better to close it.
A closed loop offers two paths for the current to go to the Gnd pin. This (approximately) halves the impedance.

But I honestly don't feel that confident about their validity. Can anyone give me more insight in this matter?
I'd also like to know if your answer - either pro or contra closing loops - applies only on the Gnd or also on supply lines.

Note 1: For the sake of this question, let us assume there is no Gnd-plane.

Note 2: The figure above is not a real PCB, only a simple drawing to make the point.


texts: Is the 3.5mm jack somehow connected to the phone's transceiver?

texts:
I could not find a clear answer to that and it's driving me nuts, because I have a microphone, which when connected to my phone via 3.5mm jack picks up a sort of buzz, as if from wireless inteference. Expectedly, the buzzing stops when I put the phone in airplane mode. Also, the mic doesn't pick up anything from other phones or WiFi routers  transmitting.

Curiously enough this buzz is not present when the mic is connected to other phones or a computer.

I have also tried different recording apps... without any improvement.

I figured this could be due to some potentially faulty connection between the phone's audio interface(?) and the transceiver, but am not sure if there is a connection between the two.

Thanks!


texts: Factors affecting the \$V_f\$ of a Schottky diode

texts:
The usual wisdom about Schottky diodes is that their \$V_f\$ is around 0.2 to 0.3 volts, but what specifically determines this?

I know that for p-n diodes, doping concentration can affect the forward voltage. Is this also true for Schottky diodes? Obviously at some point you have a non-rectifying ohmic junction, but you have a range of possible dopant concentrations below that point.

What would happen if you made a Schottky diode with germanium instead of silicon? Germanium p-n diodes have a much lower forward voltage than silicon p-n diodes, so would a germanium Schottky diode have a lower forward voltage than a silicon Schottky diode? What about a SiC Schottky diode, would it be higher?

Does the choice of metal for the metal-semiconductor junction matter? Is the forward voltage related to the metal's work function at all?


texts:
I have 3.3V 125MHz clock signal which need to be translated down to have an amplitude of 1.8V. My first idea was to use some logic inverter, run it on 1.8V, and since it probably has protection diodes on its input everything should be fine. I have found a nice model from TI, SN74LVC1G04-Q1. In the product details, it is written max frequency at nom. voltage is 150 MHz. Does this mean 150 MHz of square signal, or the highest frequency component?

Besides buying a logic inverter I was also thinking of making a discrete inverter or even use a simple transistor switch. So my questio is basically, which direction should I go?


texts: I have always wondered if it's possible to make a homemade primitive photo sensor for capturing photos in an acceptable range and in low resolution using environmental light? I know that it's possible to use the mechanism of an optical mouse for scanning documents with very low resolutions, but it fails at longer distances than a few millimeters.


texts: Is it possible to convert an non-otg port of smartphone to otg port?

texts:
I know that for OTG to work, it needs both, kernel and hardware compatibility. For kernel part, there are many solutions like OTG helper apps on play store.

Here, I want to know and understand what we can do for the hardware part ? Is there any possibility of some device (not OTG cable for pen drives) for smartphones that can make it work. What are the ideas that can make it work ?


texts: ETHERNET communication on PIC micro-controller, where to start?

texts:
I need to implement an Ethernet communication between one board with a pic micro-controller and 16-24 other boards with micro-controllers.

I don't know how to start even though i entered the microchip site and read some PDFs.

I am familiar with RS232. Is it similar?
Please help me on how to start implementing this, really the basic


texts: at89s52 the right way to drive transistor

texts:
I want to ask about this configuration, the port is connected to at89s52 pin (not P0) and some of my friend say that this should work because the at89s52 have internal R that can replace the external Rb is that true?
please give us scientific answer


texts: Y/Y/Δ or Δ/Y/Δ transformer for a series connected 12-pulse rectifier?

texts:
I'm aware that 30° shift is needed in order to obtain a 12-pulse rectification, however, I'm a bit confused about the configuration of these transformer. In most HVDC systems that appear in Alstom - HVDC for Beginners and Beyond, for example, shows a WYE winding as primary:

However, I stumbled upon this similar ResearchGate question but it was answered as the Y/Y/Δ configuration is used and that's why I got confused.

I'm doing a simulation on PLECS in stationary state of this series connected 12-pulse rectifier so as long as I can represent leakage inductances and 30° shift it's okay as I won't do neither a transient analysis nor a fault scenario. However, I want to clarify this to at least justify why I used one configuration or the other.


texts: Why aren't solenoid/electromagnet windings insulated?

texts:
This has been bugging me for a long time. Take this video for example.

I have always thought that electricity will take the shortest path. When the electromagnet's windings are uninsulated, it seems that the electricity would flow straight through the "mass of metal" created by the wire, not in the circular path needed for the electromagnet to work. I have also seen solenoids that work like this. How does this design work?


texts: How to figure out the pin out of this undocumented LCD?

texts:
I have a very tiny LCD ripped from a piece of electronic scrap. The LCD is about 1 inch by .25 inches. It does not include a backlight(it had an external LED functioning as the backlight) and is basically just a flat piece of glass. There are 16 wires coming from the board it's on. (it is just a plain "breakout" board for the small SMD connector)

The LCD board says "LCD:91-42959-B01" which does not pull up any relevant results with google.

I've tried my best to test it with a multimeter, but nothing seems to even be connected. I'm not sure how most simple LCDs work, so what can I do to try and get this to work (hopefully) without ruining it in the process?

Also, because this is a flat piece of glass, I do not believe there will be a command type of interface, because as far as I can tell, there is no actual logic connected to it. It's just 16 wires going into clear glass. Also on the breakout board they are bundled into 4 bundles with 4 wires each(with brown, orange, orange, yellow being the colors in each bundle). I have no idea if this matters, but I figured maybe it could help


texts:
A single NPN IGBT chip can usually be tested by a 9V battery between gate and emitter.

However opening up a larger module reveals many IGBT modules in parallel. I`ve seen some inverters using several of these in parallel again, together maybe 200 IGBT chips in parallel for a single phase.

In the scenarios of only parts of the IGBT have blown. Be it either 199/200 or 5/200 and assuming no visible damage. Is there any way of measuring if this is the case? The 9V battery test would perform as if no problem was present. Opening up the module for inspection ruins the module.

simulate this circuit – Schematic created using CircuitLab


texts: Spice simulation of 555 flasher will not oscillate

texts:
I am hoping that this is a very simple question.

I am trying to simulate the circuit in ngspice, but it seems that the oscillation will not initiate. I delayed the on pulse, but the expected 20Hz square wave does not appear.
I have spent an inordinate amount of time just because I am old stubborn. I might just have to build it first, but I am rearranging my stuff.
Thanks a lot for your help.
Note: the V1 pulse brings up the power supply after the simulation starts.

Circuit with a generic 555 timer.

Circuit description from ICM7555.


texts:
I am trying to do a simulation for a transmission line, I can draw below example circuit but got below two questions.

How to do this step: .model TLine LTRA(...)

It looks to define the component property and should I do it in "component attribute editor" but it doesn't work.

The 50 ohms impedance is based on the calculation SQRT(L/C), there is no column to specify this value, right?


texts: How to calculate base resistor of a NPN transistor that drives a MOSFET?

texts:
I'm currently trying to design a circuit that allows me to control a water pump running on 12V through an ESP32 microcontroller. The GPIO pins deliver only 3.3V, so I ended up controlling a NPN transistor (e.g. 2N2222) with the microcontroller and the transitor is connected to the MOSFET. Below is a schematic of what my circuit looks like:

D7 is connected to the microcontroller. My question is: How do I know what value of resistor I should use for R2? Usually that isn't such a big problem to figure out, but since I'm using a MOSFET I'm not quite sure how to do it.


texts: Running a desk fan off a car battery: How long will it last?

texts:
I'm going on a road trip and will be sleeping in the bed of the truck at night.
 I want to be able to have a fan running during this time.  I have a couple old car batteries sitting around, and I was thinking I could charge them up before I leave home, and then use them to power the fan at night.  The engine will not be running when I am using the fan, and I don't want to drain the battery that's used for starting the engine.  The thought is that I get a power inverter so that I get 120 VAC out to power typical AC desk fans (the smaller the better).

I want to calculate how long a battery can power such a fan.

Let's say the fan is a 120 V, and on the "Low" setting consumes 30 W.
Let's say the battery is a 600 CCA, 12 V, lead-acid car battery, with a 50 Ah capacity (20 Ah Rate).

How can I calculate the time that the battery will last?  I know that the power rating of the fan can give the current used (P=IV), and the capacity of the battery can tell me how long at whatever current (Capacity = Amps*hours).  But I don't know which voltage to use (12 or 120), or how to incorporate the inverter or the part about the 20 Ah Rate.

I'm also open to other ideas for running a fan with the engine off.

Another additional thought is to connect the battery in parallel to the truck's battery and that way it would be charging when I drive during the day, but the batteries are different capacities, and I don't know if there would need to be other hardware to prevent my truck battery from being drained.  If this can't be done then I will just drain the battery and when it's dead, I'll just have to wait to get back home to charge it.

Thanks!


texts: Determining the input current of an optoisolator based on output current and CTR

texts: I have an optoisloator (CTR min:20% max:400%) in my circuit whose output current (Ic) is around 10 mA. To facilitate this much output current, how to decide the input current(If)? whether i have to concentrate on min: CTR value or max: CTR value. Please clarify.


texts:
In audio interfaces (e.g. USB) you often find one input that can handle XLR and jack.
The jack input is usually used for an electric guitar input. For that, there is a "High-Z" switch to it.
It's clear for me why there is a need for a high-impedance input with pickups from electric guitars - the pickups themselves can have an impedance of a few 10k in some frequencies. To get the amplitude of the signal at the audio-interface input as independent as possible from the frequency, you want to use a high-impedance input stage (resistor-divider etc.)

What is the disadvantage of a high-impedance input?
Why do we need the possibility to make it a "not high impedance" input?
Shouldn't microphones work with high-impedance inputs as well?
Wouldn't it be more linear?

One idea that I have is, that high values of resistors are more noisy than lower values and of course you want to have as little noise in your signal as possible. But as far as I know, the high-impedance is done by using JFETs instead of BJT. Am I wrong?


texts:
I have somehow managed to make a little gizmo that primarily consists of an MCU, some sensors, and wireless connectivity. I have gone through the process of making the initial prototype, then designed a board and made an SMD version. It's small and it works nicely. It also has a nice case that I managed to 3d print then cover in a little homemade silicon sleeve. I made it for myself for fun but it works really well and everyone seems to want one. I could make maybe a few dozen of them by hand and sell them off to the people I run into that want one, but what if I run out quickly? It seems possible enough that I feel a little panicked at the thought, simply because I don't know where to start.

Where do I even begin to figure out how to take something to market? Is there a standard resource library for this sort of thing? I see no other question on the EE SE that asks quite what I'm asking (most people are looking looking for design or product advice, sigh, but I've already got that done), so maybe this is completely the wrong forum (another hint: I have no idea what to tag this), in which case I'd be happy to move it somewhere more appropriate.

Other pertinent info: I'm in the USA (NYC area) and possibly could be interested in shipping to other markets (Europe, possibly Asian markets) down the line.

Types of questions I am hoping to find advice for:

How do I find manufacturers for the different components (PCB, getting it soldered together, case, etc.)? Or maybe it's better put to say that I'm trying to find out how to shop manufacturers.

Should I split manufacturing to try to prevent IP theft?

Does the shop that assembles the boards also program them?

Certifications???

Marketing and distribution... ??? (I have a decent idea of how to get started here, but resources are always welcome)

Things I'm missing completely?

I feel like I know how to find what I need to engineer something and where to find general business advice, but the chasm between the two seems swampy and mysterious to me.


texts: Requirements for measuring PCIe 2.5GT eye diagram

texts:
What is suitable equipment for measuring an eye diagram of PCIe differential pairs. I would like to evaluate the signal integrity of a PCI lane RX/TX/CLK 2.5GT. What is the recommended minimum sampling rate of a scope capable of such?

Also is it necessary to use active differential probes for this to get a good enough measurement quality, what constitutes an adequate setup for this ?


texts: how do i actually put a diode across a motor?

texts:
I've had frequent failed switches on my portable automobile air pump. The last time it failed it shows sparks on the switch. I've been reading around and it seems that I need to add a diode across the motor, something like 1N4004 seems to do the job. However, I'm really confused to where the diode will fit?

The motor has 2 wire coming out of it. So do I put the diode across it? Then where does the switch fits afterwards?

The motor is DC 12-13.5V with max of 12A. (The label says so), it is usually
powered by ciggarate socket on the car.

One last thing, since it's DC, I've made the assumption that I didnt need to go for RC snubber circuit. Is this ok?

Thank you.


texts: Effect of zero coefficient in polynomial in Routh Hurwitz?

texts:
Consider this polynomial:
\$s^4+2s^3+3s^2+4s+5\$

What happens if we have zero in place of any coefficient in our polynomial? Will that indicate that the system is unstable?

Let say we have zero instead of '2' in  the above polynomial, will this make the system unstable?


texts: Effect of load on power factor in induction motor

texts:
I got stuck in an MCQ question. Which is as following :

  Q.1) power factor of a squirrel cage induction motor is :

  (a) Low at heavy load only

  (b) Low at light and heavy loads

  (c) Low at light load only

  (d) Low at rated load only

I am getting an answer from what I understand but answer is given some other option. telling which will bias opinions. So I would just like to knoe what your thoughts are. Also not long explanations are required (just tell what would happen to slip and why?)


texts: effect of op-amp open loop gain on THD of analog function generator

texts:
I am trying to build this analog function generator circuit on a multisim (simulator), and it is working 100%, but I have a few questions concerning the THD of the final output.
What is the effect of both the unity-gain bandwidth and the open-loop gain of all op-amps on the THD of the final output? Meaning what would happen if I change the unity-gain bandwidth or the open-loop gain of all the op-amps?
I know I can simulate this and calculate the THD using multisim, but I want to know the reasons behind the effects if any.
The op-amps have the same following characterstics,
Open-loop gain = 10k
Unity gain bandwidth = 10MHz
Slew rate = 1 GV/s
Rin = 10 Mohm
Rout = 10 ohm
The first stage is an astable multivibrator/oscillator and the output frequency is 10kHz


texts: Measuring vehicle's forward and lateral acceleration using a smartphone

texts:
I want to measure the acceleration (forward and lateral separately) using an android smartphone device in order to be able to analyse the driving behavior.

My approach would be as follows:

1. Aligning coordinate systems

Calibration (no motion / first motion):
While the car is stationary, I would calculate the magnitude of gravity using Sensor.TYPE_GRAVITY and rotate it straight to the z-axis (pointing downwards assuming a flat surface). That way, the pitch and roll angles should be near zero and equal to the angles of the car relativ to the world.

After this, I would start moving straight forward with the car to get a first motion indication using Sensor.TYPE_ACCELEROMETER and rotate this magnitude straight to the x-axis (pointing forward). This way, the yaw angle should be equal to the vehicle's heading relativ to the world.

Update Orientation (while driving):
To be able to keep the coordinate systems aligned while driving I am going to use Sensor.TYPE_GRAVITY to maintain the roll and pitch of the system via

where A_x,y,z is the acceleration of gravity.

Usually, the yaw angle would be maintained via Sensor.ROTATION_VECTOR or Sensor.MAGNETIC_FIELD. However, the reason behind not using them is because I am going to use the application also in electrical vehicles. The high amounts of volts and ampere produced by the engine would presumably make the accuracy of those sensor values suffer. Hence, the best alternative that I know (although not optimal) is using the GPS course to maintain the yaw angle.

2. Getting measurements

By applying all aforementioned rotations it should be possible to maintain an alignment between the smartphone's and vehicle's coordinate systems and, hence, giving me the pure forward and lateral acceleration values on the x-axis and y-axis.

Questions:

Is this approach applicable or did I miss something crucial?
Is there an easier/alternative approach to this?


texts:
I'm working on a personal PCB design that will include ethernet pass through. Photo attached.   Basically just ethernet in from a router, straight over the PCB to ethernet out which will go to a CPU.

The total length from the input to the output RJ45 is about 2 inches. It is a 4 layer board (L1 signal, L2 GND, L3 VCC, L4 signal). What are the main concerns from a design perspective for keeping the signal as un-distorted as possible over this short PCB run?

Here are my current design guidelines:

No 90° turns on traces (acts as antenna).
Keep input RJ45 on top side of board, output
RJ45 on bottom, so connecting input pins to outputs pins don't
require crossing over traces; i.e. pin 1 will be on the left side of
the PCB for both connectors.
No other traces crossing under/over the traces.
Only change signal layers (L1-L4) once.
Include GND copper plane around traces for additional isolation.

Any other considerations I should include for this short PCB run? Appreciate any and all help.


texts: LM317, basic voltage regulator, why does it get hot when not connected?

texts:
I have built this little voltage regulator circuit: circuit diagram

I am a hobbyist, so these may well be screamingly obvious questions. I ask because I haven't found the answer to my first question.

Why does the LM317 get hot even when current is not being drawn, ie when the ends are not connected? (To my intuition it would only get as hot as current that it is 'choking' to reduce the voltage, but if there is no current there is nothing bring down. Where does this evergy come from?)
Why are the two capacitors used in this circuit, it works fine without them? (I know this is a simple question so the technical term for it or alink would totally suffice)

Much appreciated!


texts: I got some capacitors about two years ago now, which I foolishly removed from their bag, and I quickly forgot their markings. I can't even figure out which kind of capacitor it is. Tantalum seems the most similar, but the markings are wrong for a tantalum cap. Could you please help me identify this?


texts: Potential drops in BJT in CE configuration?

texts:
In a simple p-n junction diode, there is a \$V_{eq}\$, the potential difference between the p-doped and the n-doped portion of the diode. When an external potential \$V\$ is applied in forward bias, and if the entire resistance of the diode is assumed to be at the junction (depletion region), the new potential difference between the p-n junction becomes \$V_{eq}-V\$ and the current is \$I_0(\exp(qV/k_BT)-1)\$(where \$k_B\$=boltzmann constant, \$q\$=carrier charge, \$T\$=absolute temperature). I want to extend this to a BJT.(Bipolar Junction transistor, pnp)

Let us assume we have a BJT in CE(common emmiter) configuration with \$V_{eq}^{BE}=100, V_{eq}^{BC}=80\$ as in image (1). Then the external \$V_{CE}=10\$ is applied as in image (2). (B+base, E=emitter, C=collector)

  Does this drop appear completely at the BC junction or partly at the
  BE and the BC junction? (as assumed in the image)

Next, if we have \$V_{CE}=10\$ (such that the BC junction is reverse biased) and now we also connect a small \$V_{BE}=3\$.(image (3)). In this case, the potential difference at the BE junction will always be less then \$V_{eq}^{BE}\$ on account of the non-zero forward bias \$V_{BE}\$ and hence will be forward bias (\$V<V_{eq}\$) for any value of \$V_{BE}\$.

  Then why do we say that in the cut-off state, the BE junction is also
  reverse biased? Will is not be forward biased only?

Moreover, there is almost no current (both \$I_B\$ and \$I_C\$)in the cutoff region, the reason being reverse bias of both the junctions. This should be false, and the absence of current should be due to the fact that the knee-voltage has not been reached for the forward biased BE junction?  The three images referenced to in the question is posted below.

simulate this circuit – Schematic created using CircuitLab


texts:
I write a structure into EEPRM as follows

typedef struct
{
   fract32 AmpF; // amplitude fundamental
   fract32 AmpH; // amplitude harmonic
   UINT32 b;
   UINT16 d;
   UINT16 crc;

}CoilBoardAmp_T;

// mechanic angles and salt water angles of coil stored in coil-eeprom
typedef struct
{
    ChannelData_T     channel[NUM_CHANNELS];
    CoilBoard_T       coilboard;
    CoilBoardAmp_T    coil_h;
    CoilBoardAmp_T    coil_d;
//  UINT32    gCoilSerialNumber;
//  UINT32    gInversSerialNumber;
} Coil_Eeprom_Data_T;

I set that data by a software, which writes to that structure.

The problem is when reading that structure at the first time without writing to it, I read false data.

I need to detect that point. How would I know If the data that is read is false, or how would I know that I read the data without the software.


texts:
I'm working on a solution for 2 devices to communicate with each other over a very short range. A user will be wearing device #1 around their wrist, and in that same hand will be holding device #2. The goal is that the two devices will know about each other at that short range (less than a foot).

I've looked into RFID and NFC solutions, but the cost of readers are more expensive than I'd like for something like this. A lot of RF transceivers are in the right cost range, but the shortest transmit range I could find for RF transceivers was about 10 meters (with no antenna).

Is it possible to shorten the range of an RF transceiver to fit this goal? Or, if that's not something I can do, is it possible to be able to get a relative distance between the two devices and have some code logic to ignore the device outside my desired range?

I'm really new to playing with electronics so a lot of what I'm reading online is going over my head, but I haven't seen anything that can come close to answering this.


texts: Powering a DC to DC power supply that came without an adaptor

texts:
I bought a mini ATX DC to DC power supply on eBay to use with a motherboard. Unfortunately I did not notice it came without any kind of adaptor. So what I have is basically two wires, red and black, that is supposed to connect to a "12 volt power supply". I hardly think my local gadget store sells any kind of adapter that accepts two bare wires.

Is there an adaptor for sale that is made to work with this kind of power supply?


texts:
When inspecting a PCB earlier today it occurred to me that all traces you find on modern PCB's are confined to 45 degree increments with respect to the (typically square) board edges.

What is the rationale for this?  Is this a fabrication consideration or something electrically inspired?


texts: Strange behaviour while simulating switching loss

texts:
I am trying to simulate gate charge profile and switching loss curves of transistor as in the circuit below. I used ideal current source (30uA) for load, clamp diode (piecewise-linear model with ron = 1mΩ and Vth = 5mV as shown in the picture below).

There is a strange period I don't understand, when VG < Vth, ideally the transistor current should be zero and all ideal current source (30uA) should flow through the diode. However, as you see in the picture below, the diode current is very large (more than 500uA) here. I can not explain what is happening here.
Could anyone explain this?

Here is the diode model (I got this from Cadence community forum). The diode symbol is from analogLib libray.

  subckt idealDiode (a c)  // note, the on resistance shouldn't be
  below 1mOhm D1 (a c a c) relay rclosed=1m vt1=0.0 vt2=5m
  ends idealDiode


texts: Current Transformer (CT) and Potential Transformer (PT) Sensors - How to Measure Electrical Power Usage?

texts:
I am not from Electrical Engineering background and so, does not have much idea about how energy power meters work.

I want to measure electrical power usage of a three-phase induction motor. So, I need three CT sensors and three PT sensors to collect the current and voltage readings from the power transmission line from which the induction motor is taking power. And then, using that current and voltage readings, I have to measure how much power the Induction Motor is using? Is that correct? Actually, I am confused because, when I asked the manufacturer to provide me all the instruments needed to measure electricity usage, they gave me only three CT and one PT sensors. Can any body please explain to me how the CT & PT sensors are used to measure electricity usage data (may be with a simple diagram). I just want to understand how current and voltage data are collected. The electrical power usage calculation I can do by myself. Thanks in advance.


texts: Is the theory of operation behind my FPGA design acceptable?

texts:
(This question is somewhat related to a previous question of mine.)

I'm trying to use an FPGA to drive an LED strip which contains several WS2801 ICs. (WS2801 datasheet)
The operating premise of the WS2801 is simple - clock in 24 bits of data (8 bits each for R,G,B) and then leave the clock low for 500µs. This causes the WS2801 to latch the data and change the LED color. If you have a strip of multiple WS2801s in series, you clock in 24 bits * (Number of ICs) and then hold the clock low to latch 'em all up. Simple, right?

So, I have created a "WS2801 Test Driver" module, clocked at 2MHz. (Datasheet claims it can run as fast as 25MHz but I have yet to test this in practice).

Basically, my driver is a shift register (with a pre-loaded 72-bit value) and a counter.
Why 72 bits? I wanted to test a string of 3 WS2801 ICs. In practice, I need to load in data from some kind of buffer...thing. (Any suggestions for that would be appreciated but that seems mostly out of the scope of this question.)

Here's a simple block diagram:
I will add a more accurate block diagram in a little bit, I don't think the clock enable is shown accurately.

The clock is shared between the shift register and the counter. After 72 ticks (all the data has now been shifted out), the counters output goes low, disabling the clock output and preventing data from shifting out. This is the start of the 500µS clock delay.
The clock is obviously still running the counter, which continues to keep counting. Now the counter waits 1,000 ticks and then drives the output high, enabling the output clock and serial data output.
Why 1,000 ticks? - At 2MHz, the period is .5µs. To get to 500µS,we need 500/.5 = 1,000 ticks. In practice, I've found I need to add a little fudge factor - 1,032 ticks, actually. This might be due to poor clock routing or propagation delay or something of that nature. I haven't really looked into it yet.

The design as implemented seems to work OK. I looked at the outputs on a logic analyzer, everything seems fine and I'm getting the colors on the LEDs that I expect.

My question is:

Is this a good design? If there is a better method of going about this, please suggest!

If you read the link to my previous question: Does it seem like this design will integrate nicely into the bigger picture of creating an FPGA based Ambilight clone?

Thanks for reading!


texts: Problems Re-Flashing ATtiny85 After Setting prescale to 0x00

texts:
After flashing the ATtiny85 with code including setting the clock prescale to 0x00 (in code, not flashing the fuse), the next time I try and flash I get the following errors preventing me from doing so:
avrdude.exe: error: programm enable: target doesn't answer. 1
avrdude.exe: initialization failed, rc=-1
avrdude.exe: AVR device initialized and ready to accept instructions
avrdude.exe: Device signature = 0x500075
avrdude.exe: Expected signature for ATtiny85 is 1E 93 0B

I really don't understand. Obviously the USBasp is connected correctly and working (otherwise I would not get the "AVR device initialized..." trace line. I have tried re-flashing code that I was running (CLKPR = 0x00). Then tried flashing a simple blink program (no prescale), still failed. Then tried the blink program on a different ATtiny85 - worked. Back to the original, still can't flash!!!
I tried resetting the fuse using the -B1 to -B6, nothing...
I am very much a novice, so there is probably something stupid that I am doing!

Resetting that device just before I sent the flash sees to work. However, I now appear to have a new problem when trying to flash the fused back to default!
The command that I am issuing...
avrdude  -p t85 -P COM3  -b 19200 -c avrisp  -U efuse:w::m -v -B700

The output...
avrdude.exe: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.08s

avrdude.exe: Device signature = 0x000000 (retrying)

Reading | ################################################## | 100% 0.06s

avrdude.exe: Device signature = 0x000000 (retrying)

Reading | ################################################## | 100% 0.06s

avrdude.exe: Device signature = 0x000000
avrdude.exe: Yikes!  Invalid device signature.
             Double check connections and try again, or use -F to override
             this check.

After reading round, I am pretty sure that it is clock / crystal related. I am just not too sure how to go about adding a crystal.
Thanks again,
Harold Clements


texts: Capacitive Touch Screen Stylus circuit type of thing

texts:
I am trying to figure out how to make a circuit that works much like a stylus for capacitive touch screens such as on an iPhone.

Given it's going to be a simple experiment, I was thinking of using an Arduino as the controller.

I have watched several videos and articles regarding "Aurdino Triggering Touch Screen", but none of them work reliably.

A stylus on the other hand can trigger the screen reliably and from a distance.

EDIT: A Samsung stylus triggers a on-screen pointer from at least 2 cm distance, while the tip of the stylus is a button notifying the phone to do some action, such as painting.

So what I need for my final project is to put electronics inside of a small plastic box (1.5cm^3) and the cube need to be able to trigger a spot beneath itself on the screen at regular intervals.

Is this possible?

EDIT:

To clarify this is exactly what I am looking for:

Circuitry that is placed in a 1.5 cubic centimeter box that triggers a 5 millimeter diameter circle on the screen under the box causing a virtual finger-press.

Distance between screen and actual circuitry is aprox 1mm.


texts: Does a BJT Class A Amplifier act in Reverse Mode?

texts: The signal above has negative voltage, so should I take it that it is positively clamped or biased? Or, does the NPN go in Reverse Mode, which I don't think it does (as Reverse Mode only explains the later half of the sine wave, not the negative OUT of the first half).


texts:
I am a novice who purchased several TO-220 L4940v5 chips thinking they were drop-in replacements for the inefficient TO-220 7805s that I've been using.  But not a single one seems to work.  No heat, no voltage output, nothing. Thinking I had the pins backward I tried a fresh one with the in & out swapped, but still no result.

Is the L4940v5 not pin-compatible with the 7805?

EDIT: Here is what I built.  It is the same as the reference diagram on the L4904v5 datasheet, except my output capacitor is larger (it's what I had).


texts:
Let's say I have 100W light bulb connected to battery. So let's say the lightbulb will use 100W power.

Now let's say I have 2 light bulbs:

First  100W

Second 200W

What is the power use of each light bulb if they are connetcted in series circuit? I mean cause it is series circuit will they get enough power or just part of what they "need"?


texts: Can a relay use both a flyback diode AND resistor for voltage suppression?

texts:
I have a Bosch type 5-pin relay with a built suppression resistor on the coil.

I've read that a resistor is not as efficient as a flyback diode at suppressing voltage spikes when the coil de-energizes.

Can I keep the resistor in place, and add a flyback diode across pins 86 & 85 thereby having both the resistor to dissipate the voltage and the diode to reroute the voltage? Is there any harm to this method?

Thank you everyone for chiming in. I know very little about electrical wiring and I appreciate everyone with more knowledge than me helping me with what I'm trying to do.
I'm installing a water methanol injection kit into a turbo charged track car. In the attached diagram, the AEM main controller drives the pump and solenoid that attaches to the injection nozzle to control flow and prevent leakage.

The AEM Failsafe is a computer with a flow sensor that monitors fluid flow. Too high a flow and I could hydro lock the engine, and too low and I could have detonation.
Under too high or too flow (alarm conditions) the AEM Failsafe computer will trigger two output signals. The Yellow wire output is +12V output trigger, and the Blue wire is Ground trigger. These triggers can be used to trigger a buzzer, LED light, or to the Engine management to cut turbo boost, etc...

In my application, I intend to use the Yellow trigger wire (+12V) to trigger relay #1 to cut power to the fluid pump. Yellow wire to relay pin 86, pin 85 to vehicle chassis Ground. The relay will run as NC (using pin 87A), only cutting power to the pump when energized (alarm condition).

The Blue trigger wire will trigger Relay #2 to control the solenoid. Since the Blue wire is a Ground wire, I will connect to pin 85 on the relay, pin 86 to +12V. The solenoid positive wire will connect to pin 87A, 30 pin to +12V.

The AEM Failsafe is prone to damage, many user assuming from the yellow and blue trigger wires. That's why I'm trying to use a diode across the relay coil. But the relays I purchased already have a resistor on the coil.

Anyhow, Is my overall diagram kosher???

Thank you everyone :)


texts:
I have a circuit (below) where there's an IC responsible for battery charging, voltage boosting, power/regulation, etc. It has an "Enable" pin which is pulled up to VCC by default, and determines whether it supplies power or not. (High == ON, Low == OFF)

I want to hook this up to a toggle switch so that when the toggle is "open", the "Enable" pin is pulled down to ground. Is there a simple/easy way to wire this? I'd like to avoid adding any additional components if possible.

Right now I have the leads connected as below, which works but is confusing because it is the opposite of the switch's labeling. (Open-switch turns the system on and closed switch turns it off).

Thanks!

simulate this circuit – Schematic created using CircuitLab


texts: Power and ground configuration in a schematic

texts:
I have a schematic for a commerical circuit board, and I was curious about the following:

            1.2V
             |
------------------------------------------
|      |     |      |      |      |      |
=10uF  =1uF  =.1uF  =.1uF  =.1uF  =.1uF  =.01uF
|      |     |      |      |      |      |
------------------------------------------
             |
            GND

What is this network for?  I see that for all of the ICs there is a decoupling capacitor on the input voltages near the IC.  The above, however, appears to just be caps connected between the supply and ground.  What purpose does such a network perform, and how does one decide on the value Ctotal of the network?  They all add up to Ctotal=11.41uF for the 1.2V supply.  There is also a 3.3V supply with the same network, except that Ctotal=11.43uF.

There is also a ground-ground connection I am curious about.

 ------------------
 |                |
GND              GND

What is the purpose of coupling ground to ground?


texts: Finding the Thevenin equivalent circuit for the following one

texts:
From my poor drawing , it's obvious that the resistance between A and B terminal is just

$$((((((100 || 100)+30) ||80)+20)||60)+20) = 50\Omega$$

But I am getting confused about determining the Thevenin voltage across the AB terminal.

If I remove the \$50\Omega\$ resistance from AB then I can ignore the rightmost \$20\Omega\$ resistor as no current is passing through it.

Then the equivalent resistance for the circuit would be (across the 80V source) $$((((60+20)||80)+30||100)+100) = 141.176\Omega$$

So, the current through the leftmost \$100\Omega\$ resistor is \$80/141.176 = .567\$A.

Then the current through the \$30\Omega\$ resistor is \$.567 \times 100/130 = .436\$ A and the current through the \$60\Omega\$ one is \$.436/2 = .218\$A. But then the \$V_{\text{TH}} = V60 = 60 \times .218 \text{V} = 13 \text{V}\$.

But the actual answer in my book is 10 V. What am I doing wrong here?

Source: It's an example problem from "V.K Mehta - Principles of Electronics".


texts: How do I transition from using the Arduino IDE to plain avrdude/make?

texts:
Part three of a three part series on transitioning from Arduino to a plain AVR microcontroller and minimum supporting components (part one, part two)

I already know how to use an Arduino as a programmer for an ATmega, and I know how to use an external programmer for the ATmega/Arduino using the Arduino IDE.

What do I need to know to start programming an ATmega1 with the command line tools? A brief overview of the different language features and steps to make/upload would be nice.

1. ATmega328, or a smaller/cheaper AVR microcontroller, even an ATTiny if possible, which will still run the applicaton: See this post for some details on shrinkifying to an ATTiny.


texts: How to choose between ceramic and electrolytic capacitors

texts:
I was designing a circuit, I found a lot of datasheets that don't specify if the capacitor should be ceramic or electrolytic. So I started to wonder if the value of the capacitance would tell me the kind that should be used.

Is it true that when the capacitance is of nF or pF order, ceramic capacitors should be used and when the order is of uF, electrolytic ones should be used?


texts: Can I replace the original laptop battery with an OEM battery with higher voltage / power?

texts:
My original laptop battery is 11.1V and 74 Wh. It was starting to swell and needed replacement, but I bought accidentally bought a wrong OEM battery that is 11.4v and 71 Wh.
Is it safe to proceed and use this OEM battery?


texts: SPI comunication - Only receive 0xFF (Linux)

texts:
I've been stuck in setting up the SPI communication in Linux and can't figure out any solution.

I working with a beagle bone black, which runs Linux. I have a piece of code that send data through the SPI bus if I connect MISO and MOSI pins I will receive the data that I have sent (so far so good).

The problem comes when I try to connect with the sensor I want to communicate with, everything I receive is zeros!

I am pretty sure that the problem comes from the SPI configuration in Ubuntu (since I already could communicate with the sensor, using SPI, using an Arduino for the purpose). But somehow, when I try to replicate the same very code to beaglebone I can't communicate!

In this link is an explanation of how to configure SPI on ubuntu: https://elinux.org/BeagleBone_Black_Enable_SPIDEV

I already followed the tutorial but the problem remains. Does anyone have some tip that must help me?

So, I already analyzed with the scope and I found that so intriguing, it's happening the follows:

In the cs pin and sck it's having oscillation. Nevertheless, in the MISO and MOSI pins there is any oscillation.

What's intriguing me the most is that if I connect MISO and MOSI I receive the sent data, but I cannot see any variation on these pins. Any idea what's happening here?

Here's my device tree:

/dts-v1/;
/plugin/;

/ {
    compatible = "ti,beaglebone", "ti,beaglebone-black";

/* identification */
part-number = "spi0pinmux";

fragment@0 {
    target = <&am33xx_pinmux>;
    __overlay__ {
        spi0_pins_s0: spi0_pins_s0 {
            pinctrl-single,pins = <
              0x150 0x13  /* spi0_sclk, OUTPUT_PULLUP | MODE3 */
              0x154 0x13  /* spi0_d0, INPUT_PULLUP | MODE3 */
              0x158 0x33  /* spi0_d1, OUTPUT_PULLUP | MODE3 */
              0x15c 0x13  /* spi0_cs0, OUTPUT_PULLUP | MODE3 */
            >;
        };
    };
};

fragment@1 {
    target = <&spi0>;
    __overlay__ {
         #address-cells = <1>;
         #size-cells = <0>;

         status = "okay";
         pinctrl-names = "default";
         pinctrl-0 = <&spi0_pins_s0>;

         spidev@0 {
             spi-max-frequency = <24000000>;
             reg = <0>;
             compatible = "linux,spidev";
        };
    };
};

};

I am not quite sure about the definition of the OUTPUT_PULLUP and INPUT_PULLUP, I tried to follow the tutorial above the maximum possible. You can see the Beagle bone registers by searching for "Beagle bone registers" on google.

Thanks for your help,


texts:
I have a Blue Pill (STM32F103) and connected to it a ws2812b led strip. I am trying to send data to the led strip via PWM over the TIM2 peripheral (Pin A0). To change the duty cycle of the TIM2 PWM I use a DMA channel. This works perfectly at lower speeds (eg 100khz) but as soon as I get near to the required 800khz of the leds the MCU seems to send some pulses twice, this would make sense if I overload the bus, but from what I have gotten out of the datasheet it should be able to handle 800 kbyte/s.

What makes the entire thing more complicated, is that I am trying to write this in Rust and there is no code I could compare mine too. I will try to post the relevant parts of the code and explain it as good as I can.

Main Code:

// setup pwm
let mut pwm = p.TIM2
    .pwm(
        c1,
        &mut afio.mapr,
        800.khz(),
        clocks,
        &mut rcc.apb1,
    );

let max = pwm.get_max_duty();

let one_duty = (max * 16 / 25) as u8;

let buf = singleton!(: [u8; 25] = [one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, one_duty, 0]).unwrap();

// set duty to zero
pwm.set_duty(0);
// enable pwm output
pwm.enable();
// enable the dma and wait for it to finish
pwm.write_all(channels.5, buf).wait();

WriteAll function code:

pub fn write_all<A, B>(
    self,
    mut chan: $c1_chan,
    buffer: B,
    ) -> Transfer<R, B, $c1_chan, Self>
where
    A: Unsize<[u8]>,
    B: Static<A>,
{
    {
        unsafe { (*$TIMX::ptr()).dier.modify(|_, w| {
            w   .tde().set_bit()
                .cc1de().set_bit()
        }); }

        let buffer: &[u8] = buffer.borrow();
        chan.cmar().write(|w| unsafe {
            w.ma().bits(buffer.as_ptr() as usize as u32)
        });
        chan.cndtr().write(|w| unsafe{
            w.ndt().bits(u16(buffer.len()).unwrap())
        });
        chan.cpar().write(|w| unsafe {
            w.pa().bits(&(*$TIMX::ptr()).ccr1 as *const _ as usize as u32)
        });

        atomic::compiler_fence(Ordering::SeqCst);

        chan.ccr().modify(|_, w| {
            w.mem2mem().clear_bit()
                // priority
                .pl().high()
                // size in memory
                .msize().bit8()
                .psize().bit32()
                .minc().set_bit()
                .pinc().clear_bit()
                .circ().clear_bit()
                .dir().set_bit()
                .teie().set_bit()
                .htie().set_bit()
                .tcie().set_bit()
                // enable
                .en().set_bit()
        });
    }
}

My question is: why is DMA not fast enough even though it should be as stated by the documentation?


texts:
I have a gadget (a Sonar) that stopped working (doesn’t respond to power on, power led does not turn on) and opening it to look for the typical signs of failure  I see an L7818 voltage regulator in TO-220 package that looks like it has overheated.

I’m confused about two things: First: Why would one use an 7818 circuit in a board powered by 12V DC? The board has an STM32 microcontroller and peripheral components (wifi etc) so I was expecting to see an L7805, not an 18V one. The 18V could be for powering the analog/sonar bits I suppose, but should I then not also find a 5V regulator somewhere for the logic parts? Just out of curiosity, what the likely power supply design here if input power is 12V (boat battery), and the board has a VRM requiring 20+ volts input, and having 18V as output?

Second: the product code on the VRM is a bit charred but looks like “L7818BT”. I can’t find that, but I can find an L7818CV. What is the meaning of the suffix letters in this case?

Edit: top and front view of the board. The VRM that looks overheated is the component screwed to a heat sink on the left in both pictures.

The small stacked pcb wth the large heat sink is related to the WiFi (black wire connects to a case antenna). The two large square components are both arm microcontrollers.

Update: some basic testing confirms the VRM is a red herring, or at least it's not the only issue. Applying 12V at the DC input (the 2 pin connection on the left), I can measure 12V at those solder points underneath only (see the last image). That is: there is no other place on the board that gets any voltage at all. I'd assume that means it has to be one of the very first components being bad then, or a mechanical/connection issue somewhere very near the power connector? Unfortunately the power button connection (the 2 red wires joining the PCB in a pool of yellow goo) hides a lot of the things in the area nearest to the power connection so I'm having a hard time figuring out what's going on right after the power connector.

Update2/Solution: The problem was one of the power switch wires (the one connected to the 12V end of the battery) must have come loose from the PCB, under the yellow glue. Instead of trying to repair it which would have required scraping the glue, I tried bypassing the switch and connecting 12V directly to the second power switch wire, which worked. The solution to get a working power switch was to solder a new power switch wire, directly to the +12V connector on the board (posslbly bypassing a component or two such as a diode in the process). Device works perfectly after this, including the switch.


texts:
I want to integrate a RaspberryPi into the case of my desktop PC, that has an ATX-PSU. I want the RaspberryPi to keep running, even if the PC is shut down. It would be nice to avoid the additional cable from outside the case to supply the RaspberryPi. So, is it possible to use the +5VSB to supply the RaspberryPi and the PC in parallel? It should work supposed the PSU delivers enough power via +5VSB, right?

I thought of using something similar to this, but without PS_ON:
http://www.amazon.de/Aqua-Computer-Connect-24pin-Standby-Aquaero/dp/B002BX05CM


texts: How do I detect human touch on a point on the PCB?

texts:
I want to print buttons in the silk screen of one side of the PCB. And, I want to detect if a human finger touches any of these areas. What kind of sensor should I use?

Can I do this without using a sensor product? For example, by placing traces behind the button shapes in some certain topology, and detect change in the capacitance between two points on the traces?


texts: Is the diode in this circuit connected in parallel with the resistor?

texts:
Using the example below my teacher started to explain the parallel clipping circuit.

Then he said that the diode is connected in parallel with the resistor but I couldn't understand why, because I think they are connected in series.

Could you tell me where I'm wrong?


texts: A statement which is not clear to me on NVIC configurations

texts:
See the document here.
I am interested on using external interrupts, and trying to configure NVIC at register level. The statement below, which can be found in page 215, confused me:

Each priority field holds a priority value, 0-255. The lower the
value, the greater the priority of the corresponding interrupt. The
processor implements only bits[7:4] of each field, bits[3:0] read as
zero and ignore writes.

Especially the bold part.
If that explanation was not present, I would directly think that I can write any number (0-255) to those 8 bit fields to set the priority. But now, I am confused such that whether I can use bits [3:0] or not.


texts: LTSpice simulation problem with calculus of power

texts:
I am trying to determine the optimal resistance of a simple circuit which would maximise the power harvested.

The calculus of V(Y) is funtionning

But the one of PRMS and PAVG is not

I changed my circuit (deleted Y which was indeed useless) but i still does not work. What can I do ?


texts: State Space Average Model of Non-Ideal Buck Converter

texts:
I've been learning power electronics and am trying to design a dual-switch forward converter. One of the things I've been trying to do is derive the small-signal equivalent circuit of the non-ideal forward converter. The part I'm having difficulty with is how to write the state equations when the ESR of the capacitor is included.

In order to better understand the model of the forward converter I'm following along with a state-space-averaging example of a non-ideal buck converter. This Paper describes on page 8 how perform a state space averaging on a non-ideal buck converter, which is similar to the forward converter since the forward converter is a buck-derived topology and the equations are nearly identical. The circuit is:

We can define the  state vector containing the inductor currents and capacitor variables x(t), input vector u(t) and output vector y(t) as:

Where Vg(t) is the input voltage, Ig(t) is the input current and v(t) is the output voltage.

Now, we need to write the state equations for the circuit during the first sub-interval when the transistor is on. During this interval the transistor is replaced by an equivalent resistance Rt and the free-wheeling diode is an open-circuit. The state equation of this linear circuit are of the form:

With the following matrices:

In expanded form this translates to:
\

Which are the equations for the first interval.
Where R1 is the inductor parasitic resistance, R2 is the capacitor ESR, Rt is the on resistance of the transistor and R is the load resistance.
I'm confused about the how the author derived these state equations. I'm sure there's something simple I'm missing in the circuit analysis, but I'm not able to get the KVL and KCL equations for my inductor voltage and capacitor current to match in order to get the SSA model of the converter in equillibirum. If someone could walk me through there derivation or provide hints I would greatly appreciate it. I've done SSA on various other converters and understand the process well, but the added complexity that the ESR's introduce is giving me difficulty. Thank you.


texts: I am trying to build this version of the Big Muff V7 on Eagle but can't seem to understand the schematic quite well. As you can seen on the image , there are couple 3 switches, sw 1a , sw 1b, and sw 1c , i can't understand how to connect those to the pedal switch , a.k.a Leg Switch .. My question is does anyone know how should i connect that switch to the rest of the schematic as i am quite confused ? Also does anyone have the Eagle footprint of those TRS female jack connectors ?


texts: Preferable pattern for differential length matching

texts:
When the positive and negative tracks of a differential signal are not equal in length, we add some bumpy patterns in the shorter track to make them equal. On the other hand, we usually have a rule for the gap of the two tracks in order to preserve a constant characteristic impedance for the signal (typically 100 ohms for differential signals).

So it seems that the length tuning patterns may change the impedance since they change the gap. How can we minimize the impact of the patterns on the impedance?

Generally, using a few patterns with large amplitude is preferable or more small patterns? For example, which one of these two approaches in this picture is better?


texts:
Is it hypothetically possible to triangulate the location within any accuracy of a server at an unknown location by using ping times?

9 computers with location known log on to a multiplayer server. The 10th player (unknown location) arrives. Can the pings to that machine acts as radii of circles on a map and a bunch of circle intersection math take place to narrow the location of the 10th user?

I am guessing it would depend on the correlation between ping and distance from a machine (since packets probably go through so many different routers before reaching location), but could a method like this pinpoint with more accuracy than just doing a lookup of the machine's ISP?


texts: When measuring a resistance using a multimeter it is a few percent out. Why?

texts: For example, if you were to put 5V across a \$150\Omega\$ resistor and measure its resistance with a multimeter, the reading would always be a few percent off the true value. What reasons might there be for this inaccuracy?


texts: How can I "print" traces on the back of a ceramic package?

texts:
I have a project I'm working on that is so tightly packed that I'm totally out of room. I could save the whole thing by slapping a bunch of surface mount LEDs (30 of them) on the back of a (non-surface mount) 28-pin ceramic package in my circuit and wiring them to the device's pins.

I've tried a few things without success, like gluing the LEDs in place and running very fine wire to the solder points on the surface mount LEDs and soldering them in place. The solder breaks down the glue (crazy glue almost works, but one way or another, the solder won't bond to the top of the contacts on the LEDs.)

I have copper tape that I've tried X-Acto-ing traces out of, but the soldering iron breaks down the adhesive and the whole assembly disconnects itself.

I've even tried conductive glue and conductive pens. They have such hit-or-miss impedance properties that the LEDs don't light evenly. One will be many times the brightness of another.

If I could afford the space, I'd just slap a PCB on there and call it good, but I really need the LEDs right on the back of the IC. I can fill in with epoxy after the fact to keep everything protected and in place.

Thanks...


texts: Accidently read resistance on live wires

texts: I have accidently taken readings of resistance on my digital multimeter on live mains and now the resistance function on my meter is not working. But i'm still able to use other functions in it. Is there a possible fix for it? I know that the multimeter is fused, why did'nt the fuse go off?


texts: Could you please help me about calculating the voltage on the 100 ohm resistor. I know the result is 0.708 V but how could I calculate it, is there an easy way for that?.


texts: Ripple when switching on MOSFETs with PWM

texts:
I'm currnetly trying to construct an electronic load for testing purposes and experimentation. This is my schematic:

R2 are 7 X 4.7 Ω , 150 W each, resistors in parallel to cope with power up to 1kW needed. PWM is generated from an Arduino Uno, and is seperated from the rest of the circuit with an optocoupler. 12V are used for switching the Mosfets on and off. When the PWM is high 12V are sent to ground through the optocoupler and the Mosfets are off. When the PWM is low the 12V fully open the Mosfets for the duty cycle that we set. This set up is tested with one Mosfet and seems to work. However for safety reasons and not to overheat the Mosfets from the high currents and the use for long periods of time, I want to use more. A test with 5 Mosfets in parallel mounted on a heatsink was made, however resulted in the following strange result when switching on the mosfets:

There is a strange ripple which can be seen on the oscilloscope that I can't understand the cause of it and it occurs only when switching from off to on. Is there a way to smooth things up? Thanks.


texts: My code tries to configure the CAN device, but it never leaves configuration mode. Why?

texts:
I'm using a PIC32MX534F064L, and I just started working with the CAN module. The first thing I tried was using the examples from Microchip. None of them worked. The basic problem is these lines:

CANSetOperatingMode(CAN1, CAN_NORMAL_OPERATION);
while(CANGetOperatingMode(CAN1) != CAN_NORMAL_OPERATION);

The while on the second line never completes.

I'll explain. The PIC32's CAN module has to be configured in the following order:

Enable the CAN module.
Switch the CAN module to "configuration" operation mode.
Configure the CAN module.
Switch CAN module to "normal" operation mode.

Step 2 and 4 are a little more complicated. Instead of just setting a register which would change the mode, there's a two-step process. You set a register (C1CON.REQOP) to request that the operation mode (C1CON.OPMOD) will change, and when the CAN module is ready to change, it does.

Anyway, here is the code. I'm sure I just forgot something, but scouring the Internet and trying various examples has been without result.

#include <plib.h>

#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_1

#define SYS_FREQ (80000000L)
#define CAN_BUS_SPEED 250000

BYTE CAN1MessageFifoArea[2 * 8 * 16];

int main(void)
{
    CAN_BIT_CONFIG canBitConfig;
    CAN_OP_MODE mode;
    int i;

    SYSTEMConfig(SYS_FREQ, SYS_CFG_WAIT_STATES | SYS_CFG_PCACHE);

    CANEnableModule(CAN1,TRUE);
    while(C1CONbits.ON == 0);
    CANSetOperatingMode(CAN1, CAN_CONFIGURATION);
    while(CANGetOperatingMode(CAN1) != CAN_CONFIGURATION);

    canBitConfig.phaseSeg2Tq            = CAN_BIT_3TQ;
    canBitConfig.phaseSeg1Tq            = CAN_BIT_3TQ;
    canBitConfig.propagationSegTq       = CAN_BIT_3TQ;
    canBitConfig.phaseSeg2TimeSelect    = TRUE;
    canBitConfig.sample3Time            = TRUE;
    canBitConfig.syncJumpWidth          = CAN_BIT_2TQ;
    CANSetSpeed(CAN1,&canBitConfig,SYS_FREQ,CAN_BUS_SPEED);

    CANAssignMemoryBuffer(CAN1,CAN1MessageFifoArea,(2 * 8 * 16));

    CANConfigureChannelForTx(CAN1, CAN_CHANNEL0, 8,
                             CAN_TX_RTR_DISABLED, CAN_LOW_MEDIUM_PRIORITY);
    CANConfigureChannelForRx(CAN1, CAN_CHANNEL1, 8,
                             CAN_RX_FULL_RECEIVE);

    CANConfigureFilter      (CAN1, CAN_FILTER0, 0x8004001, CAN_EID);
    CANConfigureFilterMask  (CAN1, CAN_FILTER_MASK0, 0x3FFFFFFF,
                             CAN_EID, CAN_FILTER_MASK_IDE_TYPE);
    CANLinkFilterToChannel  (CAN1, CAN_FILTER0, CAN_FILTER_MASK0, CAN_CHANNEL1);
    CANEnableFilter         (CAN1, CAN_FILTER0, TRUE);

    CANEnableChannelEvent(CAN1, CAN_CHANNEL1, CAN_RX_CHANNEL_NOT_EMPTY, TRUE);
    CANEnableModuleEvent(CAN1, CAN_RX_EVENT, TRUE);

    // The code gets stuck in the while and never finishes.
    C1CONbits.CANBUSY = 1;
    CANSetOperatingMode(CAN1, CAN_NORMAL_OPERATION);
    while(CANGetOperatingMode(CAN1) != CAN_NORMAL_OPERATION);

    // This code is never reached
    i=0;
    while(1)
        ++i;
}


texts: What to consider when powering multiple devices in parallel?

texts:
Briefly about my background, which might inform the question. I'm currently self-educating myself on some electrical engineering on-the-job. I'm learning from Art of Electronics and some other resources, and I studied physics in college.

The problem is this, I have several devices that I need to power from a single source. Their maximum power requirements are the following:

24VDC, 1A, 24W
24VDC, 1.35A, 30W max
Three with 24VDC, 46mA each
Two motors, 18VDC, 0.65A each

The total max current through my system is roughly 4.4A. I need to build a circuit that will handle power to all of these devices. My first assumption was that one should just be able to hook these all up in parallel across a 24V supply that will handle the current. What I have done, which is probably mistake number 1, is hook them all up directly to an 18V supply in parallel (the largest table-top supply we have in the lab). The result: something burned. I imagine if I had a 24V supply it would more than burn.

So, now I'm nose deep in Art of Electronics and these forums looking for principles, concepts, and precautions I should consider when trying to power such a system. I would greatly appreciate if you folks could point me in the right direction as I'm lost in the sea of technical literature.

Basically, I'm hoping someone will tell me "Hey, you need to build this standard current buffering circuit to prevent your parallel devices from drawing too much current and burning up the rest of your system" or "Go look up this concept that should lead you in the right direction as to what happens when you're drawing all kinds of currents in parallel like that"

Thanks in advance folks, hope I can be helped here.


texts:
How can ground loop be avoided when connecting two system with same ground. This happen in PC whith SATA cable or PCIe Card with seprated power cable.
My System

Board: I have two pcb each with a ground plane. The board #1 is powered up by a battery. and through board #1, battery connected to board #2 via two wire (battery V+ and V-).
Reciever: Reciever is WF111, a wifi module run @50MHz with SDIO
Transmitter: Transmitter is ZYNQ-7000 a Cortex A9 processor
Power: the processor is powered with LDO #1 (simplified) and WF111 through LDO #2(again simplified).
Signal: the signal between transmitter and reciever connected with a FFC cable between two boards.

Question
Sending gnd for current return path as suggested here, will create big ground loop and will act as a big antenna. So what you suggest.


texts:
We managed to hookup our hardware by following suggested design, and we wanted to use only CAN protocol. And on the breadboard with STN1110 DIP package everything works great on ECUSim 2000 simulator and on a actual car. BUT, when we designed a PCB and moved to QFN, we are getting weird messages from STN1110 chip.

For example, we have the same test environment for breadboard and for actual PCB, but for that PCB we just ended up with these messages from Torque "Identifying ECU" and "Check if ignition is on" (and it is on). With breadboard everything is fine, we are getting our readings.

Also, if we put on a side Torque, and if we try to communicate directly with STN1110, if we send for example ATZ, we are getting response valid response.
But if we try to run for example some command, let's say 0902 we are getting from PCB when we run the command via FTDI:
BUS INIT STOPPED
BUS INIT FB ERROR
(this is from PCB (QFN version of STN1110))

And we triple checked PCB design and all the traces between STN1110 and MCP2551 and MCP2551 and a simulator \ car, and everything is fine, we even replaced MCP2551 just in case but same error.

Any suggestion what else we can try?


texts: Can I swap an IRF7319 Dual MOSFET for another cheaper one?

texts:
I am a noob at electrical work and I want to put this little project together

There is a IRF7319 Dual MOSFET in the diagram, and this is the first time I've come across this component. Can I replace it with another MOSFET of similar rating? e.g. DMC3028. If not then what can I use and what should I be looking for?

RS Online lists as follows:

IRF7319 £1.77  and DMC3028  30p  .


texts: What is the difference between reading the FIFO registers(FIFO_DATA_OUT_L,FIFO_DATA_OUT_H) and Sensor output registers(OUTX_L_XL to OUTZ_H_XL) both are same?which is recommended to get the raw data from the sensor


texts:
I need some assistance on building a high gain amplifier using only BJTs, capacitors and resistors. I have made some before using op amps, but for this assignment I am not allowed to use Op Amps at all.

The amplifier has to be capable of providing a voltage gain of at least 1.5k V/V. We can use any value we want for the resistors, capacitors and input.

Here I attach a Multisim simulation of what I have so far:

If you can see at the end, I am able to get a gain of 1.5k, but my instructor says that I am using too many parts for it to achieve that. He said that I have to take away a lot of resistors and capacitors for it to be ok, or to use current mirrors or a differential amplifier and cut the number of components I am using. And this is the part I need help with because I do not know how to achieve that by my own.

Any advise would be gladly appreciated.


texts: UART Transmitter and Receiver on AXI bus

texts:
I designed two components: UART Transmitter and UART Receiver (sends/receives 8 bits of data). Both Tx and Rx are working fine but I'm unable to wrap them in a AXI bus interface component.
My UART Transmitter is defined as:
entity Uart_Transmitter is
port(
        start : in std_logic;
        inputData : in std_logic_vector(7 downto 0);
        txClock : in std_logic;
        txReset : in std_logic;
        bit_transmitted : out std_logic;
        stop : out std_logic;
);

Using VIVADO I created 2 AXI bus IPs mapping ports in memory, so I can control them via software (Vitis). About the Transmitter I mapped the signals in memory as follows:
status_reg0:
bit 0: uart_tx_stop bit (1 when tx ends)
ctrl_reg1:
bit 0: used to start the tx (assigned to uart_tx_start mapped to transmitter start port)
data_reg2:
7 downto 0: byte to transfer
This is the process I use to write data accessing memory. Essentially, I'm using BASE_ADDR+1 as ctrl_reg1 and BASE_ADDR+2 as data_reg2.
when b"01" =>
for byte_index in 0 to (C_S_AXI_DATA_WIDTH/8-1) loop
    if ( S_AXI_WSTRB(byte_index) = '1' ) then
    -- Respective byte enables are asserted as per write strobes
    -- slave registor 1
    ctrl_reg1(byte_index*8+7 downto byte_index*8) <=  S_AXI_WDATA(byte_index*8+7 downto byte_index*8);
    end if;
end loop;
when b"10" =>
for byte_index in 0 to (C_S_AXI_DATA_WIDTH/8-1) loop
    if ( S_AXI_WSTRB(byte_index) = '1' ) then
    -- Respective byte enables are asserted as per write strobes
    -- slave registor 2
    data_reg2(byte_index*8+7 downto byte_index*8) <= S_AXI_WDATA(byte_index*8+7 downto byte_index*8);
    end if;
end loop;

And I'm reading data as follows:
process (status_reg0, ctrl_reg1, data_reg2, slv_reg3, axi_araddr, S_AXI_ARESETN, slv_reg_rden)
variable loc_addr :std_logic_vector(OPT_MEM_ADDR_BITS downto 0);
begin
    -- Address decoding for reading registers
    loc_addr := axi_araddr(ADDR_LSB + OPT_MEM_ADDR_BITS downto ADDR_LSB);
    case loc_addr is
        when b"00" =>
        reg_data_out <= status_reg0;
        when b"01" =>
        reg_data_out <= ctrl_reg1;
        when b"10" =>
        reg_data_out <= data_reg2;
        when b"11" =>
        reg_data_out <= (others => '0');
        when others =>
        reg_data_out  <= (others => '0');
    end case;
end process;

signal uart_tx_start : std_logic;
signal uart_tx_stop : std_logic;
signal reset : std_logic;
signal uart_tx_input_data : std_logic_vector(7 downto 0);

[...]

status_reg0(0) <= uart_tx_stop;
uart_tx_start <= ctrl_reg1(0);
uart_tx_input_data <= data_reg2(7 downto 0);

uart_tx: Uart_Transmitter
port map(
        start => uart_tx_start,
        inputData => uart_tx_input_data,
        txClock => clk,
        txReset => reset,
        bit_transmitted => bit_tx,
        stop => uart_tx_stop,
);

The strange thing is that even if I write data in memory:
int * tx = (int*) TX_BASE_ADDR;
tx[2] = 0b010101;
tx[1] = 0x1;

The transmission is not starting or, at least, accessing tx[0] gives me 0 (should be 1 because status_reg0(0) <= uart_tx_stop). I tested the follow in a test bench (without AXI) and everything seems to be fine. I'm quite sure that' I'm messing up something with the AXI bus interface, maybe the writing process is broken (or the reading) or, maybe, the signals aren't correctly mapped to the UART transmitter.
Please, can someone help me? Thank you in advance :)


texts: Is it possible to test a MIDI device through its connector with a multimeter?

texts:
I have a Fluke 115 multimeter available that I'm hoping has capabilities to register (even with low fidelity) any MIDI signals flowing out of a handful of devices. There's an old keyboard that I'm testing out which has the standard MIDI IN/OUT ports on the back and so far the IN port I can verify is working because sending MIDI through my laptop over a USB to MIDI cable can trigger the notes to be played on the keyboard's speakers using the MidiOx utility. However the opposite direction is not operating and I'm hoping to test that port for some basics with a multimeter.

I'm starting from scratch here and need to learn the pins and "electrical specifications" of MIDI. I don't need a full resolution oscilloscope to see the fine grained signals for each note, I'm just hoping for a basic test using something like the Hz setting on my multimeter. Looks like the Fluke unit tops out at 50 kHz so I'm hoping an aliased signal still can be captured on the multimeter that I can reliably trigger for certain keys that would indicate something is at least working. I might be out of luck there given that the wiki article states that

  MIDI messages are made up of 8-bit words (commonly called bytes) that
  are transmitted serially at a rate of 31.25 kbit/s. This rate was
  chosen because it is an exact division of 1 MHz, the speed at which
  many early microprocessors operated.

Am I understanding things properly that pins 4 and 5 would be the ones to target? Anyone have any advice which keys to choose and if it would even matter.


texts: Hold two microcontrollers in reset at turn-off with one DPDT power switch?

texts:
I want to use the second switch to ensure that two micros are both held in reset when the switch is off.  They use different supplies and one sometimes also resets the other, so I want to use MOSFETs.  I also don't want to burn too many microamps when on.  So far I have this:

The 1-2-3 contacts of switch SW1 hold MOSFET gates near ground when the device is on, and the pull-up resistor R1 takes it high when off, turning on the MOSFETs and holding the ucs in reset.
Questions:

Is R1 too big at 2M?  I think in this application which only handles a single switch event (with bounces though) and not 500 kHz switching or something it doesn't matter.  I would use 3M if it's safe.  Even if the MOSFET behaved badly during transition I think it wouldn't matter once things stabilize?

On the general idea that sharp edges are bad when not needed I've added a 100 pF capacitor C3 giving R1-C3 time constant 0.2 ms.  This is about an order of magnitude less than the time constant for C2 at max load, so I think the ucs should always be safely in reset before C2 runs out of juice during a turn-off event.  But maybe this capacitor is pointless or potentially bad?

R2 is just to limit the discharge from C3 during bounce events during turn-off.  It probably isn't even needed?

Anything else obviously wrong or sub-optimal?


texts: Power dissipation on mosfet with PWM and current regulation

texts:
I don't understand the formula for the thermal dissipation of the STCS1A. The datasheet in chapter 8.2 states:
Pd = (Vd - Vfb) * Id + (Vcc * Icc)

Where Vd is Vcc - VLED.
Here the connection scheme:

simulate this circuit – Schematic created using CircuitLab
When the mosfet turns on, the current flows through the LEDs and the feedback resistor. Internally, the feedback voltage is fed to a comparator that turns off the mosfet when the preset current is reached.
Now, while the mosfet is on, the voltage across the diodes depends on their forward voltage with the actual current. The voltage across the mosfet is due to the Rds_on (ideally it would be a short-circuit) so it also fixed by the current. The only component that would receive the remaining voltage is the feedback resistor.
Of course, at steady-state this would be Vcc - VLED - Vds but this is never reached because the mosfet is turned off when the Vfb is ~ 100 mV in order to achieve the current regulation.
If this is correct, I don't understand why the voltage across drain-source receive the gap between VLED and Vcc. The mosfet is not used in the linear region, it's a PWM control so it's off or completely on.
If I'm wrong and the datasheet is correct (and I bet that's right!) it means that if you use a high voltage supply with few LEDs, the mosfet will dissipate a lot more. But this makes no sense to me. I selected this device because I understood it regulates the current turning off the mosfet whenever the current rises over the preselected value, so the power dissipation (during the on-state) would be just Vds * Id where Vds = Rds_on * Id.


texts: Can I take out the Atmage328 and replace with a Atega8 for programing instead of trying to program using a breadboard?


texts: Transform pulses per second (pps) to rpm

texts:
I have a stepper motor that turns at 5000 PPS and has a step angle of 1.8º.

What would be the formula to transform these pps into rpm?

Thanks in advance!


texts: I'd appreciate some help to identify a potentiometer. It's from a small handheld drill and there is no reading on an avo across the two outer terminals so I'd like to replace it if I can find something the right size. There is no name on the pot which was directly mounted on a small pcb. On the underside of the pot are three separate marks B  50  4.


texts: Amplitude plot of voltage standing wave on a transmission line

texts:
edit: I just found a site almost perfectly describe the issue, https://ophysics.com/w3.html
I found this graph on Google but couldn't find an explanation of it, it is similar to the one presented in my high-frequency engineering class.

Why aren't the curves touching 0.00(except when reflection coefficient = 1)?

-> Shouldn't all cases of standing waves have points where it is always 0.00(nodes), so the amplitude is 0.00 too?

Why aren't their minima as "sharp/pointy" as when reflection coefficient = 1?

I appreciate it if you can explain the problem in a more "graphical/less math" sense. Thanks!


texts: Will an oscillator be able to drive a transmission line

texts:
I want to build a soil moisture measurement probe based on this idea:

An oscillator feeds a transmission line burried in a soil via a termination resistor R1, XOR gate acts as a phase shift detector - it will be high untill a reflection comes back from the transmission line. More water in soil - higher the dielectric constant, longer it takes for the reflection to come back, higher the voltage after R2C1 filter. I'm going to implement the transmission line as a trace on a PCB, i'm thinking about frequency of 80MHz and transmission line length of ~40cm.

My question is will an oscillator like CB3-3C-80M0000 be able to drive the transmission line or do I need some buffering? If so, what buffer would be suitable for speeds like these?


texts:
I'm designing an adjustable high-voltage low-current power supply using UC3843 control chip.

Basic parameters: Uin = 24 V DC, Uout = 30-1000 V DC, Iout = 10 mA, Uripple < 1 V, fsw = 40 kHz

I have a few questions about one aspect of my desing - the voltage feedback. I most simple cases, the voltage feedback can be realized using a simple resistive divider, possibly with a variable resitor to achieve adjustable output voltage. However, in my case I can't use a potentiometer directly in the divider because of high voltage at the output. Instead of that, I came up with following circuit, which uses 2 op-amps, the first as voltage follower and the second, with variable gain, to achieve desired range of output voltage:

simulate this circuit – Schematic created using CircuitLab

(In blue are voltages with potentiometer set to low resistance, red is the opposite)

The IC operates in closed loop in order to achieve zero difference at the output of the error amplifier. That means, voltage between R1 and R2 will be in steady state equal to 2.5 V internal reference.

My questions are:

Is there in general something wrong using an op-amp in voltage feedback like this? Are op-amps fast enough to transfer fast changes at the input to the output?
Is op-amp MC33072 suitable for this application?
Should I place some small capacitors for better noise imunity, e.g. across R6?


texts:
Many load switches implement a fix or controlled slew-rate of its output current in order to prevent inrush currents.

I was wondering what is the step response of this kind of switches after the slew-rate time. To be exact, if I use such a switch to charge 200uF capacitors and my circuit draw some energy from those capacitors (not fully discharged, just a little dip), will the switch re-charge the capacitors instantly or will they be charged smoothly due to slew-rate time?


texts: Where to put a voltage (DC/DC) converter that must be switched on/off by the control signal?

texts:
My device only has 5 V power supply, and this is difficult to change. I must operate another, smaller device that requires 12 V. I plan to use some DC/DC converter like TMA 0512D to produce the necessary voltage. The master device has enough power.

As the small device must receive 12 V only when required, it is possible to put the control circuitry before the converter (then the converter would stay disconnected most of the time, except few seconds per hour, and power is a concern) or put it after the converter (then the converter would run all the time but may produce less noise and transients). The main device is a small computer so it is important not to reset it by chance.

How would be usually done?


texts: Finding the time constant of an RL circuit

texts:
I've the following circuit:

simulate this circuit – Schematic created using CircuitLab

And I've to find the time-constant of the voltage across the inductor.

I did the following:

The voltage across the inductor is given by:

$$U_L(t)=100\cdot10^{-3}\cdot\frac{\text{d}}{\text{d}t}\left[\mathcal{L}_\text{s}^{-1}\left\{\frac{\frac{8.6}{\text{s}}}{600+\frac{1}{\frac{1}{1800}+\frac{1}{600+100\cdot10^{-3}\cdot\text{s}}}}\cdot\frac{1800}{1800+600+100\cdot10^{-3}\cdot\text{s}}\right\}_{\left(t\right)}\right]$$

To find the rime constant I solved:

$$\frac{1}{e}\cdot U_L(0)=U_L(t)\space\Longleftrightarrow\space t=\frac{1}{10500}$$

  Question: is the answer right? And is there an easier way to the solution?


texts:
I'm using MCP4725 (datasheet) module, VCC is connected to a 4096V reference voltage. there's a steady 23mV offset:

0 - 23mV
50 - 73mV
100 - 123mV
...

How can I zero this offset error?

From the datasheet:


texts: How is ESR specified on ceramic capacitors?

texts:
I'm looking for a capacitor to use as the output capacitor with the LDO regulator SP6205EM5-L-3-3. It says it requires a 2.2 µF capacitor, with an ESR less than 0.5 ohm.

I've found the TCJA106M010R0300 type of tantalum capactior would suffice.

However, these are quite expensive, almost half the cost of the regulator... I wondered if ceramics of type C3216Y5V1H225Z/0.85 (in the specification it says ceramics are allowed) would have the low ESR required (they say 'Low ESR', but it does not have a value specified).

What does low ESR mean at the frequencies involved with this regulator?


texts: Dahlander winding: Does the voltage rating change between connections?

texts:
From my understanding, "normal" motors in delta/wye connection, have rated interphase voltage of 220V in delta, 380V in wye.

But how about Dahlander motors? These are motors that are built to achieve different speeds depending on the configuration. Do they also have different ratings depending on the connection? Or is it the same?


texts:
Let's consider the Shannon - Hartley formula for the channel capacity \$C\$:

$$C = B \log_2 (1 + S/N)$$

I have two doubts about it:

1) is it correct for TDMA, FDMA, or CDMA? And why?

2) Can a variation of the dimensions of the radio cells (base transceiver stations) reduce/increase the value of \$S/N\$?


texts: User safety for battery powerd device against misuse of power supply

texts: I want to design a safety circuit for a battery powered device which measures human body impedance. It is intended to be powered only by an external battery pack (5V) via a USB cable. But I want to make sure that even if device is connected to wrong power supply by mistake (e.g. a faulty USB charger leaking 230V), the user is safe. I am also limited in PCB size. What kind of circuit or IC should I look for this purpose? I couldn't find any regulators that can tolerate such high input voltage.


texts: Ethernet over Powerline working between apartments. Should I be worried?

texts:
We have two different apartments, side by side (same floor), with separate electrical panels. For some reason Powerline can transfer Ethernet between the two apartments (with a bit under 60Mbps bandwidth!). Some times the Powerline adapters may need to resync or just stop working, but that happens very rarely (~2 times a year).

Should I be worried that the two apartments are sharing wiring or that their panels are not separating them properly?


texts:
I always thought that the internal silicon inside ICs are called Dies(as in Silicon die). But I just stumbled upon a component from Linear Tech. It is the RH3845MK. The datasheet says DICE !!!
The screen shot is below and the datasheet is Link

What is the difference between die and dice ?


texts: Easy way to estimate the power handling capability of an unknown transformer

texts:
I have quite a lot of old scrap mains step-down transformers (220V-240V 50Hz), salvaged from old equipment during 30+ years.
Although I religiously marked the primary terminals of all of them as a "best practice", most of the times I lost track of (or I could never get) data about secondary maximum current and, especially, VA rating.
Most of them are classic E-type cored ones, but a few are toroidal.
Is there a way by simple measurements to discover a conservative estimate of their max VA rating? If I could (under)estimate that value within a 15-20% tolerance I would be happy.
IIRC I heard something about weighting the transformer and apply some proportionality factor (k VA/kg). Is that a reliable way? And which is this factor? Is it the same for any size/weight (I think the heavier I've got weighs about 10kg)? Does this method work also for toroids? Are there better methods that are more or less that easy?
EDIT
(to clarify some points)

I asked for simple measurement techniques. Ideally they should be feasible with a True RMS multimeter and an oscilloscope, but this latter possibly only to monitor the secondary (I don't have an isolation transformer nor an high voltage probe). And I don't even have a variac, but I don't consider having a variac something in the realm of "simple" measurements.

I already know, as I've stated before, the primary voltage. Knowing the secondary voltage is just a matter of measurements. The only vital parameter to reuse those transformer is knowing an estimate of their VA rating.

Please, provide a clear procedure. Saying that by measuring the secondary wire gauge will tell me its ampacity is not enough. Which formula do I have to use? I never designed a transformer, so I don't know how secondary winding geometric parameters are chosen.


texts: How does three phase full converter work?

texts: My question is for firing angle(alpha)=0,why is T1 triggered at 30?


texts: BJT switching circuit with a capacitor as a load

texts:
The circuit schematic and the resulting waveforms  look like this:

It is clear to me that when the transistor turns off, the capacitor starts charging up as:
\$u_{CL}\left ( t \right )=E_c(1-e^{\frac{-t}{R_C C_L}})\$. However, I've also been given this relation(with no explanation whatsoever):
\$U_{CL}\left ( t \right )=U_{CE} +E_c e^{\frac{-t}{R_{CE} C_L}}\$. The parameter \$R_{CE}\$ seems to represent the BJT's internal resistance. Another thing that's been bugging me is the abrubt change in capacitor voltage as the transistor goes into ON mode. Wouldn't this imply that the power dissipated \$\rightarrow \infty\$, since power is the time derivative of the energy stored in the capacitor.


texts:
I have been away of Electronics Engineering since 2008, it seems I missed a lot of basic concepts. I came across this schematic:

I found a weird wiring, the capacitor that is tied to VCC, should be open circuit at DC frequencies, how the transistor is going to be fed by VCC in that case? I suppose that the correct wiring is to tie the resistor to the VCC and take filter the output by that capacitor in parallel.


texts: How to create advanced pwm signals with Mbed ? (stm32)

texts:
Context: I need to control an h-bridge with pwm on each mosfet with bootstrap.
The low side mosfet (L1) needs to close when the high side one (H1) opens. The waveform should look like that:
Do I have to mess with the registers? If so is there an example online to create such signals?
I would like to manually set timer channel parameters, such as direction, capture/compare register or output compare mode, but all the tutorials are on keil, and it would mess with the mbed environment, right ?
Or is there a simpler way? Thanks !


texts:
In case of digital signal, here is a simple RC LPF.

simulate this circuit – Schematic created using CircuitLab

And I want to know.. does below circuit also work as LPF?

simulate this circuit

And regarding component placement,
where do you think RC filter should be placed close?
Close to IC or Close to Connector?


texts: Simpler code than bit banging to get multiple serial hardware working with 8051

texts:
I created a circuit like the following:

I have sub-circuits that all take serial data as input and do miscellaneous processing with it. Most of the sub-circuits are just light displays. I want to control such circuits with one microcontroller with simple code.

For simplicity, lets assume all these sub-circuits have no option for a data reset and that the only inputs allowed to them are clock and data into 74HC164's of each sub-circuit. I have illustrated that on the right-hand side of the shown circuit.

Due to PCB wiring and such, I ended up connecting pins 4 and 5 of the 74HC138 decoder to the TXD line which (according to several resources can function as a clock in serial mode 0). I connected pin 6 to a GPIO pin in an attempt to prevent false alarms.

What I want to do in software is to easily select any one device and send data to it preferably with the fewest instruction cycles as possible.

Because serial port mode 0 for 8051 is a good candidate, I thought about it by using code like this:

mov P1,#8Fh ;use 1st device
clr TI
mov SBUF,A ;A=8 bits of data
jnb TI,$ ;wait for full transmission
mov P1,#9Fh ;use 2nd device
clr TI
mov SBUF,A ;A=8 bits of data
jnb TI,$ ;wait for full transmission
clr TI
mov SBUF,A ;A=8 bits of data
jnb TI,$ ;wait for full transmission - here we sent 16 bytes to device 2.

That's the kind of code I ultimately like to use, but I feel theres a slight problem because if I'm not mistaken, one document online claimed the TXD line goes from low to high when it signals data is ready. and it makes me think TXD will stay low if no data is transmitted. If that document is correct, then if I choose to switch devices then the last device used will have a low to high transition (meaning an extra unwanted bit is to be processed).

My only other options are to explore other serial modes and if that wont work, I may have to bit bang or redo the entire hardware (which is an option I will not take).

Anyone have any solid solution to this?


texts: Arduino relay buzzing sound at higher voltages

texts:
I have three arduino 4 channel relays connected to the three phases of mains supply. I am currently powering the Vcc of relays through an LM 7805 regulator which is taking input 12V and giving an output of 5V. I have also connected a 220V/12V 1Amp transformer to rectify my supply to 12V DC which is then fed to the LM 7805. On slowly increasing my input supply from 0-220V (Phase voltage) by an autotransformer, when I reach around 160V, the relay makes a buzzing sound (not the tick-tock sound which it makes when switching On and Off), and I have to immediately switch off my supply(afraid of blowing off the relay).

I have connected 22 microfarad and 1000 microfarad capacitors in the two ends of the LM 7805 respectively, for smoothing. Is the buzzing noise because the relay is staying put in On/Off condition, or is it something else?(I intend to use the relays in NC condition.)

Also, the R, Y, B phases of the main supply are connected to the three relays, and I have taken the rectifier's supply from the R phase, so, when I give Vcc to relays, the power contacts of the relays also get line voltage.

This is how I connected the regulator

This is my full circuit

(I have not shown the connections between the arduino and acs 712).
Thanking in advance!