texts: Simple question: pros and cons of choosing MESH or NODE methods?

texts:
My question is about MESH and NODE methods, how I choose to use one over the other?

For example if I have this circuit, my professor used the node method, but also a mesh method could be used? Why?

simulate this circuit – Schematic created using CircuitLab

Known data:
\$R1=1,\$
\$R2=1,\$
\$R3=3,\$
\$I1=3,\$
\$I2=8,\$
\$V1=15\$

I'm asked to find all voltages referred to the resistors.

I haven't tried to resolve it with the mesh method, I resolved it only with the node method (alone and then I checked the professor's solution).


texts:
So I was creating my own circuit based closely off the minty boost charging diagram for iDevices and I had slightly messed up on my calculations. If all my math was correct, I accidentally bought resistors 1000 times stronger than the ones I actually needed. What caused me to make that mistake? The original diagram I had based my circuit off of was in the thousands.

My question is, would it be possible to create a voltage regulator following the same diagram and using the same values for the resistors except 1000 times less (eg 43k is only a 43)? If so, then would would be the reason to use a 43k instead of a 43 ohm? What about using a 43k ohm if the specified voltage regulator schematic asked for a 43 ohm? Are there any advantages/disadvantages to either?


texts: Drawing 100mA / common ground for a bus-powered USB hub

texts:
I am trying to provide an external 5V power supply to a (previously) bus-powered USB hub.

My first attempt at this was to just connect the USB host's data pins to the hub's data pins, and the external 5V to the hub's power pins, like so:

PSU 5V  ----- Hub VCC In
PSU GND ----- Hub GND In
Host D+ ----- Hub D+
Host D- ----- Hub D-

However, the hub (and attached devices) were not detected by the host PC.  My assumption was that as the Host GND and Hub GND were no longer connected, the levels were off, so I added that connection:

PSU 5V  ----- Hub VCC In
PSU GND ---=- Hub GND In
Host GND--/
Host D+ ----- Hub D+
Host D- ----- Hub D-

Still no luck.  I then read that a USB host expects a device to draw around 100mA in order for it to be detected, so assuming that the host would output 5V, I added 50R of resistance between it and the host GND so that 100mA would always be drawn:

PSU 5V  ------ Hub VCC In
PSU GND ----=- Hub GND In
Host GND -=/
          |
         50R
          |
Host 5V -/
Host D+ ----- Hub D+
Host D- ----- Hub D-

In this configuration, with the host PC and the PSU turned on, I measure 70 mV across the resistor and zero resistance.  When I unplug the USB cable from the host, I measure the 50R properly.

Am I missing something here?  Why would the USB host not detect the hub, and why would it appear to short its own 5V and GND pins?

Note: I have read this question, in which the answers suggest that just connecting the ground lines would be enough, and this one, which confirms my belief that it's OK for the USB hub to just draw 100mA and not negotiate for its current requirements.


texts: Does a sound card low pass filter input?

texts:
I ask this question just because I'm curious to find out.

As far as I understand, the Nyquist theorem says that the sampling frequency must be at least twice the bandwidth of the signal to be sampled. So, if we want to sample a signal with a sample rate that is too low for its bandwidth, we have to low pass filter the signal prior to sampling to avoid aliasing. Or am I wrong?

My laptop has an integrated sound card. In Audacity I can select any arbitrary sample frequency. Does that mean, that my sound card contains an adjustable low pass filter at the input to filter the signal to the selected sampling rate?

How is such a variable filter designed in an integrated circuit?

Thank you!


texts:
There is an enclosure with 2 separate pcbs.  Pcb A amplifies a mV level signal (10Hz to 100kHz) coming from an external sensor.

The amplified analog signal is sent to pcb B, which digitizes it and processes it, and contains lots of digital circuitry (fpga, microcontroller, ethernet PHYs, radio transceiver, etc).

Both Pcbs get power from a common DC input (star configuration).

There was the preliminary fear that the ground loop created by the analog output reference would allow return AC currents to flow from Pcb B back to the power input via Pcb A and that those currents would inject noise at the amplifier's input stage (the sensor is referenced to ground), even though this would be considered when laying out the ground plane in Pcb A, and pcb B has plenty of bulk & bypass capacitance.

For this reason the analog output was made (pseudo) differential and goes into a differential ADC in Pcb B.  Common mode voltage is kept constant at mid-voltage.  Because the system ground is the same, and the ground return current is theoretically minimal, the ground wire was not included, breaking the ground loop.

Now it is all built and it turns out that it works fine (very high SNR) with or without the ground wire, it makes no practical difference.

My question is what the consensus is of whether this technique of breaking the ground loop is sound or not, even though it made no difference in this particular case.


texts:
In order to make a comparison between an ordinary (3D) half - wavelength dipole and its printed (planar version), I've done a simulation in both cases. Both were designed to work at 3GHz (100mm wavelength). Input port is a voltage source with 75Ohm of impedance. To avoid dielectric effects, I've not considered any dielectric substrate for the printed dipole.

The 3D dipole has been built with:

Length 45mm (a bit lower than half-wavelength. That's a choice the result of the simulator optimization).

Radius 1mm (much lower than the Length)

Gap1  1mm (much lower than the Length)

The results are:
S11 (reflection coefficient). It's minimum at 3GHz. So it's fine.

Radiation pattern cuts (at 3GHz)

The printed dipole has the same size values (Length 45mm, Width 1mm, Gap 1mm) of the 3D one, except for the fact it's a strip.

The results are:
S11 (reflection coefficient).

Radiation pattern cuts (at 3GHz).

In conclusion:

same resonance frequency (for a fixed length)
same matching at the resonance frequence
same pattern shape and same directivity values

(Only very very very small differences are present in the previous graphs)
but a printed dipole has lots of advantages, being lightweight, easily embeddable with active devices in PCB, and flexible to make flexible pcb.
I can't believe there isn't at least one disadvantage in choosing the printed version. I would have expected a big variation in radiation pattern, since the 3d dipole has the same shape if seen from each direction on the transverse plane, while a printed dipole is a strip if observed frontally, and a wire if observed laterally. But the simulations say I'm wrong: the printed dipole is as omnidirectional (and with same directivity value) as the 3D dipole.


texts: Dc motor as torque transducer for BLDC motor

texts:
I bought a cheap BLDC motor on some Chinese website and could not find its characteristics. However, I have A28-400 24V amp flow Dc motor with its characteristics. If I'm able to build a test rig to load the BLDC by connecting the shaft of BLDC motor to that of Dc motor and power up the BLDC using a commercial controller and measure current from DC motor (acting as a generator with a rheostat in series to vary load torque) and try to  map values of current to shaft torque of Dc motor using its chart.
How accurate and reliable is this method to measure torque assuming zero slippage at the coupling of the motor shafts?
And I'll be loading BLDC motor till it stalls by gradually increasing its power and decreasing resistance on the other side.


texts:
I know I'm asking a basic Question. But it will be very useful for me to continue my Micro-controller Experience. Consider I am using a controller with 256 KB  Flash and 8 KB Ram. My Questions are

I know about memory mapping like code, Data, Stack and Heap Segment, which variable will store in which segment. But are these allocated in RAM or Flash
If I am declaring a buffer, I know it is allocating in RAM. Whether it will deallocate after the function ends (if that Buffer is Locally declared)
Where the Register Variable will allocate the memory.


texts: Fundamental difference between DC IV measured current leakage and AC CV measured conductance

texts:
I am a physicist with an general EE measurement question, thanks in advance for the advice!

I am measuring the properties of a majority carrier diode that I am designing, and usually just take DC IV sweeps.  I know that there is shunt conductance mechanism which I am trying to minimize.  I have starting taking CV sweeps as well (1 MHz, 50 mV AC ripple) over the same DC bias range, under a C || G model.  For all of these, I am essentially comparing reverse bias DC leakage to CV profiling data (also reverse bias, of course).

Everything qualitatively makes sense, the less leaky diodes show lower conductance, extracting depletion widths, doping concentrations by textbook formulas are accurate.

I basically have two questions.  Since I am dealing with some relatively leaky diodes, how confident should I be in trusting the CV data?  I have been told you cannot use if if you have large leakage conductance, I have been using the rough rule of 2*pifC>G, is this ok?

Second, is there a fundamental difference in trends in measured AC conductance vs. DC current?  For instance, some diodes see trends in the conductance, which I might ascribe to details of the leakage mechanism. But is CV conductance data really noteworthy, or just "slop" to tell you if you can trust the capacitance?  In other words, am I getting any more information than my DC IV?

Thanks again, any refs would be much appreciated!


texts: Solenoid and mechanical damping, options for ways to minimize

texts:
I have an iron rod supported by a coil spring that vibrates vertically within a solenoid coil. The solenoid has a 5 ohm dc resistance. There is no physical contact between the coil and rod.

As I increase the current through the solenoid, the natural (mechanical) frequency of the system changes - this is desired. Unfortunately mechanical damping also appears to increase with current.

I understand this damping may be related to two phenomena: eddy current losses and back-emf.

For the eddy current component I understand I may be able to reduce this by using a ferrite (non conductive) rod in place of iron. Please correct me if this is wrong.

For the back-emf component, what are my options? Some advice I was given was that adding a large resistance (100 to 1000ohms) in series with the coil would reduce it. Is this true? If it would work then the problem with the solution is  the massive increase in power consumption of my system in order to achieve the same current through the solenoid coil. Are there more power efficient solutions?

UPDATE:

I attempted a comparison with the system powered via a lab bench supply set to be a voltage source versus set to be a current source and the damping was identical with both settings.

Is this bench supply inappropriate for this purpose or does this result suggest the dominant factor is eddy currents instead of back-emf?


texts: a standard method for flowing down EMC/EMI requirements to internal modules

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EMC/EMI standards (conducted/radiated emission/susceptibility) are well established for system boxes. However there appears to be no standards, nor methods for deriving a specification for internal modules that are inside the RFI filter protected Faraday cage.

I am looking at frequencies below lambda/100 relative to the module size. I am particulalrly concerned with sensors that are noise floor limited where it is difficult to detect additional injected noise, or noise that is exported to other modules within the enclosure.

Being below lambda/100 the coupling will be essentially near field i.e. capacitive, and occasionally inductive, and the main threat will be the chassis itself because of the system box's RFI filters (where the Y capacitors induce half supply noise on the chassis relative to the '0V' supply return).

Possible modules include pluggable PCB's, Camera and Image Intensifier modules (which are near photon noise limited and will alias and mix any injected noises).

I'm looking for documented/public methods and test procedures that can be used as formal references for a Statement of Work and for sub-Module specifications.


texts:
The following chart represents almost 5 hours of input received by a sonometer (BENETECH GM1356) at each second in an apartment room.

How can I find the answers to the following questions from this chart:

How many minutes in total are above 60 dB?
What level of dB is the most dominant?
What is the level of background/underlying noise and what is the level of actual sound?

But, most importantly: How can I convert dB to dBA?


texts: What is an example of driver and receiver chips for a PCB?

texts: I am watching some tutorials on signal integrity and the instructor keeps referring to a driver and a receiver. I am a little confused what exactly this would be when designing a PCB is the driver like a microcontroller sending the signal? What is the receiver then?


texts: How to design a large 125kHz loop antenna for long range RFID application?

texts: I am designing a large loop antenna working at 125 kHz. To maximize the range of my system I am aiming for 1m diameter loop antenna with as many turns as I can allocate (e.g. ~100 for 18 AWG). I have succesfully designed antennas of diameter=40cm with L=5mH. However, when trying larger geometries (or smaller wire gauge) the antennas turn out to be purely capacitve. What do I need to consider to avoid this issue?


texts: Is program code copied to SRAM from flash on microcontroller?

texts:
On PC, program executable is read from hard disk, and loaded into RAM to execute it. On microcontroller, program is stored on flash.

Is it loaded into SRAM when microcontroller starts up?
If yes, then STM32F103 document says, flash is 64KiB, SRAM is 20KiB. Program doesn't fit into SRAM. (Same for other microcontrollers as well).
If you will say that not all flash content is loaded into SRAM, what purpose does the remaining data on flash serve to? All operations are done on SRAM already in program codes.


texts:
I have a question about the operation of a voltage regulator. The supply is 12V and can provide 15W (max current draw 1.25A). Now when I use a linear voltage regulator down to 5V do the 15W still apply (3A current draw)?
Or do the 1.25A from the power source still apply since no current is being transformed?


texts: Driving a MOSFET with a lower Vgs than required?

texts:
I'm working on a project where I need to control a MOSFET through an arduino uno.
The MOSFET I've selected is a IRFP460, and the Vgs characteristic is Vgs = 10V.
Can I run it through an arduino PWM pin, even if its output only reaches 5V?
What would be the negatives?
I've quickly tested it and it seems to work so far.
Thank you for any help!
Here's the MOSFET datasheet


texts: Why is a clamp meter unaffected by nearby wires?

texts:
I understand a clamp meter works by measuring the magnetic field generated by current flowing through a wire.

It's well known that clamping 2 wires carrying the same current in opposite directions will show a null reading because one magnetic field is cancelling the other.

What I find surprising though is that if the second wire carrying the opposite current is placed immediately outside the clamp, it has no measurable effect. I was expecting its magnetic field to couple with the clamp to some degree but that seems not to be the case. Why?


texts:
I would like to manufacture DIY PCB. I am planning to make a UV box like on this link, then I wonder how I can determine the best UV exposure time?

or if I use the Sun as the UV source, how I can determine the exposure time as the strength of sun light varies over the time?

What happened if the board exposed the UV light longer than it supposed to?


texts: Is ADC over-voltage protection needed when input isn't external?

texts:
In a situation where an ADC is measuring an internal voltage node rather than an external input (where one has little control over input voltage), does one need to implement some over voltage protection for the ADC (clamping diodes etc.)?
In the circuit below an opamp buffers some internal signal which cannot exceed 30V, and additionally the buffers power rail limits the output to the 30V rail. Following that there is a divider which limits the maximum voltage that the ADC receives to 3V.

simulate this circuit – Schematic created using CircuitLab
In this situation would it be acceptable to omit over-voltage protection for ADC, or what would be the justification for adding such protection?


texts:
I have read the answers to the question,"How do crystal oscillator start to work" in this forum. And the common answer which I got is that, there are many frequency around the crystal. The crystal will pick up these all noise signal frequencies and send it to the internal amplifier and filter which will select the frequency and send it back to the crystal again which the barkhausan criterion being satisfied? Am I right? Please correct if I am wrong.

My doubt is that, I have a quartz crystal of 8MHz connected to an MCU. When I don't power the MCU, I am not getting any signal from the ends of the crystal (I probed using an Oscilloscope). I should get the noise frequencies at one end of the crystal,right? Since, the MCU (system) is powered down, I may not get the desired 8MHz with amplification. But I should get some signals at the ends of crystal,right? Or am I wrong?


texts: How do I quantify the effect of stack lamination on a stator and on a rotor of an induction motor?

texts:
Image from here:
I would like to design (or to calculate the existing of) an induction motor, either 3 phases or single phase. I understand that both stator and the rotor made from a stacked-laminated high permeability steel lamination, intended to reduce Eddy's current. It is said that the thinner the steel lamination, the better. But how exactly to calculate or to quantify the (performance/efficiency) improvement, I have no clue. So, how can I calculate it? Say that I would like to design an 0.5 HP induction motor, either 3 phases or single phase. If the calculation for both are different, then just simply take the single phase as it is the mostly used for low output power.


texts: Finding replacement for transistor, what to look for

texts:
I have a schematics that uses the BS270 FET transistor, but I want to know what to do if one is not available or one wants to adapt the schematics to a different transistor

What quantities should I look for in order to match a transistor to another? Gate, Source, Drain voltages, etc.

For example, I have 2SK246 Toshiba FET, and I have both datasheets open, but not sure how to go about to modify the schematics or which values to consider in order for the calculations

Edit the application is using the FET as a switching device for a LED with a Beaglebone


texts: What determines Nixie tube digit stack order?

texts:
I recently watched a video of Nixie tubes being built and another user had asked what determines the stack order of the digits in front of the anode. I searched around trying to find the answer but I couldn't find anything other than several sites with a carbon-copy response that barely mentioned their ordering at all. Originally I assumed it might have something to do with visibility of each digit behind other digits but the order seems almost opposite to me if that were the case. Then I assumed it might have something to do with surface area of a digit and its distance to the anode but again the ordering didn't quite seem to make sense to me if that were the driving factor. Even the Wikipedia page itself shows examples of different stack orders in its pictures of tubes. So my question here is: What determines the order in which the digits are stacked in the Nixie tube assembly?

https://en.wikipedia.org/wiki/Nixie_tube:

  One such arrangement is 6 7 5 8 4 3 9 2 0 1 from front (6) to back
  (1).[7][8] Russian NH-12A & NH-12B tubes use the number arrangement 1
  6 2 7 5 0 4 9 8 3 from back to front, with the 5 being an upside down
  2.


texts: Help with understanding common-emitter amplifier

texts: I'm trying to analyze a common-emitter amplifier circuit, but am not sure why \$R_1\$ and \$R_2\$ make sense for making a quiescent Volt of \$5 V\$. In this, \$\beta=100\$. I've calculated \$I_c =  I_e = 0.5\text{ mA}\$, \$I_b = 5 \mu \text{A}\$, so the voltage drop over \$R_e = 0.5\text{ V}\$, which means the voltage at the base is \$0.5\text{ V}\$ and \$0.6\text{ V}\$, from the voltage drop of the transistor, which equals \$1.1\text{ V}\$. But I'm not sure why this matters for \$R_1\$ and \$R_2\$. Is it having to do with the need to ensure the transistor is not broken by too large of a voltage input?


texts: How to connect a high current sensor to power line

texts:
What is the best way of connecting LEM LAH 100-P to power lines.
The power cable will have 50 to 60 amps. I am working with 4 gauge AWG wire. What are the connectors designed for? What kind of PCB or other medium could be best. We are prototyping now so how to best connect the wires? Is the only solution a lot of solder?


texts: How to design a combinational circuit that finds the minimum among multiple given numbers?

texts:
There are quite a few articles (for example, this) that can be found online discussing the design of a comparator that takes two numbers (say, A and B) as inputs, and outputs whether A > B, A < B or A = B. But what if I want to compare multiple numbers?

Let's say we have four 4-bit binary numbers denoted as i0, i1, i2 and i3. I want the output of the circuit to be the index of the minimum value
among them. Below are some examples:

The highlighted value in each row represents the minimum value among the four which the output should correspond to.

I've thought of comparing the bits one-by-one starting from the MSB, but things got ugly when I tried to realize using combinational gates. Is there any efficient ways to do this?


texts: Develop with FPGAs, but target discrete hardware?

texts:
Where I work, we are transitioning to a Agile methodology for our software development.  We would also like to explore the same for hardware development, but the mental impedance mismatch might get in the way.  Specifically, a big part of most Agile methodologies is that you work on a prioritized set of features.  In software, that's fine because you can always go back and refactor/rework past code.  But in hardware-- at least for a large, sophisticated design-- means you're respinning boards at each iteration.  Or, you're building your system around programmable logic.

So why not just start with (and end with) a FPGA-based design?  Well, as a software engineer I have no problem with that, but sometimes the hardware folk have legitimate reasons not to.  But putting that aside, I'm curious if developing with a FPGA for speed and agility but at the end of hardware deelopment transitioning to discrete logic is something that is commonly (or at least sometimes) done.


texts: Solving a circuit using Ohm's law and Kerchoff's laws

texts:
I feel I am missing some understanding about Kirchoff’s law and Ohm’s law. I was in the lab today and I didn’t get a chance to build the circuit in question, but I ran it in multisim later to test my answers and they were wrong. I am not sure I understand why, so below I have detailed the question and my steps to attempt to answer the question. Throughout the lab I was using a 9v battery with a 7.7v charge left, thus Vbatt = 7v.

Calculate the current through the loop using ohm’s law, combining the resistors into a single resistor for ease.

\$I = V/R = 7.7V/1.3M\Omega = 5.5\mu A\$
Calculate the node voltages \$V_a\$, and \$V_b\$ using Ohm’s law.

\$V_a = IR_1 = (5.5\mu A)(1M\Omega) =  5.5V\$
Calculate $V_b$ the same, this time R = \$R_1 + R_2\$

\$V_b = I(R1 + R2) = (5.5\mu A)(1.1M\Omega) = 6.05V\$
Calculate the voltage drop using node voltages as reference

\$V_1 = V_{batt} – V_a = 7.7v – 5.5v = 2.2v\$

\$V_2 = V_b – V_a = .55V\$

\$V_3 = V_b = 6.05\$

These answers are obviously wrong because V1, V2, and V3 must add to Vbatt according to Kirchoff’s loop law, but I don’t know what I am misunderstanding.


texts: Could devices on one circuit affect devices on another?

texts: I recently swapped out some light switches on an electrical circuit in my home.  Ever since then, I’ve noticed some slight flickering of the fixed lighting which resides on a separate circuit in the home.  I was under the impression that each circuit was entirely isolated from one another.  Is this true?


texts:
I have a 160W solar panel that has a built in regulator that I have hooked up to a 100Ah 4 cell Lithium Ferro Phosphate battery.
When I connect them the panel starts charging anywhere between 5 - 7 amps and get the battery to full without issues. The problem I have is once night time has passed, the panel will not charge the battery unless I unpug it from the battery first. The battery box voltage meter sits at 13.4v when fully charged, and with the 12v fridge running on it through the night it got down to 13.1v. I waited till midday and the voltage remained at 13.1 even though the panel was in full sun by that time and my inline amp meter displayed 0amps the few times I checked it though out the morning. Strangly with the fridge still running the battery voltage did not drop further either though it only used 0.3 V for the whole evening proir and night. When I disconnected the panel and reconnected it immediately, it started charging at 6 amps. While it was charging, I then covered the panel and it went to 0amps as expected. When I removed the cover, it started charging just fine. I am at a loss as to why it wont start charging by itself in the morning.

EDIT
After a comment about the potentially non standard battery voltage got me a little worried, I have added the information I could find.
The battery spec sheet


texts: Automotive signal isolation - alternatives to optocouplers

texts:
I'm working on an automotive project, where I'd like to interface various digital signals to an MCU. The signals can either be ON/OFF (e.g. radiator fans) or measurements of pulse frequency, width, duration, etc. (e.g. tachometer or speed). The amplitude of the logic level high can be 5V, 9V or 12V. I would like to protect the MCU inputs from overvoltage conditions (e.g. voltages up to 40V) as well as reverse polarity conditions.

In testing and prototyping, I've used the below basic optocoupler circuit, selecting a suitable R1 value to ensure the current through D2 at 40V is within the specifications for the optocoupler:

This circuit works as intended, but I'm concerned about the longevity of the optocoupler LED and the degradation of the CTR over time. Is there an alternate method of providing isolated coupling for a wide range of voltage inputs, which has better long-term reliability and better high frequency characteristics than optocouplers?


texts: What material is used for the PCB traces?

texts:
Are the traces of a PCB always made of copper,  we can use another conducting material?
Also, is there is another conducting material that can be used in the cladding layer instead of copper, or do we always use copper clad?


texts:
I need a 12v 5A power supply for a heating element. I found out there are two main types of smps: first one is mounted in a metallic case and usually cooled by fan (in some websites it is called "industrial smps"), second type is similar to laptop charger without any fan.
It seems for long-time usage e. g. weeks or months of supplying power, the actively cooled would be more efficient but I am not sure.
On the other hand, since its case is perforated, using it in industrial sites will attract dust and particles in the circuit.
And maybe there are other pros and cons which I am not aware. So which one should I use?


texts: How to make a device that keeps water in sink and bath at desired temperature?

texts:
I have tight taps in my sinks and bathroom which are difficult to control — it's either too hot or too cold and never easy to manually set the preferrable temperature. I'd like to solve this old problem electronically.

I figure I'd need (per sink) a temperature sensor, at least two motors (with belts to wrap around each valve, I don't want to interfere with the insides) and a device that polls the sensor several times per second and rotates the motors. I'd like to keep it simple and cheap.


texts: Shot noise variance of a channel for different bits

texts:
I've come across a question, where I had to calculate shot noise variance calculations of an optical link.

As per the definition, shot noise in an optical channel is the current that arises from the statistical nature of production and collection of photo electrons. In this question, I had a data given; dark current (Id), that is the current from electron/hole pairs that are thermally generated in the pn junction.

The calculations I had to make is the shot noise variance for bit 1 and bit 0 separately. I could calculate the photo current and using that I can calculate the shot noise variance for bit 1. The issue is with bit 0.

I'm asking this question here, to clarify the fact that if it is correct, if I use dark current as the photo current when calculating the shot noise variance for bit 0 as there is no incident light as per the bit level and the only current that will be available to generate shot noise is the dark current itself.

For reference, following are the equations to calculate variance of shot noise current and variance of dark current;

$$<i^2_{shot}> = 2qI_pB_e$$
$$<i^2_{dark}> = 2qI_dB_e$$


texts: Real time spectrum analyzer and Fourier Transform

texts:
I am studying spectrum analyzers and a doubt came to me about real time spectrum analyzers.

Suppose you have a signal in the time domain: in order to calculate the Fourier Transform, you need to know that signal at every time instant. In other words: the computation of the Fourier Transform is something which can be done only after a signal has somehow propagated, because by definition you integrate over all time instants.

Question: how does a spectrum analyzer perform a real time frequency domain analysis of a signal if this signal still has to exist? I mean, if you have a signal in the time interval [t1, t2], how can you perform the Fourier Transform of the signal in real time? If you're recording for example a sound, this sound will gradually arrive to the spectrum analyzer, thus you ignore the future values of the signal, because the generic time instant t* at which you're receiving the signal is smaller than t2, and then you ignore all the values the signal assumes in the time interval [t*, t2]. But by definition of Fourier Transform, you must integrate all over the time interval [t1, t2], meaning that you must know a priori the shape of the function at every time instant.

Thank you


texts: STM32F4Discovery, an HTTP server and a web page on the SD card

texts:
I have an STM32F4Discovery board, and I have implemented an HTTP server on it using the LwIP v1.41 stack. I also have implemented a microSD card reader with SDIO and FatFs, and USB FS as a mass storage device. All of this is working fine together.

Can I store the webpages on the SD card in binary format instead of using the fsdata.c inside the microcontroller flash? If so, how can I do that? Is there an example?


texts: How would one connect multiple PCB's together for compact designs?

texts: I was recently looking at the site hello.is/technology as I was interested on how they fit so much in such a small package. So I was wondering what options their where to connecting Multiple PCB's together and their pro's and con's


texts:
I have a PSOC Cypress board which generates a 5V PWM signal to drive a laser diode. The idea is to design a programmable pulse which I could control the on-time period and current in the pulse. The problem I'm facing is how will I be able to control the current in the pulse?

In other words, I want to program the board to provide specific pulse but I would like to have an external circuit which will allow me to control the average current in the pulse without changing the duty cycle or the time specs of the pulse. I was thinking to use an op amp circuit in voltage controlled current source but I can't figure out how that could be done.


texts: Led dimming circuit is not able to switch off the led

texts:
We are working on an LED dimmer circuit which supports DALI2.0 Interface. We already received the hardware and working on software only. LED driver circuit is based TPS92515HV and below is the circuitry

But the issue is LED is not switching off even if the control signal which is Iadj is 0. We tried shorting Iadj to GND and still, there is a current of 3.5mA through LED which makes LED on always unless power is removed. This will lead to non-complinace of DALI OFF command. The board is powered externally and we cannot control it and also we cannot afford any major component addition like relays to control power line to the driver chip. Is there anything to do with TPS92515HV configuration.??


texts: What are important parameters for an op. amp. used to AC couple and bias a sine signal to prevent noise/distorsion?

texts:
As I am not very skilled with analog design I would like to get some pointers to what to look for/avoid common pitfalls.

I have a signal generator that outputs a sine wave. I want to center this sine wave at a specific voltage (V+/2). So the circuit I am designing is shown in the picture below.

What are the most important parameters to approach the ideal op. amp. in this case?

Other information that might be useful:

It is to be used on a battery-driven devices so low power consumption is positive.
Rail-to-Rail Input / Output.
3.3V op. amp. preferred.

Circuit:


texts:
I have a module in verilog called jtag_sw that expects a 4 bit input. It is a mux. A smaller verison of the code is below as an example.

Only 3 signals [0:3] of JTAG_TDIare physicaly assigned to pins (by me). However, when I compile JTAG_TDI[4] is assigned to a random pin by Quartus, which I want to prevent. How could I do this? I think it is related to assigning different widths but I'm really not sure.

module test ( JTAG_TDI, DEB8_TDI);

output [3:0] JTAG_TDI;
input DEB8_TDI;

jtag_sw u7 (

        .TDI_in(DEB8_TDI),
        .TDI_out(JTAG_TDI), // 4 bit input

);


texts: TLC5940 SOUT/SIN signal broken after 4th daisy-chained IC

texts:
I have a PCB with 5 TLC5940's daisy-chained. The first 4 work fine, but the fifth doesn't work. The LEDs connected to that one just go on at full brightness and that's it. When I measure the SOUT to SIN signals, they look fine up until the 4th TLC, but the signal coming out of the 4th one looks to be pulled up to VCC:

Channel 1 is showing SIN at the MCU, driving the first TLC with 3.3V logic, so that's why the bursts are a bit lower. Channel 2 is showing SOUT to SIN between TLC 4 and 5.

For reference, I've added an image showing SOUT/SIN between TLC no 3. and no.4:

There are no shorts between that line and any others, continuity tests between SOUT and SIN pins are fine. Any suggestions on how to possibly fix this?

Here's the layout (most of the LED section aren't included or blacked out), The MCU (on the left) is a Teensy board. So the SIN run from left to right. I have already checked if the strength of all the other signals like SCLK/GSCLK/XLAT/BLANK is ok by connecting the MCU on the right side headers. This shows identical behavior. The distance from left to right is about 40cm.

and a closeup between TLC 4 & 5:

Trace width is 4 mil, spacing is half the pin pitch of HTSSOP-28 (0.33 mm). This made it convenient to run all the tracks straight on the backside and connect with the smallest vias (0.3/0.45) to the TLC pins. Not sure if this was a good idea in hindsight :).

I have GND on layer 2 and all the empty space on 1 & 4. 5V plane on 3.


texts: Why do electronic circuits need their power supply to be DC, or rectified AC?

texts:
I'm pretty sure the answer to this should be obvious - even to me ...

It's been a while I've been reading and attempting to construct simple electronic circuits. The supply almost always is either through a battery/cell, or AC duly rectified to DC.

I have the impression electronic circuits rarely ever work off an AC supply.

Is this impression correct?
If yes, why is an electronic circuit rarely (if ever) powered/biased using straight AC?


texts: Choosing Resonator for AtMega328P design

texts:
The ATMega328P datasheet specifies a load capacitance for a resonator from 12-22pF but the only 2 Resonators that will fit in my design (from Digikey) have 10pF and 33pF internal capacitors. Which one should I use, the 10pF or the 33pF, and what are the tradeoffs?

AtMega328P
http://www.atmel.com/Images/Atmel-8271-8-bit-AVR-Microcontroller-ATmega48A-48PA-88A-88PA-168A-168PA-328-328P_datasheet.pdf

Resonator - CSTCE8M00G52-R0
http://www.murata.com/products/catalog/pdf/p16e.pdf


texts: Amplified 80dBA 40KHz Sound From 3V Square Wave?

texts:
How can a loud high-frequency tone be produced from a 3V square wave?

Given that:

the square wave is 3V and can have a varying frequency (max 4mA)
12VDC high-current supply is available

Requirements:

It should be as loud as possible (distortion doesn't matter, unless it reduces output power)
Inexpensive (if a transistor can do the trick, why use an IC?)
Simple (preferable)

Just hooking up the PWM to the piezo works, but it's very quiet.
Using a MOSFET or NPN (3904) does not deliver any more volume when connected like:

3V 50% square wave -> 100R -> B
12V -> Speaker+
Speaker-  -> E
C -> Gnd

Adding a high-pass filter (small capacitor) before the Base removes the offset, but really reduces the signal voltage. There is no sound in this case (the input frequency was changed to 10KHz for the test below):

Can an NPN transistor, such as the 3904 keep up with 20KHz?  40KHz? It seems to be switching at 2KHz when given an input of 10KHz. And even though 12Vdc is connected to the emitter, only 4V is output at the Collector:

But the main issue is that the sound is not amplified (and is not drawing any noticeable power from the 12V supply).

Is a bridge required on the speaker terminals? What is the best way to get loud volume out of a high-frequency piezo?

Update:

Just using opposite 3V square waves on each terminal of the piezo gives a decent sound level, although nowhere near as powerful as the speaker can handle.

The voltage at the piezo terminals:


texts: Explain how this astable chain(?) circuit works

texts:
The circuit below fades on and off a cascading series of leds in an alternating fashion.

I tried reproducing it on a breadboard with 5 leds to try to understand it how it works, and got all sorts of weird results.

The resistor values don't seem to matter that much
removing a capacitor doesn't seem to affect the circuit at all. It seems to be using the total or average of all of the capacitors. the capacitor values seem to affect it in some non-linear way that I can't figure out.
it only works with an odd number of leds. 3, 5, 7, etc.

Does this circuit have a name? What determines the brightness and periods of the leds?

Found here https://boldport.com/shop/ananas


texts:
I have not done a lot of work with SMD LEDs and have a question about the pad layout. I have done quite a bit of research and haven't found much helpful info yet.

I am working with 7030 SMD LEDs purchased from eBay https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F182474024179

There are 3 pads on the bottom of the LEDs, as pictured below. As I understand it, the center pad is used for heat dissipation (though I'm not sure of that). The problem I am having is that the center pad on the bottom of these LEDs I purchased is the anode. While the LEDs that I am replacing look identical but the center pad is the cathode.
Is anyone familiar with this style of LED and know whether this is normal? It doesn't make a lot of sense to me to have a heat sync connected to positive voltage. So I am wondering if I just purchased a bad batch of LEDs or if I just need to search harder for 7030 LEDs with a datasheet and cathode on the middle pad. Most similar SMD LEDs datasheets I've seen seem to only have that bottom center pad as the cathode.

So are these abnormal LEDs, or did I just buy the wrong ones? Thanks for your help! I hope this is on topic enough.


texts: Upper limit for resistance values in voltage divider?

texts:
I am measuring the voltage of a 24 V battery using the ADC from Arduino Uno. I use a voltage divider to bring the voltage below 5V (the maximum the ADC can accept).

I noticed that as long as the ratio of R1 and R2 is the same for my voltage divider - it's better to use higher resistance values to avoid slowly discharging the battery. I tried using resistors up to mega-ohm range. What do I sacrifice by using higher and higher resistances? The intuition tells me, that this cannot go forever, because high enough resistor would be equivalent to an open circuit.

By reading other similar questions it seems I might be sacrificing accuracy, but I am not sure, as other questions typically have a different setup.

If it is accuracy, is there a formula for that? When does the standard voltage divider formula break down? Giga-ohms, Tera-ohms? How to calculate that?

P.S.
I am aware of this question, however the answer there seems very convoluted, comparing load and no-load scenarios (where I don't have any load at all). If that is the answer, I do not understand it.


texts: How to set a resistance between two points by a digital input

texts:
For context, this is my first real delve into electronics.

For my current project, I need  that varies the resistance given input from an arduino.

What I was trying to do was, in conjunction with a voltage regulator, control the voltage going to a large LED array via arduino so the LED brightness can be set according to time of day.

In the comments below, it was noted that what I'm actually looking for in this application is an LED driver.


texts: How can I bias this Differential amp. circuit at the best operating point?

texts:
I'm looking to find a way to bias this circuit:

I've written down a couple of equations for DC load line(and also DC half circuit):

and these two as AC Load line:

Rc is given by 1K and you can see even by giving DC bias voltage to base pins of transistors, it comes out to have Ic=0 !!!!!
NOW the question is : what am I doing wrong?


texts:
I'm testing a few different circuits for basic gates, made in DTL (Diode-Transistor Logic). One of the more popular layouts for NAND seems to be:

simulate this circuit – Schematic created using CircuitLab

This is actually a NOT gate, but can be easily extended into NAND by adding more inputs (square wave on schematic). When I actually created the circuit, I've noticed that the rise and fall times are asymmetric. Initially I thought it might be my oscilloscope's capacitance, but it shows even in simulations. To be precise: although fall time of the gate is very small (a few microseconds at most), rise time is pretty large - 100us in my circuit, >50us in simulations. Why is that? I found that changing 47k resistor into smaller one helps, but I'd prefer to know the underlying reason.

I'm confused that the 47k is the culprit, because assuming the time constant is roughly RC, then C would have to be 100us/47kohm = 2nF, which is much too high for wire, oscilloscope's or other parasitic capacitances. Perhaps there's some effect I'm not aware of in the BJT itself, but from my research their parasitic capacitances are typically a few pF, which doesn't explain the problem either.

Effects of simulation:


texts: I have a laptop that is working but one of the hinges is broken, I have a android tablet, is it possible to detach laptop screen and attache it to the tablet and get the tablet screen on laptop screen?


texts:
I've got some ZVP201A PMOS transistor and I want to use one as a switch to control a little 5V 110-150mA light bulb with an Arduino. Here is my schematic:

Is it correct? Is the ZVP201A the right transistor for my application? The 10k pull down resistor is really needed? How can I choose the right value for the Gate resistor?


texts: Role of ALU in executing MOV instruction

texts:
1.What is the role of ALU in executing instructions such as MOV, SET bit, Reset bit which doesn't require any computational feature of ALU?
2.Arithmetic part of ALU makes use of logic gate combination to implement arithematic operation, is it safe to say ALU is basically composed of logic gates?


texts: How to use a 10 pin dip switch on a 8x3 Encoder (IC 74LS148)?

texts: I've been trying to get an 8x3 encoder (IC 74LS148) working using a 10 pin dip switch, I simply connect the 1-7 ON sides of the switch as inputs for the encoder and the OFF sides of the switch to the VCC. The A0 output of the Encoder I get is always a High logic level or "1" (LED light turns on) regardless if any switch is on or not.


texts: In this diagram, from what I understand the voltage between the positive terminal and the first earth ground is \$ 0V \$ and the voltage between the negative terminal and the earth ground is \$ 0V \$.  So why then would you do this earth grounding? In what situation would the current flow between the earth grounds?


texts:
We have made a mistake. We created this pcb with accelerometer , a very good one (ADXL345) datasheet here and it sleeps ,and waking up on acceleration event. in our case we set it to almost the minimum possible of 124mg thresh .

What happens is that it works great almost for any touch or move that you apply to it by hands, means if its on a table even a tiny move will fire it on .

But, when its mounted to a door, or window, if you open the door not quickly enough it just won't wake up .

We have tried everything, including taking sensitivity to maximum.

Seems that it only needs a change that is not occur on an average door opening .

Is there anything you can do to improve this not including migrating to other sensors ?
We have a free GPIO connected to interrupt, we can add some part there, that will sense this tiny movement, is there anything like tilt sensor that will do it?

Thanks .


texts: Supplying two temp controllers with a single element thermocouple

texts: I am installing a process temperature controller and an overtemp controller for a heater bundle. Normally I would just install two thermocouples, one for each controller. But space is limited and I can only fit one probe. So if I were to have two separate T/C wires coming out of one probe, would that affect the temp readings? Has anyone tried this before? I am aware of a dual element probe but that is something I would have to purchase, whereas I have the single element probe in hand. Your thoughts?


texts: Understanding digital MEMS microphone sensitivity and obtained bits for a given input SPL

texts:
I'm trying to understand /simulate the communication between 2 smartphones by means of ultrasounds. As this is a general study I'm considering that the smartphones are equipped with the "typical" most common kind of transducers. One of them is broadcasting a sound and the other recording it. I would like to know under what conditions is the transmitted sound properly recorded. The first thing I did was trying to understand how directivity at this frequency affected the transmission. You can see that analysis here .

Now I'm trying to understand the technical parameters in the MEMS digital microphone and microspeaker (the kind of sound transducers most commonly used in smartphones). I'll assume that the transmitting smartphone is equipped with a speaker of  this type and that the receiver is equipped with a microphone of this type.

In the speaker specification I can see :

Rated Input Power : 0.5W(2.0Vrms)

S.P.L : 83±3dB/0.1m/0.1W at 0.8,1.0,1.2,1.5KHz average

The speaker frequency response is:

In the microphone specification I can see :

Sensitivity : 94 dB SPL at 1 kHz : -26 dBFS

The microphone frequency response is:

My questions are:

Is the sensitivity the difference between maximum acoustic signal (maximum SPL) at the mic input (which causes full-scale digital word, 16 bits? ) and the 94 dB SPL reference? So, if the mic sensitivity is –26 dBFS at 94 dBSPL, is maximum SPL 120 dBSPL? (–26 dBFS  = 94 dBSPL – 120 dBSPL) Is it alright to mix dBFS and dBSPL ?
This is a PDM smartphone so it's output is only 1 bit. But if we assume that after proper conversion we obtain a 16 bit when the maximum acoustic signal (120 dBSPL) is being received, at 94 dBSPL will its output be about 11 bits?
Assuming that we are working at 1 kHz if the speaker generates 83±3 dBSPL at 10 cm and we place the microphone at this distance, how many useful bits will it output?
What can I do to find out the speaker generated SPL when it is supplied with 0.5W (instead of 0.1 W which is the only data given)?
What can I do to find out the speaker generated SPL and microphone sensitivity at, lets say, 18 kHz?
If mic SNR is 64.5 dB. How many useful bits above the noise floor can it work with?


texts: Altium Designer "Copy Room" function not working properly

texts:
I have used the "Copy Room Formats" before in altium designer for PCBs that have duplicate circuits and it worked fine. But now for the first time i have placed in the PCB Room ( that i want to copy ) components on both sides of the PCB.

The Problem: when i copy the format : the Traces , Vias and buttom layer components are copied properly , BUT the Top layer components are being copied in a CRAZY way best described as if you have flipped the PCB. A Picture is worth thousand words :

( Notice in the Copied Room how the IC body (U14) is on the bottum layer but the pads are on the top layer )

Question : does anyone faced similar issue ? and how to solve ?
           does anyone know the proper way of copying rooms (with parts on both sides)

Note: I'm working in Altium 15.0. , and i have used Flip Board in View menu when i was routing the buttom layer.

Thanks!


texts:
I've just bought an Arduino Uno kit, and am going through all the projects in the booklet that comes with the kit. From even the simplest LED and resistor circuit, to get a feel for the Arduino board, breadboarding, and to dust off my electronics knowledge that's been unused for some 30 years. It needs dusting off.

One of the circuits is simply to demo power switching using a motor and a NPN transistor. I understand every aspect of this most basic of cuicuits except for the function of a diode, that as far as I can tell, plays no role in the circuit's operation. It is surely there for a reason, so my question is: what is that reason?


texts: 120v 1,500w heater: is the temperature control knob most likely a standard potentiometer?

texts:
Are the temperature adjustment knobs on most high-power AC (infrared or radiant) heaters just standard potentiometers, the same that would be found in low-power DC devices? I'm asking about the knobs that go from "low" to "high", not ones that list a specific temperature (like "76F").

More information (in response to comments):

I haven't yet opened the actual heater I'm referring to (it's difficult), but coincidentally I chanced upon an already-opened radiant heater and took a picture of the back of the knob and the internals.

What do you think it is? Is it safe to assume that a similar device is controlling my 1,500 watt IR heater? It's difficult for me to open the 1,500 watt unit, otherwise I would have done so already.

(I tried to post links to the heaters, but it wouldn't let me because I don't have enough reputation).

UPDATE: I finally took apart the IR heater that I was originally referring to. Sorry it took so long. It wasn't easy.

Here is a picture:

I tested the resistance on the 2 contacts, and it starts at 260K at the lowest setting, ending at around 80ohms at the highest heat setting.


texts: Capacitor behavior on collector of a BJT?

texts:
In this circuit:

simulate this circuit – Schematic created using CircuitLab

As soon as power on, the transistor will start conducting in
saturation. This will make V1 ~ 100mV (\$ Vce_{sat}\$). Since
initially there is no charge on the capacitor, V2 will be equal to
100mV as well.

But suppose that we wait. AFAIK, transistor will not leave the
saturation no matter how much we wait. Hence, V2 will always be 100mV.

But after we wait a sufficient (long) amount of time, will V1 be equal to 9V,
giving a voltage drop of 8.9V over the capacitor, or will it be 9.1V,
giving a voltage drop of 9V over the capacitor (or will it be
something else)?

In either case, could you explain why this is the case?


texts: Control MOSFET with PWM signal from attiny85

texts: I am trying to make a simple attiny circuit that switches 5V through PWM into 3.2V. The load will be a vape coil that draws 2A at 3.2V, so the 490Hz PWM signal is fine. When I tested the circuit with an LED that draws ~1A at 3.2V, the LED just flashed on and off quickly, as if the attiny was resetting itself. I tested the mosfet with a pwm generator, and it worked fine. What it happening?


texts: How does the negative feedback actually feeds back the voltage to the inverting terminal

texts:
How does it do it i want to know the whole process

Is it beacuse of the movement of the current.
Lets say initially at time=0 voltage at v1 was 5 volt so voltage at g was also 5 so this voltage gets amplified negatively and produces lets assume -1000v now due to voltage difference between v1 and Vo current will flow from v1 to Vo so there will be voltage drop across R1 so the point g will have lower voltage than v1 but higher than Vo so the new voltage at g will again get amplified but this time the Vo produced will be lower, again this Vo draws current from V1 and agains there is new potential drop at g and this goes on. Is my understanding right if wrong please explain and also explain why the op amp always try to maintain same voltage.


texts: Second moments (i.e E[X^2]) for this WSS random process

texts:
I've attempted the question, please see attached image of my working out and solution to the question. My main question is how to go from the last line of my working out to “2Rx(0) - 2Rx(t) in the solution"

Please could you help me in understanding how to work out the solutions to this question regarding second moments (i.e E[X^2]) for the WSS random process

Many Thanks


texts: STMicro library for setting RTC Alarm on Sunday is incorrect?

texts:
I'm using a stm32fxx ARM Cortex-M3. When setting an RTC alarm for Sunday, I realized that the stm32l1xx_rtc.h header file defined Sunday as:

#define RTC_Weekday_Sunday             ((uint8_t)0x07)

In code, I do this:

rtc_alarm.RTC_AlarmDateWeekDay      = RTC_Weekday_Sunday;

But no alarm is fired when I used this value. Instead, I tried inputting 0x0 whenever I want to set an alarm on Sunday, then that seems to work just fine! So here is my hypothesis:

I have used the wrong header file for the F series
I have to do a mod 7 operation when setting weekday? I found nothing on a spec that mentioned this.
STMicro header file has a bug

If someone with knowledge can help me understand this problem?


texts: How to plot response of a non-linear state space model in Simulink?

texts:
I am trying to plot a non-linear model in order to compare it with it's linearized counterpart.

I am following this paper Nonlinear Model & Controller Design for Magnetic Levitation System and trying to reproduce the results the authors obtained. In particular I am trying to plot:

The above equations can be represented in vector format as follows:

I found no references on how to plot non linear state space model representations on MathWorks.

The Simulink state-space block is used to implement linear state-space systems and not non linear ones.

So, how can I plot the response of a non-linear state space model in Simulink ? Any suggestions would be appreciated.


texts:
I am trying to modify a Netgear GS108 8-Port gigabit switch with POE on 4 of the ports. Problem is that when I go to test to find out what pins 4/5 and 7/8 are in order to place the positive and negative terminals too, it shows continuity on every pin of each of the 8!

So in other words, no matter what pin I test for, it always shows continuity so I never know what pin is not being used!

Here is a picture of the board:

Any help would be greatly appreciated since I do not want to fry it :o)

update

If I were to connect pins 4/5 (positive) and 7/8 (negative) to the first 6 ports (ports 1-6) I understand that they would be forced to use 10/100mbps instead of 10/100/1000mbps. That being said, would the other 2 ports (7 & 8) be forced to use 10/100mbps as well or would they operate at the normal 10/100/1000mbps?


texts:
I'm little confused about the baud rate calculating equation of LPC2148

In data sheet equation is

But in every tutorial I could find

equation is

Second equation sets the baud rate as required.

Am I missing something?

Tutorials that I checked

Link1
Link2
Link3


texts: Average of AC signal measured with oscilloscope

texts:
I'm wondering why the oscilloscope displays that average rectifier ripple voltage value measured in AC mode is higher than zero. Moreover, the minimum value happens also to be higher than zero. Shouldn't average value equals or be very close to zero?

Is it for sure my own mistake or there is some explanation? Thank you a lot in advance.


texts:
Background:

I bought a material 77 ferrite rod for a homemade inductor. The core was 0.5" in diameter and 7.5" long with a claimed initial permeability of 2000.

When I recieved it, I tested it out using 18 AWG wire that I wrapped around the ferrite core for the entire length. Granted, the windings were not perfect and had some gaps between parts of the wire and the ferrite core (probably 1 cm max),

Upon testing the inductor with my LCR meter, I measured a mere 0.04 mH.

QUESTION:

How come my inductor isn't exhibiting a relative permeability of 2000?

Here are a few pictures of my set up:


texts: Using ground vs virtual ground in a single-supply Sallen-Key low-pass filter

texts:
This is the filter in question (courtesy of Wikipedia):

The opamp supplies are +5 V and 0 V, and I'm already using a buffered 2.5 V reference elsewhere in the circuit. I'm debating whether or not to change the ground node at capacitor C2 into the 2.5 V virtual ground. Doing so seems intuitive to me since I'm dealing with a single-supply filter.

But then I realized that if I were dealing with a passive RC low pass filter, I would not connect its capacitor to a 2.5 V virtual ground even if the input signal had a DC offset of 2.5 V.

What should I keep in mind when making my decision? Is one option always better than the other (though perhaps sometimes negligibly so), or are there some cases were real ground is better and others were virtual ground is better? Note that this filter will be used in a high-precision application.

PS: I wanted to know what would happen if I modeled the C2 capacitor leakage current as a parallel resistance. As I lowered this resistance, the gain of the system became lower. Furthermore, using the 2.5 V virtual ground kept the output centered around 2.5 V, whereas using the normal ground did not (the output DC bias was scaled by the gain).


texts: What's inside a reed switch that cannot be tested with a multimeter?

texts:
I'm shopping for reed contacts that are rated for 230V AC, because I don't want to use an always-on power supply just for a relay and a reed switch. This is surprisingly difficult, but I found this product:

https://www.ebay.com/itm/Black-NC-Magnetic-Proximity-Contact-Reed-Switch-AC-110-220V-for-Door/253489168964

In the description it says:

  Note: The multimeter can not be used to test the opening and closing of the door switch.

What does that tell me about the inner workings of this thing?


texts: Simplest circuit for making Christmas lights flash

texts: I bought a Christmas LED light yesterday but it is static. I don't know much about electronic circuits but I learned something in college on RC circuits. I am wondering if we can build a flasher with one capacitor and resistor and put them in series with the AC socket. I Googled the idea of flashing Christmas lights but all schematics shown online were too complicated for me.


texts:
Hey everyone I'm working on a project where I want to be able to power a thin mini-itx motherboard two different ways.  Here is what I'm trying to do:

19V battery will be connected to a relay which is connected to the DC input of the motherboard.  The port for the power adapter will also be connected through a relay to the DC-IN of the motherboard and to the charging port of the battery.  When the adapter is present the adapter relay is closed and the battery relay is opened.  When no adapter is present it closes the battery relay and opens the adapter relay.  The goal being that the motherboard always has power and I can charge the battery without discharging the battery at the same time since the power adapter can handle both powering the motherboard and charging the battery.

Since the battery voltage will vary based on its charge i'm concerned that there may be short periods of time where a <19V battery will be connected to the constant 19V power adapter.

So my questions are:

In the case of a <19V battery being connected to the 19V power adapter do I need to worry about current flowing back into the battery?  The battery has both a charging port and a output port.  I'm not really sure what electronics are present on the output port.   Maybe use Diodes to prevent current flowing back into the output port of the battery?

Do you think that when a adapter is connected I could switch the battery relay off and the adapter relay on fast enough to not interrupt power to the motherboard?  This question somewhat effects the one above.  Because I don't really have a feel for how much time I have.  I don't have that much experience with relays.  I was thinking of using a microprocessor to control the relays in which case I could disconnect the battery relay first then milliseconds later activate the power adapter relay which should mitigate the problem of connecting the adapter and battery together.  However, I'm not really sure if that will be fast enough to maintain power to the motherboard.

Lastly do you see other concerns with this method that I have not yet thought of?  Mainly safety concerns for the equipment.

Hopefully this is understandable.  First time posting this type of question on a board.

Thanks everybody.


texts:
I am attempting to create a 32-bit shift register in Verilog with two inputs, DATA0 and DATA1.  DATA0 is driven low to input a 0 to the register and DATA1 is driven low to input a 1 to the register.  DATA0 and DATA1 are held high when they are not being used.

The issue that I am running into is when I drive DATA0 low, it replaces all of the bits in the register with zeroes.  DATA1 works fine, shifting the register and adding a one to the end.  My code is as follows:

module shift(
databits,   //The register
reset   ,   // reset Input
DATA0   ,   //Input for a 0
DATA1           //Input for a 1
);

//------------Output Ports--------------
    output [31:0] databits;
//------------Input Ports--------------
     input reset, DATA0, DATA1;
//------------Internal Variables--------
     reg [31:0] databits;
//-------------Code Starts Here-------

always @(posedge reset or negedge DATA0 or negedge DATA1) begin

    if(reset) begin
        databits <= 0;
    end

    //If DATA0 triggered this, write a 0
    else if (~DATA0) begin
        databits <= databits << 1;
    end

    //If DATA1 triggered this, write a 1
    else if (~DATA1) begin
        databits <= { databits[30:0], 1'b1 };
    end

end

endmodule

I tried using DATA0 to also input ones to the register, but it overwrote the entire reigsters with ones.  It is my understanding that the always block should execute once when DATA0 goes low, so I do not understand why it is doing this.


texts: Energy calculation for a short circuit of a battery

texts:
I have a battery cell with the given datasheet: WB-LYP100AHA

So I can calculate the short circuit current with the internal resistance as:

$$ \frac{3.5V}{0.00045Ohm} = 7777.78A $$

So the internal power generated is:

$$7777.78A^2*0.00045Ohm = 27222.23W$$

Energy it takes to heat up a cell by 35 kelvin. Cell weight: $3.3kg$

With a heat capacity of \$4 \frac {kJ}{kg * K}\$ I get:
$$4000 \frac{Ws}{kg*K} * 3.3kg * 35K = 462000Ws$$

Time it takes the cell to heat up by \$35\$ kelvin:
$$ \frac{462000Ws}{27222.23W} = 16.97sec$$

Are these steps ok for a rough calculation or is there a mistake / better way?


texts: How do you wire up the OV3640 camera module?

texts:
I've been wanting to do a project with this module in mind and have found some resources on it (mainly arducam) but I have no idea how to connect it to a micro controller.

The data sheets show that it has an I2C connection but there are also 9 data wires which seem to have some sort of purpose?

If someone could tell me or point me in the right direction I would be very happy :)


texts: How to calculate reactance from an impedance analyzer circuit?

texts:
Background

I have an impedance analyzer that uses the below circuit:

Source

One can measure impedance of the device under test (DUT) by using the following formulas:

Z_load = Z_ref * (V_C1 - V_C2) / V_C2

One can measure the phase by comparing the phase difference between V_C1 and V_C2.

Let's say positive phase is when V_C2 lags V_C1.

Question

How does one get from this information/formulas to be able to calculate resistance and reactance of the load?

Does one need to make assumptions about the load?  For example, in this article they assume series RC or RL, or parallel RC or RL circuits.


texts:
I have a lossy passive two-port network with some input mismatch, so, $$ S_{11} \neq 0 $$
By simulation, I find the S11 and S21 parameters. What I would like to know is the losses within the network, when a wave is incident at port 1. I first thought it should be
$$ 1 - |S_{11}|^2 - |S_{21}|^2 $$ because what is not reflected and not transmitted must be lost within the network. However, a discussion with a colleague gave rise to the idea that $$S_{21}$$ is somehow contained within $$S_{11}$$... So, is it possible to find the losses from S-Parameters?


texts: Control theory in PLC (programmable logic controller)?

texts:
What is the control theory of PLCs (programmable logic controller)?

PLCs fall in category of linear control or non linear control?


texts: What transistor is this with SMD marking 72C9?

texts:
I am not sure what this part could be, and using some SMD codes on the web, didn't help.
The case size is either SC70 or SOT-523


texts: How to deal with PS/2 keyboard input and CPU interrupts

texts:
First of all, I'm not sure if this is the right place to ask this question or not. It was either here or the Computer Science stack exchange site, but I thought perhaps it would be better posted here since it feels like a lower level question more about the design of circuits than anything else.

My question is about two different things, the PS/2 protocol and device-to-host communication, and CPU interrupts related to the PS/2 input.

I've only been learning about electronics and computer architecture for a few weeks now, so maybe I'm missing something obvious, but I've been having a hard time understanding how to tell when a scan code has been sent from a keyboard to a computer and how to deal with the input after it has been sent.

What I mean by that is, I think I understand the protocol on paper, but I'm not sure how it would be built as an actual circuit.

From what I've learnt so far, and from what I understand from the protocol, I think I should be able to just connect the VCC, GND, Clock and Data wires up to a shift register of some kind (SIPO?) and just read the input data from the shift register.

If this is the case then how do I tell that the input has actually fully arrived in the shift register? Is it enough to just connect the shift register outputs up to some more circuitry which checks the start, stop and parity bits?

This leads to my second question about CPU interrupts. When I have verified that I do actually have a full scan code from the keyboard, I'm not sure what I should do with that input when it comes to CPU interrupts.

What I mean by that is, should I copy the data that's in the shift register out to RAM somewhere? Or should the CPU just access the data directly in the shift register?

The reason I ask this is because I'm not sure if it's possible for the shift register to have been overwritten with some other data while the CPU is in the middle of trying to handle the interrupt. If that is a possibility then I thought that trying to copy the data out to somewhere like RAM would be safer than trying to get the CPU to just read each scan code directly/indirectly from the shift register.

Also, since some scan codes are made up of more than one byte of data I'm not sure if reading directly from the shift register would be the correct way to do it in the first place.

I've tried looking around on Google for information about this but I mostly just get results for PS/2 adapters, or the PlayStation 2 etc., so if anyone has any information about how to deal with the data from a PS/2 keyboard it would be very much appreciated.


texts: Why would I need a capacitor in front of a LED strip?

texts:
Guides for connecting RGB led strips like WS2812B, which can be addressed individually, often suggest to add a capacitor in front. For example, the NeoPixel Guide states that

  Before connecting NeoPixels to any large power source (DC “wall wart” or even a large battery), add a capacitor (1000 µF, 6.3V or higher) across the + and – terminals […] The capacitor buffers sudden changes in the current drawn by the strip.

But why would I want to buffer that? What happens if I don’t add a capacitor?

fyi – I do not have a background in electronics, and I probably lack fundamentas here.


texts: Part Identification - Humidity Sensor Oregon Scientific BAR208HGA

texts:
The humidity sensor in my Oregon Scientific Weather Station (BAR208HGA) is stuck at 27% in vastly varying conditions.  Having declared it dead, I'm looking for a replacement.  (Edit: indoor unit; sat on my desk and suffers from old age.)

The white square at the bottom with interlaced traces and a "3" is the humidity sensor. Edit: back side is unmarked. Its legs are connected to 1.5K and 1.5M resistors (by measurement, not color code) above, and then the 1.5K side takes off to an epoxied chip.

Digikey shows 2 pin sensors reporting in pico-farads, and in ohms impedance @ 1KHz. Pricing is ~US$6 (and way up) in 1K quantity.  Most are polymer based.

Newark has some MULTICOMP HCZ-H8-B (from Europe) at US$0.63 in 1K quantity.  These are Polymer on Alumina substrate.  Might mine be a previous generation???

Perhaps what I have is ancient and/or Chinese, so not in the current parts catalogs.

Does anyone want to guess at the specifications for my broken sensor?


texts: Solar Module Voltage when bypass diode activate?

texts:
What happen to the voltage level when a solar module is shaded and one of its bypass diode is activated? Assuming this solar module has 3 bypass diodes.

I have been reading and can't seem to understand the theory. Should one bypass diode activate, I will assume the voltage should be 2/3 of the maximum Voc of a solar module?

Thank you.


texts: Pulldown Resistor on a Unity Gain Buffer

texts:
I have a sensor connected to a simple unity gain buffer with its output connected to an Arduino analog pin.

I'm trying to work out if there's a way I can stop the Arduino reading jumping around when there is no real voltage being fed into the unity gain buffer circuit, such as when the sensor is not connected.

Kinda the way a pull-down/up resistor works. Is this sort of thing possible?


texts: I know that CAN bus has two states. Dominant states where CANH goes 3.5V and CANL goes to 1.5V and in recessive state, both CANH and CANL goes to 2.5V. My question is, how much current does it draw in dominant and recessive states?


texts: ESP8266 - PULLUP resistor using Arduino code

texts:
I'm having some trouble with this ESP8266, to switch UP, DOWN, OFF dual relay, using Arduino code and a physical 3 states switch.

The code defines input GPIOs 12,14 as INPUT_PULLUP to avoid cases that from time to time ( say once a day ), I get a phenomena that is typically for not using a pull-up resistor.

What can cause such a thing?
Can it be that GPIO12, GPIO14 does not HAVE a pull-up resistor on-board?

Relevant code (that defines inputs and outputs):

void setup() {

        Serial.begin(9600);

        pinMode(switchUpPin, INPUT_PULLUP);
        pinMode(switchDownPin, INPUT_PULLUP);
        pinMode(relayUpPin, OUTPUT);
        pinMode(relayDownPin, OUTPUT);

        digitalWrite(relayUpPin,HIGH);
        digitalWrite(relayDownPin,HIGH);


texts:
For context: I am looking to step up 12V AC at ~25Hz to ~75V. Required output current is no more than 3W.
I'm looking for a small PCB mountable transformer which would do this job. I think that I understand the basic premise of transformers and that the ratio between the primary and secondary coils should be somewhere in the region of 1:6 to achieve this step up.
I've been looking at a variety of Flyback transformers such as this one: https://docs.rs-online.com/40b2/0900766b810a6c6a.pdf. The datasheet has a diagram as follows:

This implies to me that there are 3 primary and 3 secondary coils. I am presuming this is to allow for a variety of ratios to be used, as required. However, it is not at all clear from the datasheet what those ratios are.
The datasheet seemingly gives some example turn ratios:

Though these seem somewhat incomplete. My questions are:

Am I reading this diagram correctly? Are there indeed 3 coils on each side?
How do you go about determining the number of turns on each coil?
The datasheet says the ratio of 1-3:5-6 is 2.8:1. How is this possible? Looking at the diagram, those coils seem to be both on the same side of the transformer

Edit: It’s feasible this is an X-Y problem and there’s a better solution. I’m looking to make a ring generator for an old analogue phone. I have a prepackaged unit made by PowerDSine but as a learning exercise it seemed interesting to make one. Sample circuit I’m working off is below. I have a 12V input and a 555 + RC filter generating a decent sine wave at the frequency I want - I figured I could feed it into a couple of MOSFETs and then step up to 75v.


texts: Concerns in H-bridge switching times with common (one) gate control line

texts:
I have a FET based H-bridge being controlled by a micro. I was worried about software errors being able to turn on the top and bottom FETs at the same time, so I opted for the control scheme below for each half of the bridge. While this works fine, difference in the switching times of the two FETs means a partial short occurs - I see the voltage on Vcc is pulled down (even though it has quite a lot of capacitance) during switching. The duration of the 'short' is very brief (looks like <10us on my scope).

Is this inevitable with this control scheme, or can I get some improvement? I tried making R1 and R2 bigger in simulation and then strapping diodes across them (pretty sure I had seen this done before somewhere), so that the FETs turn off faster than they turn on. This seems susceptible to variations in threshold voltage, temperature changes etc. Is there any better solution?

I'm aware that there are ICs dedicated to this function, but I'd like to try and keep this simple. If the only way to do it is with more transistors, then so be it, but I wanted to make sure there isn't some simple solution involving R/Cs, diodes etc that I haven't thought of.


texts: Using a capacitor to smooth momentary voltage cuts

texts:
I'm building a model of a trolleytruck (very similar to a trolleybus). The steering system works with a servo but, because the overhead wires are not perfect and there are short voltage cuts, the servo moves randomly. I'm thinking of connecting a capacitor to smooth the voltage but I can't find any information on Google (everything that I can find is about rectifier circuits). So my questions are: Can I directly connect a capacitor between the servo power wires to smooth the voltage? If that's possible, how can I calculate the capacitance that it should have?

Thanks in advance and sorry for my bad English.


texts:
Is this the correct result?

a and b and c = not((a nand b) or not c)

simulate this circuit – Schematic created using CircuitLab

Is there any better decomposition?


texts: What kind of a MOSFET is this / how can I tell what kind of a MOSFET this is? The markings say C3L01 8D, and searching reveals that it's made by Toshiba, but I cannot find a datasheet, and it isn't available at e.g. Digikey. I would like to figure out what kind of MOSFET it is, in order to pick a suitable replacement. It's from a late 90s era DC universal motor speed controller, the board of which is also pictured.


texts: Cancelling transient state in RLC circuit

texts:
I have a problem asking the following question:

  We have a LRC circuit (L,R,C all in series) with a source \$ E(t) =
Vsin(\omega t + \phi)\$. Is it possible to chose the phase \$\phi\$ so
  that we can cancel transient state and pass directly to steady state
  at \$ t = 0+ \$ ? The charge in the capacitor and the current in the
  inductor are initially zero.

Solutions book is vague and only states (translation might be bad):

  Impossible due to quadrature relationships.

Could anyone tell me why it is impossible, in a detailed enough solution?

I did a similar exercise with a RC circuit, and came easily to the conclusion that, in order to cancel steady state, I must have \$ \phi = arctg \left ( RC \omega \right )\$.
The way I solved it was to calculate for which phase I get zero in the Laplace transform of the response. The problem with a 2nd order system such as a LRC circuit is that I cannot use the same method rapidly and reliably enough because of how complicated the equations become when isolating the transient response in the s-domain.

Is there a way to know it's impossible without spending two hours in Laplace equations?

Thanks!


texts:
How to calculate the time that a piece of wire can last before it melts when constant current is applied?

Assume it has a fixed cross-sectional area, I know longer the wire quicker it will melt, but whats the math to calculate the exact time based on different wire length? Thanks.


texts: What is wrong with this dsPIC30F2020 blink example?

texts:
I have coded a simple blink example for a dsPIC30F2020. I think that the schematic is correct, but I am unsure of the configuration bits.

Tools :

MCU : dsPIC30F2020
Programmer : PICKit 2
IDE : MPLAB X IDE v3.60

Here is the code:

#include "xc.h"
#include "libpic30.h"
#include "stdio.h"
#include "stdlib.h"
#include "p30F2020.h"

// xtal
#define _XTAL_FREQ 16000000

// DSPIC30F2020 Configuration Bit Settings
// 'C' source line config statements

// FBS
#pragma config BWRP = BWRP_OFF          // Boot Segment Write Protect (Boot Segment may be written)
#pragma config BSS = NO_BOOT_CODE       // Boot Segment Program Flash Code Protection (No Boot Segment)

// FGS
#pragma config GWRP = GWRP_OFF          // General Code Segment Write Protect (General Segment may be written)
#pragma config GSS = GSS_OFF            // General Segment Code Protection (Disabled)

// FOSCSEL
#pragma config FNOSC = PRIOSC           // Oscillator Mode (Primary Oscillator (HS, EC))

// FOSC
#pragma config POSCMD = HS              // Primary Oscillator Source (HS Oscillator Mode)
#pragma config OSCIOFNC = OSC2_CLKO     // OSCI/OSCO Pin Function (OSCO pin has clock out function)
#pragma config FRANGE = FRC_HI_RANGE    // Frequency Range Select (High Range)
#pragma config FCKSM = CSW_FSCM_OFF     // Clock Switching and Monitor (Sw Disabled, Mon Disabled)

// FWDT
#pragma config WDTPS = WDTPOST_PS32768  // Watchdog Timer Postscaler (1:32,768)
#pragma config FWPSA0 = WDTPRE_PR128    // WDT Prescaler (1:128)
#pragma config WWDTEN = WINDIS_OFF      // Watchdog Timer Window (Non-Window mode)
#pragma config FWDTEN = FWDTEN_OFF      // Watchdog Timer Enable (Disable)

// FPOR
#pragma config FPWRT = PWRT_128         // POR Timer Value (128ms)

// FICD
#pragma config ICS = ICS_PGD            // Comm Channel Select (Use PGC/EMUC and PGD/EMUD)

int main(){
    _TRISD0 = 0x00;

    while(1){
        _RD0 = 0xff;
        __delay32(150000000);
        _RD0 = 0x00;
        __delay32(150000000);
    }
    return 0;
}

And here is the schematic:

Pickit 2 screenshot :

When I connect the LED to RD0 (pin 15), the LED lights up all the time; it does not blink.

What might be wrong?

[UPDATE]
I think the __delay32() is the problem. Any idea?


texts: A question about power amplification concept of a BJT

texts:
In a text I'm confused about a part concerning BJT transistor operation:

Below is the paragraph regarding the above transistor models:

The text explains the transistor operation for the PNP transistor.

What does the text mean here? It says "the output circuit carries the same current". Here Im really confused. Isnt the the output circuit current is beta times the base current? The text says "the same current".. Or am I misunderstanding something?


texts:
Kindly help me with this Binary calculation

Add the following 2's complement numbers
11  +01010101 = ?

How i solve it :

0000 0011 + 01010101 = 01011000      but the book say its 84???

Please help!


texts: Multiple AVR Projects Sharing Code - Managing Large Projects

texts:
I'm working on a group project that is based around designing an automotive CAN bus system. Essentially there are multiple different nodes on the bus, acting as sensors, displays, controllers or transmitters. My question is how to share/include common code?

Each node is based around an Atmel AVR µC, usually an Atmega or Attiny. All the nodes are making use of Microchip MCP2515 CAN Controllers and MCP2561 CAN Transceivers. Our team consists of multiple members each working on their own nodes. We are using Github & SourceTree for source control.

Some code is common to each node, mainly the SPI/CAN functions for TX and RX. We have this working at proof of concept level at the moment. I'm used to working on individual projects however I'm lost as how to share code among projects effectively.

Really what I would like to do is have each node's code in its own directory and then have the common 'library' code in a directory that is referenced in each nodes source code. This way changes to the 'library' code only need to happen in one place and not in multiple copies.

Something like this:

    Code>>
      Display Node>>
        Display_main.c
      Sensor Node>>
        Sensor_main.c
      TX Node>>
        TX_main.c
      Shared lib>>
        SPI.c
        SPI.h
        MCP2515_func.c
        MCP2515_func.h

I am using Eclipse + AVR plugin for my dev, other members are using Atmel Studio.

I'm not too sure if I should:
a) Lump all the shared code in a folder and #include "../Shared lib/xxxx.h"

b) Lump all the shared code in a folder and set Eclipse compiler to include this folder? then #include "xxxx.h" will work ? (what about ATStudio friends? )

c) Create an Eclipse project without a main.c, that contains all the code and include this project with my other projects?

d) Compile the code into a 'static library' ?

I've done a fair bit of research and haven't found any good idea of direction. I guess it comes down to how to manage multiple code projects (nodes) by multiple members on multiple platforms ? I seem to be pretty good at basic stuff but this is the next level in code organization for me.

EDIT:

To add to this question, how could I create a Github project with all my own custom librarys and macros that I can keep updated and then just include in any project I work on?


texts: I would like to devise certain rules of thumb to help solve certain computer design/architecture challenges. Hence, in memory, which operations typically take longer to execute: loads or stores?? I think this might help make my choices more realistic during the design process.


texts: I would like to make a long range (5Km) quadcopter. As of right now, I'm just trying to find out the best way to control it. I  know that there are some 5Km R/C transmitters but they are the size of brick which is a little inconvenient. I was wondering if communication could be made through GSM, GPS or other wireless protocol that would be cheaper and/or weigh less. Any ideas on how to achieve this long range is accepted.


texts:
First time poster, apologize if I accidentally missed any rules.

I've built a circuit that keeps a relay closed that is attached to battery power for a specific amount of time so my Raspberry Pi has time to shutdown.

I followed this circuit as guidance Shutdown Controller for Raspberry Pi in a car.

Somewhere though something is going wrong. When the circuit is assembled on bread board and I use a bench supply it will run for approximately 30 seconds. This would be a perfect amount of time for the Pi to run through its shutdown sequence. I even upped the capacitance a bit and was able to get a full minute of time which would hopefully give the Pi time to start and shutdown if the power was inadvertently turned on for a short amount of time.

When I install the circuit in the car however things go wrong. The circuit will only last 15 seconds no matter what size capacitor I run. I've run the meter all over the vehicle trying to figure out what might be causing this and can't find anything for the life of me. Putting the meter on the gate of the MOSFET and ground I can watch the Voltage drop to 3V from 12V almost instantly whereas on the bench it takes a longer time. This is with 2x 1,000 uF capacitors in parallel. Originally for the 30 second setup I was using a 470 uF capacitor. No matter what though the relay will always lose it's field and end up open in about 15 seconds. with the 2,000 uF worth of capacitors on the bench it will last well over a minute.

At first I was thinking maybe the car has something that is cutting either battery power or ground to the car stereo wire harness where I spliced in. Some sort of fail safe other than a fuse. I kept the meter on each of the separate wires during the sequence and Batt always stays about 11V, IGN obviously falls off when IGN is turned off, and GND always keeps continuity with the chassis.

The only possible thing I can think of being different between the car's power system and the bench supply is the ground. Do I need a resistor between the C1/R1 loop and ground? What's the difference in the ground symbols in the diagram I referenced?


texts:
Using the QT600 development kit under Studio 7 in order to develop a touch interface, I can not get the kit to show up when not in programmer mode.

I've managed to write the example HEX onto the ATtiny88 board but when going out of programmer mode the kit won't show up on Studio.

Has anyone used this kit successfully? What steps are required to get the demos up and running?

Any help will be appreciated, the documentation I've read is really outdated.


texts: How to calculated weighted gain of antenna?

texts:
I have this test specification for testing antennas and it defines weighted gain as follows:

The weighted gain is calculated from the transfer function (S21) using only the gain values within the specified in-band frequencies. The average represents the nominal gain of the LNA assembly. The tolerance specifies the maximum difference between the average and the measured weighted gain of the DUT.

My question is, what exactly is the weighting function here? I have a VNA that performs an S21 measurement and produces a log magnitude graph (Hz vs. dB) with various points between the two frequencies which I also have.

Am I supposed to take the average of all these points in the band? Is this the weighted gain? If so, how does it make sense when it says to take the difference between the average and the measured weighted gain when the average is the weighted gain?

I'm not an antenna expert and everything I've looked up talks about just the normal gain antenna as being a function of directivity and efficiency, and it mentions nothing about a weighting. Usually when something is weighted, there's usually some weighting function specified...

If anyone could clarify, I'd greatly appreciate it.


texts: How to reason about this 'adder with memory' circuit?

texts:
I'm reading through "Code" by Charles Petzold and I had a question about the following circuit illustrated in the book:
Let's assume that the latches in the 16-bit counter and the 8-bit latch are edge-triggered D latches. Thus, when clk goes from 0 to 1 the counter will naturally 'increment' (e.g. 0007hex to 0008hex) and the 8-bit latch will 'save' its contents.
However, it seems that the 16-bit counter would 'increment' when clk goes from 1 to 0 too because in the implementation of a counter the book offers the following circuit:
Note how the first bit of the counter is just inverted clk. Thus, the 'adder with memory' circuit proposed wouldn't work, right? Because we'd only be adding every other number in memory?


texts: COB LEDs array in parallel driving circuit

texts:
I need to connect half a dozen COB LEDs (36V, 300mA). I can only connect them in parallel, not in series, because of wiring considerations.
For them to all be at the same brightness, my understanding is that I need one constant current LED driver for each. But could I use instead one Constant Voltage driver at 36V, 2A and one resistor of 120Ohms / 12W for each COB?
Will the system be prone to thermal runaway and will I get different brightnesses due to slight manufacturing differences of the COBs?
Also, if I want to dim all LEDs at once, will it work if I put a PWM dimmer between the constant voltage driver and the LEDs?


texts: what is critical in handling Heat dissipation of mosfet - Source or Drain!

texts:
I am working on a board which is connected to a DC power source of 12V/20A. To control the power to the load , I am using a PMOS as high side switch as shown below :-

My Doubt is, from power dissipation point of view, I should worry about the source or drain of the mosfet?? or Its about the complete package that gets heated. Why I am asking is because I have a bigger pad pin for drain & a smaller one for drain. While routing, I need to provide vias & more copper. I want to understand whether if I only put more Vias @ source pad, can I get away with the heat or do I need vias for drain pad also. Layout is as below :-

If anyone has any suggestion regarding:-

Power dissipation @ 12V/20A through IRF5305, please guide. Datasheet link :-
http://www.infineon.com/dgdl/irf5305spbf.pdf?fileId=5546d462533600a4015355e378101995
How to handle the dissipation?


texts:
My gas soldering iron now emits a yellow flame, and does not light internally. What is the problem and what can I do to rectify it? It has been filled using 100% butane gas and is only 6 months old.

Link to model datasheet
http://doc.ferm.com/Servotool/documents/SGM6013%20Ma%20%200806-06.pdf


texts: What is the best way to turn on 12V light at specific time for 5 minutes?

texts:
I have 12V/3A power supply which is supplying 12V light. I need to turn on light at 6am, 14pm and 20pm for 5 minutes. What is the best way to do that?

I was thinking about RTC module which has it's own time battery but I didn't find way to program that to turn on at specific time. I also searched for 555 timer circuits but it isn't used for long delays like mine.


texts: Capacitance of a particular transmission line

texts:
Is it possible to derive the expressione of the equivalent capacitance seen by AB for this kind of transmission line, where w is the width of the wire, d the spacing, l the length of the repeated part and n the number of meanders?

I know that for a typical transmission line without this meander part, the capacitance per unit length is given by

$$
c=\frac{\pi\epsilon}{log(d/w)}
$$

Now in this case, as a first approximation, I can calculate the capacitance between the first neighbors and than add them in series. Is this correct? Or should I also take in consideration the second neighbors and so on? How can I add them?

Edit: to simplify the problem, you can consider l big, so that you can neglect the effect of the corners and of the connection between one segment and the other. You can also assume w << d, if this can help.


texts: How many device classes can a single USB composite device implement?

texts:
I'm looking to use an LPC1345 microcontroller to run a USB hub.  Thanks to this question, I know that a single USB device can be used to act as multiple classes but how many?

The USB hub would have four slots, so I'd need four MSD classes implemented if I understand this properly.  It'd also be nice to have the DFU class in case I need to update the firmware at a later time.

Is there a limit in the USB standard on how many classes that can be implemented in a composite device or is there some characteristic of a particular controller I'd need to look into to determine if the controller is capable of doing so?


texts: I have always wondered how an only 1 wire line (signal and ground) can make a whole color image appear on a screen full of thousands of pixels. How exactly do these signals work and what characteristics make tv's show different things?


texts: How to obtain a high precision mV signal within a specific interval using a variable resistor?

texts:
I want to design a circuit which outputs a signal ranging from 0-70 mV using a variable resistor ranging from 80.51 Ohm - 183.05 Ohm and a supply voltage of 12 V. My idea so far has been to make a wheatstone bridge differential amplifier using an instrumentation amplifier with unity gain to subtract a constant offset voltage from the varying input signal. From what I have read, an in-amp is much more preferred than using a single op-amp because of its improved CMMR. I am not sure if it is superior with only unity gain, though.

As seen in the image, I tried drawing this circuit in LTSpice using LT1168 as In-amp. R42 would be the variable resistance, and it will be located on a separate PCA from the rest of the components. Hence, I fear more noise might be picked up on the positive input. I calculated that R43 would either need to be 17313.87 Ohm or 0.85 Ohm i.o.t. have 70 mV difference between the two edge cases for R42. I thought it would be better to go for the first option so as to limit the power dissipation over the resistors.

Hence the offset to be subtracted is formed by voltage divider R21 + R22. With R42 being 183.05 Ohm the output from the In-amp should in theory be 70 mV, and 0 mV when R42 = 80.51 Ohm.

When simulating, however, I only get 500-600 mV as output for any of the cases. It must be said that I am a beginner to LTspice, so I am not sure how accurate the simulation is, but it still gets me concerned. Will it be impossible to achieve such low voltages using this method, assuming that 0.1% resistors and suitable filtering are used? I would gladly accept suggestions for alternative ways of solving the problem as well as any advice for attenuating as much noise as possible.


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I am trying to design a transformer in FEMM and I have this issue.

First of all, I simulated my transformer with 0Hz frequency and the Magnetic field is illustrated in the following figure

Then, I did the same simulation with 50 Hz frequency and the Magnetic field is illustrated in the following figure

If someone observes these two figures, it can be seen that they are pretty similar. However, we all know that the transformer operates under AC current/voltage, so someone could expect that the results of the simulation when f=0Hz to be very different than the results when f=50 Hz. I can not understand why the transformer at 0 Hz operates similarly with the transformer at 50 Hz.


texts: Where should a switching regulator be placed in relation to analog and digital circuitry?

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General Layout:

I've partitioned a mixed-signal board as follows:

The dashed blue line indicates the analog/digital divide, but it is NOT a ground cut. This layout is intended to avoid analog and digital return currents from overlapping.

Note that one of the mixed signals ICs is an 18-bit DAC operating at 5 Volts. This means it has a voltage resolution of approximately 19 microvolts. I want to keep noise below this level to get full performance out of the chip.

Regulators

The power from VCC is immediately routed to a switching regulator. It in turn feeds various low-dropout linear regulators. Each LDO regulator is used to power either analog or digital circuitry (not both!), and is placed on the analog side or the digital side accordingly.

Questions

In order to minimize noise in the analog and mixed signal circuitry:

Which side (analog or digital) should the switching regulator be placed on?
If proper layout of the regulator and its surrounding caps and inductor do not allow them to fit exclusively on the correct side of the board, should a ground cut be employed? Where would the cut go?

Implementing Advice

Here's a new layout that uses the feedback I've received:

The solid blue horizontal line is a ground cut, while the dashed blue vertical line is not. No traces run through the ground cut.

Follow Up Question

Can LDO regulators be placed on the back side of the PCB opposite to the switching regulator in order to avoid wasting that space? I get the feeling that this would cause the switching regulator's noise to couple directly to the LDO outputs. If this happened it would render the LDOs' great PSRR moot and result in unacceptably noisy power lines.