texts: How to null offset on op amp without affecting gain?

texts:
I realize that there are a lot of questions relating to op amp offset here on electronics.se; however, none of them seemed to answer my exact question. If some of them are too similar, feel free to close.

I have a very simple non-inverting single-supply 3.3v-0v LTC6240 circut. This op amp doesn't have an offset null pin. I am running this op amp at a very high gain (>1000) with a 40khz input signal. The circuit works perfectly fine most of the time; however, I have an unpredictable ~500uV offset on the negative input, which (with some op-amps and some populated boards) works out to an output offset that the rest of my circuit can't compensate for.

I thought the best solution was this. I put a 10uf cap in series to ground as the answer describes and somehow, my gain at 40khz went away. I've replicated this in ltspice, even though I don't understand why it happens; the impedance of a 10uf cap at 40khz is only ~0.5 ohm. Here's a schematic of how I connected it:

As for putting a potentiometer in to correct the offset as described here, unfortunately I don't have a negative voltage available on the board, so all the pot can do is raise the offset.


texts: "Order" of a digital filter (FIR and IIR)

texts:
I have some doubts about the meaning of order for digital filters. All I'll put here is taken from these slides.

1) Let's start from the definition of FIR filters:

From this definition we see that order means the number of delayed input values in the input - output equation of the filter.

So my question is: is there a link with the concept of "order" in control theory? For instance, in control theory a second order system (or filter) has a transfer function with a second - degree polynomial at the denominator, and this happens also in analog filters (where it is sometimes equal to the number of reactive components of the circuit). Is it applicable also here?

2) Let's consider the so called windows design method:

Basically it tries to realize (in an approximate way) a filter by selecting a window of the desired pulse response of the filter, and you may see from the expression of w(n) that the length of the window is equal to the order of the filter (M-1).

So my question is: which is the link between the order of the filter (as described in 1) and the number of samples of the window?


texts: Two 12 volt batteries lowering reaches power

texts:
I just added an extra deep cycle 12 volt battery to my camper. I used half inch 15ft  (or so) wire to connect the positive to the older batterys positive and the same for the negative. My older battery was reading 13.8 volts before I added in the second. Now not 45 mins later my battery monitor (which is connected to the older battery) has dropped to 13.0 Volts.
And only 80% of battery life remaining. Why is it dropping??

Thank you!


texts: Understanding the AVCC pin wiring on ArduinoLeonardo (low-pass filter?)

texts:
The Arduino Leonardo has an interesting difference with previous boards: the AVCC pin of the ATMEGA32U4 is connected to +5V through a MH2029-300Y ferrite beads and to GND through a 1uF capacitor.

In ArduinoUno and ArduinoMega2560, this pin was simply connected to VCC. According to the atmel datasheet, this pin should be connected to a Low-Pass filter when the ADC converted is used.

Arduino Leonardo schema

Is this really a low pass filter? If yes, how does it work? How would you call that type of circuit? How do you model it?


texts: Designing a purely reactive circuit with the following requirements

texts:
how would you design a purely reactive circuit with:
Infinite impedance in f = 0 Hz and f = 800 Hz
Zero impedance in f = 5000 Hz and 11000 Hz
At 7000 Hz, has a reactance of 181.85 Ohms

How to proceed here using MATLAB


texts: WRL-1368 (ESP8266) wifi module briefly flashes blue LED once when powered up, then nothing happens

texts:
I bought a WRL-13678 wifi module, but when I connect it to a 3.3V power source, the blue LED flashes once, then nothing happens.

I tried powering it from a 3.3V breadboard power supply (connected to a 9V DC adapter). The same happens if I connect it to my Arduino 3.3V rail.

I checked the Arduino serial monitor and nothing is coming over the wire.

Is the module DOA, did I fry it somehow, or am I doing something else wrong?


texts: I'm considering using l293B motor driver ic. But it seems i won't be able to get the ses5001 diode which they refer in the data sheet. What would be the best ses5001 alternative?


texts: Difference between top pad master and top solder mask gerber files?

texts:
I generated gerber files to the pcb manufacturer, but I noticed that the top pad master (.GPT) was not generated, the top solder mask (.gts) was.

The pcb manufacturer did not complain, but I'm wondering, what can happen if top pad master (.GPT) was not generated ?
Why it did not appear as option to be choosen in altium when I generate the gerber files ?

With my best regards


texts: MC34063 Switching Regulator IC: When was it introduced?

texts:
I'm a bit curious when the classic MC34063 IC was introduced, today available as the -A version (MC34063A).

I'm trying to get an idea when some of the classic switching controller ICs were introduced because it marks the point when switchers started to become ubiquitous.

It appears that 1975-1977 were the years when the allegedly first PWM controller IC, SG1524, was developed and introduced into the market (IEEE, Power Electronics Magazine, NASA - pdf, p. 468). To get a better idea, I am also interested in other ICs that were and are widely used, like the MC34063(A).

If I read the available information correctly, it was Motorola (now OnSemi) who first made this part, and it was or is also available from competitors such as Sipex, TI, ST, Fairchild and some smaller ones I've never heard before. Some of these just seem to have slapped their logo on top of the original data sheet, copying even the original scope screenshot along with the typical data diagrams B34063A, UTCMC34063A, HTC, MC34063, CP34063A. Looking at all these cross-references (knock offs?!), one could get the idea that the original design team is invited to feel very honored, loosely quoting Confucius.

The earliest individual Motorola Data Sheet I could find is Rev 5, dated 1996 and the device is also listed in Motorola's Linear / Interface ICs Device Data Book, Vol. 1, Rev. 4, 1993, but it's not a new device in this source either.

1990 seems to mark the upgrade from the MC34063 to the MC34063A: In Motorola's Linear & Interface IC Data Book, 1990, the MC34063 is listed as "Not For New Deisgn-Ins", and the -A version's data is printed on the following pages.

I couldn't find any earlier sources, and I don't have any early data books by Motorola on my shelves. Any sources, preferably with pdf download links, are welcome!


texts: Best design choice: linear regulator or switch converter

texts:
I need to power a Thermoelectric module with 10A maximum load current. I'm designing a card with a minimal design in order to change the current or the voltage across the load, given a standard voltage source.

I just need a minimal regulation of the load, which is, just be able to decrease the power of the thermoelectric module from 100% to maybe 80-90%. Thus I was thinking to control the module by voltage, since precise regulation is not needed and voltage control is usually much easier than current control.

I am choosing among a linear voltage or a switching regulator solution. The point is that the output voltage should be absolutely flat, with Maximum 5% ripple. A potentiometer should be used to "regulate" the power of the system.
That's why to start with I was looking into linear voltage regulators. The point is that, to be on the safe side, I would require at least a 15V max output voltage and 20A output current model. Thus I was thinking in designing several regulators in parallel, but I am aware that this is a bad idea. How could I design a safe parallel regulator circuit?

If the linear regulator is a bad idea, is there any off-the-shelf step down switching regulator which does not require any external components (no coils or caps) more than a few resistors?

As said I'm not concerned about the accuracy of the system but just about reliability, design robustness and cost.


texts: Pool pump 20amp AC motor - significant inductive arcing when shutting off

texts:
My pool uses a 110V, 20 amp pump motor, specifically a Hayward Super Pump. Not sure on the HP rating but I believe it's the 1HP model based on the amperage. The pump uses a NEMA 5-20 plug, into a 20 amp GFCI socket, into 20 amp dedicated circuit.

In between the plug and the socket, I've added an Intermatic HB114 Heavy Duty timer, rated for up to 2HP motors. Ideally, I'd like the pump to turn on and off three times a day at various times, which I tweak depending on season, usage, and weather. The problem with that is, each time it turns off, there is a large arc. It seems unreasonably large to me. The arc is clearly visible through the opaque plastic housing of the timer, not just through gaps, but it actually illuminates the plastic. I believe the arc is destroying my timers, as their reliability significantly decreases after a month or so of operation, to the point that the mechanism doesn't turn properly and they no longer reliably turn the pump on or off and have to be replaced.

After giving up on the timer idea, I tried plugging and unplugging the motor manually, usually on a daily basis. Unfortunately, the arcing continued, and a month or so of doing that appears to have damaged both the socket and the plug. The tips of one of the prongs is visibly shortened from what it was before, and looks like it has been attacked by an angle grinder. Speaking with the previous owners, they confirmed the problem and explained that they simply left the pump plugged in 24/7. Due to rising electricity prices, this is not a reasonable option for me.

Aside from repairing all this damage that I did last year, I want to avoid a repeat of the situation this year. Is there anything I can do to avoid this situation in the future? Would a more expensive digital rather than mechanical timer help? Would hard-wiring the pump help? Is there some kind of arc-suppressor device or some kind of switch or power supply or capacitor that would help? Do I need a new/different pump? Should I consult an electrician?


texts: Is another diode needed when using a tip120 transistor?

texts: I am using the circuit in the second picture, which clearly uses a diode. (Found here) However the TIP120 data sheet transistor already has a diode in the schematic symbol.  Do I need to add another diode (like in the schematic) or should I remove the diode in the circuit, as the transistor has one built in?


texts: Is it possible to reset NXP LPC2100 microcontroller from code

texts: I'm curious? A watchdog timer could do this, but I would like to do it manually.


texts:
I've been designing a FPGA board that will become a single node of many in a computation cluster I am building for some scientific computing. The hope is to make it scale-able and allow me to update it to expand into further forms of computation (security, simulations, etc.).

Essentially I have been using development boards to simulate and test GPIO and USB, Ethernet and the like. However, my implementation currently uses 4 FPGAs, and I intend to increase that number and my budget simply does not support buying multiple development boards to test moving job data between the FPGAs.

I essentially need to simulate my environment, and even though I have plenty of computational ability (I have an entire lab at my disposal), I am currently trying to develop a test bench for moving data between the FPGAs as well as a DDR3 memory controller that I intend to implement for large data movement and manipulation.

Since most of my work with FPGAs has allowed me to avoid the use of a test bench, I have yet to develop one in order to verify my simulated results. All of which is done on Xilinx thusfar.

Any ideas on where I may start with developing a VHDL test bench?


texts: Solution for adapting to USB current draw limits?

texts:
Summary: I'm setting up a USB-powered Li-ion charging circuit and would of course like to draw the maximum charge current possible situationally -- but also want to ensure I don't violate the USB specification on current draw. While I have been able to satisfy one/two of the USB conditions individually, I am having a little trouble thinking of a smart way to satisfy them all. Here is what's happening...

Four USB spec rules (three regarding Current draw maximums, and one regarding Inrush current limiting) pertinent to my particular situation are as follows:
(Note: I'm showing different time-stages in this diagram:)

The good news is...

I happen to be using an FTDI USB-UART IC, the FT232R (datasheet), which takes care of the enumeration and also has outputs that indicate Enumeration status and Suspend status, which would be useful for setting when to draw what level of current.

Also helpful is that I'm using a Li-ion charger IC, the MCP73871 (datasheet), which has ChargeEnable pin, as well as Prog2 pin and Prog1 pin which allow setting Charge current limits.

The functions of these useful pins for both above ICs are summarized in my (rough) attempted layout below. It's not yet complete, as indicated by the Question-marks at certain connections:

My layout

Current-draw specs

Finally, here are the situational current-draw specs for the two ICs. Of course, these current draws also have to be counted into the 0.5 / 100 / 500 mA current-draw limits on the USB supply:

QUESTION: There seems to be a solution to adjust my layout so as to satisfy all the four rules/conditions at once, but I'm not seeing it; Any ideas?

As you could see in my layout earlier, I've set up an unconnected circuit (RC combination on MOSFET) for the soft start problem; and I've got the limit-setting resistor on the PROG1 pin, which could perhaps be used as part of a divider for partially solving the 500mA vs 100mA vs 0.5mA problem (based partly on FTDI's strategy in this app note). But that's as far as I was able to reach.


texts:
Will start off by saying I know very little about electrical engineering :/

so I basically need to make some sort of push/pull extending rod

it Doesn't have to be particularly strong, just needs to sort of hold the weight of an apple

the only problem is it needs to use a 12v power supply, iv'e looked everywhere and can't find a single reference as to where to either buy or try and attempt to make such a thing.

it needs to extend/detract about the length of an iphone 6 (sorry about the weird measurements, it was a rushed job)

if anyone could point me in the right direction or offer a little bit of advice it would be greatly appreciated


texts: Choosing correct transistor for simple Arduino 9V power switch

texts:
Okay so I haven't had any luck finding an answer on here that I was able to understand (I'm in a BioE program, just dabbling on the electrical side for a project). Overall its a pretty simple circuit I am making.

Here's what I am trying to accomplish:

Use Arduino code as a switch to control the on/off power of 4 vibrating motors, which will be wired in parallel (specs: https://www.adafruit.com/product/1201)
Motors are powered by an external 9V battery
I want to have around 4.5V across the vibrating motors, which I got with a 50 Ohm resistor in series with the 4 motors in parallel
Current draw by each motor at 4.5V will be ~90 mA

Here's what I think might work:

Need to use a transistor between the 9V (collector) and the (50 Ohm resistor + motors) (emitter)
I would use the Arduino Uno digital output Pin 3 (PWM output) and connect it to the "base" of the transistor

Question:

First off, do I have the right idea here?

Lastly, I have never worked with transistors before, how do I figure out which transistor will be correct for this application? i.e. what calculations do I need to make?

Thanks!


texts:
What is the meaning of the "Thermal hysteresis" in shunt regulator datasheet ?

Will it contribute to output tolerance ?

FYI: It's TL4050C50-Q1 datasheet.


texts:
I'm working on a fairly simple PCB that interconnects three arduinos. There are also MOSFETs for switching some solenoids. The system runs off of a 24V DC power supply. I was running a LM7812 voltage regulator, but I added a pair of cooling fans and they draw about an amp combined so I switched out the LM7812 for a R-78B12-2.0 DC-DC regulator.

I dropped in the 78B12 and everything looked fine. I ran the pair of fans for a couple of hours and everything seemed good. Nothing was warm, voltages were stable. I dropped in my arduinos and fired it back up and clearly something went wrong.

The trace from from 3.3uF input cap on the 78B12 to ground was smoked and the 78B12 is now shorting 24V straight out. That blew up one of my Arduinos and both of my cooling fans.

I'm not sure where to start to diagnose what happened and would appreciate the help.

EDIT:
Here are my schematics (with fixed ground on U6 and correct C1)


texts: Designing a 100 W 150 kHz sine wave oscillator

texts:
Problem: I need to design an oscillator that is capable of producing a sine wave at 150 kHz using 100 W (50 V and 2 A).
This signal will be used to drive a pretty heft induction coil for resonant charging. I've poked around some forums and it's recommended to use a sine wave over square wave for these operations. The problem is that I am having trouble coming up with a sufficient circuit design for such a problem.
This circuit needs to eventually be mounted on a PCB. There's an onboard MCU as well if that poses assistance in the circuit.
Thanks in advance for any help. Will gladly reply if any more details are needed
Note: Supplied 50 V is DC


texts: Connect Arduino to existing circuit with seperate power supply

texts:
I have an existing closed system that exposes several inputs that I would like to drive with an Arduino.  The existing system (Neptune Apex Controller with break out box) is designed to sense the closing of dry contact switches between the input connector and the ground connector.  The obvious easy solution would be to use relays to close the connection, however, I will need to change the input state every second or two which would burn a relay out in a matter of months if my math is correct.

Ideally I'd like to use an Arduino digital output pin to pull the existing system's input to ground.  However, this means that both the existing system and my Arduino need to have the same ground voltage.  I can't power the Arduino from the existing systems power supply easily since it's a black magic box with no details.  All I know is that it uses 12V.  I don't know if the supply is floating or not in relation to earth ground.

What would be the safest way to connect the Arduino to the existing system?  Is it possible to use a floating 5V supply and simply connect the negative terminal from the 5V supply to the ground of the existing system?  I'm not too familiar with what happens when the ground of floating and non floating or floating and floating power supplies gets connected.  I would think that if the ground of the two supplies are at different potentials then I would have current flowing from one ground to the other which might burn out the existing systems circuitry.


texts: How do I make an LED turn on when my output reaches 5v?

texts:
I'm a hobbyist and pretty new to many of the components involved, so I hope you guys can help me here. I'm trying to keep the circuit as simple as possible.

I made a small variable power supply with a buck converter and would like an LED to come on when my output reaches 5V. I'm not really concerned about it staying on after 5V is exceeded, but I definitely want it off if the voltage is lower than that. After looking into it a bit, I'm assuming I'll need a MOSFET or a transistor of some sort but I don't know enough about either of them to begin finding the correct one. If it matters, here is the buck converter I'm using:

The only other things in the circuit are a volt meter wired to the output and powered from Vin and GND and I replaced the potentiometer with a larger one.


texts: Can I use 250μF capacitor instead of 100μF?

texts: I am trying to drive a stepper motor from an old DVD drive with the Pololu A4988 driver and an Arduino. The data sheet says I need a 100μF capacitor to prevent voltage spikes when using a 12V PSU (I'm using a PSU from an external hard drive enclosure, 12V 2A). I don't have any capacitors laying around and I see there are some 250μF capacitors on the board of the DVD drive that I took the stepper motor out of. Can I safely use the 250μF capacitor instead of the 100μF capacitor?


texts:
I have 20 LEDs on  my board. Due to current limitation, I can not increase LED current after certain point and I need more light illumination or reflection.
Can PCB with white colour help here rather than usual green PCB colour. I am using white colour LED.

Also is there any other way to achieve reflection from PCB ? (use of optics doesn't fit in my application)


texts: Guitar Amp Headphone OUT Jack. What Pot to use?

texts: With a Guitar amplifier's Headphone out jack, I need to attenuate the signal about 80%, adjustable. Would a 1k Audio Taper Pot be my best choice? I am attempting to use the headphone outs of my 2 15 watt amps to feed into an old cheap mixer board that goes into a Behringer box into my Linux PC. Without measuring yet, as I have no jacks or plugs and no resistors, I don't know what resistance to work towards. Someone told me 20 ohm, but that sounds like way too little.


texts: Non linear behaviour of a pure LC: Is it real or LT Spice is broken?

texts:
Questions:
1) Is the observed behaviour correct? (both cases at the resonant frequency and at a lower frequency) If it's not correct, why LT Spice is giving this result?
2) Why does circuit lab give a different result?
I've been playing with LT Spice and LC filters and made a couple of simulation in the frequency and time domain. So I've come across a strange phenomenon that I don't understand, and I'm also doubting that it is real, maybe it's a "defect" of the conditions set for the simulation.
Here is the simple circuit:

simulate this circuit – Schematic created using CircuitLab
The transfer function is like this:
$$
H(S)=\frac{1}{(1+LCS^2)}
$$
With the values set for L and C, the resonant frequency is roughly \$ f_0 =50.33 kHz\$.
Let the input signal frequency be \$f_s\$, so I expect that

When \$f_s << f_0\$, Vout is almost identical to V1: no amplitude or phase difference between them. At this frequency the module of the transfer function is close to 0 dB.
When \$f_s = f_0\$, Vout is amplified, the filter is resonating. We're at the peak of the bode diagram. In the time domain, I expect the have an oscillation with an increasing amplitude until it reaches a maximum amplitude. It then continues oscillating at that amplitude and at the resonant frequency.

In particular, the circuit is linear, so the output frequency shall be the same as the input frequency.
It doesn't really seem the case though:

Above is the simulation result with \$f_s = 1kHz\$ (blue = Vout, red = V1, green = I(V1) ), and it is clear that 1 kHz is not the only harmonic of this signal. The FFT of LTSpice gives this result:

There is a small, peak at the resonant frequency.
Where does this mathematically come from? The reverse laplace transform of the transfer function doesn't give any frequency different from the input signal frequency. So where does this come from? What calculations is LT Spice doing that gives this result?
Furthermore, there is another strange phenomenon with this circuit simulated with LT Spice.
When \$ f_s = 50.33 kHz\$, a transient simulation gives a waveform that never gets to a "steady state", in contrast to what I expected.

The image above is a 20ms time frame with \$f_s = f_0\$.
For completeness sake, here is the schematic used for the simulation:

Final note: simulating the same circuit with circuit lab gives the result that I expected for both case (\$fs = f0 \$ and \$fs << f0\$ ). For some reason they're giving different results...


texts:
I am designing a DC/DC converter. I chose the fullbridge topology.
The requirements are as follows:

Vin = 75 - 125 Vdc
Vout = 200V
P = 600W
Fs = 100 Khz

The basic schematic is as follows:

I use ZVS for soft switching.  The problem is the big spike in the Vds on the MOSFETs.

The image above shows the Vds on the down MOSFETs and the Vgs for all MOSFETs.

signal A is the up - left mosfet
signal B is up - right mosfet
signal C is down - left mosfet
the signal D is down - right mosfet

I see that the voltage spike is generated in right leg transition (when D switch is falling).  The same spike occurs on the primary current.  Why does it occur?  Is the problem in the primary or secondary?

I provide a large time for discharging the parasitic capacitances (over 400ns). Which components oscillate in my design?


texts:
im learning about the CAN protocol, and bought the transceiver module MCP2551 like this:

I made the driver for CAN controller first in loopback mode for debug, im sending the numbers 1,2,3 and 4 with 1s of interval. Without the transceiver connected to the microcontroller, messages are sent correctly, for example when the number 2 is sent with an ID of 0xff;

But when i connect the transceiver to the mcu, the message is corrupted:

So i think that is something related to the transceiver itself, it is not a driver problem, I checked the connections and everything is fine, has anyone had this problem to help me?
The peripheral connection is below:

There is one more connection thas is not in the image which is the gnd of STM with gnd of arduino, but the problem is before, because i have not tested the CAN in normal mode but in loopback. I think that the problem is (PA12, CTx) AND (PA11, CRx) connection or with the transceiver. This is more likely.


texts: Noise issues when driving DC motor with PWM

texts:
I have a PWM-based controller with an Attiny13 to control the motor of a cassette tape player (similar to this layout.) Attiny13 is producing PWM of varying pulse width with a frequency of about 75 Hz.

When I start decreasing the tape speed with the pot (by changing pulse width,) I start hearing a low frequency noise injected in the audio of the tape player. My assumption is that this is from the PWM getting into the audio part of the circuit.

What is the best way to remove the noise? Filter the PWM? I tried filter caps on the motor terminals, which did not help.

Circuit diagram:


texts: Where does current go in these circuits?

texts: In both these schematics, the 9V source drives current through the circuit, but there doesn't seem to be any way in which the current can 'return' to the source to complete the circuit. In what ways would current flow through both these circuits from the DC source, and where would the current end up? Wouldn't all the current just go to ground? This is for an audio circuit, input is from a electric instrument and output goes to the speakers/recording equipment.


texts: How to use a SPDT with no negative capability for audio signal routing?

texts:
I have a couple of SGM3005 chips and want to use them as switches in an audio circuit, but they don't support negative signals. The classical solution would be to bias the COM1 input, right? But, what if instead of biasing the input pin, I apply some negative voltage to the GND pin, will it work?

http://www.kean.com.au/oshw/oximeter/SGM3005%20Dual%20Analog%20Switch.pdf


texts:
I'm studying the constant current portion of the schematic for the Agilent E3610A DC Lab Power Supply, redrawn below for reference.

The current reference supply develops a negative voltage \$V_{CREF}\$, adjustable using the ten-turn pot VR19. \$V_{CREF}\$ represents the constant current setpoint, with the value -2mV/mA of the current limit. This feeds a 20-to-1 resistive summing point connected on its other end to the current sample voltage of 0.1mV/mA of output current. The resulting error signal is fed into the current error amplifier to control the pass device as necessary.

My question has to do with the capacitor C20 across the input terminals to U4A, the inverting op amp circuit that generates \$V_{CREF}\$.

I'm assuming, based on the answer to an earlier question of mine about this sort of capacitor placement, that C20 is there to reduce high-frequency noise that might either produce drift in the setpoint, introduce noise into the power supply output, or both.

My question is "How would I go about sizing this capacitor?". I'd like to understand the design steps rather than just plop in an 18pF cap whenever I design a similar circuit :)

The current state of my transfer function derivation skills is to start with the characteristic gain formula for the op amp circuit, e.g. \$G(s) = -Z_f/Z_g\$, replace the impedances with \$R\$, \$1/sC\$, etc., and crank through the algebra. But unfortunately in this case C20 doesn't fit into the classic gain formula.

I can see it forms a low-pass filter with R28, with a breakpoint at about 100kHz. But I'm not sure how the value of VR19 might fit in, if at all, and I'm not sure how to arrive at 100kHz as an appropriate breakpoint in this case.

What would be the analysis/design steps for a thoughtful selection of the value for C20?


texts: 24vdc variable circuit with analog input(0-10 vdc)

texts: Im trying to find electronic circuit that powered with 24vdc.  An input 0-10 vdc analog signal.  And gives me an output 24vdc variable (0-24) vdc


texts: Is reactance in AC circuit is also alternating?

texts:
Usually the capacitive reactance in a a circuit is represent in phasor form as X(c)= |X(c)|\$\angle 90\$.

If we convert this phasor expression to sinusoidal expression we get.
X(c)= |X(c)|sin(wt-90).

Does this mean that capacitive reactance is also time changing ?

If that is the case then at t=0 we get.

X(c) = |Xc|sin(0-90) = -|Xc|. so at t=0 we are getting negative reactance. I really do not understand how reactance can be negative.


texts: Detecting an electrical connection without a complete circuit

texts:
Wired Fencing

In a regular (wired) fencing system (for sabre and foil,) contact is determined simply by applying a current to the weapon through a wire and forming a circuit between a conductive jacket called a lame which is in turn connected to a wire - naively, the circuit contains a light which indicates a current flowing.

An image of a sabre lame is shown:

Wireless Fencing

It is desirable to eliminate the wires - this has been done however how this is done is a trade secret. Each fencer wears a pack on their waist which connects to their lame and weapon.

Some wireless fencing systems are pretty bad, some are not, which suggests there is some variation in how they operate.

The Task

Therefore, I need to determine whether two (conductive! - this is a wireless fencing system, to give an idea of scale) objects are in contact, the catch is that there is no return path for a simple DC circuit. As far as I'm aware, this can be done using time domain reflectometry, however this would require a fairly complicated ADC + FPGA setup (reflections would be on the order of 10nS or less.)

I think this is also possible by treating the conductors as antennae/waveguides: Send a radio signal from one side and detect it on the other, as a single wire transmission line.

Does this sound feasible (there seems to be a patent documenting a similar system but that doesn't mean it works,) and does this problem have a name that I've missed (i.e. existing literature?)


texts: ngspice, malloc: internal error can't allocate -8 bytes

texts:
I am new to ngspice and trying to simulate my first circuit. I have posted my spice.net and my simulation.cmd below with a picture of my schematic. When I run the simulation I get the error message:

  malloc: internal error can't allocate -8 bytes.

Does anyone know what the problem might be?

Thanks

* gnetlist -g spice-sdb -o spice.net v-monitor.sch
************************************************** *******
* Spice file generated by gnetlist *
* spice-sdb version 4.28.2007 by SDB -- *
* provides advanced spice netlisting capability. *
* Documentation at http://www.brorson.com/gEDA/SPICE/ *
************************************************** *******
*vvvvvvvv Included SPICE model from /home/matt/Documents/gEDA/model/BC108.mod vvvvvvvv
.MODEL BC108 NPN(Is=1.8E-14 Ise=5.0E-14 Nf=.9955 Ne=1.46 Bf=400
+ Br=35.5 Ikf=.14 Ikr=.03 Isc=1.72E-13 Nc=1.27 Nr=1.005
+ Rb=.56 Re=.6 Rc=.25 Vaf=80 Var=12.5
+ Cje=13E-12 Cjc=4E-12 Vjc=.54 Mjc=.33
+ Tf=.64E-9 Tr=50.72E-9)
* ST pid=23 case=TO18

*^^^^^^^^ End of included SPICE model from /home/matt/Documents/gEDA/models/BC108.mod ^^^^^^^^
*
*vvvvvvvv Included SPICE model from /home/matt/Documents/gEDA/models/BC178.mod vvvvvvvv
.model BC178 pnp(IS=3.50E-15 VAF=80.5 BF=330 IKF=0.1018 NE=1.3140
+ ISE=3.816E-16 IKR=0.03 ISC=5.00E-13 NC=1.6 NR=1 BR=5 RC=0.35
+ CJC=8.80E-12
+ FC=0.5 MJC=0.28 VJC=1 CJE=1.00E-11 MJE=0.38 VJE=0.4 TF=7.00E-10
+ ITF=0.6 VTF=3 XTF=11.5 RB=100 IRB=0.0001 RBM=10 RE=0.75
+ TR=2.00E-07)
*

*^^^^^^^^ End of included SPICE model from /home/matt/Documents/gEDA/models/BC178.mod ^^^^^^^^
*
*============== Begin SPICE netlist of main design ============
.INCLUDE /home/matt/Documents/gEDA/Simulation.cmd
Vcc Vcc 0 DC 15V
Rnb 4 3 4K
Rpb 2 5 22K
Q2 1 5 Vcc BC178
Vpulse 4 0 pulse 0 5 1m 1u 1u 1m 3m
Q1 2 3 0 BC108
R2 0 Vout 1K
R1 Vout 1 2K
.end

P
* .AC DEC 20 1Hz 100MegHz
.DC Vpulse 0 5 .01
* .DC VINPUT 1 2 .01
.plot dc v(Vout) v(Vin)
.print dc v(Vout) v(Vin)


texts:
As we know the power equations are P=VI, P=V2/R or P=I2*R.

My question is:
how I can increase the power by increasing and decreasing the resistance?

In the formula P=V2/R, if I want to increase the power I have to reduce the resistance value as much as I can, but if I decrease the R in the other formula P=I^2*R the power will decrease.

If we have R= small value in first formula, the power will increase regardless of voltage and the amount of R. In the second formula the power will decrease regardless of current, how?

I hope my question is clear:)


texts: Eagle Cad: How to get copper on both layers for a pin header

texts:
I am making a PCB for prototyping, I need solder pads for a male header on the top and bottom layers. In my previous PCB, I had SMD's and pin header pads on the top layer, Its always better to solder the pins on the other side, unfortunately no pads on the bottom layer for the header. I was also thinking about adding vias
What should I do on the software to add pads on the bottom layer?
or Should I jut tell the vendor to add plated holes?

-Thanks
Sandeep


texts: Intuition for stability differences between PMOS and NMOS linear power supplies

texts:
Reading this question and the linked TI's LDO document led me to a more direct comparison between the two approaches:

Notes:

I'm using a separate V+ for the general purpose opamp to provide more head room to the positive rail and exclude PSRR from the analysis
The low values for the voltage divider are just to simply provide a high load current (these are ideal resistors anyway)
External compensations are intentionally not included, for a more direct comparison

The circuit with a PMOS is a beautiful oscillator (not even considering the overshoot here):

An AC analysis on the input voltage seems to show why:

Analyzing \$V_{GS}\$ in two approaches (assuming both MOSFETs in saturation -- \$V_{DS}\$ changes don't change source/drain current):

with the NMOS, a +1 V step on the the input doesn't directly affect \$V_{GS}\$, hence the source current is not directly affected

with the PMOS, a +1 V step on the the input directly affects \$V_{GS}\$, hence the source current is directly affected (increased)

the NMOS provides a direct negative feedback for load changes (\$V_{GS}\$ increases with a reduction in the load resistance), which is not present with the PMOS configuration

Question: is the above reasoning correct as an intuition on why the PMOS circuit requires more attention to obtain a stable behavior?
This old question provides some interesting discussion around the "positive" feedback.


texts: Charging a bank of batteries in series with a resistor

texts:
Few days ago I was trying to recharge a bank of ten batteries connected in parallel.  I connected the charger directly to the battery terminals at 13.75 V as specified in battery manufacturer datasheet.

The problem: the batteries were about 11.4 V at that time and my DC supply transformer was supplying a the maximum current of 50 A. Well ... 50 A for  10 \$\times\$ 9 Ah batteries is way too much, not to mention that the wires started to melt due to high current so I realised that I need something to limit the current and quickly figured it out that I need a resistor.

I've seen numerous youtube videos and documentation about how a resistor works and it's limitations, I ended up using this calculator.

13.75 V at 4 A = 3.4375 \$\Omega\$ resistor, but I found a 3.3 \$\Omega\$ resistor which (based on the calculator) should be capable to limit current at 4.16 A, dissipating with 57.29 W of heat.

Big surprise when I connected it on positive terminal (tried on negative also) and only about 0.6 A of current was flowing to the batteries, despite the fact that the batteries were discharged and without any kind of resistor they alone would draw  > 30 A.

So my question is: why is that?  Why does the 3.3 \$\Omega\$ resistor limit the current to 0.6 A and not to 4.16 A as calculated.
Is there a possible difference in resistance which doesn't allow the current to flow at max capacity?

I've also tested the resistor with a multimeter and the resistance is fine. I've also connected it to positive and negative of a single battery and about 4.3 A of current was flowing - so it works as it should but not when connected with the charger.

I have absolutely no clue about it, could someone please help me to figure it out?

Thank you!


texts: Could smartphones benefit from the same charging mechanism as in electronic watches?

texts:
A long time ago I learned that electronic wristwatches have a charging device that draws energy from hand movement while the wearer walks. I don't know how much power a wristwatch generates but maybe this sort of tech could be used in modern smartphones to charge them while you're walking. Would the power output of the same generator as in watches be enough to let a smartphone never run out of power? If not, how much more power would be needed? Would such a charger be feasible?

The main point of this charging method is that it should be effortless. With a dynamo generator that definitely outputs much more power you'd absolutely notice getting tired.


texts: The voltage between the plates of a capacitor

texts:
I have read in one book that:

  the potential difference between the plates of a capacitor when it's connected to a DC source (a battery) is in opposite direction to the potential difference of that battery.

I don't really get that point, and I don't know how could this help in the break of the DC after the capacitor charges.
I used to think that when connecting a battery to a capacitor the plate connected to the positive terminal gets a positive charge and the plate connected to the negative terminal gets a negative charge. So, how will the PD be in the opposite direction to the PD of the battery? Could someone clarify it?


texts: Difference and compatibility between AVR xxxA and xxx/xxxV series

texts:
This is kind of two questions(difference & compatibility), but since an extensive answer to the latter will probably include an answer to the former, I think it's okay.

Anyway, on to the question:
I've made a certain device prototype on a solderless breadboard using an ATTiny13A-PU (the PDIP8 one) and would now like to make an actual PCB with the SMD (-SU/-SSU) version of it (since the device is supposed to be watch-sized). However, the place I usually order my parts from only has the SMD version of ATTiny13V in stock. So, I'd like to know how those two are different and whether my code (in C) for the former will be compatible with the latter and whether that's true for other AVRs as well (for example, '2313A vs '2313/'2313V).

As for my own research, the summary sections of the respective datasheets don't seem to reflect any major differences and I'm not inclined to scan and the whole thing. The other thing I noted is that avr-gcc does not consider the '13 & '13A the same MCU, so there definitely are some differences, I just can't figure out what they are. (while avrdude does, but AFAIK it only handles the uploading, not the code).

edit/clarification:
This question is mostly about differences in and portability of code for the A vs. non-A series (which do exist, according to avr-gcc). Listing other differences is, of course, welcome, but secondary.


texts: why ultrasonic module sends out 8 cycles ? and , why the trigger pulse is 10us?

texts:
this is the operation of the ultarsonic module HC-sr04 :

  The timing diagram of HC-SR04 is shown. To start measurement, Trig of
  SR04 must receive a pulse of high (5V) for at least 10us, this will
  initiate the sensor will transmit out 8 cycle of ultrasonic burst at
  40kHz and wait for the reflected ultrasonic burst. When the sensor
  detected ultrasonic from receiver, it will set the Echo pin to high
  (5V) and delay for a period (width) which proportion to distance. To
  obtain the distance, measure the width (Ton) of Echo pin.

is the number of 8 cycles related to the microcontroller of the module ,I think that but why?

don't forget the second question why the trigger is 10us ?


texts: Solar Plane, Voltage drop when under a load

texts:
This is a project with a group of high school kids who want to be engineers.  The students have built a solar power airplane.  We are using maxeon solar cells.

Here is a link to the test video from yesterday.  Notice the voltage drop when we start the motor.  The cells are rated at .58v (Vmpp) at 6amps (Impp).

Some of the cells have minor damage due to this being a group of high school kids, so that could very well be contributing to the problem.

Here is the video, any thoughts.
Static Run Up


texts: Prefered schematic symbol for voltage rail and bus labels

texts:
Working on a schematic meant for the documentation of a system I'm building (an airsoft prop as a strongpoint for the game).

Since I am using this as a learning experience, I want to really do it as good as possible, even though it's not really needed. I'm working with inkscape designing my own library (originally wanted to use the Wikipedia lib, but I found it lacking in some places, so I pretty much started from scratch).

In schematics in my textbooks, I've run across a few different symbols for rails. I was wondering if there is any difference between these symbols. If so, what does each mean, and what others should I consider. If not, which is preferred? Most of my textbook use the middle symbol (black line with voltage written on top/under it. Positive voltages are labeled as seen here, negative voltages are mirrored horizontally, so the text is under the symbol.)

As a followup question - what is the preferred way to mark bus names in schematics?

I have a bus that is my LCD data, and I would like to label it as such for clarity, but I don't really know what the proper way to do this is. Just write the name above the bus like this?


texts:
I have a project regarding the application of logic gates. I decided to build a sound reactive LED's.but before that here's my first diagram,

As you can see, there's no TIP31C on that diagram. the question is, is it possible to insert that TIP31c on this diagram to make my sound reactive led work? because I based the sound reactive led from this circuit diagram.
Can I place that TIP31C on my first diagram just to make my desired output which is to have an audio/sound reactive LED's? Thanks for any help.


texts: How to Control an I-Beam Trolley with a PLC

texts: I recently bought an i-beam trolley, and want to control it via my PLC instead of the pendant. I cut the pendant cord and found 3 wires. Green/yellow (presumably the ground), blue, and pink. Using the relays, I connected the ground to the blue wire, then the ground to the pink wire, but nothing happened. Even tried connecting the pink and blue wires, but still nothing. The trolley worked with the pendant, and the PLC setup works with other 3-wire motors. What else could it be? Perhaps there's something different required for A/C current?


texts: Identify component (diode?) based on photo

texts:
I am currently fixing a Akai MPK Mini mk2 midi controller with a loose USB port.
In addition to the USB, it is missing one part labeled as D1. It can be seen in the attached picture circled in red. I think the text on the component reads 62S? Any idea on what component it could be? All help is appreciated!


texts: Calculating the transfer function of this op-amp circuit

texts:
The first op-amp is a differential, second one is a follower and third one is a second order low pass filter. I've been struggling with the low pass and the final output of the circuit and I am not sure whether my calculations are correct or not, they are still incomplete though(Always had troubles with these kind of circuits).
Refer to the input voltage as Vi, first stage output as Vo1, second stage output as Vo2 and final output as Vo.

My calculations so far:


texts:
I am trying to understand how this data interface works.

It's supposed to:

translate (read) "OT" current difference into logical OUT (<10mA = 0, >17mA = 1)
send logical IN to "OT" by varying the voltage across OT (<7V = 0, >15V = 1)

The voltage across OT terminals is around 18V and the current ~5..9mA when idle.

Specifically I don't understand how current sensing works in this circuit. Does D5, D6 or both play a role?

Note: the interface is for an OpenTherm 2.0 master, though I hope I have provided all the relevant details about the interface in the question itself such that any further knowledge of OpenTherm is not required to answer the question (if it is, please comment about what exactly is missing and I will provide it).


texts: Read (High/Low) Arduino Output with an Raspberry GPIO Input Port

texts:
I want to trigger events on the raspberry (3) with an Arduino. Because of very contrary statements to this, i am kinda Lost. Arduino outputs 5V, that should be read by an Input of the Raspberry. Just slow Low/High Values, kinda like Buttons presses.

Different Possibilities I found:

Voltage Divider from 5v to 3,3v for Raspberry Pi (for example: 10k and 18k, for ~3v on the Input): That would the way that I think it is the easiest. But I stumbled over a lot of statements that say they would not recommend that, because of burned GPIOs. And the pullups of the Raspberry GPIO should be a problem. Later I found that the raspberry has software set able pull up/down resistors. It feels like lots of people don't know that they can disable them?
Voltage Level Breakout boards: That would be the easy way to go, but costs money and I don't need a bidirectional connection.
Levelshifter ICs: self explanatory.
Circtuit with a Transitor: Self explanatory, that would be my choice if Voltage Divider don't work.

So perhaps you can explain me what fact is against using a Voltage divider to connect these two boards. I just want to understand the issue, if there is one. :)

Cheers Michael


texts: How do I Analyze Crosstalk in an Unbraided Multi-Cable?

texts:
Near-end crosstalk (NEXT) and far-end crosstalk (FEXT) are defined for twisted cable pairs [1], while both FFT and Baum-Liu-Tesche equations have been applied to analyze crosstalk in bidirectional coaxial cables[2]. In contrast, I wish to simulate a model for straight unidirectional wires in a multi-lead cable.

My goal is to visualize the crosstalk and how it affects the "pure" signal. I only have access to a compound signal and not the individual leads. However, this is a broadband signal, where I can isolate the narrowband components and the momentary phase.

How can I study crosstalk in multiple pairs of straight wires that share direction of current, but with varying phase*?

* The phase is neither exclusively odd nor even, but is subject to continuous phase shifts. The wires belong to circuits with independent power sources.

Edit: Resources

These are the materials I am working with right now:

Rise time of model systems (wiki)

I also found this resource interesting:

  "The error rate in multipair cable systems is affected by the
  transmitted signal, level, cable loss, crosstalk, and the required
  receiver signal-to-noise ratio."—Digital Transmission Systems, Ch.
  7.8.

I still haven't figured out if the equation 7.25 applies though. It involves "the transfer function of the baseband code".

In extension to "straight", these types are also of interest:

||   parallel

\/ fanning

X crossing

> < kissing

<< bending

Question moved from physics.stacksexchange.com


texts: What is Access RAM in PIC18 series and how is it exactly used?

texts: I'm reading resources related to PIC optimizations and I've found document called MPLAB® C18 OPTIMIZATION TIPS. One of the things it mentions is Access RAM. I know that it is the part of RAM which can be used without the need to use the bank access register and that it allows for faster access to variables stored in it, but it's still not very clear to me how exactly should I use it manually and when I should expect the compiler to populate it with variables.


texts:
I've built a simple 2 stage active/passive phono preamp. Everything in terms of amplification/frequency response/lack of distortion works fine - just as it was designed. The only thing is that hum can be heard despite connecting GND to turntable grounding wire. It gets lower but doesn't disappear and can be heard on higher volume settings.

The interesting thing is that depending on turntable used, hum level gets higher or lower. Another thing i've noticed is that when i connect a device such as mobile phone to the input (via mini jack - rca connector) hum disappears.

Another interesting thing is that two channels have different hum... The right channel hum doesn't have "even order" harmonics (i mean 2, 4, 6). More on this subject on the photos. But this case can be completely unimportant, although it confuses me.

The device is powered by 16V AC wall transformer - then 16V AC is converted to +/- 15V DC supply by voltage doubler. I've measured supply ripple with oscilloscope - the rails have perfect DC - ripple can't be seen because of oscilloscope noise (setting: 10mV/div).

I think that design is too simple to have some mistakes, but i'll attach the schematic anyway. The thing that bothers me is maybe the quality of PCB design. Note: PCB is single layer.

So... i just can't get rid of this hum - my only idea is ground loop... but where?

btw i've built some single stage full active eq phono preamplifiers and they didn't need some special shielding - worked just fine without enclosure or in plastic enclosures. I thing that proper shielding is not the case.

IMPORTANT EDIT:

Thanks for the input guys. All the tips are regarding power supply. I didn't mention the most important thing... sorry about that. When i remove inductors and cut off the power supply completely and then provide +/- 9V to rails with a battery (!) the hum doesn't disappear. That's the thing that bothers me the most.

Thanks for your attention, i will appreciate your help. Cheers!


texts: Method for selecting unique resistor values in all combinations

texts:
I do controls, and sometimes I want to monitor more dry contacts than I have digital inputs for.  I'm cheap, and don't want to pay for more points, so sometimes I'll put some resistors in parallel with the contacts, and put the (resistor||contact) pairs in series, and read them using an RTD input.  With three contacts, it's easy to pick three resistor values that give me 8 unique combinations within a comfortable range and with comfortable distance in between.  Say 10k, 7.5k, and 15k.  Moving on up to six contacts, I've now got 64 states, and picking 6 resistances from the E12 series that can satisfy 64 states may not even be possible.

Is there a succinct way to solve this problem of picking x resistances from a standard series, sticking within one decade?  Something I can stick into Excel?
 Maybe it's very obvious once I restate the problem mathematically in terms of sets or combinatorics, but I worked hard in those classes once so I'd never have to do it again.

Electrically there are obviously many ways to convert a six bit digital value to an analog value, including using resistors and more decades, but anything more complex than single resistors pretty much moves me into "buying a pre-built" solution territory.


texts:
Recently I've been trying to make a simple brushed DC motor out of copper wire, neodymium magnets, AA battery and some parts that I want to print on 3D printer. I searched on internet how other people made this motor and I found these videos:
https://youtu.be/GVUDGFKfOa4
https://youtu.be/BD0EV3hmtOc
What strikes me is that they basically create a short circuit. Isn't it bad for battery? Or is there any chance that it'll explode?
I checked it myself and connected copper coil to AA battery. There are some sparks at first but no heat is being produced on battery. So is it actually ok to do this?
I tried adding 100ohm resistor but resulting field was too weak to influence magnets. However when I added 10ohm resistor it just burned down.
Is there any way to make this DC motor without any health hazards?
Thanks in advance


texts: What does this symbol on a contactor represent?

texts: What does this symbol represent?  It is connected to a contactor.


texts: Newbie : Overheat LD1117 3.3V Regulator (Input Voltage 5V-2A)

texts:
I am trying to get a 3.3V voltage from 5V (2A) power supply to power my Arduino Pro Mini 3.3V.

I am using LD1117 3.3V Regulator (TO-220). I haven't connected any coupling capacitor as the datasheet suggested yet. I just connected the Vin and measure the output Vout on pin 2.

The problem I am facing is that, I think I am burning up the regulator because on Vout, I am measuring almost 3A current output. The regulator is very hot!

I read that LD1117 regulator is able to output 800mA max and please correct me if I am wrong but I think my Arduino Pro Mini can work pretty well with just 800mA. I am also hooking it up to a RFM89HW transceiver.

Questions:

How can a 2A power supply output 3A current? I don't understand the logic, output more than input?
How do I limit the input current so I don't burn out my regulator? 800mA outuput current is fine.

Thank you for your time.

Edited (added circuit)


texts: What are the real properties of an ordinary LED?

texts:
I would like to simulate a typical LED in MATLAB. However, I need the following info:

Internal resistance (in Ohms)
Internal capacity (in Farads)
Self-Inductance ( in Henries )

All of the values should be really small but they do matter in my simulation.


texts: What is the name of the syntax standard Keithley is using for remote control over serial?

texts:
Keithey (and other manufacturers) have a standard syntax for communicating over serial. Typically, commands look like (source):

:SENSe:FUNCtion “RESistance”
:SENSe:RESistance:RANGe <n>
:SENSe:RESistance:MODE <name>
:SENSe:RESistance:OCOMpensated <state>
:SENSe:VOLTage:PROTection <n>
:SENSe:CURRent:PROTection <n>
:SOURce:FUNCtion <name>
:SYSTem:RSENse <state>
:OUTPut <state>
:READ?

What is the the of this standard syntax?


texts: In asynchronous communication how is the frequency same but clocks of both devices different?

texts:
Am currently studying 8051 microcontroller and in the course the lecturer told that in communication the frequencies of sender and receiver should be same else they will get different bits of data at different speeds and that would result in either data loss or extra useless data.

In synchronous communication both clock and frequency is same and in asynchronous communication clocks are different.

But as per my understanding the frequency generates the clock , then how are they both different?


texts: Is the rated speed of an induction motor the synchronous speed?

texts:
E.g, if a motor is rated at 50Hz, 400V, 22A, 8.29kW, and 1460 rpm, does this means that the motor should be operated from a source voltage of 50Hz, and this corresponds to a synchronous speed of the motor of 1460 rpm?

The reason I ask is because an example question and answer I have seen says the following:

Q: Estimate the number of poles the motor described above has

A: formula for synchronous speed is n=120f/p

closest synchronous speed for given rotor is 1500rpm

1500=120*50/p

p=4

I'm guessing the reason they rounded 1460 to 1500 is because the number of poles must be an integer.

So when you see a motor with a speed rating in rpm, what does this value actually mean? And how does this relate to the synchronous speed (like it has in my example question)?

Thanks!


texts: Any tricks for finding the path taken by small ESD sparks across a PCB?

texts:
A small ESD spark is able to find its way across my PCB at a relatively low voltage (low kV). It is not obvious which path the spark is taking and the sparks only jump when the board is sealed up inside an assembly so it is not possible to visually see it happen.

Are there any tricks for getting the spark path to leave some sort of trail so after the event we can look at the board and figure out which gaps it is jumping?

I'm thinking there might be some kind of powder or film that discolors or fuses when a spark passes though it, leaving a visual witness mark of the sparks passage.

Any ideas?


texts:
I am trying to build a 260V input mains circuit for a 36V output and 25W Power. I have calculated the required Resistance, Capacitor, and Inductance, I have got the required results. However, I am required to make a closed-loop PWM. Could anybody please help? Thanks!

PS: I am very new to LT Spice and Power Electronics.


texts:
It is a common practice, for high power loads such as boilers, furnaces, etc., to install a circuit breaker that "cuts" both live and neutral wires - at least in Europe.

In my search for EVSE, I saw the following figure, in which AC and DC circuit breakers, again, cut both wires.

I understand that it is possible to have a high voltage potential (up to 40 or 50 V) between neutral and earth - due to bad earthing - but is this reason good enough to cut the neutral? Are there any other reasons?


texts:
We are trying to realize a simple processor in silicon by using semiconductor IP cores. And one part is to have a USB port interfaced using UART. I have been looking into some semiconductor IP cores that I can use to interface USB using UART and I've found this project to be useful.

I've studied this project and the codes behind it and understood how UART works. The UART serves just an interface between the processor/FPGA and USB but I was wondering if I plan to interface a USB Flash drive, how would I show that it's working? That the USB UART interface that I borrowed from an IP Core is working and that I can transmit and receive data to the USB Flash drive?

edit: I think my question should be first: What are good examples of things that can be easily interfaced using UART and that can also be easily tested and verified? Also, I should be looking for a controller, I guess.


texts: How to do a DC sweep on an oscilloscope?

texts:
I created the circuit for a project of mine on Orcad Capture (Pspice). I ran a DC sweep on it and got the desired output. Now I have built the identical circuit on a breadboard but I am not getting the same output on the oscilloscope that I am on the DC sweep graph on my simulation. Is there a certain way to do a DC sweep on an oscilloscope?

Here is my circuit:

Here is my DC sweep graphical output:


texts: Why is zener current preferred to be more than load current in a voltage regulator?

texts:
In a simple Zener Voltage Regulator, such as this

Why should current passing through the zener diode(zener current) be more than the current passing through the load(load current)?

or

No such conditions exist

P.S. In my school notes, it was simply mentioned that this condition is required for "good load regulation"


texts: Hall effect flow meter; measuring total volume

texts:
I'm playing with this Hall effect flow meter from Adafruit. In the description it states:

  By counting the pulses from the output of the sensor, you can easily track fluid movement: each pulse is approximately 2.25 milliliters.

By this then:

$$\text{Total Volume (ml)} = \text{#Pulses} \times 2.25$$

Simple, right?

Well I'm reading the Adafruit kegerator code and they seem to want to make life difficult for themselves by using the time between pulses to get a flow rate, then turning that into a total volume.

Is there a better method? How do I get an accurate reading for total volume from this sensor?


texts: STM32F429 ignoring writes to EXTI mux registers

texts:
The following code is at the start of my main() function:

SystemInit();
SystemCoreClockUpdate();

SysTick_Config(168); // 1 us ticks
NVIC_SetPriority(SysTick_IRQn, 0);

RCC->AHB1ENR |= RCC_AHB1ENR_GPIOBEN;

// Set EXTI on PB0 for CLK
SYSCFG->EXTICR[0] |= 0b0001;
SET(EXTI->RTSR, EXTI_RTSR_TR0);
SET(EXTI->IMR, EXTI_IMR_MR0);
NVIC_SetPriority(EXTI0_IRQn, 1);
NVIC_EnableIRQ(EXTI0_IRQn);

However, despite the fact that I'm setting the bit flag for the EXTI0 triggered by port B, it's still generating it when PA0 has a rising edge and not when PB0 does. When using a debugger to step through the code, EXTICR1 is indeed unchanged, despite the fact that it is being written to (verified through the disassembly) and even if I use the debugger to set the register, it does not actually change.

What am I doing wrong? I can't find any clock or flag that I need to enable. Stranger still, I recall it working previously with essentially the same code, although I was not using any sort of version control so I can't check the precise details of it.


texts: I just installed Micropython on my ESP8266 and realized that TCP/IP works fine with it. This made me realize I don't know where it's defined - options that came to my head are: 1) in Micropython code, 2) ESP8266 closed-source API, 3) the chip. Which one is correct?


texts:
so I've been trying to solve some questions in the book Free Range VHDL. The question I have problems with is:
Provide a VHDL behavioral model of the D flip-flop. The S and R inputs are an active low asynchronous preset and clear. If both the S and R inputs are asserted simultaneously, the output of the flip-flop will toggle.
My code is:
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity sds is
    Port ( d,clk,s,r :in std_logic;
           f: out STD_LOGIC);
end sds;

architecture Behavioral of sds is
signal sr: std_logic_vector(1 downto 0);
signal outs : std_logic;
begin

sr <= s & r; --concatenating set and reset

process(clk,sr)

begin
case sr is
when "00" => outs <= not outs; --should toggle when both set and reset are 0
when "01" => outs <= '1'; --output should be 1 when set is 0
when "10" => outs <= '0'; --output should be zero when set is 1 and reset is 0
when "11" => if rising_edge(clk) then outs <= d; --classic d flip flop
end if;
when others => outs <= '0';

end case;
end process;
f <= outs;
end Behavioral;

The code works fine on my FPGA except for the toggling part. I cannot make the output toggle when both set and reset are 0. It always produces 1. Where is my mistake in the code? Thank you all.


texts:
I have a DC motor and the sticker says its rated for 24Vdc and 3700rpm.
There is an AC tacho inside it which I am using to measure the speed of the motor.
So when I run the motor with a 24Vdc supply and measure the AC tacho output I get a frequency of around 900Hz. So I am correct in assuming there is a gearbox inside the motor that is speeding the tacho up?
And if so, is it accurate enough to calculate the gearbox ratio based on the motor speed and AC tacho frequency? I want to use it to calculate the motor speed?
Would appreciate any help, thanks everyone.!

EDIT
See image of oscilloscope with motor running full speed and no load


texts:
This might belong on the new Makers site, but it could be applicable here too.

I'd like to position a device on a 1 meter linear shaft to within 50 microns.  I can currently, with steppers, get down to 20 microns but I have all the disadvantages of steppers.  However, I have the awesome upside of steppers, in that I'm spending about $50 total (more like $200 for 4 steppers, but still).  Being DIY, budget is pretty important, as is not increasing the mass of the device on the shaft by more than a couple dozen grams.

I don't know the best way to approach this.

linear encoder strip of some manner
optical encoder on brushed DC motors and limit switches at 0m and 1m
stick with steppers


texts: Need Hall sensor output to be 5 volts (high) instead of 0 volts (low) when magnet detected

texts:
First time asking a question here. I have a Hall sensor A3144 that goes to low when a magnet activates it. So I can use a magnet with it to complete a circuit, say, connecting the output to a red LED to 5V.
But I want the output to connect to the gate of a MOSFET so I can turn on an electromagnet with higher voltage using drain and source. For testing, I'm using a green LED instead of an electromagnet.
The problem is that I get the opposite of what I want. With no magnet, the Hall sensor outputs a small voltage (in this case around 1 volt), and the MOSFET receives this small voltage to the gate, and the green LED turns on. With a magnet, the Hall sensor drops to 0 volts and the green LED turns off.
I need the opposite to happen. I need the green LED (or the electromagnet) to turn on when the Hall sensor detects a magnet and be off otherwise. Can you help me do this?


texts: How should I chose a resistor for a home-made electromagnet?

texts:
I have a magnetic wire and I want to use it to make an electromagnet. The electromagnet will be powered by a 5V, 2A power supply.

How do I know what resistor should I use in series in order to avoid damaging the power supply?

I suppose that I can use Ohm's law, which would mean that I would need a 2.5 Ω resistor. Since the resistance of the wire itself is 0.5 Ω, it means that a 2 Ω resistor would be enough.

I also suppose that if I use a higher resistor, such as 4.7 Ω, the electromagnet would be less powerful.

Am I right, or have I missed something?


texts: Linking and the ELF - use of PC-relative addressing, GOT and PLT

texts:
So that we're on the same page, I'll try to explain what I think I know about Symbol Relocation and ask questions as they come up.
Symbol Relocation:

Absolute addresses – replace the reference for the actual address. This happens when a global variable we need to reference is in the .data section of an executable object file. The downside of this is that when the reference is to a variable or function in a static library (.a file), whenever we update the static library, we’d have to re-link all of our object files to get that new address in the .data file. (Essentially, parts of the .a file are carved into the executable, hence the recreation of the executable, or the relink.)
PC-relative address – tells the program counter to jump a certain number of bytes. This useful when functions are near each other and is useful in creating PIC code. The idea is that some things in the .data and some things in the .write sections stay the same distance apart, including the two sections themselves, so we could refer jump a certain number of bytes to refer to that code we need.

Question 1: Couldn't we simply use absolute addressing in such cases if we’re just using static libraries? For example: callq 0xaddress.
Question 2: Say a PC relative address of 5 is calculated. The assembly increments the PC by 5 at a certain point. Is this to say we cannot use absolute addresses, say 0x480480 because then the PC would get incremented by 0x480480? In other words, function calls need PC-type instructions to call them.
Question 3: But doesn’t the assembly callq take the address of a function?
(Potential) Answers for 1-3: Absolute addresses are computed at link time, while PC-relative addresses are computed at compile this, which saves time. We use PC-relative addresses only in the case functions that stay near other functions, not anywhere else. We could use absolute addressing here, but that might be worse (in terms of time).

GOT – included in any module that references variables in a .so file (a shared library). This is "program independent code" (PIC) because .text sections refer to the entries in the GOT, which refer to absolute addresses load time. It is used specifically in the case of shared libraries because we don’t want to keep the library information with the executable in order to update the shared library as we wish.

Question 4: Isn’t this the same if we the did not use a GOT? Since entries in the GOT get relocated anyway, what is the purpose of using it? Our code gets changed. If the benefit is we do not have to recreate our executables and just defer everything to load time, what’s the benefit of static linking?

PLT+GOT – included in any module that refers to procedures (functions) in .so files. The idea is to “defer binding of each procedure address until the first time the procedure is called” (i.e., put the address of the procedure in the GOT until the first time the procedure is called). For example, if we have a call to a function defined in a .so, we call to PLT, the first time* calling the dynamic linker to put the address of the function in the GOT and the succeeding times calling to PLT (still) but using the new address in the GOT.
(*The first time: GOT holds a special address to start the execution of instructions that will get the address of the function we need and put it in the GOT.)

Question 5: Why don’t we just keep the addresses of the functions in GOT like how we did for variables? Is it just to save a little bit of OS time?
Question 6: And if the GOT+PLT combination is good, why not use it for all our purposes?


texts:
Good morning. I am using the chip45 bootloader for an Atmega chip.
The chip being used is the Atmega32U4 chip ("chip45boot2_atmega32u4_uart1_v2.9Q").

I am having a strange error. I burn the bootloader with a success message from the AVR ISP.
Then when I use the chip45 GUI it says no bootloader.
Then I decide to see if there is anything written in my flash. I do a read of the flash.
I see an anomaly. Almost everything is written except the last couple of lines. I think this is causing the
error message I am pasting the actual boot and the read boot below.

Actual boot -

:107EE0000801811102C08BE201C08DE20E94463C74
:107EF000BCCDF999FECF92BD81BDF89A992780B586
:107F00000895DC01CB0103C02D910E948C3F4150AC
:107F10005040D0F70895262FF999FECF1FBA92BD91
:107F200081BD20BD0FB6F894FA9AF99A0FBE01965A
:027F30000895B2
:040000030000780081
:00000001FF

Read boot -

:107EE0000801811102C08BE201C08DE20E94463C74
:107EF000BCCDF999FECF92BD81BDF89A992780B586
:107F00000895DC01CB0103C02D910E948C3F4150AC
:107F10005040D0F70895262FF999FECF1FBA92BD91
:107F200081BD20BD0FB6F894FA9AF99A0FBE01965A
:107F30000895FFFFFFFFFFFFFFFFFFFFFFFFFFFFB2
:107F4000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF41
:107F5000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF31
:107F6000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF21
:107F7000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF11
:107F8000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF01
:107F9000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF1
:107FA000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFE1
:107FB000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFD1
:107FC000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFC1
:107FD000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFB1
:107FE000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFA1
:107FF000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF91
:00000001FF

Sir, as you can see from above, after the line (":107F200081BD20BD0FB6F894FA9AF99A0FBE01965A") there is some confusion.
Have any of you encountered such an issue before.
I then tried checking if anything is wrong with the clock and such. I am able to program
the chip and also toggle a pin using the AVR studio.

I know its a very narrow doubt which I should ask chip45 directly, but in case anyone can help me it would be great.

Thank you.


texts: LT6105 Current Sense Amplifier Output Problem

texts:
I am using the LT6105 current sense amplifier Link. I am giving it a supply(Vcc) of 7V and the voltage to the Rsense is 5V. The Rin = 100Ohms and Rout = 4.7K.

The schematic is -

Now, based on the Vout formula, it should be 1.18V if the current through R13 is 1.19A. But, I am getting Vout of 5.52V.

Now, if the load is removed I am still getting Vout of 5.52V.

Am I missing something here as the parameters are all fine for Rin and Rout.


texts: Simulating a transmissive photo interrupter sensor with Arduino

texts:
First of all hello.
I find myself in trouble while trying to simulate the behaviour of a photo interrupter sensor by using Arduino Uno R3.
The idea is to get rid of the sensor and use Arduino to send the signals instead, in order to be able to control over device by my own demand.

According to the datasheet - the sensor is powered by 3.3V and has the following outputs.
HIGH - if voltage is >2.4V
LOW - if voltage is < 0.4V

I have connected my Arduino's PWM pin10 to sensor's output pin and GND to GND and wrote a simple test code that does the state change inside a loop like this:

analogWrite(PinNr, 170);// send High signal 170 = 3.3v PWM output
delay(120); // wait 120ms
analogWrite(PinNr,0); // send Low signal
delay(120); // wait 120ms

Problem is that it does not work this way.

If I connect a simple 3V battery to sensor's output Pin and GND to GND through a simple push button and quickly push and release the button this method works perfect.
I need to be able to do this by using Arduino and not by hand so I think the problem relates to the type of signal (Arduino PWM vs analog).

I looked into a way of converting the Arduino PWM signal to analog by using a Low pass filter, yet I have trouble understanding what is the cufoff frequency and the response time of the RC filter that I should take into consideration.
For example I know Arduino PWM pin 10 runs at a 500hz frequency and I would like that the filter should respond to the state change HIGH- delay(120)-LOW-delay(120) as fast as possible.
Sensor datasheet specifies that any voltage > 2.4v will be interpreted as a HIGH signal and any voltage < 0.4v will be interpreted as a LOW voltage, so I think that ripple can have a greater marje.

Please help me understand what values to choose for the RC


texts:
I am writing a program to control a dot matrix LCD and display some text on it via PC serial port interface. The LCD have a Pin to Input Clock Signals. I have searched a lot on internet about clock input signals but I sill cant fully understand it. Yet what I got is that the clock signal is a continuous chain of ONs and OFFs right after each other, should be send to the device in parallel with data. When its state changes it pushes data to device. The time period of each ON or OFF pulse should be same as the data pulse.

Clock Signal: 10101010
Data Signal : 11010011

Now if I am right, why don't we simply use an appropriate oscillator with device to produce clock signals? And if I am wrong please guide me to the right direction.


texts: How do you match an LDMOS FET to 50 Ohms?

texts:
I'm considering using one of the following LDMOS FETs as an RF amplifier:

AFM907N (8W)
AFT05MS031NR1 (30W)
AFT05MP075NR1 (70W)

The datasheets provide \$Z_{source}\$ and \$Z_{load}\$ metrics for some frequencies (as below), but not for all frequencies they support and not for the frequency that I'm looking for (146MHz center)---though the FETs do support that frequency.  If I can get the \$Z_{source}\$ and \$Z_{load}\$ at 146MHz, then I could use those numbers to create a matching network (L/Pi/Tee).

If you were to match this component to 50 Ohms, how would you do so?
What information from the datasheet do you use to calculate a matching network at 146MHz?
Is there an online calculator (or some formula) into which I would plug in that information?
If it helps you answer the question, the Icom IC-9700 uses the AFT05MP075NR1:

The service manual PDF is available here
Page 8 (2-2) has a photo of the components labeled "PA-A"
Page 87 (10-14) shows the TX amplifier pipeline schematic in orange (RX is green)

Here is NXP's test fixture from the AFM907N datasheet on Page 11:


texts: Maximum attainable delay with Micro controller

texts:
I am designing a microcontroller based delay circuit to implement delays of 2 hours, 1 hour, 45 minutes, and 30 minutes. The circuit will automatically turn on off a relay after this time period has elapsed.

I am stuck with a narrow selection of microcontrollers available locally in market:

89C51
89C52
89S51
89S52
89C2051
PIC 16C71
PIC 16F84

I have checked the datasheets of these microcontrollers but there is no information about the maximum delay they can produce.

What is the maximum delay that can be produced with these microcontrollers?


texts: KCL - calculating current when voltage source is present

texts:
simulate this circuit – Schematic created using CircuitLab

In the above circuit, using KVL loops I'm getting the correct answer, \$ Va = 24V \$
However using KCL I am stuck at writing an expression for \$ i_1 \$ because of the voltage source in series with the resistor.
Is below expression correct ?  $$i_1 = (0-Va)/12 $$

Those 60V sources are throwing me off. Appreciate any help. Thanks!


texts: Best solution for making a LAN with 2 untwisted lines

texts:
I need to provide a best solution for establish a LAN for old train carriages in order to transfer low quality video surveillance data.

Only existing lines are 2 wires untwisted throughout all cabins, max number of cabins are 16-18. Hopefully can achieve 100Mbps bandwidth within the LAN. High reliability.

------------   ------------  ------------
|        =========================      |
|          |   |          |  |          |
| cabin 1  |   | cabin 2  |  | cabin N  |
------------   ------------  ------------

My thoughts are:

power line communications (like existing power line modems) attached in parallel to the bus.
ADSL connections, where cabin N always connect to cabin N+1. wires broken into (N-1) pieces, and total (N-1) connections.
VDSL similar concept to ADSL

Has anyone had similar experience before?

ALSO: They are moving and LAN is (digital local area network) and My application with based on UDP+TCP and IP protocols


texts: Understand USB suspended or unconnected mode

texts:
I'm trying to understand a problem I'm having related to a USB connection. I'm working with a Mini PCIe 4G module (Quectel EC25 Mini PCle 4G/LTE) and at this moment my goal is to put it in sleep mode. I'm communicating with the module via UART (RX and TX) from which I send AT commands through a microcontroller (I'm using an atmega4809). I also have the module connected to a Raspberry Pi 4 through USB.
In order to put the module to sleep three conditions must be fulfilled (pag. 25 of manual):

Write the AT Command for sleep mode
Pull DTR pin to high
Put the USB connection in suspended mode.

Following these rules, the module enters sleep mode.
My problem is that I'm trying to put the 4G module in sleep mode with the third condition replaced by turning off the RPI (that is connected with USB). It doesn't work and I'm trying to figure out why. If I execute condition 1, then condition 2, followed by turning off the RPI the module does not enter in sleep mode. However, if after turning the RPI off I disconnect manually the USB connection, the module enters sleep mode. So, it should be something related to USB suspended mode.
What is the standard for USB suspended mode and how is different from a disconnected cable? And any idea on how can I "simulate" a USB suspended mode to trick the 4G module to think that whatever is connected in the USB is in suspended mode
This is schematics of the USB connector and the 4G module:

PS: I'm not a professional, just currently a hobbyist trying to develop a DIY project.


texts: What part is like a male header with long pins on both sides?

texts: What is the part in the picture below? It's like a male header, but with long pins on both sides. I've got some temperature probes I've built that end in female connectors and I'd like to use something similar to use the probes with a breadboard. I've looked on Digikey under headers and haven't been able to find anything.


texts: Proper biasing to virtual ground with TLE2426

texts:
I've made simple circuit - it attenuates the signal 10 times, bare bones voltage divider:

simulate this circuit – Schematic created using CircuitLab

Now I want to bias the signal to half of my system voltage. I tried using another voltage divider(with equal resistors) for that or TLE2426 chip, which is used specifically for dividing voltage in half. I applied bias voltage(i.e. virtual ground) as in circuit below.

simulate this circuit

When I used the TLE2426 chip I used this circuit:

The question
For example I have 3.3 voltage system, so I have 1.65 virtual ground in the middle applied to Vbias. I have the following measurements on the Output:

When Input is floating - Output is 1.48 V
When Input is connected to system GND - Output is 1.36 V

This is pretty much the same with either TLE2426 or simple voltage divider biasing. I understand that in theory when I ground the input I divide this 1.65 volts with my 900k/100k divider, hence I should get 1.48 (I probably get 1.36 because of non-ideal resistors). For floating input my own explanation that float is close to GND, but not exactly, hence the difference...

Anyway the real question for me is - how can I get 1.65 volts on the output when the signal is grounded(or floating, but not necessary). Obvious solution for me is to take trimmer resistor and use it as a divider to get 1.65 point, but this seems like a cheap workaround, I would like to know if there is a away to make it with TLE2426 chip, after all it is made for this kind of things.


texts: Is it possible to set up multiple wake up interrupts on STM32. ? How to manage multiple sensor reading intervals?

texts:
I am new to developing applications on STM32 development boards.
Currently i have STM32 IoT discovery kit. I am able to configure all the sensors and read data. I am interested in low power design especially STOP2 mode, when i can retain all the variables on SRAM. I want to achieve low power consumption keeping sensor reading intervals low. Imagine having 3 different sensors, reading sensor data at 3 diffrent intervals for e.g.

Sensor A - read every 15mins
Sensor B - read every 30mins
sensor C - read every hour.

So far i have implemented a storing mechanism to store data. I have also implemented the stop2 mode sample which wakeup every 33seconds (from examples). How can i achieve functionality where i can read/poll at diffrent intervals and keep the MCU in stop2 mode after the reading is finished.?


texts:
We have a successful CAN gateway product based on dsPIC33EP. The firmware is quite complicated and took years to develop. Written in C, the main loop calls many state machines, which each are quite portable to other platforms. Of course, the low level code is tailored specifically to dsPIC.

My job is to make a second generation hardware within 6 months. My dilemma is, whether I should stick to the dsPIC, or take my chances and go to 32-bit PIC33MZ or perhaps another 32-bit processor like Infineon TriCore TC1797.

The main reason I am considering the move, is that the current design is using a lot of computational capacity of dsPIC, and modern vehicles have even faster CAN communication and I am fearing the possibility of not being able to keep up with future vehicles.

I am an experienced designer, and know all the risks. This question is specifically asking those, who did such a migration in recent time and could share with me the actual experience.


texts:
When trying to delete a via that I placed in the board manually I get this error. The via (yellow error) was placed to stitch the ground planes together and has nothing to do with the schematic.

Why am I getting this error?

I'm using Eagle 6.6.0 on a windows 10 64bit machine. It seems eagle started acting weird when I went to windows 10. I did a completely clean reformat and install.


texts: I am watching this video over and over again and I can't visualize the current flow from the eel, to the two metal plates, to the Christmas tree. Is there a voltage difference between the two plates, thus causing a current to flow between the plate closest to the eel (highest potential) through the tree and back to the other plate (lowest potential), or does the electricity harvesting work differently?


texts:
Does anyone know if a 5v battery exists? I'm looking for a small battery - N size is perfect - that puts out between 5v and 5.5v. A coin cell 2032 or similar would be fine too.

I can use a 9v N and regulate it, but that seems such a waste.

The application is a remote control.


texts: How can I return an Arduino digital pin to floating state?

texts: I am trying to setup a programmed reset function for a 3.3V BlueTooth module that resets when its reset pin is pulsed LOW for a short period of time.  There is a 47K pull-up resistor in the BT module that keeps its reset pin at 3.3V until the reset pin is grounded or sent LOW.  So there is no issue with random noise due to the BT pull-up resistor.  Can I define the Arduino pin as input and leave it floating, then digitalwrite LOW to reset, then return the pin to floating so the BT module can carry on after the reset?  I can't digitalwrite HIGH because the 5V from the Arduino will destroy the 3.3V BT module.


texts: How does two inverting op-amps phase cancel eachother out?

texts:
When doing a frequency sweep simulation of the circuit below in CircuitLab, I can see that at \$V_{out1}\$ there is a phase invertion and at \$V_{out2}\$ there is not. I know that the inverting amplifier do phase shift by 180 degrees and that two of these cascaded will give a 360 degree phase shift that equals to 0 degrees and a delay. What I don't understand is how the two inverting amplifiers cascaded "cancel eachother out" when looking at the frequency sweep. Can someone try to explain this to me?

simulate this circuit – Schematic created using CircuitLab


texts:
I repair electric appliances and tools. Every once in a while, the main circuit breaker trips when I plug in a device. I don't want to prevent a circuit breaker from doing its job, but I would prefer not reset the breaker at the panel every time it happens.

How could I configure this to prevent nuisance panel-breaker trips?
(I don't even know what search terms to use.)


texts: The Hall sensor in a BLDC - winding magnetic field interference?

texts: I am wondering what is the impact of the magnetic field generated by the BLDC windings being energized on the rotor position measurements with the Hall sensor. I found some unclear explains stating that that impact is irrelevant comparing to the impact of the rotor magnet's field. But why? Aren't the Hall sensors oriented orthogonally to the direction of magnetic field created by the windings?


texts:
I was reading my textbook(razavi) and came across this circuit where to calculate vout2/vin1 he drew a thevenin equivalent of nmos.
I dont understand how thevenin voltage(Vt) and Rt  in the equivalent circuit is Vin1 and 1/gm1??

The procedure for calculating thevenin was to zero out independent sources and then calculate R across the 2 terminals across which you wanna find. Here if we zero out vin1 we will be in a situation where mos will be off, right? also how Vt calculated to be Vin1?

How can thevenin theorem be appliied to mosfets??

texbook is cmos analog circuit design by razavi.


texts: How many flip flops are required to build a digital circuit?

texts:
Here is an example:

The periode of the this circuit is 9, and i want to build a digital circuit with only J-K flip flops.

Here is my argument, I can tell there is nine different states that leads to four possible combinations, for instance 0 results in 00 ... . In order to describe these nine states we need at least four bits, so we need four J-K flip flops to fully design the digital circuit.

There is also another argument, says, count the number of maximum occurrence, this would be  the minimum number of logical ports that require to build the circuit. To clarify myself, here the 11 state comes four times and the rest each one or three times.

Are these two arguments equivalent? I had a very brief course on digital circuit at college, so i appreciate any reference to a reliable source if my question too general to be answered here.


texts: Booting the processor on a Xilinx Zynq 7000 before the logic

texts: I am testing some code on an Xilinx Zynq 7000 and I need to be sure that the processor will boot up before the logic does.  After reading through some of the manual it seems that this may be the standard case for this device, however, I cannot confirm whether this is truly the case.  If it is not the standard for this device how do I ensure that the processor boots?


texts: What component is this? It's from a led light strip on a backlight on a car.


texts: How to measure the efficiency of a full wave rectifier?

texts:
Given a full wave rectifier (http://www.electronics-tutorials.ws/diode/diode_6.html) with an RC filter on the DC output, how can I measure the efficiency of conversion?

simulate this circuit – Schematic created using CircuitLab

I've seen the formulas to compute the efficiency.  I'd like to actually verify this in the full wave rectifier that I built.

The DC side seems simple.  Measure the voltage across the load resistor.  That gives me \$V_{DC}\$.  Knowing the resistance, I can calculate \$i_{DC}\$.  Then \$P_{DC} = (V_{DC}) x (i_{DC}) \$.

The AC side confuses me.  \$V_{AC}\$ is easy to measure with a scope.  Is the only option to calculate \$i_{AC}\$?  or simulate the circuit?  (I don't have an AC current probe, only a DC current probe)  Can a load or shunt resistor be added to measure the current?

The application of this rectifier will help explain the goal.  My son is trying to convert acoustic energy into electrical energy (it is a very low yield process).  He has already built a speaker array, connected them in series and connected them to this rectifier.  He chose Schottky diodes to reduce the bias voltage below the typical Zener diode.

What he has found is that the process is a lot less efficient than he expected.  I'm trying help him measure the electrical power conversion efficiency.  We're using a Function Generator for the AC source.  In the actual application \$V_{DC} < 500 mV\$ even with (x6) 10 inch speakers.

I've been trying to help him understand where he is losing all his power.  One way to investigate this is to evaluate the rectifier with a Function Generator.  He's also built a Spice model (LT Spice) and is trying to compare his measurements / characterization with that model.


texts: What is the slip factor for an induction generator in an island network?

texts:
Most textbooks covering induction machines cover only the motor use-case scenario. When the machine is used as a motor, the slip factor is determined by the frequency of the stator current by the equation

\$ \Huge{s=f_s - \frac{\frac{p}{2} \cdot \frac{n_r}{60}}{f_s}} = \frac{n_s - n_r}{n_s} \$

where

\$ s \$ is the slip factor,

\$ f_s \$ is the stator frequency

\$ p \$ is the number of poles

\$ n_s \$ is the motor synchronous speed in rpm

\$ n_r \$ is the actual rotor speed in rpm

This all makes perfect sense when the machine is being operated as a motor and/or is connected directly to the transmission network which provides magnetizing current and a stable frequency to the stator windings.

My question: What happens if the machine is being operated as a generator and is on an island network? I understand that we need a source of reactive power -- provided by soft-start capacitor bank, for example -- but if the speed of the machine is variable, how in heaven's name is the slip factor determined? There's no alternating current magnetization, and hence no frequency on the stator winding. How is the frequency being set?

And how can I create a simple model of this that I can use in Simulink or in Scilab xcos?

I want to model a wind generating system on an island network, or a variable-speed system coupled to the transmission network via a rectifier and then a DC-DC converter. As usual I bit off more than I could chew and now I understand why everybody else does these models with permanent magnet synchronous machines: it's way easier.

Perhaps you can prove me wrong?


texts: I need help to understand a sniffer circuit schematic

texts:
I'm an electrical engineering students and for a school project I need to understand a circuit schematic. First, I will provide some context. The school project I'm working on is the modification of a sniffer in order to add the decoding of another protocol.  The one already implemented is a proprietary serial protocol very much like the Dali protocol. The Dali protocol is used for Lighting. In my case a control device send frames to a security lighting. The sniffer is plugged in between. Frames looks like that:

The Idle state is high and it uses biphased code. First I want to investigate the hardware to see how the first one was implemented and what kind of modification will be needed but I'm pretty overwhelmed by the amount of complexity of the schematic so I will try to understand it one small part at a time. Here is a part of the schematic:

The full schematic is 4 pages long so I don't know if it would not be too much. The circuit was designed by a deutsche engineering team.The High Level voltage is 24 V and the low level is <= 4.5 V .The DALI_line_1 is the input which transmit the frames.DALI_line_OUT_1 is the output that will send the frame to the security lighting. The DALI_RX_1 is connected to the pin of a microcontroller that will read logical level to decode the frames and print it on a terminal.

I'm currently interested in understanding the part commanded by the optocoupler V50. This is I assume the part that produce the logical level. And this is what I'm currently trying to understand. I have basic electronics knowledge so I know what every component does, but I don't understand why they are assembled the way they are.

I don't understand what the capacitors C65 and C64 are used for since they will block the current.
What is the middle branch with R91 and C64 supposed to do?
When the optocoupler is on, will the current flow through the base of the transistor V53 or to the ground through R89? For me the BE junction doesn't have any resistance, so the current will keep going through the base.

I'm pretty lost so any help is welcome. Thanks in advance.


texts: Is this an acceptable 100Mhz OCXO output?

texts:
I was looking for a 100Mhz sinwave OCXO output.

I picked up a used one and I have the following output:

Each vertical square is 1 volt.

I was expecting it to look exactly like a mathematically plotted sine wave - are my expectations too high and this distortion at the extremities are to be expected in practice?

Even if it should be smoother and more like a sine wave will the leading edges still probably be enough for timing?

If I also ran this output through a power divider do you think the leading edge would be enough for timing (I know this probably quite vague unfortunately the documentation I have on the input pin requirements of the receiving chip is non-existent.


texts: Things to watch out when applying FCC CE

texts:
I have a bluetooth remote control device that uses 2 AA batteries.
Due to positive feedback and responses,
I'm thinking to sell it to mass market. Thus I need FCC certification.

After reading many articles including all the FCC related questions in this site,
I'm still confused.

There are many of wireless products in US market that don't have FCC / CE certification. Many of imported products sold in Amazon don't have the certification.
With such a high cost ($10,000-$20,000), I don't think many small company can afford to get this certification.  What is consequences if you sell the product without FCC certification?
Before I apply for FCC, what are the things that I need to watch out, especially my PCB. Do I have to care about the box(enclosure)?
I mean, my product uses 2 batteries, I don't think it will cause a fire hazard or short circuit. Or if I have to watch out for fire hazard, what component should I add?
The bluetooth module is already certified by FCC and CE. So I will be exempted for the Bluetooth test. But I guess they still need test the product as a whole.
What if you failed for the first test, do you have to redo all over again and pay another $10,000?

Thank you.

Dan

Additional info:
Q:  I’m a retailer, why should I care about FCC regulations?
A:  It is illegal to import, sell, or operate covered equipment that has not undergone the required equipment authorization procedure. Illegal merchandise can be subject to forfeiture, and you may be subject to fine. Imported merchandise that does not have FCC may be held at customs. Also lack of FCC compliance means the merchandise has never been evaluated for electronic compatibility. This is a sign of bad quality. What other safety or chemical regulatory requirements might not have been evaluated?  FCC enforcement action is often levied against retailers and end users, especially where the manufacturer is located outside US jurisdiction.
FCC FAQ