texts: GSM Interference with Meanwell Switch mode PSU

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I am having trouble with interference from a GSM modem and my switch mode PSU.

I do not know much about interference and how the radiation patterns works for GSM. Below is an image of the circuit which we build for a client. The unit worked perfectly when they previously had an external antenna installed, however it was getting vandalized, so we then installed this anti-vandalism antenna. Since then, when we close the box, the switch mode PSU dies. I assume it goes into a protection mode. And you have to cycle the power in order to get it to recover.

PSU: Meanwell MDR-10-12

Now the antenna and PSU are fairly far from one another. I can simulate the PSU behavior on another unit of mine, but putting the antenna right up against the PSU. (however it doesn't immediately die, it seems random).

Questions that come to mind:

Where is the interference coming from?

the antenna,
the cable,
the modem?

The PSU is connected to earth, would this not help ground the EMI?
I could swap the blue device & the modem around so that the PSU & Modem are not so close to one another, however my gut feel is that it is the antenna causing the issues.
What measures can be taken to prevent the antennas EMI from turning the PSU off?


texts:
I am currently developing a small low power (high switching) Buck converter and have run into a strange issue that I have never seen before and was looking for some insight into the issue. I am also controlling the FETS from an MCU, so I can set up arbitrary dead-times ect.

On the falling edge of the lowside gate, the high side immediately turns on. (As shown below) The first jump in the yellow trace is the HS turning on from the falling edge of the LS signal, while the second jump is the actual HS gate signal. This is regardless of the load I place on Vout.

*EDIT
I have revised the image such that it shows the SW node and the Voltage on the gate. The reason I know that it is turning on is that I am getting ~25mA current draw through the main supply signifying a shoot-through occuring. This is again without any load on the IC. There should be ~.6V when the low side turns off since the inductor is causing the diode to forward bias.

I have tried a few different gate drivers that I have available, but they are all acting like this.

I assume that this is a layout issue, but I am not sure exactly what is going on to cause this to happen. I know that it has something to do with the FET input capacitance, but I don't really know how to measure/improve.

Troubleshooting performed:

Increased gate resistors to slow down switching
Placed pull down resistors on gates (HS to SW node)
Tried clamping SW point to HS gate with shotcky diode

As for the layout (this was a prototype board to test out a couple of ideas) I am severally constrained in terms of space to ~1" width on the board and 2 layers (as this is from a local protoboard shop).

Thus the FET driver is located on the opposite side as the FETs, but I have done as much as possible to lower the inductance (multiple VIAs, large traces, ect)

I should also note that there is a throughhole decoupling cap across the GateDrviers VCC/COM that is not shown here. Also there is a LS gate resistor that is not shown in the image.

I am quite puzzled over this, hoping that someone has seen this issue before and can lend some insight.

Thanks!

EDIT 1
To anwser some questions:

1) I have posted another scope print out that shows the SW voltage. The HS is coming on when the LS falls. I can also see this through the current (~25mA @17VDC, also the current draw is directly related to the input voltage...)

2) I am using a MCU to control the PWM, so there is no controller. The MOSFETS are BUK7Y153-100E.


texts: What does this symbol mean on a schematic (like an audio jack with a zigzag line inside)?

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Symbol in question:

The symbol is found in multiple places below:

To me it looks like an audio jack (side vide 2d) with a zigzag line in it.

I saw this on the schematic of the RAMBo mini (i.e. 3D printer controller).

I don't know what it means/ the name of it.

What is it for? I'm guessing some sort of protection.


texts: Reflection in low frequency conductors (not transmission line)

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Is the reflection phenomenon common in RF work with unmatched source/load pairs also present at low frequencies? Or are the wavelengths so much longer than the physical conductor lengths that reflections do not matter? I.e, are reflections strictly a function of wavelength relative to the conductors lengths?
Say for example I have a square wave fed into a pi-filter whose purpose is to extract a 100kHz fundamental (1/4 λ = about half a mile). The source and the pi-filter (and load) are unmatched. Does the power reflect back to the source? The wavelength of the signal is much, much greater than the length of the conductors (about 10,000 times, for example, for 3" traces on a PCB). So I'm not sure how that would interfere with the source signal. Perhaps the wavelengths of the higher harmonics would eventually be of "meaningful" lengths, but they should be at much lower power levels.
Would I see a distorted signal at the source due to a reflection from the pi-filter? Could the reflection damage the source? If the power is not reflected, is it absorbed by the filter? Where does it go?
Since we can often "get away" without terminating signals in low frequency designs, I hardly ever worry about reflections. I've typically only worried about them at at high MHz signals (and higher), and when interfacing signals across backplanes, or long board interconnects. But, it occurs to me that there should be reflections all the time. How is it that they don't typically matter (in low frequency designs)? How is it that sources driving unmatched loads are not "blown up" more often due to these reflections?


texts: Solenoid fastest possible release - for how long should reversed polarity be applied?

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If I understand correctly, a regular solenoid like this one

does not have a permanent magnet as core and as such it doesn't matter with what polarity it is activated (please correct me if that's wrong).

Since the current in the winding takes some time to decay, it's apparently possible to release the solenoid faster by applying reverse voltage (to "flush out" the current)

but since the polarity doesn't matter to activate the solenoid, I assume that there is a specific duration for which this reversed polarity should be applied or otherwise the magnetic field just builds up again in the other direction and pulls the solenoid back in.

How can I compute the duration for which the reversed polarity should be applied (based on rated voltage and current of the solenoid as well as number of windings) in order to achieve fastest release?


texts: How is capacity calculated when adding a battery in parallel with a faded or damaged one?

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I was intrigued by the answer and comments on this question about connecting a second battery in parallel to increase capacity. The original battery has obviously lost capacity and is nearing its end of life. The OP wanted to add a second in parallel to increase capacity, which might make sense if 1) the UPS was compatible with doing so, and 2) the original battery was not faded/damaged.

Marcus indicated in the answer that adding a second battery in parallel would add "but 25% more capacity than just the new one."

I'm unsure how that figure was arrived at. If two identical batteries in parallel are twice the capacity of one alone, how does one calculate that capacity when the batteries differ in capacity or age? It seems to me that a deficient cell would obviously contribute less than 100%, but could also parasitically drag down the newer battery if they attempt to equalize. (That's my assumption.)

Is the 25% figure given based on a rule of thumb, a best-estimate based on the limited information in the original question, or something else?


texts: How does the continuous/peak charge/discharge current change when combining cells with known values in series / parallel arrangements?

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Example
16 identical battery cells rated as below:

3.2V 100Ah
LiFePO4
Max Continuous Discharge 100A / 1C
Max Peak Discharge 200A / 2C for 100s
Max Continuous Charge 50A / 0.5C
Max Peak Charge 100A / 1C for 100s

Scenario 1
Cells arranged in 8S2P configuration (2 blocks in parallel, 8 of these in a row in series, 16 blocks total)

New voltage 25.6V
New capacity 200Ah

Scenario 2
Cells arranged in 2S8P configuration (8 blocks in parallel, 2 of these in a row in series, 16 blocks total)

New voltage 6.4V
New capacity 800Ah

Questions

In each scenario, what are the values of continuous/peak charge/discharge currents and why?
Does this change with differing battery chemistry (given otherwise same spec)?

Edit

Purpose of this is to understand what loads can be attached to a given battery bank constructed from the cells (max discharge current) and what a safe charging current would/should be (max charge current).


texts: What is the point of Geiger counter calibration?

texts:
I understand that the three ways Geiger counters can be calibrated are electronic calibration and energy calibration, which both use a pulse generator, and radiological calibration which uses a check source.

Electronic calibration simply involves sending pulses to the Geiger counter, which registers them as counts. But why is this necessary? I thought every ionization in the Geiger–Müller tube registered as a count anyway, without the need for calibration using electrical pulses beforehand. So what is there to calibrate? One ionization always equals one count.

Radiological calibration involves exposing the Geiger counter to a radioactive check source and setting the Geiger counter's measurement of the radioactivity to match the actual known radioactivity of the check source. But instead, why not simply program the Geiger counter to know that x cpm from a particular source = x µSv/h as detected by a particular model of Geiger–Müller tube?

I sort of understand the usefulness of energy calibration; I understand that it determines the voltage threshold for each ionization; but I cannot see the point of the other two methods.


texts:
Lots of new batteries (for mobile devices, MP3 players, etc) have connectors with 3 pins.
I would like to know what is the purpose of this and how should I use these three pins?

They are usually marked as (+) plus, (-) minus, and T.


texts: In semiconductor physics, how can we know which units to use for Boltzmann's constant?

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I'm working through Example 3.9 from Sima Dimitrijev's Principles of Semiconductor Devices textbook, and I'm not sure how to know which units to use for k in solving for \$v_{th}\$ in part a. The result there is obtainable using the Boltzmann constant k with units in J/K. So far in this textbook we've been using k with units in eV/K. I need insight into knowing which version of k to use, as both versions lead to a final answer with the same units.

When I divide eV/J in Wolfram|Alpha I get a unitless number \$1.602 \times 10^{-19}\$, which I recognize as the value of electron charge with units in Coulombs. I feel like this is key to understanding my question but I'm not quite there. Any help is greatly appreciated!


texts: Input across RC circuit is not showing a square wave though the input is a square wave

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I wanted to observe the transient response of the capacitor so applied a square wave of 205mHz from a function generator as that would allow complete charging and discharging for the capacitor in the circuit below (results came as they were expected), but to compare the difference in input and output signal when i placed the second probe of the oscilloscope across the input it gave the weird waveform below instead of a square wave. Any reason for that ?

R=1 k ohms, C = 470 uF , f = 205 mHz


texts: Maximising entropy generation rate via an ADC's reference voltage

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I have a circuit that generates random noise which I've measured with a 10 bit ADC.  The following is the sample distribution:-

You will notice that it's a log normal distribution, characteristic of a Zener diode in avalanche breakdown.  The maximum reading can be 1023 analogue units.  You will also notice that not all of the horizontal scale is utilised as the maximum reference voltage for the ADC was 2.5V.  So ADC reading 0 = 0V and ADC reading 1023 = 2.5V.  I can alter this reference voltage and as I do the histogram widens and narrows proportionately.  The second histogram is for a reference voltage of 1.1V.  You can see that approximately 14,000 samples were at a value of 1023 or above. Both histograms show 10 million samples each. (I think that there might be  weirdness with the gnuplot tally).

As the samples are taken, they are effectively a source of random entropy.  This leads to a Shannon entropy rate per sample, in say bits /sample. So for example at Vref = 2.5V, entropy was generated at 0.98 bits/ sample.  In order to maximise efficiency of this entropy generator, I wish to maximise the entropy rate it produces by altering the reference voltage.

Following a comment:  You will see that in the first histogram, one standard deviation of results (68% - the majority) is spread over perhaps 100 analogue units.  In the second, it's spread over maybe 250. That means more entropy, but some readings are clipped at 1023.  I think that there is a sweet spot whereby the distribution can be scaled (by reducing Vref) to maximise entropy, which will then fall thereafter as Vref decreases towards 0V.

Q.  What reference voltage will maximise the entropy generation rate in bits /sample?

Note:  I am not asking how to build a random number generator.   I am not asking how to build a random number generator.  I write it twice so that answers do not consist of brain dumps on how to build random number generators, debiasing or that a pseudo random number generator would be better.  I am looking for a maximisation of Shannon's information entropy formula (or min. entropy which would be better for cryptographic purposes) specific to this question.  No commercial TRNG creates it's final output from hardware alone.  All use software processing and randomness extraction in distribution whitening phases.  I am asking about the hardware phase to maximise entropy.  It is important to distinguish between entropy and uniformly distributed random numbers.  They are not the same.  Why am I having to state this? This is the 3rd time I've asked this question across 3 different forums and not received a relevant answer.  This is a mathematics and voltage question to which the answer will consist of just one singular number of volts.  Could it be that multi-disciplinary questions are unsuitable for SE?


texts:
I've attempted to set up a 556 timer on a breadboard. I bought two 556 timers because the project I will be using it in requires 3 timers, and I wanted to be cost effective.

I have followed a tutorial online about how to wire it on a breadboard, and for right now I am only using one of the timers on the 556 chip. Unfortunately, there is no output going into the LED, i.e it isn't flashing like it should be. I've read the data sheet, turned my LED and capacitor around, and tried a second chip that I have. No luck so far

Have I wired it incorrectly, or did I just have bad luck and end up with 2 busted chips?

Thanks for your help

Here's a picture of my breadboard:

Link to 556 datasheet


texts: What terms to differentiate between a quasi-synchronous motor (eg an induction motor ) and a completely asynchronous motor (eg a universal motor)?

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I am editing a table of motors.

I am looking for the correct terms to distinguish two types of motors: motors whose speed is less than the AC frequency (all inductions / squirrel cage motors) from motors whose speed is completely independent of the AC frequency (universal motors and repulsion motors).

Normally, the former is called "asynchronous" thought they are "quasi-synchronous".

What about the latter? They are too "asynchronous" but they are completely asynchronous.


texts: What AC mains phase information can be deduced from measuring at two distinct devices, connected via ethernet?

texts:
I a have a house with 3x20A grid connection. With the usual big loads like washing machines, kitchen. For each socket in the house (many...) I want to determine the phase a wall socket is connected to in a digital way using a microcontroller telling me what phase it is on relative to another device connected to another socket (with known phase number). The result on a display could be e.g. ‘same phase’ or ‘other phase’ or even ‘lagging phase’.

I know how I would do this in an ‘analog’ way: measure current of the three grid connection phases using CT’s and switch on a significant load on the target socket and see which one responds.

But as a thought experiment I wanted to explore if there is something you can measure on the device, receive something TCP/UDP from the reference device with known phase and determine wheter it is the same phase or not. My engineering mind tells me it cannot be done since I cannot think further than a zero crossing detector with 100 crossings/s at 50Hz comparing which are only shifted >60 or <-60 degrees at 50Hz compared to the other phases, resulting in 20/6ms time difference. I then believe that is too short to receive a TCP (or UDP) reference signal to compare it to.

This is in my head as impossible for quite some time now. Just want to explore with you if you have ideas.


texts: Raspberry pi to sense voltages 12 to 24, what buffer is good?

texts: Hello I’m looking to use my raspberry pi in an automotive application where it will be used to detect when the vehicles ignition is activated and de activated. I would like the system to be 24 volt tolerant just to maintain application flexibility. I was thinking something like a buffer which would translate input voltages 12 to 24 to 3.3v logic for the raspberry Pi to detect. What’s the most suitable hardware or circuit to use? Regards


texts:
I have an old (1960's) Whippany Dart combo organ. Each set of three keys has a tuning pot that raises and lowers the pitch of those three notes (turning clockwise lowers the pitch, and counterclockwise raises the pitch). I'm not sure what determines the pitch of the three distinct notes within each group.

For one particular set, turning the pot as far as it wil go counterclockwise still leave each note in the set about a half note below the desired pitch.

My question: Is there an obvious way to raise the collective pitch of one of these sets? Perhaps adding or changing one of the resistors in the group?

(I do not have a schematic.)


texts:
I have a homework problem that was solved by our instructor:

"Calculate the electric current of the inductor at \$t=0^+\$."

He calculated \$1/30\$ but the answer sheet was says \$-1/30\$.

Which of them is correct?

Our instructor's work:


texts: can the efficiency of flyback converter be less than 50%?

texts:
Let's see the worked example in pressman's book:

specification of the converter :

now let's see the primary rms current (for 38v dc input) :

the input power = 2.7*38=102.6W for output power =50W!

he assumed 80% efficiency in the derivation of these formulas, is that the situation where we should recalculate with this new efficiency? or is it something about power factor?


texts: Sine Wave Input for Op Amp Integrator but Output Looks Weird

texts: The input is in sine form (AC input) but the output (in blue color) is the straight line. So what is wrong with my schematic in LT Spice this time? I thought I should've got output in sine form if I have input in sine form


texts: Why do some SMA connectors have a rectangular center pins?

texts:
I came across an edge mount SMA connector where the soldering portion of the center pin is rectangular rather than round like normal. My initial assumption is a stronger solder joint. Any other ideas? What affect might this have on RF performance?
https://belfuse.com/resources/drawings/cinchconnectivitysolutions/johnson/dr-ccs-john-142-0701-841.pdf


texts: Do electric motors have the same efficiency when operating as generators?

texts: Its in the title.  I'm just curious and it turns out that either this is such a stupid question that no one has bothered to answer it, or i'm just not good at googling today.  I guess I'm thinking specifically about the permanent magnet synchronous motor (PMSM) in my car, but any answer however general would interest me.


texts: How to make a nice PCB enclosure for a product?

texts:
I have my PCB ready and now am looking at the various options that exist for getting a nice PCB enclosure made. I was wondering if there are any good tools out there specifically suited for PCB which will help me create a cad model for the design I have in mind. What are the free open source alternatives for me to design a 3d enclosure and are there any samples which I can use as a base to get started, like if I google for eagle schematics I can find tons of them and modify it to suit my own needs and use it as a starting step.

Also once I have the CAD model , whats the best way to get it manufactured. Its going to be in small quantites so I was thinking along the lines of sending it to a 3d printing

Also in case it works out to bee too expensive to manufacture my own case what are the best sites I can look at which have off the shelf solutions?


texts: So I'm using a PIC32, it's rated for 80 MHz operation. But my crystal might be inaccurate, so it could oscillate at 80.01 MHz. I can presume this is okay, but what if I were to use a 7.3728 MHz crystal and an 11x PLL, would running it at ~81 MHz be okay? I suppose what I'm asking is how far is too far? And why do manufacturers not include a bit of overun (for example rating it at 81 MHz?)


texts: Smart charging circuit for NiMH battery pack

texts: I want to build a solar powered charger for a niMh battery pack to run a microcontroller. What are the fundamentals of building a smart circuit that will not overcharge the battery and will also allow current to be pulled directly from the panel


texts: Does the MOSFET Rds(on) value really matter?

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I am using MOSFETs in the ubiquitous RAMPS 1.4 Arduino shield for 3D printing use.

The MOSFETs switch the voltage to the heated bed and the hotend (where the filament comes out).

I need to replace one of the original MOSFETs, which is a STMicroelectronics STP55NF06L (datasheet). I chose to replace it with a TI CSD18532KCS (datasheet). Same TO-220 package, but I don't know if it will work properly.

So here are the specs for the STP55NF06L:

And here are the specs for the CSD18532KCS:

It appears that for most values, the two MOSFETs are very similar. But for RDS(on) (highlighted in red), the test characteristics are different, and the results are different. It's not a big difference (RDS(on) equals about 20 milliohms for the ST chip and about 4.5 milliohms for the TI chip).

I understand that RDS(on) is the resistance of the MOSFET when the gate-source voltage is at the sample VGS level. Because the difference between the two MOSFETS in RDS(on) is so minor, this shouldn't be an issue, right? The circuit isn't precise to more than 2 or 3 degrees of C for the heater cartridges anyway, so I believe it won't make a difference.

Are these MOSFETS interchangeable?


texts: How to calculate measurement error in an exponentially non-linear sensor? (self made pressure sensor)

texts:
I'm trying to calculate the measurement error from a home-made pressure sensor which I have in a voltage divider circuit. It has the same negative exponential non-linear resistance characteristics as an NTC thermistor: with increasing force [N] the resistance [ohms] decreases non-linearly. The pressure sensor acts as a variable resistor, and I am measuring the voltage drop across it using an 8bit ADC.
So far, I have taken resistance measurements (with a multimeter accuracy to .1 ohm) of the homemade velostat pressure sensor at exerted forces from 1 to 10 N using a force gauge (with an accuracy of 0.05N), with 5 resistance measurements at each force value. The average of the 5 measurements are graphed below.
My plan to calculate the exerted force [N] is to use a "power function" which is created from the data in Excel and rearrange it to solve for X (force) at a certain Y (resistance). The resistance (Y) is derived from the voltage measured by the ADC.
Is this a good approach, or should I use a lookup table or linear interpolation? (I'm not sure on how to do either of these yet.)
How do I calculate the measurement error from the sensor seeing as resistance changes only a small amount in higher force ranges, and resistance changes a lot (sensitive) at small exerted force ranges?

EDIT: added chart of my resistance measurements with max and min values graphed (the 20 measurements at each value of F [N] not shown in table).


texts: 12 V / 140 Ah lead acid battery charging with 24 V / 150 A alternator

texts: Can I connect two 12 V / 140 Ah lead acid batteries in series to get 24 V / 140 Ah and connect directly to a 24 V/ 150 A alternator to charge them? Or do I need any charging / protection circuit in between?


texts: How to create an IN pin for 5v - 5 pin spdt relay

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I have this relay module which has one IN pin, basically that in pin comes from Arduino board , which switches the states of the relay.

I also have the single relay but they don't have the IN pin.
does any one have the idea how to create the IN pin for single relays on a breadboard.


texts: I have a question in designing crystal oscillator

texts:
I want to design a crystal oscillator (pierce) but I'm having trouble.
Proposed oscillation frequency is around 39 MHz and I used crystal
L~4mH C~4.1fF R~10ohm; Co~2pF

C1,C2=20pF (shunt cap for drain to GND & gate to GND)

Feedback resistor ~ 1 Mohm;
Vdd~1.5V
Transistor gm~80u

However, my oscillator input/output settles to same voltage, and does not oscillate.

When I change crystal cap to 200 fF then it starts oscillation.

Can crystal motional cap affect to oscillation?
What is the cause for non oscillating?

This is the schematic of my design.


texts: Can someone explain how this truth table was filled in from a Mealy model?

texts: I'm having a bit of trouble figuring out how the truth table was filled in. I understand how to draw the diagram from the first table and I understand the boolean expression given from the truth table but I can't quite grasp how the truth table was filled in. Could anyone do me a favor and explain it for me?


texts: How much RAM can I get from a MAX V logic element?

texts:
I need a CPLD or an FPGA in a hobby project. Since I have no experience of it I am trying to evaluate the different options and brands based on the constraints I already know, so that I can buy an appropriate development board and start learning.

I mostly need it for glue logic so I am reasonably sure that a CPLD will be enough when it comes to complexity - the simplicity of a CPLD is appealing in many ways. However, I also want to implement a function that requires a small amount of RAM.

There are packages with integrated block RAM, but since I need a large package for all my I/O but not much logic, I estimate that I will end up with a number of unused gates. My question now is: How can I estimate the RAM I can get from one LE/Macrocell?

For example, the MAX V Product Catalog has the following to say:

  Unused LEs can be converted to memory. The total number of available LE RAM bits depends on the memory mode, depth, and width configurations of the instantiated memory.

Fair enough, it obviously depends on a myriad of options, which is why I need help from someone who has more experience. Is it possible to give an order-of-magnitude range here, so I can figure out if my project is even close to feasible with a given family?


texts:
According to the following simple PID control system:

(source: umich.edu)

We could create the equation:

$$(R(s)-Y(s))C(s)P(s) = Y(s)$$

Wich will lead us to

$$\frac{Y}{R}=\frac{CP}{1+CP}$$

So, if we want to minimize error (which is \$R-Y\$), then it makes sense to think that ideally we want to make \$Y=R\$ (which means the output is following the input at best).
Although, this would lead us to:

$$\frac{Y}{R}=1=\frac{CP}{1+CP}$$
$$1+CP=CP$$
$$1=0$$

Which is obviously wrong. I believe that I did not miss anything stupid in the mathematical steps. So, what does this contradiction mean in the control context? And why did this appeared in the equations?


texts: Question about capacitive sensor designs with direct touch to copper or aluminum

texts:
I've seen some DIY capacitive touch sensor projects where the sensors themselves are strips of aluminum or copper soldered to a non-grounded wire, where the user touches these strips directly with their finger to be sensed.
I'm a bit unclear as to why this design is considered "capacitive". My understanding of stuff like glass touchscreens is that there is a cathode on one end of the glass, and when a user touches the glass it forms the anode, with the glass serving as the dielectric.
But if the aluminum or copper strip is the cathode, and the finger touches it directly - wouldn't this be a resistive phenomenon? I thought capacitance implied a separation of two charged surfaces.


texts:
I'm looking for powering up the Raspberry Pi by a few 18650.
It looks like MT3608+TP4056 are somewhat cheap/common way of managing LiPo batteries as a backup power.
I checked the specs and looks like MT3608 has a potentiometer to calibrate the output voltage - I read it as that there's no voltage stabilizer. So if a battery voltage drops by 0.5V - that will essentially make RPi unstable because of undervoltage.
What would be a better DIY alternative to have a power supply of 4 x 18650 batteries to supply RPi 5V/2A for extended period of time?


texts: Connecting several power regulators to a single voltage input

texts:
I am trying to make a power source to feed the following:

3x DC motors, that need to work under changeable voltage; not
supposed to operate over 2A RS385-ST
1x Servomotor 12V not over 1.5A
2x 5V 1A for this L293D
1x 9v 0.1A (for control unit)

I am using a LM317 to control the voltage each motor receives; so I am using three of this regulators, one for each motor. The picture shows the circuit. The motor loads are modeled with resistances. Circuit in picture does not include other regulators:

As noted there is also a couple of 7805 for the 5V outs, one 7812 for the 12V servomotor and a 7809 for the control unit's power. They are all part of the 78xx family. All the regulators are connected to the bridge's output.

My problem is that no matter what capacitor I use for smoothing the bridge's output, the simulation fails. I am simulating in Multisim.

I think that my problem is that the input voltage is too high for some of the regulators.  All ideas, from changing the circuit to finding a different duty, are welcomed.


texts: How to connect old 18650 different capacity cells as a 2S2P pack?

texts:
Recently I've opened up a laptop battery pack and got 6 18650 cells and two of them were 0V and the other four had 3.75V.

I fully charged them with a Imax b6 charger and discharged them at 1.0A to 3V.
The capacity readings are:

1152 mAh
1121 mAh
931 mAh
871 mAh

I was thinking of building a 2S2P pack for my Arduino project.

Since these batteries have different capacities, is it a good idea to put them as a pack?  If it's okay, how should I arrange these cells?


texts: NPN Differential Pair - Emitter Voltage Variation

texts:
My understanding of how this circuit should work is :
DC:

The transistor bases are at about 0V DC due to R5 and R6. Some base current flows due to the constant current bias, so there is a small (~40uV) offset voltage across each resistor.

Emitter currents for both transistors are about equal to {I1}/2 = 250uA

Since equal current is flowing, there is equal voltage drop across both base-emitter junctions, meaning V_BE is equal for both transistors
These conditions are all confirmed in LTSPICE.

However, things stop making sense to me at AC:
From Wikipedia:
"At differential mode (the two input voltages change in opposite directions), the two voltage (emitter) followers oppose each other - while one of them tries to increase the voltage of the common emitter point, the other tries to decrease it (figuratively speaking, one of them "pulls up" the common point while the other "pulls down" it so that it stays immovable) and v.v. So, the common point does not change its voltage; it behaves like a virtual ground with a magnitude determined by the common-mode input voltages." -
This makes sense to me, and is what I expect. However, my simulation results show V_E vary about 10mV peak-to-peak, equivalent to the half input signal magnitude.
What is going on here? Am I missing something obvious? Is this a simulation error?
I am simulating with the default LTSPICE settings. I am waiting on parts to build a +12/-12V power supply, so I have not been able to try this circuit in reality yet.


texts:
A Samsung switching power supply AD-3014STN delivers 14V 2.14A. The rectifier consists of 3 SB3150 (150V 3A) diodes connected in parallel. One of the diodes was short-circuited, see picture, the defective diode is removed.

What I don't understand is, why are 3 diodes connected in parallel that can deliver a total of 9A, but the power supply only delivers 2.14A. One diode should do it, right?

Furthermore the high blocking voltage of 150V is mysterious to me.  Does anyone know the answer to these questions?

EDIT:
Here is the solder side photo:

A power supply for an LCD monitor is an extremely price-sensitive product, so I wonder about the 3 diodes in parallel and also the high reverse voltage. In this diode family there are products with a lower reverse voltage which are also cheaper. Using only one diode with a lower reverse voltage may save approx. 0.10 USD per unit, but with 1,000,000 power supplies that's 100,000 USD savings, so why does a manufacturer install 3 diodes?


texts:
I am wondering is it possible to design a differential (or instrumentation) amplifier that will operate from single supply?

I have a 2Vp-p and 0.2Vp-p sine wave signals that need to go thru the differential amplifier. They both swing positive and negative.

But currently for this project I have only positive power supply. I can add an inverting converter if necessary but would like to know if I can reduce the costs.

If it is possible, could you please show an example.

Thanks


texts:
I want to implement a circuit which allows to regulate the current flowing to the load.

I have two use cases:

Case 1 is the normal case where I would set the max. allowed current with a potentiometer to say 5 amps and read the value into an ADC of the controller which then sets a specific duty cycle of the pwm. The low pass creates an analog value and give this to an amplifying buffer which lets current flow through the nmos. If the current (depending on the load) is below 5A, everything is fine, but once it raises above 5 amps, I want to lower the duty cycle to regulate the V_GS down, to reduce the current.

The other case is a short circuit protection, if the current raises way over 5A (like 8...10A) I want to shut off directly.

Is this concept going to work with a circuit like this?


texts:
I have seen a number of similar questions but no one ever seems to actually answer this question, so let me pose it a different way.  Let's suppose I am stuck on a space ship (so I can't go buy some other parts) and I must replace a blown DPDT relay. I have a handful of NPN and PNP transistors, a few resistors and capacitors of various sizes, and some diodes. I have to replace the relay using only the parts I have. For the sake of argument, assume the components I have will handle the same voltage and current as the relay.

What I thought would work is to create a sort of H-bridge using NPNs for two of the switches and PNPs for the other two. That way, when the switch controlling the old relay's coil was on, the NPN circuit would activate, and when the switch was off, the PNP circuit would activate. I added a pull-down resistor to make sure the circuit was grounded when the coil switch was off. I have only tried this in iCircult so far, but it doesn't seem to work. I tried adding some diodes like I have seen in some h-bridge diagrams (even though I don't think they should be necessary for this configuration) and it didn't help.

Here is my example circuit diagram. I'm showing an unknown device in the center of the h-bridge that could represent a DC motor but doesn't have to. I don't want to get into discussion about flyback diodes and inrush current. The important thing is that current flows one direction when the coil switch is on and the other way when it is off. I know I probably need a base resistor in addition to the pull-down but, as a general concept, I don't understand why this doesn't work when I simulate it.

simulate this circuit – Schematic created using CircuitLab

Here is the original circuit with the relay I need to replace:

simulate this circuit


texts: Best method to route high current PCB with in a tight space constraint

texts:
I was wondering if someone can give me advice in routing this PCB.

The PCB contains several triacs driving AC loads and digital end which contains a micro and several digital I/Os. So far, I have decided on the following:

Use 18 AWG wire to connect the LIVE via the spade terminals.
Use 5oz copper on the top layer to reduce the track width for the high current tracks for triac output to AC load spade terminal.
Solder Y caps underneath the board with insulation and hot melt glue.
Use 4 layers
First layer contains AC tracks on the mains side and DC signal tracks on the digital side.
Second layer contains ground layer on the digital side with some signals.
Third layer contains digital VCC layer on the digital side with some signals.
Fourth layer contains signals on digital and secondary voltage from the transformer.

I have few constraints in the design like the placements of the headers and AC spade terminals cannot be modified plus the board size cannot be changed. I have placed the heatsink/triacs and spade terminals so I can route the signal tracks to the optocouplers and secondary output of the transformer via the middle of the PCB. I am trying to ensure there is a least 2.5mm separation for the AC tracks.

Do anyone see any issues or problems with this layout or have any suggestions?

Regards
Paul


texts: Exporting particular data points of simulations from ltspice

texts:
The simulation does repeated analysis with a parameters which grows at each new analysis. For each of those analysis which depends only on the value of the parameter which is growing, I would like to export 1 point at a certain time t0. The goal is just to see how evolve the point in function of the parameter which is growing. Does I need to export the data from LTspice ? And how can I specify when (at t0) I want to export the point ? Or is it possible to see it on LTspice ? Otherwise is it possible to export each all datas of each analysis ? I could do a post treatment of the overall datas.

Thank you very much !


texts:
We're only a week in to the first EE class here at Uni and I'm already stumped. I can build a power supply in my sleep  but anything theory-related turns me upside down. Now, I've done KVL on the following circuit six times now, and have been working at it for nearly an hour, and something just isn't making sense here.

simulate this circuit – Schematic created using CircuitLab

I'm trying to find the voltage across the 25 ohm and 10 ohm resistors, as well as the power absorbed by the 25 ohm. It really seems like I'm missing something extremely simple here, but my calculations just aren't working out properly.

Here's how I approached KVL the most recent time. V3 is the 15 ohm resistor's voltage drop and the sign (from my understanding) shouldn't matter as it will work itself out when solve. Starting from the bottom-left:

-20V + V3 + 30V + V1 - V2 = 0

  *simplified*

10V + V3 + V1 = V2

That's easy. Now since the circuit elements are all in series the current should be the same for all elements. I applied ohm's law as follows:

V1 = IR1 = 25I
V2 = IR2 = 10I
V3 = IR3 = 15I

Looking good, narrowing down to one variable lets me solve for current.

10V + 15I + 25I = 10I
10V + 40I = 10I
10V = -30I
-1/3 A = I

Here I assume that current is just flowing counter-clockwise when we approached KVL in the clockwise direction, which is where the negative sign comes from.

So finding voltages across the resistors should be as easy as plugging the current back in to ohm's law.

V1 = 25(1/3) = 8.333 V
V2 = 10(1/3) = 3.333 V
V3 = 15(1/3) = 5 V

This is where I hit a snag. These are not correct according to the answers in the book. I don't know where I'm going wrong here. This is the last in a series of KVL/KCL problems and I had no issues with any of the other circuits. For some reason this one is just throwing me way off.

If I'm missing something very fundamental here, please tell me. If my assumptions stated above are dead wrong, please tell me. I like to think I know a decent amount about hands-on electrical topics, but this theory stuff really makes me struggle.


texts: Yields in DRAM and other Massively Redundant Processes

texts:
I'm right now combing the electrical engineering literature on the sorts of strategies employed to reliably produce highly complex but also extremely fragile systems such as DRAM, where you have an array of many millions of components and where a single failure can brick the whole system.

It seems like a common strategy that's employed is the manufacturing of a much larger system, and then the selective disabling of damaged rows/columns using settable fuses. I've read[1] that (as of 2008) no DRAM module comes off the line functioning, and that for 1GB DDR3 modules, with all of the repair technologies in place, the overall yield goes from ~0% to around 70%.

That's just one data point, however. What I'm wondering is, is this something that gets advertised in the field? Is there a decent source for discussing the improvement in yield compared to the SoA? I have sources like this[2], that do a decent job of discussing yield from first principles reasoning, but that's 1991, and I imagine/hope that things are better now.

Additionally, is the use of redundant rows/columns still employed even today? How much additional board space does this redundancy technology require?

I've also been looking at other parallel systems like TFT displays. A colleague mentioned that Samsung, at one point, found it cheaper to manufacture broken displays and then repair them rather than improve their process to an acceptable yield. I've yet to find a decent source on this, however.

Refs

[1]: Gutmann, Ronald J, et al. Wafer Level 3-d Ics Process Technology. New York: Springer, 2008.
[2]: Horiguchi, Masahi, et al. "A flexible redundancy technique for high-density DRAMs." Solid-State Circuits, IEEE Journal of 26.1 (1991): 12-17.


texts: What does a junction do inside a MOSFET?

texts:
Today I found an application note that stunned me.

Onsemi is quite a big manufacturer for discrete power devices. So I was astonished to read within that Application note about junction temperatures inside a MOSFET.

As a MOSFET does not have a junction as a functional element, I'm asking myself, what do they mean? Is it just imprecise language or has it some background. A colleague searched and found the word mentioned within a datasheet for a MOSFET from TI, so it's not completely uncommon.

Back to the AN. The graphic illustrations insinuate that junction is here a pars pro toto for the whole die. So why don't the use the term "die" instead?

I think of the following possible explanations:

When talking about thermal issues the wording forged in bipolar days was transferred to the field effect ages without caring about the meaning of the word
Similar, but quite not the same, someone considered the source-body- or source-drain-junctions as something worth referring to. Perhaps they are also thermal very active? I don't think so as most of conduction losses should occur within the channel
Junction has just a broader meaning than I thought, encompassing all current conducting or blocking parts of discrete semiconductors. (I've got to add, I'm not a native speaker)

I may miss some historical details. I know this question might be off-topic because it could solicitate opinions, doesn't deal with a material engineering problem and might as well be completely unanswerable.
But I think, this is an engineering related question, because it is vital to have a common terminology in engineering. Furthermore engineering history is not completely irrelevant for solving current problems.


texts: Should I separate grounds with optocoupler and dc converter?

texts:
I have a 24V input to a DC/DC converter, output is 3.3V.
the 24V is also passed to an opto-coupler (diode side) while the secondary side (NPN) has a 3.3V-made from the 24V. So the opto-coupler is used as a level shifter.

I thought about separating the grounds for the opto-coupler. The input 24V will have a gnd1, while the 3.3V will have a gnd2 to raise the noise immunity. But, the 3.3V is transformed from the same 24V passed to the input of the opto-coupler (which has a different ground).
In this situation, will this give good results in terms of EMI, SI, point of view?
Thanks all!


texts: What is the maximum input value (Vi) that can be applied without zener diode gets damaged knowing that the maximum power rating  of the zener diode is \$ P_m = 500mW \$,the breakdown voltage is \$ V_Z = 10V \$ and the ripple in the output voltage is +-3% ? Any help is appreciated! Thanks in advance!


texts: Which connector type is used in practice in this case?

texts:
I'm planning to use STP twinax cable for diff. inputs to a data-acquisition board. The cable will look like this:

I don't want to use screw terminals and need something easy plug and play for others. I can make a connector board for the DAQ and add connectors to the cables.

But what connector type is used in practice for such pourpose? BNC connector would not work since it is for coaxial cables where the shield is one of the terminal.


texts: Is it good idea to use more than two output from one step down converter?

texts:
I want to use below step down converter to change 24V to 12V. But I need to connect to two circuits which require 12V to operate. Will it be ok to do this?

Should I buy another step down converter so each board have one step down converter from battery?


texts: Current feedback amplifier input structure

texts:
This is an input stage of some obsolete CFA (current feedback amplifier):

Current feedback amplifier is a transimpedance amplifier, which converts current signal at its input into voltage signal at its output. R_in of non-inverting pin is high resistance input, while other R_in of inverting pin is low resistance input.
In general, if R_in goes to infinity, then the input only sees the voltage at its input nodes and if R_in goes to zero, then the input only sees the current at its input nodes, right? However, in case of this CFA, -Vin sees current signal rather than voltage (due to lower input resistance) and +Vin sees voltage signal rather than current (due to higher input resistance), right? On what fact should one decide, whether this amplifier is transimpedance amplifier? I would say that when it operates as inverting amplifier, it is transimpedance amplifier (I to V conversion) and when it operates as non-inverting amplifier, it is voltage amplifier (V to V conversion). But I may be wrong.

It is easier to determine the type of amplifier in case of differential input structure, where both inputs are high impedance inputs (case of VFA - voltage feedback amplifier).


texts: Sanity check: would this configuration work to address an item in a grid?

texts:
This is a follow-on to this question.
The circuit that I have in mind is represented below.

simulate this circuit – Schematic created using CircuitLab
The idea is that I want to be able to detect if and where specific, unique components are plugged into an 8x8 grid. To avoid having 64 individual circuits, I want to try this: I have 16 I2C circuits, 8 rows and 8 columns. Each location in the grid would look like the schematic above when the component was inserted; when a component is not inserted, the four t-gates are shorted together.
First, I'll check the rows, so C2 will pull low and C1 will pull high. Each of the eight circuits will read which components are where. I'll store the column value for each component identified. Then I'll check the columns, so C2 will pull high and C1 will pull low. I'll store the row value for each component identified. In this way, I'll know which of the unique components are in a circuit and which of the 64 spots in the grid that are occupying.
First question: does the preceding make sense?
Second question: would what I described work?
Third question: is there a better way to do this? (I'm certain that there is, but I've been wracking my brain to try and figure out a way to accomplish this)
Edit: in speaking with another engineer that I know, he said that the circuit that I had in mind could work, but that T-gates are "clunky". He's really busy, so I haven't been able to get clarification on what that means, though. Anyone have any thoughts on what he could mean?
Edit: never mind; the other guy thought that the T-gates were attached to the power lines, not the data lines.


texts: How does a real current source change its pd to keep constant current

texts:
An ideal current source is able to change its potential difference at the output to keep the same current at the output regardless of the load imepedance there. Real current sources are able to do this till a limit, I think. I wish to know how do they do it?

Also, what exactly does "load" mean in circuits, when a component loads another too much, does it source too much current? A high impedance would load on a voltage source would load less by drawing less current. A high impedance however would make a current source try harder and have opposite effect, does the concept of loading apply differently to voltage and current source?


texts: How do compact AM radios establish a ground?

texts:
I am trying to construct a radio and, at the first stage, I have finally detected circuit a signal. My previous attempts have failed and I have discovered that it is because it was not properly grounded.

Originally I was using the ground from my oscilloscope, but it wasn't until I accidentally touched the grounding wire to a my aluminum window frame that all the noise disappeared and a much cleaner, oscillating wave, appeared.

So I would like to know, how do compact AM Radio sets establish a ground? I tried grounding to the wall, grounding to the Earth, and even a medium sized sheet of copper and nothing worked except when I attached it to my aluminium window (which is quite large).

For a while, I wasn't sure if my window was actually acting as an antenna, but, after switching things around (the antenna and the ground), the circuit did not work.

Therefore, I would like to know how compact radios establish a ground? I mean, they don't have a water pipe to connect to so how do they do it? Please do not make references to heterodyning since I am building a simpler version of an AM Radio.

My circuit:

simulate this circuit – Schematic created using CircuitLab

EDIT: Note, I have also tried connecting my ground to the wall ground and it only slightly better than grounding to Earth.


texts: Change of Gate-Source Voltage of a NMOS Transistor due to Temperature

texts:
Consider the circuit below. I am performing a corner simulation in Cadence with temperatures of -40°C, 27°C and 85°C, to see how the gate-source voltage changes with temperature. Before simulating I calculated that by hand.

Since the transistor is in Saturation, the following formula can be applied to calculate the drain current (Sah / Shichman & Hodges Equation).

$$
I_D=\frac{\beta }{2}(V_{GS}-V_T)^2
$$

The formula can be rearranged to calculate \$V_{GS}\$ (since \$ I_D \$ is given by the current source).

$$
V_{GS}=\pm \sqrt{\frac{2}{\beta }I_D} + V_T
$$

Furthermore the temperature dependence of the simulated transistor is the following.

$$
V_T=V(T_0)+TCV(T-T_0)
$$

We can assume that \$TCV=-1.1mV/°C\$, \$ T_0 = 27°C \$, \$ \beta =\frac{75}{2} \mu A/V^2 \$, \$ I_D=10\mu A \$. Therefore the calculated gate-source voltages for the three different temperatures are

$$
V_{GS}(-40°C)=\pm \sqrt \frac{20\mu A}{\frac{75}{2} \frac{\mu A}{V^2}} + 0.6V - 1.1\frac{mV}{°C}(-40°C-27°C)=1.404V \\
V_{GS}(27°C) = 1.33V \\
V_{GS}(85°C) = 1.266V
$$

We can see that with increasing temperature \$ V_T \$ goes down and so does \$ V_{GS} \$. But strangely the simulation shows me the opposite. Only the calculated \$ V_{GS} \$ at \$ 27°C \$ is correct.

Why is that the case? Did I do something wrong in my calculations?


texts: Creating a breakout panel for a Raspberry Pi GPIO lines

texts:
From the elinux.org documentation for this GPIO, I have summarized the following information:

  The Raspberry Pi Model A+ and B+ boards, and the Pi 2 Model B, have a
  40-pin 2.54 mm header marked J8, arranged as 2x20 pins. GPIO voltage
  levels are 3.3 V and are not 5 V tolerant. There is no over-voltage
  protection on the board - the intention is that people interested in
  serious interfacing will use an external board with buffers, level
  conversion and analog I/O rather than soldering directly onto the main
  board.

The header looks like this:

What I would like to do is create a breakout panel that provides, primarily, easy to access and labelled jumper lead sockets for the GPIO lines from the header on the Pi board. I would like to add over-voltage protection for 3.3V, and also possibly an LED for each line to indicate it's high or low status.

I haven't been active in electronics for a long time, so I would like to know what the ideal socket type would be, as opposed to large and clumsy olden day "banana plugs", and then how to provide over-voltage protection. The sockets should be further spaced and much harder to incorrectly select than the fine spacing on a breadboard based breakout.

One of the first and simplest experiments with the Pi is powering an LED, with resistor, directly connected to a ground and output pin on the GPIO header. If possible, I would like to include such an LED for each GPIO line on my breakout panel, but can I do this without affecting the normal function of that line with whatever circuit it is actually used to communicate with.


texts:
I am trying to understand the Source Follower amplifier as a primitive buffer, and am running some simulations with a SPICE simulator.  I have the amplifier hooked up as shown below with a current source acting as the bias for the NMOS transistor M1.

I am able to see a relatively good copy of the square-wave input on the the source leg of M1 with a slightly smaller amplitude and no phase change, which I understand is the case with the source follower (Gain less than 1.0).

However, the amplifier shifts the output bias point by one volt. For example, if the square wave Vin is biased around 0.5V, the output on the source leg is biased around -0.5 V. Changing the magnitude of the Ibias current source only affects the shape of the square wave output waveform, it does not shift the bias point of the output.

In order to keep the input and output roughly centered around the same bias point, what modifications would you suggest to the amplifier? Do I need to look at resistors at the drain? Or perhaps a bias network on the gate?


texts: The use of fuses in small electronics projects

texts:
I am new to electronics so I hope this question is acceptable. I have been playing around with an Arduino. I have use the USB output from a computer as a power source. I also have a 9V battery. I am a bit concerned about creating a short somewhere and damaging the computer or the battery. I am guessing that this is what a fuse is for, is that right?

For small projects (not necessarily involving an Arduino) what type of fuses should be used? Is it, for example, possible to get a 1A 9V fuse? I have searched online and I only see things like 1A 250B fuses. Will these work well for small electronics projects?


texts: Possibility of dissipating 20 W via Nichrome wire safely

texts: I am looking to use 1 foot (0.3 meters) of 32 AWG nichrome wire to dissipate roughly 20 watts of power. Assuming the wire was submersed in still transformer oil, would I be able to do this without melting the nichrome?


texts:
Below shows the effect of a CM choke on the CM interference:

And below is a CM choke with ferrite ring for a USB cable(there is no capacitor installed):

In above examples there are no Y caps to earth ground installed yet the CM choke seems to work.

But in some filters there are also Y caps right after the CM choke for currents to return to earth ground as below:

Why are there these Y caps in some filters and not in some others?
When do one need the Y caps right after the CM choke?

Edit:

Adding capacitors causes very high gain for some band, Isn't it very risky? Yes it attenuates sharper but also makes a peak for muddle band. What could be done?


texts: BJT vs OPAMP for RF signal amplification: BJT performs better, why?

texts:
I am working on developing RF wave generation from a DDS IC (AD9834-Analog device). The voltage we require as an RF signal is 6 times (3V peak to peak, sinusoidal, DDS output~=0.5V with supply to the board 3.3V from LiPo battery (3.7V) ). Initially I started with opamp (LMV794, dual opamp from TI, GBW Product=88Mhz). One of the opamps is used as difference amplifier (DDS has two output, 180 phase difference only): technically doubles the voltage and then fed to a non-inverting configuration for further amplification(Gain=3) with the other opamp. It turned out that the amplification I was gaining was some kind of unstable. It generated a lot of noise. And sometimes, final output (output of non-inverting one) of OPAMP (LMV794) is around 1V with a HF noise (8 Mhz or 10.93MHz)even when DDS is not feeding any voltage. I replaced the OPAMP several times with new ones thinking that the OPAMP might be damaged. But since the final output did not satisfy me, I could not move on to proceed with the PCB.

I switched to 2 stage class A amplifier built with NPN transistors(BC33740TA) on bread board, the input is fed from DDS on PCB. The output is quite satisfying, the class A amplifier proves to respond well with different RF frequency (5-15 MHz). I am planning to redesign the PCB with transistor (class A amplifier) instead of OPMAMP based amplifier. But, I need to know what I was missing with OPMAMP based amplifier. Can anybody explain?

-Thanks in advance
edited: added the schematic and formatted the question into two paragraphs


texts: Flyback converter Transformer calculation verification

texts:
Kindly verify the transformer design for this wide input power supply using LM5022
i am designing the power supply for my solar inverter in which output of solar panel (750Vdc to 800Vdc) directly fed to the flyback power supply by using PMP7760 circuit.
i/p : 20v to 800V
o/p : 12V/ 1.5A & 5 V / 800mA
Fsw: 70kHz
efficiency :  75max. duty Cycle: 90% in CCM Mode
i wanted to get 2 secondary ouput in which Sec_1 : 12 Volt/1.5A & Sec_2: 5 Volt/800 mA.
Currently I've calculated the transformer turn, inductance and all with respect to 12 Volt/1.5 A.and for 5 volt/800mA  is remaining.
will anybody please verify it give me there valuable feedback on it.
i will follow the PMP7760 exact circuit for the same so that you can consider it respectively.
also suggest me that can i use multiple tapping for generate more supply voltage on secondary side ?
Regards,


texts:
I am using timer1 as my 100 ms interrupt clock timer. I don't use hardware WDT, I do this myself. Can I sleep (or idle) the processor and just wake up when the 100 ms clock interrupt goes off? If so, how do I do this?

I have read the section of the data sheet on power managed modes but am not sure if this will work (and actually save current usage). I am using the 100 ms clock for accurate timing and reporting to a server and am also concerned that sleep/wakeup cycle will add a few clock cycles to the interrupt timing. Additionally, I am using SPI for communications with an SiLABS radio transmitter and I get an interrupt when it gets a packet.


texts: For mains attached circuits: what do I need to protect against and how do I do it?

texts:
I don't have a lot of experience with mains voltage and designing protection circuits for them.  I'm not sure:

A) What do I need to protect against?  I know I don't need to worry about 10kV voltage transients on the mains line, but what about 300V spikes?  Mains voltage is 120Vrms nominal (in the US, for residential users), but what is the maximum that should be expected and planned for.

B) How do I protect against it?  For voltage transients I can use a TVS diode, or a MOV, but I don't know how to select one.  When do I use one over the other?  For overvoltage protection, is there an AC version of a crowbar?

What are good guidelines about what to protect against, and how to do it for mains circuits?

Note:

To try and head off the inevitable "close for too vague" votes, I want to mention that I'm only interested in:

"what are the common voltage issues that residential mains wiring will present to a circuit on it" and
"what are the basics of protecting against these issues"

I realize that there are probably many books written about circuit protection circuits, but I think that a very basic answer would be very appropriate here.


texts:
I'm trying to understand these earings from ebay.

Here is my attempt to reverse engineer the schematic:

If this is correct, I don't understand the function of the diode. If the diode is for demodulation how does going between ground and the filter work? This looks very different to a standard crystal radio:

I am also not sure why the resistor. Would it not reduce the efficiency?


texts: Methods of sliding PCB in straight line on drill press

texts:
I use a drill press like the first one in the linked answer at home for drilling my PCBs. If there was a way of sliding a PCB along a straight line left-to-right (or front-to-back) it would make drilling holes which are in a straight line much faster.

Do such slider systems exist without big costs? Or is there a design someone can share for making one? If there could be a system which also has ratchet-type stops every 0.1 inch, and which is equipped with a "latch" to switch between left-right and forward-back, that would really help.


texts: Hall element - Hall effect sensor identification needed (40 year old component)

texts: Attached is a pic of a Hall element/Hall effect sensor from a 40 year old motor with PLL speed stability in the motor controller.  The Hall sensor on top is the original.  The new one below it is one that replaced it in 2003.  I am looking for any info anyone might have such as part number, manufacturer, case type, etc. for both in the picture. The motor was made by TDK about 40 years ago.


texts: need help deciphering accel/gyro datasheet for i2c communication using python RPi

texts:
I have barely any knowledge in this area, the most I have done is used my RPi3 with pre-built python libraries for sensors such as ADS1115 so I didn't have to go through the process of understanding the nut and bolts of communicating with the device.

I am trying to use a accel/gyro (choice based on performance, needed something good). I am attempting to decipher how to communicate with the device using i2c on my RPi..it may as well be in another language.

I am hoping someone would be so kind as to give me some pointers / potentially help me develop my code to read the accel/gyro values.

For specifics: I want to read the accel at 16g, the gyro at 2000dps, both at 6664Hz..any filters or anything to improve the accuracy would also be good

datasheet

Based on tutorials/i2c python doc, I would imagine the code would go something like:

import smbus
i2c_ch = 1
i2c_address = ?x?? #whatever comes up when I detect the i2c address after connecting SDA/SCL wires
bus = smbus.SMBus(i2c_ch)
reg_accel = ? #need help
reg_gyro = ? #need help
reg_config = ? #need help
bus.write_i2c_block_data(i2c_address, reg_config, ?) #send commands to config to get the desired operating characteristics

accel = bus.read_i2c_block_data(i2c_address, reg_accel, ?) #read raw accel data
gyro = bus.read_i2c_block_data(i2c_address, reg_gyro, ?) #read raw gyro data

Please someone help me!! Not my area of expertise


texts:
Here is an inductor I found lying around, and I have no idea what the inductance is.

In order to estimate the inductance, I am using the equation \$L=\mu \dfrac{N^2 A}{l}\$.  Here are the relevant measurements:

Outer diameter: 0.5" (0.0127 m)

Inner diameter: 0.3" (0.00762 m)

Width (outer radius minus inner radius): 0.1" (0.00254 m)

Thickness (depth): 0.2" (0.00508 m)

Cross-Sectional Area: 12.9 mm\$^2\$

Length: \$l=\pi \left( 0.01016 \text{ m} \right) = 0.03192\$ m.

Number of Turns: About 30?

Therefore \$L = \mu \dfrac{30^2 \left( 0.0000129 \text{ m}^2 \right) }{0.03192 \text{ m}} = 0.3638 \mu_r \mu_0\ = 4.572 \times 10^{-7} \mu_r\$

The only constant I am missing is the relative permeability \$ \mu_r \$ , which I am not completely sure what value to use because I do not know what material is being used.  I would guess something ferrite-based, but the picture shows a very strange yellow-colored material (looks almost plastic?).


texts: What is the intuition behind the formula P = 2n in computing alternator stator poles?

texts: So from my reference for alternators and even in the Internet, it says that the number of poles P, produced in the rotating field is P = 2n where n is the number of stator slots/pole/phase. I've seen an explanation that says n also represents the number of pairs of poles and that is why you multiply 2 to get the actual number of stator poles. But I don't get it. How does the number of stator slots/pole/phase become the pairs of poles? Yeah I get the per phase part since computations of three phase machines are done per phase but how about the slots? How do you consider the slots/pole to become just the pair of poles? Is there like a visual understanding of how this works?


texts: Is it possible to record a range of radio frequencies in one go?

texts:
I am wondering if the following is theoretically possible:

The device can record say 1 hour of electromagnetic wave/radio signals today, and in the future recreate/replay that, so people can listen to 1 hour of historical radio show and freely change radio channels (like from FM100 to FM96), even to frequencies with only noise.

I don't want to record channels individually, but use one receiver to receive a range of frequencies.


texts: Is connecting a grounding rod to the positive side of a battery wrong?

texts: I have a 12 V battery being charged by a wind generator. The installation instructions show the grounding rod on the negative side. I have been having power issues with the batteries draining to quickly. When trying to troubleshoot the issue, I have found that the grounding rod is connected to the positive terminal. Could this be causing a problem?


texts: Why is this pair of electric brakes not working in series (as intended), but works in parallel?

texts:
My uncle has a 48V electric boom lift that sat for awhile and we're trying to get up and running again. We had a lot of stuff replaced and refurbished and we're almost there, but there's one last hurdle. There are two motors that drive the wheels. We sent these away to be refurbished. The brakes are part of these motors. The brakes are engaged by springs (I'm assuming). When you go to move the lift the brakes are energized and they release and as soon as you stop moving the springs once again stop the wheels. For whatever reason the wiring for the brakes is separate from the motors. There's two terminals with 16 AWG wire on each.

One of the two brakes won't release. I thought the two were separate, but I've discovered they're actually receiving 40v (the schematic says 48V) in series from the B+ wire (so going in). Power goes into the terminal on the right brake, a wire comes out the second terminal, into a loom and end up at one terminal at the second brake before coming out the second "return" wire. I've tried every configuration of hookup on these four terminals and the right brake is always the one that's working (I would have thought if I swapped it the left would be the only working one at some point, but that was not the case). If give the left brake 48V from battery power it works. I can get them both working by wiring them in parallel, but then they see 48V when I believe they should see 24v (if they're wired in series, right?). I don't know if that's going to damage them.

So that's where I am right now and I'm not sure how to proceed. Current flows through both, I'd expect them both to work. Maybe the resistance on the left one is higher? But I thought it'd still work, just maybe not as well. Maybe because it's only seeing 40v to begin with (as opposed to 48v) the voltage at the second one is too low to activate? This is pure speculation and it's probably flat out wrong.

There are two sets of four batteries. I believe each set it wired in parallel and then the two are wired in series for 48V input. My plan for if I can't figure this out would be to use two 48V relays to send 24V from one group of batteries to each brake and use the original 48V wire as the trigger.

Obviously my understanding of electricity is lackluster, but I know how to avoid getting zapped. If anyone can shed some light on what's going on I'd greatly appreciate it.

UPDATE: The schematic is on page 96 (3-20):

https://csapps.jlg.com/OnlineManuals/Manuals/JLG/JLG%20Boom%20Lifts/30_35_40_45E/Service_3120743_10-01-01_ANSI_English.pdf

UPDATE 2: Left brake (the problematic one) measures 18.6 ohms, the right one measures 18.9 ohms.

I also forgot to mention I've tried swapping around the terminals to see if maybe they were reinstalled incorrectly, but it didn't make a difference. I tried AB-CD, AB-DC, BA-CD, BA-DC. On a related note, is there polarity? there's no markings. Obviously the original connectors had a wire in mind for each terminal, but those have been dismantled and it moves the same way no matter how its hooked up.


texts: Can someone help me figure out why a simulated circuit I made wont work on Tinkercad?

texts:
I'm trying to build a circuit on Tinkercad, which I'm pretty sure is known as an astable multivibrator, but whenever I try to simulate it, either the says capacitors are inversely polarized, the LED's don't blink, which they are supposed to, or the circuit is unable to simulate.

Can someone help me figure out whether this circuit is wrong or if it's an issue with the simulator?

EDIT: I've added an image of the circuit without the capacitors so you can see whats under them.


texts: In a 3 phase rectifier, why is the output always the highest voltage?

texts:
Consider following circuit

At t=0 I can wrap my mind around the fact that Vout equals whatever value the highest phase has since the others are negative or zero. But after that only one of the three phases has a zero voltage value. Blue is rising while red is falling. Why isnt the output here blue + red? Since purple is negative, the diode should block any current from flowing but the others are positive.

How can I mathematically prove that Vout is always equal to whatever the highest value of the voltage is? Whenever I watch a video about it, they always say "highest voltage wins" with no explanation.

Maybe its too trivial but could someone help me anyways?


texts: Can open circuits have 0 potential difference?

texts: So I do know that the capacitor will be an open circuit at t < 0 (also at t > 0) since it is connected to a DC source. But since at t < 0, the switch is also open, meaning i will have another open circuit. What will happen to Vc? Will it be 0 volts? Or will it be the negative of the voltage across the 5 ohm resistor?


texts: Why is my amplifier circuit amplifying more than I expect?

texts:
My Question

Why is my amplifier circuit amplifying more than I expect, and what can I do to fix it?

What I want to accomplish

I want to amplify an input that, at most, is 1.5[V] to, at most, be 2[V].

What I have tried

I have the below circuit set up. When I measure the voltage of OUT against GND, I get values that are 7 times higher than the value IN.

I used the following formula:

$$V_o = V_i * (1 + \frac{R_2}{R_1})$$

Plugging in \$2\$ for \$V_o\$ and \$1.5\$ for \$V_i\$ evaluates to:

$$R_1 = 3R_2$$

I tried using 300[Ω] and 100[Ω] for \$R_1\$ and \$R_2\$ respectively, which yielded a different, but also undesirable, gain. I recall that it was a bit lower.

What I got

Measuring the voltage at IN and OUT against GND using a multimeter gives me about 0.5[V] for IN and 3.5[V] for OUT.

simulate this circuit – Schematic created using CircuitLab


texts: Determining whether an LED module should use a constant current or constant voltage driver

texts:
I recently read a seller's description of an LED module that said it should be driven by a constant voltage source but that a version intended for use with constant current power supplies was available upon request.

This got me wondering what differences in the design of an LED module (or array) would dictate whether it should use a constant current or constant voltage driver, and if I bought an LED module whose documentation did not specify what type of driver to use, what should I look for to determine what type of driver I should use?


texts:
If I want to model a simple register I would expect to have an internal 'reg' element to hold the value and I would connect this with a 'wire' output. The reg drives an internal output.

However, I've looked up several examples and most use an output of type 'reg'. I don't understand why you would do that. Aren't you storing the value in two places this way? Is there a difference in behavior?


texts: calculating circuit for NiCr at a set temp

texts:
This may be a primer for most, but this is the first time working with resistance wire and I'm unfamiliar with it's qualities

I want to create a circuit that will heat a length of wire to a set temp.

My question:  With a supply of 12vdc is it possible to calculate what resistance is needed to heat a 20ft length of wire to a temp of 90 degF?

Thanks for your time.


texts: I'm designing a product that charges USB devices from its 2 internal Li-Ion cells that are in series, how can I maintain the 5V out across the output? The batteries I am using are 2x 3.7V 2250mAh Batteries: datasheet. How can I account for the discharge of the cells and still get 5V on my output?


texts: Connecting TVS before or behind Ethernet transformer?

texts:
I looked at several designs and recomendations.

Why do TVS diodes sometimes connect before and behind transformer?

What are the pros and cons of connecting before or behind?


texts: Are low volume products RoHS exempt in the EU?

texts:
Are small companies that intend to sell less than 100 units in the EU market required to comply with RoHS?

This Forbes article seems to state that exemptions are possible till 2017?

  REACH and RoHS both started with companies shipping high volumes of product into the EU, giving exemptions to lower-volume companies, but eventually all companies conducting business in Europe will need to comply (in most cases by 2017)."

(source)


texts:
I am new to the world of oscillators, so take it easy on me.

I have been attempting to analyze the following common source ring oscillator:

However, I am having some trouble here. So based on my understanding: Each stage of the FETs provides 270 degrees of phase shift total. 180 from the inverting common source, and 90 from a pole due to the capacitor. In order to oscillate we need 360 degrees total. With only two stages of the CS FETs, the necessary phase shift for oscillation is there but would be stable at either rail. Can someone explain this? Why would it still be stable?

Now, at 3 stages, the circuit oscillates provided the gain of each stage is greater than or equal to 2. Can someone explain this as well? I do not understand why it is 2 instead of one, nor can I seem to understand the math behind this.

Thank you for your time and help.


texts: Would low frequency signal (10kHz) have reflection on conducting wires as well?

texts:
I am connecting a signal source of 10kHz sine wave with a driver which is a voltage follower made by an OpAmp. The follower has one input and two identical outputs. One output is connected with a device(LOAD) to drive the device(LOAD); the other is connected with an oscilloscope for measuring.

The OpAmp used is ADA4610

simulate this circuit – Schematic created using CircuitLab

The first picture:  Voltage follower is not connected with the device(LOAD) and its output signal is pure.

The second picture: Voltage follower is connected with the device(LOAD). It can be observed that there are harmonic noises showing up.

Updated observation:

When I change the load to 1kOhm resistor, the output of OpAmp does not show any distortion.
When actual load is used (around 50Ohm), distortion shows up.
My suspect is that large output current could lead to distortion. However, I did not find related information in the datasheet.

My question is:

Are the harmonics caused by reflection?
Would very low frequency signals have reflection as well?
How to export pure sine waves without distortion in this case?


texts: Selecting a power supply for a device with 625A 1ms peak current

texts:
I have a question regarding a power supply setup I was presented with. I don't know how it should work.

I have a device with these electrical characteristics:

VDC = 48 V ± 1%
Continues DC current <= 425 A
Peak current 628 A for 1ms

I have been offered a solution with 4 power supplies, "tx500048" (see the tx500048 data sheet).

I don't really understand how 4 power supplies could support the peak current of the device. What parameters determine that the power supplies are capable of such currents?


texts: Building a variable frequency magnetic pulser

texts:
I'm starting a little project that will run a square wave through a copper coil to make magnetic pulses. I imagine the project would be quite straight forward if I were a little more experienced with making electronics.

The exact specifications of the coil and magnetic pulses are essentially not that important. I don't want to go into too many details about why, but suffice it to say the device should "work", i.e. it should generate magnetic pulses that are easily detectable with, say, a steel washer. The frequency range I'm targeting is about 50-120Hz which I'll generate with the PWM module in the PIC.

Here is what I have so far:

I'll use a 2155 type 1A xformer, and I'll be using the 6.3 and 15V taps.

I'll use the 6.3V to drive a 5V VR to power a PIC16F877A (I think those are the ones I alread have lying around). The PIC will use a potentiometer set up as a voltage divider on an analog pin to control the frequency between a given range (I've never done any analog or ADC stuff before). The PIC will also drive a small 8-segment display to show the frequency, and I'll use a crystal oscillator to give the PIC a more stable clock (I've had issues with timing in PICs before). The square wave will be between 0 and 5V.

For the coil, I basically want as much as possible, so I'll use the 15V to drive a 12V VR. I'll use the square wave output of the PIC (positive only) as a 5V input to an OpAmp. 5V -> 12V is a gain of 2.4, so I'll use a 240K and 100K resistor for the feedback of the OpAmp (I've also never used an OpAmp before either). I'll also use a schotky diode, reversed, to prevent the collapsing field to burn anything out.

I hope that all makes sense and sounds more-or-less reasonable. I know I don't need to use a PIC, but I've used them before and they're easy to program use, and I'm a lot less confident doing analog frequency adjustment with, say, a 555 (also never used these before either, lol), and using an 8-segment driver. I just want something that works and that's within my capabilities.

Here are some parts I have so far: (I'll be using 240V mains)

2155 type 1A transformer with 6.3, 7.5, 8.5, 9.5, 12.6, and 15V taps.
7805T 5V regulator
7812T 12V regulator
BR104 10A 400V rectifier x2 (one for the 6.3 and one for the 15V)
8Mhz crystal for the PIC
1K linear VCU pot
SB560 schottky diode 60V 5A
0.5mm 500g enamelled copper wire (approx 180m length)

I'll also have some electrolytic caps before and ceramic caps after the rectifiers in the power supply sections. I've got a bunch of these lying around in my drawer already.

I have a few questions:

If I've said anything absurd so far, please point it out.
Let me know if any of these components seem wildly overkill, e.g. the schottky diode or rectifier, for example.
I'm not sure if I even need a voltage regulator for the high(er) voltage section. If I can avoid it and just use bigger caps, I can drive the coil at 15V which would be "better".
I have no idea what OpAmp to get. I'm looking at the LM301AN which seems reasonable.
I'll wrap the coil reasonably tight. It's ~180m and I aim to have it in a small package around 4x4x2cm approx. I don't know how many turns this will be, but probably "a lot". I can only assume that driving a 0.5mm copper coil at 15V @ 120hz should be fine? (i.e. won't burn out)

Sorry for being so vague. If you comment with a question I can actually answer, I'll do so.

Thanks for your help.

If I get some things clarified here, I'll order the parts online and post a circuit diagram in the next few days, and then we can all laugh together at how bad it is.


texts: How to Calculate the time of Charging and Discharging of battery?

texts: How do I calculate the approximated time for the Charging and Discharging of the battery? Is there any equation available for the purpose? If yes, then please provide me.


texts: The second component on the board says Diode CKT. What is that? Doesn't the left handed side of that component look like a resistor?


texts: Swap between two colors without an additional light?

texts:
A Quick Note

I'm not sure of a more accurate name for this question. If you can think of a better name, feel free to edit and change the name. Also, I'm not the greatest with technical terminology so please forgive me if I'm not explaining something correctly. If you need clarification please ask and I will update the post.

Legend

T = Top
B = Bottom
L = Left
R = Right/Rear

Overview

I currently have two other posts (here and here) related to this one, both solving different issues. This is a new issue, and the idea seems rather complex to me. This is an in depth lighting kit for my car. It involves a multi-function light, under glow, interior lighting, engine bay lighting (via the hood), and grill lighting.

I have eight LED strips that each have the following four wires:

Positive
Negative

Red Channel
Green Channel
Blue Channel

Four of the LED strips (engine bay and grill) are wired together to come on as a single entity displaying purple so the hookup is:

simulate this circuit – Schematic created using CircuitLab

The other four strips are located under the car along each edge. Currently, three of those are wired together to display purple with the fourth connected to the brake light displaying red:

This is where I begin having a hard time describing things; so please bear with me. The idea is to have all eight lights display purple when the switch is in the on position; and the lights under the car display as follows when the switch is in the off position.

Bumper (F): White (Hooked to head-lights)
Bumper (R): Red (Hooked to brake light)
Side Panel (L/R): Amber/Orange (Hooked to turn signals)

To add to the complexity, I would also like to add in my relays (see this post for details on the relays) to have the side panel lights blink between amber/orange and off, with the turn signals whether the switch is on or off; and if the switch is on, it changes the color to amber/orange and blinks with the turn signals (again in the on/off fashion instead of blinking between amber/orange and purple); then when the turn signal stops completely it turns back to purple).

My Questions

How can I achieve most (if not all) of the above?

I believe I may be able to use jumper wires to route the signal but I'm afraid this will cause white lights when the switch is in the on position.

Notes

I prefer all of this to go through my single switch if possible.
My car is a 2016 Mitsubishi Lancer.


texts: Switching over from Xtal to variable oscillator with minimal hardware?

texts:
I have an old circuit with an 8bit Z80 CPU. The oscillator circuit is a standard Xtal with two load caps. I'm interested in slowing down the operation of the circuit with a tune-able oscillator which I did and it works as expected (more or less).

Question is - I'm controlling the variable oscillator using a potentiometer and switch-over is done using a toggle switch which lifts one leg of the Xtal and connects the variable oscillator's output instead. I would like to integrate everything to a single potentiometer due to lack of space for another button.

The digital approach would evolve a reed relay, digital pot, mcu, encoder and I am trying to make something minimal. If anyone has suggestions for a better circuit please let me know.


texts: Interfacing incompletely documented logic signal where resistor affects output voltage level

texts:
So I've got this marginally documented 12V logic signal from something I have to regard as a black box that I'd like to interface to a pi or arduino (i.e. c 3V).

I have 3 lines - 0V, +12V and signal (in the 100mA ballpark).  The signal line is either 0 or 12V as per its logic state.  All documented to this point.  I can measure and confirm the behaviour with a meter.

That's all fine, but if I take the 0V and signal lines for the input into another circuit either via a pair of resistors in a voltage divider or a single resistor protecting the input side of an optocoupler, the voltage appears to drop away so low that its useless.

What might be going on here?  Can anyone suggest a way forward, please?  Would a mosfet or similar in front of the optocoupler help?  I know nothing more about the source, but also don't want to damage it.


texts: DC/DC converter 12V > 5V providing 400 Watts?

texts:
I'm not acquainted with electronics, so please be patient with me ...

I want to drive a large LED strip from a car battery.

Unfortunately, the LED strip requires a maximum of 400 Watts @ 5V.

Now I need some device to convert the car battery's 12 V to 5 V while providing a maximum of 400 Watts.

Can someone please point me to a device that allows me to fulfill this requirement?

Aside question: How long will a fully loaded car battery be able to provide the LED strip with power and still be able to start the car?

EDIT: @PeterBennett's and @DaveTweed's answer go into the right direction here.

Thank you for your valuable answers so far!

@DaveTweed: Yes, you are right. I'm using two 5m strips, each requiring a maximum of 200 Watts (no joke, manufacturer's data). Yet I do only have a single 86A marine battery. The strips are laid out in a star pattern and joined at the battery. Given that, what would the circuit/wiring be?

For testing purposes at home I want to use a power adapter, yielding 12 V DC from 220 V AC. At this time it's hard for me to find a matching power adaptor yielding 400 Watts. So I am worrying whether a battery will withstand such large strain for long.

I should add that what I'm looking for is supposed to be outdoor equipment, used below the engine bonnet. Size and cost should be minimal (the transformation unit should not be larger than a few centimeters).


texts: I would like to use an arduino device to control a 12V 17W water pump and filter, what type of part to I need that can switch the 12V power on and off?


texts: Long three cables connection: can I use an audio stereo cable?

texts:
I'm building small project where I need to connect a few sonar sensors to an Arduino.
Each of these sensors are connected via 3 wires to the arduino. My problems is that I need to place these sensors quite far from the main box, and since they need to moved easily I would like to use a pre-made 3 wires cable with plug and sockets.

I'm was wondering if I could use a standard stereo audio cable for that, and then on the sensor's side solder the wires from the 3 sonars's pins to an audio socket, and the same on the arduino's side, and then connect the two with a standard audio cable. They should have 3 wires, right? Ground, left and right signal. I need to transfer ground, 5V and analog signal.

The sensor I'm using is a Maxbotix MB1000 LV-MaxSonar-EZ0

If audio cable is not a good solution, what should I use?

Thank you and sorry if this might be a stupid question, but I'm just a programmer starting to explore the microcontrollers' world, and quite newbie for all things electrical.

Simone


texts:
I am trying to understand a contactor control circuit that I took apart from a broken GIGAVAC GX14BAB.

Here is a list of parts that I think are the closest representation of what is on the PCB:

C1:

Capacitance unknown

R1:

SMD 104
100 kOhm

R2:

SMD 512
5.1 kOhm

D1:

SMD WX104
Device Type bi-directional TVS diode SMAJ10A

D2 and D4:

SMD YR103
Device Type bi-directional TVS diode SMAJ40A

D3:

SMD RZ102
Device Type uni-directional TVS diode SMAJ100A

Q1:

N-channel MOSFET FQP16N25C

The coils were missing from the contactor, so I'm not sure what P1, P2, and P3 are connected to, but my best guess is that P1 connectors to the primary coil, P2 is ground, and P3 connects to the secondary coil.  From the data sheet:

  Contactor has two coils. Both are used for pick-up, and
  then in approximately 75 milliseconds, one coil is electronically
  removed from the coil drive circuit.

Electrical engineering is not my strongest suit, my best guess at this circuit is that C1, R1, and R2 governs how fast the secondary coil gets shut down. R1 and R2 is a voltage divider for the Q1 MOSFET.  When the voltage is at a suitable level after 75ms, the drain and source will connect and ground the secondary coil.  Am I correct with this guess?

Also, can I calculate the capacitance of C1 by using the 75ms as the time constant:

75ms = R * C = 100k * 0.75u

to estimate the value as 0.75 uF?

Finally, are the purposes of the diodes mainly for circuit protection and voltage clamping?  Here's an image of the PCB.


texts:
(It's really a continuation of a previous question but it is old so I decided to ask a new one with more detail)

I have a colpitts oscillator designed for 27 MHz going into a short monopole antenna of 1/20 of the wavelength, or 55 cm. The radiation resistance is 2 Ohms, with capacitance of 5 pF (calculated with this calculator). This means that to bring it to the resonance I am to use 6.9 uH inductor, according to the same calculator. My colpitts oscillator has output impedance of 300 ohms, which I matched to 50 ohm load. If I understand correctly now I have to make my 2 ohm real resistance load look like it is 50 ohm load. So here's what I came up with:

simulate this circuit – Schematic created using CircuitLab

I am not sure if this is really done this way.  Is the impedance of the antenna (after I include tuning inductor of 6.9uH) really 2 ohm real resistance, or is it calculated in some other way? The other question is if matching both the source and the load to 50 ohms is done this way, or the calculation for when both of them should be matched is different (I am not sure if the L and C elements from different L networks would influence each other and the outcome?


texts: Interview question, testing a sorting network

texts:
Here is a question that I stumbled upon:

http://asicdigitaldesign.wordpress.com/2007/06/08/puzzle-4-the-min-max-question/

MinMax2 is a component with 2 inputs, A and B, and 2 outputs, Max and Min. You guessed it, you connect 2 numbers at the inputs and the component drives the Max output with the bigger of the two and the Min output with the smaller of the two.

Your job is to design a component MinMax4, with 4 inputs and 4 outputs, which sorts the 4 numbers using only MinMax2 components. Try to use as few MinMax2 components as possible.

Here is the solution:
http://asicdigitaldesign.wordpress.com/2007/06/24/puzzle-4-solution/

I succeeded in solving it, but what I didn't successfully answer is: how many different input sequences are needed to verify the logical behavior of MinMax4?

The obvious answer is $4!$, but as I understand there is a more minimal solution.


texts: Do I still need to ground this Generator?

texts:
We have a 3-Phase  AC Electricity Generator (19KW) which comes with tires for ease of transportation, even though it requires a crane for lifting.

We have it installed in such a way that its main body is sitting on concrete blocks which are directly attached to the soil/earth below them without any insulation in between and the rubber tires are free.

Do we still need to connect the Ground terminal on the Generator to the earth below it? It would appear that since the terminal is connected to the body of the Generator and the Body has a direct connection to the ground by virtue of it resting on the ground itself there would not be any need for that but it was advised that the Cement blocks in between break that connection.

Edit:

We did act upon the Electrician's advice and he did ground it like he said it was supposed to. This question is just for learning how important that was.

Illustration

Image Source: www.deepelectric.com


texts:
I am trying to simulate a Bubba Ocsillator on MATLAB, Simulink . The problem is that i am not able to generate the sinusoidal from the circuit.

This below is my circuit :

And this below is my result(Simulated for 10sec) :

Zoomed result(Simulated for 10sec) :

Error Received :

Where did i go wrong? How to achieve a pure sinusoidal waveform from this bubba oscillator...


texts: I-type register format maximum size of a constant

texts: The above picture is an I-type format register. I am confused as to why the largest constant possible is $$2^{15}$$ Should the largest possible constant be $$2^{16} -1$$


texts: Arduino controlled stepper motor alternate that can be powered with AA batteries?

texts:
I would like to make an automatic fish feeder using a low power microcontroller (probably an Arduino Mini Pro, unless there are better suggestions). Something like this. It is basically a drill bit rotated by a stepper motor. I don't have access to an electrical outlet so would like to design this for battery power. It looks like the motor consumes a lot of energy and will likely drain 2 AA batteries in a few days, if not sooner. The stepper motor seems the culprit. Any suggestions on alternate motor or something else?
An AA battery gives me a juice of about 400-600 mAh per cell. So maybe I can double that with more batteries. But still, 800-1200mAh seems insufficient to run this setup for more than a few days. and yes, even if tried high capacity (2500mAh+) batteries, the problem is still with the large energy draw by the motor.
Per my calculations (based on datasheets/info I found online), the stepper motor draws about 170-200 mAh over 1 day, even though it runs for just 5 minutes total. That is huge.
Calculations:
The microcontroller will wake up and run the stepper for about 5 minutes per day. As a buffer, I've taken that as 12 minutes or 0.2 Hours.
Total power draw per day (mAh) = MCU power + Stepper Motor
MCU power consumed = Active consumption + Idle consumption
= (4.75mA x 0.2 Hrs) + (0.3mA x 23.8 hrs )
= 8mAh/day
Thus I'm not too worried about MCU power consumption.
Stepper motor power consumed =  Active consumption + Idle consumption
= (240 mA x 0.2Hrs) + (5 mA x 23.8)
= 167 mAh/day
Note: the idle current draw for the stepper motor - I can't find any data on actual value. So I've assumed a best case draw of about 5mA when the driver  is put into sleep mode (A4988 stepper motor driver)


texts: Can I increase the signal strength by combining two radio transmitters with an antenna? İt has only one oscillator and two transmitter circuit. Same signal. I connect antenna coil together in one antenna .


texts: Making a bench power supply to test car & bike starter motors at no load?

texts:
Does anyone have any information on how much current does a car starter motor draw at no load? It's from a BMW E46 .The motor specs:

Power max: 1.4kW
Voltage: 12VDC
Armature resistance: 0.61 ohm
Brand: Bosch
Model No.: 1740374

A little history into why I'm trying to find this information.

I'm trying to make a DIY bench power supply to test car and bike motors after rebuilding it. Usually the smaller motors are pretty easy to test as long as their current draw is under 17 Amps.So, a modified ATX supply and Lead acid battery does the job. But testing starter motors is not that easy due to their larger current requirements as the ATX supply can never handle them even at no load. Until recently I used to use a spare car battery to test outside without no loads. But since the climate I'm living is quite hot during summer (like 113F) the battery goes out pretty quickly in a year and half. So, this power supply would be a great replacement for the battery.

So, for this project I used a transformer from an old center tapped 700VA Tripplite UPS. The output wire of the transformer is a 10AWG which means it should be under 35 Amps I guess. So, I connected the transformer via a KBPC3510 bridge rectifier. It can handle 35A at 1000V. So connecting the transformer leads to the rectifier and taking the output across the rectifier + and the center tap through a 15000uF 25V cap I was able to obtain 13.21 VDC. So, I tried connecting the starter motor mentioned above without the solenoid and no load to the setup and after 3 seconds the bridge rectifier gave its magic smoke and went out. The transformer wire was also little warm. I have another transformer from a 2000VA UPS and its massive. I think it can handle 55Amps but again currently I have only a KBPC5010 rectifier and it can take only 50 Amps almost. Currently I can only test motorbike starters almost without any worries.