texts: Does input offset voltage for amplifiers remain almost same

texts: In Op-amp datasheets, input offset voltages are specified. Does this input offset voltage remain same (no significant difference) for each IC or can it change significantly each time I use the device? e.g. if the offset is defined to be ±1mV in datasheet and I measure it +0.5mV for one IC. Can I expect it to remain +0.5mV (±some uV) for that particular IC within its lifetime or can it have any value between +1mV to -1mV every time I switch on the device?


texts:
In the following lecture by Prof. Anant Agarwal  at 36:00, he intuitively proves Thevenin's Theorem using the following circuit

simulate this circuit – Schematic created using CircuitLab

If we consider the voltage across, points a & b, we will be able to guess the form of the answer using superposition theorem as the sum of Voltage sources and current sources multiplied by a corresponding factor, So,
$$e= \alpha _1 V_1 + \alpha _2 V_2 + ... + \beta_1 I_1 + \beta_2 I_2 +... + \mathbf i\, \mathbf R_{th} \\ e= \sum \alpha_n V_n + \sum \beta_n I_n + \mathbf i\,\mathbf R_{th}$$

The primary terms \$\sum \alpha_n V_n + \sum \beta_n I_n\$ ultimately form an voltage, so we can write them as \$V_{th}\$ and so the total circuit can be reduced to an Voltage source( \$V_{th}\$) and a Resistor(\$R_{th}\$) in series with current source.

simulate this circuit

My Question

If the current source in the circuit was replaced by a resistor,

simulate this circuit

then there would be no \$\mathbf i \mathbf R_{th}\$ term in the equation for \$e\$ . So we will just be able to reduce the circuit into an voltage source \$V_{th}\$ in series with the current source.

Absurd Thevenin's equivalent \$\downarrow\$

simulate this circuit

So how will you keep up the argument when there is no current source?

I know I'm obviously wrong at two places

I'm wrong when I say, that the source \$V_{th}\$ and \$R_{th}\$ are in series with the current source.
That new Thevenin's equivalent is absurd .

But I don't know why?
In short, prove Thevenin's circuit intuitively with superposition theorem

In almost, every proof I visited, they introduce a current source between the nodes(under study). But in the actual circuit there may not be a current source, but we can use Thevenin's theorem to find the current across any Resistor or generally two nodes. So, why do they introduce a test current source to prove the theorem?

PS: How to decrease the size of the circuit?


texts: Voltage readings in Transistor used as switch

texts:
I have been trying to understand the operation of transistors for a while now. Today I thought to put what I learnt into test. Cutoff operation of a NPN transistor. As I read in one of the transistor tutorials in Sparkfun, in order to push transistor to Cut off state Vb < Vc and Vb < Ve. So here goes my test circuit to understand the cut off operation better and the voltage readings I got when measured using a Multimeter.

simulate this circuit – Schematic created using CircuitLab

In the above I got few questions

Why there is negative voltage of -0.34v exhibited across LED? ( its green LED rated 2v / 20mA and I measured with Positive probe in Anode and Negative in Cathode )
I have read there exist leakage current even when the transistor is in Cut off state, what exactly is the source of this leakage current? Does it originate from Collector and flows to emitter?
If there is a leakage current why there is no voltage drop across the resistor R2?
Are there any other current flow in this circuit except for the leakage current?

Kindly help me in understanding this. Any leads or links where I can find answers will be highly appreciated.


texts: How to determine preload resistance needed for an ATX power supply to power up?

texts:
I want to make a benchtop power supply from a 20 pin ATX power supply from the last millennium.  I have seen posts, but still need help.
So far, I have shorted PWR_ON to ground and have connected an LED to PWR_OK. I connected a 12V fan to a 5 pin peripheral connection.  When I connect a CD drive to to 5V, the LED lights up and the fan spins.  I measured 5.05V between the CD's supply and ground and 0.55A across it.  I took this to mean that I should use a 9 - 10 ohm power resistor (2.7775 watt?!) for a preload.
After removing the CD drive, I connected a 50 ohm 25 watt potentiometer to 5V. PWR_OK comes up (repeatably) only when the resistance drops to below 1.2 ohm.  I measure 4.5V across the potentiometer and 3.2A going through it (it gets on hot side of warm). When I try to slightly change the resistance up or down the PWR_OK LED goes out.
What accounts for the apparent difference in behavior between attaching the CD drive and this external resistance?  Is this getting distorted by looking at the low end of the potentiometer and my meter?
Despite my abuse, the ATX psu seems to work.  Would I have better luck building a benchtop supply using a more recent ATX?


texts: Polarities of high current bypass, and short circuit protection, transistors on LM7912 - NPN or PNP?

texts:
With reference to Olin's answer to Connecting Voltage Regulators 7812 in Parallel for High Current, and likewise the examples from the Fairchild, TI and ST datasheets, a PNP transistor is used (i.e. TIP42, BD536, 2N6133, BD536, respectively) to provide the higher current, when using an LM7812.

Looking at the Fairchild example:

I would assume that (in a dual rail supply), for the negative rail, using an LM7912, a complementary NPN transistor equivalent would be required (i.e. TIP41, BD535, 2N6130), instead of the PNP for the 7812. Is that correct?

Likewise, for the short circuit protection schematic using the LM7812, an additional PNP transistor is used (i.e. 2N6124 (for the TI and ST datasheet examples), and TIP42 (for the Fairchild example)). Taking the Fairchild example again:

So, for the LM7912, is an NPN transistor equivalent used for the short circuit protection transistor (i.e. 2N6121 and TIP41)?

In addition, I presume that the orientation of the transistors is the same - that is to say, the Collectors and the Emitters of the NPN equivalents remain connected the same - and they are not reversed? To be exact, the Collectors of the two NPN transistors go to the input and output, respectively, of the LM7812?

I only ask as neither the NS nor the TI LM7912 datasheets show a high current (with or without short circuit protection) schematic, hence my doubt.

Please note I'm not looking for component recommendation, but rather I would like to confirm that I have got the BJT polarity configurations (PNP versus NPN) correct. I have merely included the component identifiers for completion.


texts:
I am now designing an FM demodulator circuit. And the first step is turning FM into AM, so I could use envelope detector afterwards. Modulator circuit is designed using Colpitts topology. So frequency varies from 2,336 MHz to 2,411 MHz (according to my calculations).
The resonance frequency of the following circuit with C5=10pF and L2=435uH is about 2,413MHz. So the amplitude of the output should change depending on the frequency of modulator circuit.
Unfortunately I can't "observe" it neither at my "voltage-time" plot nor at FFT. Maybe I am doing smth. wrong or some basic considerations are not proper. Thank you in advance!


texts:
So here's my circuit for powering 4 LEDs with my arduino. Right now it seems to be working perfectly. I send HIGH to any of the pins and it lights the LED. I was wondering if I take in account the voltage drop, if any, across the MOSFET when calculating the current limiting resistor value. Right now I just calculate \$\frac{V_S-V_{LED}}{I_{LED}}\$.

Also, do I need any pull up resistor or anything to increase its efficiency or reliability?

I'm using a BS170 N MOSFET

Thanks!


texts:
I am experimenting with surface mount components for a project.  All the other components seem to be OK and I have deduced that it is the surface mount bead core that is the problem.  When I remove the surface mount bead core and replace it with the through hole, things work again.  When I swap it out again for the surface mount, things don't work.  I tried it many times so it seems like this component is the problem.

Previously, I was using this component:

and I replaced it with this component:

When I measure the ohms of the through hole component, I at first get around 50 ohms then it decreases to about 30 ohms.  Which is about what I would expect.

However, when I measure the resistance of the surface mount component I basically get that it has infinite resistance.  For this component, I am putting the probes on the two silver parts of the component.  I did this for 4 different SMD so I don't think it is a faulty device.

Are these two components not "interchangeable"?  Why is the resistance of the SMD infinite?


texts: Simple wire continuity tester, but also needs to check shorts

texts:
I am trying to create a simple cable tester, that needs to check continuity of a multiwire cable.
My first thought was to connect all wires at one end to a positive voltage, and connect LEDs at the other end.
If there are 5 wires inside the cable, this would test continuity of all 5 wires at once. 5V to all wires at one end, LEDs and resistors at the other end. If all 5 wires are good, 5 LEDs will light up.
This would work fine - but if any wire was shorted to another wire, it would give a false positve.
Any thoughts about how to create a simple continuity tester that could test multiple wires at one time, but also not give false positives if any of the wires were shorted to each other?


texts: I am designing a PCB board, and it has lots of components on it. It has like 8 MOSFETs, diodes, fuses, current sensors, a STM32 and other components, and with an exception to a few (like mosfets and diodes) the datasheets don't include thermal resistance. To get to the point - I am getting concerned about if my PCB will get too hot, despite having more than appropriate trace specs (3oz copper rated for <20 C rise ). Is there a way to have a general heat sink that just sits on the board? Or am I better off selecting one components and attaching a heat sink to it? or sitting a heat sink on like a copper pad not connected to a component? And if I select a component, how do I decide which one?


texts: Mechanically strong way to connect wires T-junction way

texts:
I have an existing LED light curtain but I would like to redo it in more robust way. It has a main cable with 6 branches hanging down like this:

Battery&DC-DC___________________
                |  |  |  |  |  |
                o  o  o  o  o  o
                o  o  o  o  o  o
                o  o  o  o  o  o
                o  o  o  o  o  o

At the moment the T-branches are just twisted and soldered around the main but soldering tends to break because branches are flexing a lot.

Are there some recommended T-connectors available? It can be permanent or detachable.

Edit: The wire gauge is not fixed, I think at the moment it uses 0.75 mm²


texts:
I'm currently working on a project that makes a device "IoT-ready".
So im looking for a switch, which got two inputs and two outputs.

When I close the circuit on the one side, it should close it on the other side, too.

Is there something available which does what im looking for?


texts:
The original circuit is:

To make the model for small signals, the capacitors behave as short circuits.

Is the model for small signals right?


texts: How to supply limited power to a hungry BMS for li-ion charging

texts:
I am building a li-ion battery pack in a 7-series (3.6V) cell configuration. That gives 25.2V nominal voltage and 29.4V charging voltage.

I have a BMS with balancing charging capabilities. This BMS has high current limits, 45A for discharge and 8A for charge.
I also have a buck converter what for lowering the voltage from my 42V/2A DC power supply to the 29.4V required for charging.

And here cometh my problem on account of my lack of abilities to understand anything more complicated than a toothpick: since the BMS can chooch at up to 8A when charging, what's keeping it from overloading my 84W power supply or the buck converter betwixt her and said BMS?
What I want to achieve is keep the charging current at around 2A max, as opposed to the 8A max of the BMS. This would ensure that no more current is drawn from the PSU than her rated 2A.
Am I right in suspecting that my lame buck converter is not up to the task as I need a CC/CV converter and not a CV only? That is, a converter that allows me to set the current as well and not only the voltage?
Or, if my power supply says she's regulated and protected against over-current, does that help me here? Can I count on the BMS not being able to pull too much current THROUGH the buck converter FROM the supply because of her being regulated? Would that limit the whole system to not more than 84W? Or will the supply simply cut off electrocity when overloaded, so that no angry pixies come out of it at all, aborting my charging?
The supply is made for charging my kickscooter with li-ion batteries inside. Is that kikkskooter limiting the charging current within its brain box, or is it relying on the supply as described above?
Any response is appreciated. Sorry if the answers can be found somewhere around here, I couldn't find anything that would help me.


texts: Really faint hissing sound from my new 12v AC to DC Power Supply

texts:
Just bought this Power supply today and once plugged in to AC, I hear a really faint hissing sound coming from the unit. Is this normal? Or should I have this replaced?

Click here to see the video


texts: Passive voltage drop from 6V DC to 5V DC for 3W circuit

texts:
I plan to put an Arduino onboard of my hub-generator powered bicycle circuitry.

Currently, I have a circuit consisting of:

6V/3W AC hub generator (variable frequency and power);
Rectifier bridge;
6v/5W Zener regulator;
6800 uF electrolytic capacitor;

With this circuit, I can safely drive anything needing 6V up to the 3W limit.

Now for the Arduino, I'd want to provide 5V at Vin, and for that I would like something like this:

link Vin to GND with a 5V Zener (and possibly a generous capacitor);
insert some voltage drop between 6V output and Vin;
drive external loads with transistors (BC 548 have served me well for up to 100mA per transistor);
(of course) ground everything together;

But I am not sure if voltage-dropping is a good practice, or if I would find a suitable diode with the desired drop.

If everything I proposed is b*shit, I would like some guidance, preferably involving only simple components. Absolute efficiency is not a must, and I can leave with some lost current through the regulators (zeners for example).

Update: I plan to add a battery to this circuit, but it should be able to run only from generator by design, anyway.

More update: I have read something about "Low Drop Out" regulators (LDO). Can I build one myself? Is there any off-the-shelf, widely available component for that? Can I use some of these together with the Zener and the capacitor, or it wouldn't make sense then?

Yet another update: a coworker suggested the TPS-76650 (Texas). Are there "non-proprietary" components with similar characteristics?


texts:
I'm looking at some components of an inkjet

Does anyone know why it uses an optical encoder on the scroller shaft? Doesn't the shaft rotate by a step whenever the print head reaches the head? Why is there a need for the printer to keep track of the number of mechanical rotations?


texts: Is the connector marked CR4s detachable or soldered?

texts:
First, pardon for the absolute noob level of this question.

I want to replace a faulty tactile key on board, shown on the image below. To get it away from the machine I need to detach a connector with 4 wires marked as CR4s. Is this something that can be pulled off or does it need to be soldered? I do not want to apply force and break it.

Next I need to find a replacement for this 6x6 mm micro switch/button but that is a separate question.

Edit: more pictures

Edit: after slightly brutal desoldering (did not have pump at hand) it indeed looks like the connections were crimped


texts: How can I fix delay between Instruction and Program Counter?

texts:
I am designing the MIPS processor, this includes Data Memory and Instruction memory for testing.
I had a problem with IM synthesis covered in this question (How to make a synthesizable Instruction Memory in SystemVerilog?) and after rewriting it as adviced (ff with a case statement) another problem occured.
The problem:
Insruction in CPU has one cycle delay from the Program Counter. Thus, when branch instruction (number i) come, the Program Counter is already (i+1) and then come instr (i+1) and PC is PC_branch. How can I fix it? Delay is caused by this ff in IM.
Code and waveforms are below.
The code:
always_ff @(posedge clk) begin
case (addr)
        32'd0 : rom_ff <= 32'h2408000F; // a = F
        32'd1 : rom_ff <= 32'h240A0000; // res = 0

        32'd2 : rom_ff <= 32'h01485021; // (*) res = res + a
        32'd3 : rom_ff <= 32'h2508FFFF; // a = a - 1

        32'd4 : rom_ff <= 32'h1500FFFD; // if (a != 0) goto (*)
        32'd5 : rom_ff <= 32'hAC0A0ADD;
        default : rom_ff <= 32'h0;
    endcase
end

The waveform of CPU signals:


texts:
I'm currently designing a PCB and I need to use hatched polygons in order to get my PCB produced (my manufacturer accepts only hatched polygons). The problem is the following: in only one of the layers I'm getting those weird squared holes in the hatched polygons

for the others layers the settings of the hatched polygons are the same, and they look like normal solid copper regions (see the red polygons underneath the wrong one).
The settings I'm using are the following:

and if I set "solid(copper region)" this is the result (which is the same that I expect also with the hatched one):

I've checked the polygons rules and everything is as it should, there is no rule concerning only this specific layer. I've also tried to delete and redo the polygon, close and open Altium 17 , and open the project on another computer with a newer version of the software. Have you ever had such problem? Thank you in advance

EDIT:

After playing a bit, since the problem was appearing only in one layer, I tried to copy all the traces and transfer them in a new layer. The problem is relatively disappeared, I'm not getting those holes anymore but now the problem is that close to some pads, there are some small traces not connected to the polygon, as you can see here :

the settings are the same as before, and this is the overall result:

this is better than before  but stil it is not ideal. I also tried to copy the files in a new project, but the result is still the same.


texts:
Simplfy the following circuit:

My try:

The easy way to do this is seeing no current passes through across the branch (2,5,8) and hence we can remove it. However, I was trying to combine parallel branches and running into trouble.
Notice that 1 is same potential at 7 and 2 is same potential as 8, I got that I can combine resistor at between 1-2 and 7-8 but I can't seem to figure out the conenctivity of resulting circuit after I combine both.
However, if I combine the lower half and upper half at same time then it's easy for me to visualize (aka folding a circuit),  hence I only want to understand how the circuit looks when folding section wise.


texts: Transformerless inverter from 20*12V batteries

texts:
Is it possible to convert 240VDC from 20*12V batteries to 180VAC-240VAC pure Sine Wave?
i have an idea using H-Bridge mosfet drivers....But i have seen on web that 350Vdc is must to convert it to 240VDC...


texts: Exporting LTspice waveforms to txt or csv

texts: I have used the file _>export facility to generate txt /csv file for subsequent analysis in Matlab. The problem is that the exported waveform time steps are not uniform and the waveform is quantized. Is there a way to avoid this happening to get uniform time steps? As it is I can't use the exported txt waveform.


texts: Determining values of voltage divider resistors which interface an OpAmp and an input impedance?

texts:
Above schematics is just a representation of an OpAmp circuit coupled to a measuring device. Imagine we know the values of the following parameters: Vcc, Vout, R_feedback and R_measuring device. R_measuring_device can be the input impedance of a scope or a DAQ hardware. V_out is the output voltage of the circuit which is coupled to a voltage divider in the schematics.

If one wants to couple V_out to the measuring device, one may need to scale V_out in many cases(for example to lower the voltage). In this case the ratio of R1 and R2 matters and by selecting the right ratio we can scale the output voltage. So far I understand..

But we don't choose in real life R1 = 22 ohm and R2 = 10 ohm for instance. I mean the ratio is easy to figure out when we aim to scale the voltage, but how about the optimum resistor values for R1 and R2?

What is the criteria here? Okay I might guess if R1 and R2 is too small, the OpAmp could be loaded with too much current? But how to quantify the R1 and R2 to prevent it to load. Should we check the max current output of this OpAmp from the schematics?

Same confusion with the relation of R1 and R2 with input impedance of the measuring device(R_measuring_device). If R1 and R2 are too big or too small it could be problem?

And there is also a relation or limitation to R1 and R2 coming from R_feedback I guess. Is that right? R_feedback is connected to the output of many opAmp circuits? Does R_feedback have effect on choosing R1 and R2 values?

These all three things are in relation with R1 and R2 here. How can one quantify R1 and R2 considering surrounding resistors are known(R_feedbcak, R_measuring_device) as well as Vcc and V_out are also known? Is there a rule of thumb or a practical easy way?


texts: Need a very low power, low force motor/actuator

texts: What are some alternative types of motors/actuators that can be used instead of servos?  I need some way of inducing a slight bit of motion/movement but with very little force and power consumption.  Even the tiniest sub-micro servos use quite a bit of current and may have quite a bit more torque than is necessary.  I thought about using muscle wire, but I need something that doesn't take up much space, and they don't appear to have shorter lengths of wire available.  Not only that, but I would prefer to have a rotary rather than a linear actuator.  What would be some options for such an actuator running at say 3v and requiring somewhere in the range of 20-40 mA of current?


texts:
Can you connect a Pyramid PS36KX 12-15V 32A DC Power Supply in parallel with a Tripp-lite PR 25 to get more amperage for my Ham Shack
Please follow this link and please let me know if this is possible using this method
https://www.keysight.com/main/editorial.jspx%3Fcc%3DUS%26lc%3Deng%26ckey%3D520808%26nid%3D-11143.0.00%26id%3D520808


texts: Mains transformer as line matching audio transformer

texts:
If we were to use a small mains transformer in place of a line matching transformer to drive a speaker, would it work at all?

Are there differences in laminations or core materials that set them drastically apart?

I’m not expecting audiophile results but I figure just because mains is 50-60hz, doesn’t imply that the transformer won’t perform decently at higher frequencies.


texts: 4bit demultiplexer with address entries in the EXCESS-3 code

texts: My question is: how to make truth table for inputs on E3? There is only space for 2 bits, and E3 is written on 4 bits as I saw. Should I add more inputs for this situation or do this in different way?


texts: How can I high pass (DSP) filter a low frequency signal without introducing lag?

texts:
I need to high pass filter a signal, and my design just isn't cutting it.  The part that's making it tricky is that I can't tolerate lag.  I am sampling at 20Hz, the signal I care about is 1/12 to 1/4Hz, and my system has to be as real time as possible (a lag of 2 seconds for signal processing is about all I can handle).  The corner frequency is flexible, but has to be below 1/10Hz worst case.

I have been using an IIR-like lowpass filter like this:

signal_low_freq(n) = (signal_low_freq(n-1)*(filter_constant - 1) + (sensor_data(n))) /filter_constant;

signal_ac(n) = sensor_data(n) - signal_low_freq(n);

where filter_constant = 165.

It has low latency, but also introduces a large amount of phase related error (I measured it at about 100 samples of lag).

I have used Matlab's fdatool, and can get great results with a high order FIR filter, but that's obviously far too much lag.

Does anybody have a good solution to this DSP problem?

As a note: in the audio range, it's analogous to sampling at 48kHz and high-pass filtering with a corner frequency somewhere between 150Hz and 240Hz.


texts:
I made a simple circuit to alternate its output between two inputs: a photovoltaic panel and a 12V DC voltage source.
The schematic:

The step source represents the photovoltaic panel and the two resistors represent two bilge pumps of 12 VDC 30 W.

It's done in a way that the normal closed contact is fed by the net. But when there's sun, there is voltage and then the relay (12 V rated) changes its contacts. Pumps are then fed with power coming from the panel.

The problem that I got, was that the release/decoupling voltage (voltage to change the the contacts back to normal) isn't the same as the operating voltage of the relay.  The relay comes back to normal when the voltage is approximately 3 V, so when it's going dark and the panel is generating between 3 V and 12 V, my pumps aren't going to work properly or at all. They have to be ON 24hrs/day.

Only when it reaches so dark that the voltage is lower than 3 V do the pumps get fed with power from the net again.

What can I do to solve this problem? Is it possible to keep the relay strategy or do I have to change it to something else?

Thanks in advance.


texts: Why do some Eagle devices have minuscule value labels?

texts:
I've just finished the first pass of layout on a board in Eagle, and I turned on all the board layers and ran a design rule check. I got a considerable number of errors, because a number of my parts that I'm using from Eagle's builtin libraries have tiny >VALUE labels right in their centers, under the stop mask. This yields stop mask DRC errors for every vector in the label. In the image below, I've used a stock TPPAD1-13 from the Eagle library testpad.

The offending value label can be seen in the very center of that test pad. I've found that I can smash the package, then set the value label's display attribute to off, which makes it disappear, but I'm not positive this is the best way, nor do I want to do this for every part – there are over 900 similar errors.

So, two questions:

Why were these packages designed this way?
What is the best way to fix the errors caused by these labels?


texts:
We could use boolean algebra to analyse the digital circuit and use boolean simplification to optimise the circuit.

In boolean expression "1 + A" is 1, whatever A is 1 or 0.

But in the real digital world, the result would be 0 if expression is "1+1" and  result is 1 bit. Does it mean we can't use the boolean algebra in any electronic case or I misunderstand something?


texts: Does a 40 MHz radio frequency have any interference to Bluetooth signal?

texts:
From my understanding, the Bluetooth signal is using a 2.4 GHz frequency.

However, when someone is playing with a 40 MHz RC vehicle, the Bluetooth signal keep on getting interrupted or disconnected.

Does the 40 MHz RC vehicle is the root cause that cause the Bluetooth to get interrupt or disconnect?

If it is not the RC vehicle, what might likely cause such interference to the Bluetooth signal?

Thank you.


texts: What resistor should I buy (More than 2kW peak power)

texts:
Im using a resistor (68Ohm) to discharge a capacitor bank rated at around 400V. This is the graph of the current and the power in the resistor, as you can see there is a 2KW (4.5A) peak. But it's just in around 100ms, I wont repeat the pulse in 3 seconds or more. What value should I use for the power rating of the resistor ? Thanks.

RMS in 2 seconds: ~20W
RMS in 3 seconds: ~13.5W


texts: do I have to separate grounds when using opto-coupler in boost converter?

texts:
I have a DC-DC boost converter:

where the mosfet is driven by  PWM signal generated with a PIC18F4550.

However, the PWM isn't directly feed in the mosfet. It passes through an opto-coupler first. Since I didn't find the specific component I'm using (TLP250), I tried my best to draw it:

So, basically we have "3 grounds":

PIC GND
Opto supply GND (supply of 15 [V])
Converter supply (5 [V])

In the practice, the supply is a dual supply one feeding 15 [V] and the other 5 [V] and the PIC is being powered from USB (computer).

The first ground (PIC GND) isn't the same as the last two grounds. The latter two grounds are CONNECTED and the same point in the real circuit. My question: is that ok? should 3 of them be connected? all of them separated?

For reference: the circuit is now mounted in a breadboard:


texts: As the title says, is the DMF always unique? And if no, is there an example of a function that has more than one DMF?


texts: Using the raspberry pi to measure multiple electrical circuits

texts:
I am looking to use the raspberry pi to measure the power consumption of multiple household electronics and record the information to analyze later on. However, I'm not sure if it's possible to connect as many devices as I would like to the Pi (up to 40). So far, I've done a little research on my own and found an 8-channel, 10-bit ADC (http://www.adafruit.com/datasheets/MCP3008.pdf) which seems promising. However, to be able to connect 40 devices, I would need 5 of these and some way of multiplexing the 10bit output.

This is where I'm currently stuck. I'm not sure what the best way is to pull the potential 50bit output into the raspberry pi. Perhaps I could use a number of shift registers connected in series? Would this work or is there a better solution?

Thanks


texts: How to deal with routing density issues near uController

texts:
I am routing a board that I cannot make larger. It is fairly dense with lots of SMD parts. I am trying to route traces to and from a 100 pin uController to various chips on the board.

It is a 4 layer board with GND on layer 2. Mostly power planes on layer 3 so I have layer 1 and 4 for the signal traces. But layer 1 is really dense with parts.

I have routed about 80 percent of the lines but now I'm finding I'm running out of space to route the remainder. I'm finding the need to make long winding traces for the rest of the lines.

On two of the sides of the uController there are some traces going to a 20 mhz crystal and a 32768 khz crystal. There are grounded copper pours oing around those crystals so that takes up some board real-estate there.

In the middle of the chip there are fan-outs of lots of vias and I have run out of room there.

What techniques are there for routing these things short of going to more layers?

I've gotten the trace width and clearances down to the minimum the board manufacturer will allow me (.006)

I've used the smallest vias I can, but I cannot make blind, buried vias nor do I want to put vias inside of the larger pads.

I cannot put parts on the underside of the board. I cannot make the board bigger.

How much of an issue will there be if I use a part of the layer 2 (GND) for this?  The highest frequency item on the board is the 20 mhz crystal. Everything else runs at 1/4 that speed. I have a buck converter running at around 1.2 mhz but that's in an area that I'm done routing.

Or would it be best to rip up the lines and try re-routing from the uController chip out? I didn't want to do that since my uController allows a lot of pin re-arrangement in software.

I'm using Diptrace.


texts:
Some vendors categorize power supplies with many different parameters.

What is meant by line regulation and load regulation below?

If one is interested in stability of the supply voltage mean value which parameter should he consider to look at? Lets say you want a 24V DC power supply not to vary much with load or ect. from 24.0 rated voltage. Which parameter indicates this?


texts: How can I find the bandwidth of a sinc function?

texts:
I have a solved problem and it says the bandwidth of the function:

$$sinc(\frac \omega {20000}) \cdot rect(\frac \omega {20000 \pi})$$

is 10 kHz. Why it is not 20 kHz or 40 kHz ?


texts: Bipolar capacitor replacement with very different dimension

texts:
I need to replace a 25VNP / 10MFD bipolar capacitor (the gray one in the picture).
I have a 35VNP / 10MFD (bipolar) capacitor replacement. However it's very small compared to the 25VNP one. The gray one comes from a 1977 CRT board, and the green one is brand new. Should I care about the capacitor dimensions or it's irrelevant?


texts: AVR local and global variable program size

texts: I work on ATmega8 and I need to optimize my code as well as I can, because I am over limit and I saw something surprising. I have a few 8bit integers declared as global variables and a few 8bit integer declered as local variables. And in some case when I change global variable to local I get extra bytes of program and in same cases when I change local variable to global I also get extra bytes. Can anyone explain me why in same cases global variables generate smaller size of program and sometimes local variables do that?


texts: Why ADC Differential Driver feedback resistors are small in hundreds range?

texts:
I noticed that the differential ADC driver circuits always using small values for feedback network resistors, an example is shown in the attached picture.

Can we use large Values for feedback resistors(in Kohms) to reduce the power consumption in these resistors? or it could cause any issues?


texts: Least sub-optimal configuration of flooded lead-acid cells with different capacities

texts:
I am aware it's best to use cells of the same capacity, same age, etc. However, until I can replace the cells I have I need to make use of these.

The batteries I have are 2V flooded lead-acid cells, 6x 400Ah and 12x 225Ah (both at C10). I need 12V at the highest possible capacity with the cells available (without destroying/overcharging any cells, obviously).

What I want to accomplish is parallel the 12x 225Ah to create a 12V 450Ah battery and then parallel this with the 6x 400Ah in series (=12V 400Ah) to yield 12V ~800Ah. This should not result in overcharging any cells, since only like voltages are paralleled.

It only should result in a slight underuse of the capacity of the 12x 225Ah cells (~11%), but that seems acceptable (especially since the 225Ah cells are a little older than the 400Ah cells, so their capacity is probably a little nearer to 200Ah anyway).

What would be the best way to connect the 12x 225Ah cells for this? I can think of two ways to connect the cells:

Create six pairs of 2x 2V 225Ah in parallel and connect these 6 pairs in series, or,
Create two strings of 6x 2V 225Ah in series, and parallel these two strings.

Am I correct in thinking that option 2 only yields 3x225Ah=675Ah in practice, since I am effectively paralleling 400Ah, 225Ah, 225Ah (and the 400Ah battery will perform as if it were a third 225Ah battery), while only option 1 will yield the desired 800Ah; paralleling 400Ah and (225Ah+225Ah=450Ah) (where the 450Ah battery will perform as a 400Ah)?

Also, am I perhaps missing another possible (better) way to connect these cells? Thanks!


texts: Why don't I need device drivers for a UART to communicate with a Linux box but need device drivers if USB is to be used for communication?

texts:
I have a Linux box.  I want to troubleshoot certain things and I was told that I need to custom solder pins to communicate using UART as perhaps it doesnt have device drivers to communicate using a USB port which is only there for charging and missing drivers to use TTL.
Why don't I need device drivers to communicate with Linux using UART but need to add drivers if I have to use the USB port?
This is incontext to this blog where author mentions:

Loading the code
Point 1). is easy; by powering ON the RetroMini while pressing B, the CPU will switch into a special mode where it will listen for commands on the USB bus. By sending specially crafted commands, it is possible to load custom code to the RetroMini

and then

Debugging the code via UART
The simplest way to debug your code is to just make it print stuff to the output console. Print register contents, print “success” if your check worked, print “oh noes” if it failed… If your program outputs text to the console, the whole process of writing a program becomes much easier.

Despite the fact that USB port is present, then why the need to solder extra wires to use UART protocol?


texts: AC circuit to model blood flow - circuit analysis

texts:
The Windkessel model is used to model cardiovascular flow. It models arteries, which can store blood, as capacitors, and peripheral vessels (which resist flow due to contact of the fluid with the vessel wall), as resistors. Below is the 3 element Windkessel model, figure from "Model of Aortic Blood Flow" (Catanho, Sinha, Vijayan):

3 Element Windkessel - 2 impedance elements, 1 capacitor

My question is, how do you derive the equation for P(t), an AC element, which represents blood pressure in the pulmonary artery? This is essentially a circuit analysis question.

Here is what I tried:

\$I(t) = -P(t)/r\$

\$I(t) = C*dP(t)/dt + P(t)/R \$

\$-P(t)/r = C*dP(t)/dt + P(t)/R\$

\$-P(t)/r - P(t)/R= C*dP(t)/dt\$

However, this is different from the equation in the paper:

\$(1 + r/R)*i(t) + CR_1*di(t)/dt = P(t)/R + C*dP(t)/dt\$

How did they derive this equation from the circuit?


texts:
I am trying to troubleshoot a faulty camcorder PCB and stumbled upon this resistor(?) that is right near the DC jack.
The resistance between it is 0 Ohms.
What is this component? I couldn't find anything searching for this value on the internet.

Thanks in advance for any help!


texts: Has anyone transmitted data across a badly coupled transformer and recovered the data correctly

texts:
EDITED June 9th 2013 to give more detail (hopefully)
I've recently set-up a data transmission system on a rotating machine. The data was collected and serialized from several ADCs connected to strain gauges mounted on turbine blades of the machine.

The power to the rotor-mounted system was coupled magnetically at 600kHz. We managed to get a few watts across the "gap".

Sending data back off the rotor electronics was tricky because we couldn't use "in-line" or end-of-shaft" optical coupling, rather, we transmitted the data across a badly coupled transformer. Hopefully this diagram will explain: -

The top of the diagram shows two square loops that carried the data. I've shown the loops as square for reasons of making it easier for me to draw - they were circular around a shaft on the machine.

The bottom of the diagram shows the static receiver part. A small loop ran parallel to the rotating loops and received a small and differentiated signal representing the data. The system works fine but I'm also aware it's on the edge of working and leaves me a little uncomfortable about its long-term performance.

What makes the data system so flimsy is the magnetics that transfer power. This is a resonant coil system operating at 600kHz and a few inches away from the data coils. The data is scrambled and encoded so that if no data were present there would be a high low transition every 75ns (13.3MHz). Top data rate is 80Mbpsec. Because of the power magnetics, the data signal received is riding up and down on a sinewave of 600kHz so special filters were developed to remove this but it reshapes the data somewhat making it harder to detect.

  I'm looking for advice on how to make the data transmission more
  solid.

Additions - there is little possibility of data packaging with CRCs and block retries - the electronics on the rotor is very basic/simple and doesn't have facilities for a receiver.

I've also developed a system that does use frequency modulation to carry the data - this uses a single loop for power and data transmission because there was absolutely no space for anything else. Because it is modulated the lowest frequency is about 78MHz and this gives decent spectral clearance between received signal and the 600kHz power pick-up.


texts:
I have a special power supply requirement for Agro Based Applications..

After stepping down conventional primary 230VAC, 50Hz Single phase single line supply to secondary 80VAC (4Amps to 6Amps), I need to convert the secondary voltage to dual DC supplies of 5VDC (3Amps) and 15VDC (500mAmps).

The 5VDC is to power my own sensor board designs and the 15VDC is to trigger a relay in it for only special cases.

However, since I have a limitation which compels me to connect N number of boards to the DC power converted from the same single phase AC supply, I estimate a voltage drop to even as low as 15VAC at secondary once Nth board is connected.

There are very few reference designs for power supply categories below 80VAC and I am at a loss here. Can anyone suggest a suitable cost effective method to achieve this low AC to Dual DC conversion?

Thanks...


texts: Driving LEDs with Specific drivers or buck/boost regulation

texts:
I have a circuit that is driving 3 x LED rings and an Arduino/ATmega @ 5v through a standard 5v regulator.

Each LED ring draws 11v @ 300mA and is PwM switched using a 2n7000 Mosfet from the ATmega's output pins.

The total supply feed is 11.5v @ 1amp, and is a buck/boost regulated supply.

My question is....

Given the rings are being supplied at a constant value from the buck/boost regulator upstream, do I need to add additional individual LED drivers such as the NUD4001 to further regulate the power feed to each ring?

The circuit works and does not overheat or cause any visual issues with PwM without the NUD4001's but I would like to confirm that this is right/wrong or good./bad practice.

I do not want to add additional components to the circuit if I do not need to.


texts: USB is not recognized by device manager but seen by vender's software

texts: I am trying to acquire data in real time from a sensor mounted on an evaluation board. This evaluation board has a software, when I connect the USB to PC, it automatically recognizes the USB and it sees the device. My problem is I would like to acquire data from this sensor by MATLAB and I need to see the port or com, but device manager doesn't show anything. How can I check my USB connection in device manager?


texts:
I'm stuck at this seemingly simple thing. I have a NMEA GPS module. It doesn't matter how it operates, it just transmit serial data stream at a baud rate of 38400.

I have an arduino Mega which has several hardware serial modules. If i directly connect GPS Tx to Arduinos Tx pin (and program arduino to not to use default serial module, Serial0) then i can observe raw GPS sentences transmitted by the GPS module using the arduino serial monitor.

What I really want is to read the GPS module to arduino Serial1 port and forward the receiving data through the default serial port Serial0 without doing anything. So that i should be able to monitor the data from the serial monitor as exactly in the previous case.

I tried something like follows, but it's not working (it gives a stream of digits, i tried doing all the possible changes but nothing worked)

void setup(){
  Serial.begin(38400); // the default serial module, serial0
  Serial1.begin(38400); // GPS is connected to this
}

void loop(){
  if(Serial1.available()){ // if GPS data available
    Serial.print(Serial1.read()); // write it to serial0
  }
}

Hope someone here will be able to give me some solution.


texts: How to calculate Resistor needed in PNP Transistor Circuit

texts:
I am trying to calculate the resistor value I need to achieve 35mA in my circuit. Vcc is 5V. Can someone explain the values I need to find in the datasheet as well as formula to use to find the correct Resistor value? I would like to learn this for future projects using transistors.

Transistor used is S8550
UV LED used is here

simulate this circuit – Schematic created using CircuitLab


texts: Understanding MOSFETs Driven by Analog vs. Digital Signal

texts:
I plan to run a circuit with two 18650s in parallel to get 7Ah of capacity and a 3.3V rail (for running the ESP32 MCU). I'll use an LDO to get my 3.3V until the battery voltage drops to 3.3V. At that point, I'd like to use MOSFETs to rearrange them into series configuration for charging via 2-cell balancing and charging ICs (inspired by this Adafruit product but in reverse).

I'm wondering how to set up my MOSFETs to achieve this. I could use P-channel enhancement-mode MOSFETs that are by default ON if the gate voltage from the batteries is >3.3V and then shut off when the voltage drops below 3.3V to open up a new branch. I've modelled this below using SPDT switches for readability.

Would it be better to turn the MOSFETs on/off via a digital signal from the MCU? I could monitor the battery voltage using a comparator and some code and have it all controlled in software. That way I don't have the output of my pack voltage driving the switches that are reconnecting the output of my pack voltage.


texts: I want to measure the stand-by current of the PIC, but my DVM has minimum 2000micro (u) amper switch. It shows 0 micro amps when in 2000 u amps mode. Without building circuit a complex (more than 3-4 components) circuit, how can I measure nano amps?


texts: You have an RC element. After the RC element there is a comparator. After a given time of X minutes(X * 60 = R * C), the comparator reacts. Does voltage drop lead to time distortion, provided that also the comparator is connected to the same power source?


texts: tear drops disappearing during mirroring in altium

texts:
I have recently faced a problem...whenever I mirror my pcb by using the shortcut>>M+i
all of the tear drops which are defined in my design will be disappeared! does anyone know why this problem happens??
thank you in advance!


texts:
I am planning of building a solar water fountain which would serve as a bird bath in my backyard this summer.

My requirements are simple:
The fountain should be powered by solar energy, a small output motor (or whatever) connected to this solar source which pumps out the water. I just need a small working model in a economic price.

I have no experience in building basic electronics model, please guide me on how this can be accomplished, where I can get solar panels and how do I configure it with a motor etc. I am from India and would like to purchase raw materials available in India rather than getting it shipped from elsewhere. Any help is greatly appreciated.

Thanks,
Raj


texts: Using Pre-Certified (FCC) Emitter - do I need unintentional transmission testing?

texts:
I'm making a device - a keyboard - that uses a pre-certified RF module.  I host this device on my custom PCB, and have programmed it to receive the keystrokes (from switches on the host PCB) and transmit them to another, identical RF module on top of an Arduino - which interfaces with the computer.

With the exception of the module (and, I suppose, the Arduino which already ought to be certified as well), nothing else in my device exceeds 1.7Mhz, which - as I understand - is the cutoff for devices to be verified.  This comes from the exemption list, which states:

"Digital devices in which both the highest frequency generated and the highest frequency used are less than 1.705 MHz and which do not operate from the AC power lines or contain provisions for operation while connected to the AC power lines."

It's battery powered (the receiver is USB-powered).  Do I need unintentional transmission testing?  Do I need certification?  I'm just lost.


texts: What is GNSS EPO orbit prediction in SIM868?

texts:
I'm little bit confused about the purpose of GNSS EPO orbit prediction functionality in SIM868 over a hot start,cold start or warm start.
I'm working on a GPS tracker project and which among the fixing technologies mentioned in the SIM868_GNSS_AGPS_Application Note_V1.00 can be used in my application for best results?
The Microcontroller used is STM32L4 .
Regards,
Joe


texts: Can anybody help me modifying a reverb circuit on a guitar amp to an FX loop circuit?

texts:
I have a solid state guitar amplifier with a reverb tank. I have done a bit of research as to how these work. I now want to replace the reverb tank with an FX loop for normal pedals (instrument level). Therefore, the system in the amp that drives the reverb tank needs to be modified so it sends and returns correct levels. My guitar outputs about 800mV max. So the FX send needs to output about 800mV without additional gain from the preamp. The return signal of the reverb tank is obviously very weak and it is (just like the send signal) amplified with a 4558 amplifier ic. I have done a bit of reverse engineering and I have found out which part on the schematic refers to which part on the pcb.

Now my question is: Can anyone help me with modifying the reverb section so that the incoming signal and the signal that goes back to the rest of the system doesn't change, but just the send and return values?

Let me know which terminals I have to check with my multimeter when I have the amp on clean. This way I'm sure I won't give you useless information.

PS: The coils at send and return will be gone. Those refer to the reverb tank's systems. I will basically replace them with 1/4" jacks so J6 and J7 are positive and negative terminals (tip and sleeve). Same for J8 and J9.

Thanks!


texts: Is there a better way to jumper 3 terminals together?

texts: I can't find terminal block jumpers for sets of 3 and 5 terminals, just 10 and 2. So I took some 2-terminal jumpers and tried to accomplish what I needed to do but it looks unsightly and seems likely to fail due to the torque induced on adjacent blocks. Is there a better way to gang three and five terminal blocks together? See picture below:


texts: How to know if a motorcycle battery and power generator is enough to keep an device turned on without discharging the battery?

texts:
I have an arduino project in mind but I have some questions before I can start to make it.

I need to plug an arduino Uno on my motorcycle, but I dont know if it will consume too much energy and lower the battery level over time. I know an Arduino Uno alone consumes too few energy, so probably it will not make any difference on the electrical system of the motorcycle. But I will probably plug some shields and the whole project will have other electrical components, consuming more energy.

To be more specific about the project: I want to put an RGB LED system on my motorcycle, with its colors controlled by bluetooth (or maybe wifi). So the final question is...

How can I measure if the motorcycle battery and power generator is enough to keep the whole project turned on without discharging the battery, damaging any part of the electrical system or putting my whole motorcycle on fire?


texts: How does DTH (satellite receiver at home) convert EM waves into an electrical signal?

texts:
Any DTH consist of a parabolic reflector,  a feedhorn, a waveguide, LNBF etc. The signal passes from the parabolic reflector to LNBF via feedhorn and waveguide.

Upto waveguide the signals are in the form of EM wave and before LNB circuit they are in the form of electrical signal.

How are EM waves converted into an electrical signal in this stage? Is there something (or any antenna) in between waveguide and LNB PCB which does this job?


texts: Inductor calculations for buck converter

texts:
I found this application report Basic Calculation of a Buck Converter's Power Stage
Q :

Can I use this report for products of other companies like ROHM, ALpha and Omega Semi...

For the selection of the inductor, did (Lpeak=Iout+Delta_Iout/2 = 4.4A ) represent the current rating of the inductor. what margin is required to choose the saturation current.

This is the circuit that I designed.  Can anyone make a revision to it.
I am working with AOZ1284 Datasheet


texts:
I've been looking at audio ADCs with most rated at 192Ksps with 24 bit audio.  Typically the output is in I2S, but I understand that the signal is not intended to go far.  I understand that HDMI can transmit I2S but ideally I'd also like to send power over the interface as well, where the 5V at 50mA standard is not going to work.
At worst case, other pins could be stolen for power to use HDMI in a non-standard configuration, but I'm interested in knowing if I could pipe the data across an RJ45 with differential pairs at a distance of 6ft minimum to 20ft max.  Data conversion is flexible, I just don't have any real experience with how sensitive I2S is over distance, and I understand that impedance is a fairly important aspect in reliable transfer, causing most RJ45 interfaces to be very short if used.  Any help or redirection is appreciated, I'm still fairly new to this subject.


texts: Capacitor and inductor working principle

texts: I want to know that there is opposition mechanism of current in inductor say back emf than what is opposition mechanism of voltage in capacitor ??? And also want to know that when inductor suddenly open it generates very huge voltage to keep current constant does it violate conservation of energy ???


texts: Running ngspice from command line on a Linux and Windows machine.


texts: Locating ground and other pins on circuit board

texts:
I am a beginner attempting to learn how to hack RC cars like is demonstrated in this video.

My problem is I can't spot the ground pin and the other pins related to the wheel drive functions except I randomly test pins with my multimeter.

In an old pair of RC cars, after a long time of trial and error I finally located the ground and one of the pins connected to a wheel.

However, I just wonder if there is a technique for locating ground and other pins in a circuit, please?

I want to learn how to locate the relevant pins so I can hack these cars.


texts: Power dissipation in Fets synchronous switcher

texts:
I'm working on a design that includes a synchronous buck switching regulator and I've been trying to understand how much power each FET will have to dissipate.   I've been looking at different formulas and several seem to be in the form below.  The  answers I keep getting don't make sense to me.  I feel like they're off by more than an order of magnitude and that I end up with the wrong units in the end:

Here's the formula taken from powerelectronics.com

Edit: Not enough rep to post image so the formula is on that page half way down as:

\$ J = 10^{-9} \cdot (\dfrac{V_{in} \cdot I_{out}}{I_{drive}} + \dfrac{Q_g}{Q_{sw}}\cdot V_{drive})*f_{sw} \$

(in W/nC)

So just for the high-side I know the following from my design:
Vin = 12V
Iout = 30A
Vdrive = 5V
Idrive = 300mA
Fsw = 1Mhz

Then from the FET datasheet I get:
Qg = 11nC
Qsw = 5.6nC

If I plug all that in to the equation I get 1.215 V/sec.  Even if my units came out as W/nC that would still be 11*1.215 or 13.365W.  Maybe this is right and I need more Idrive but the units come out wrong so I'm not confident in my math so far. What am I missing here?

Power electronics formulae copied from here

They define J & K as follows (their text)

Since switching losses are proportional to MOSFET size and conduction losses have an inverse relationship to MOSFET size, there exists a point where their sum, total loss, is minimized. This drives the MOSFET optimization process, selecting the MOSFET that has minimum total losses. To that end, we will define two parameters. J will be the switching losses per unit switch charge (W/nC) and K will be the conduction losses per unit drain-source on resistance (W/mΩ). Losses that are independent of MOSFET size have little impact on MOSFET optimization, so are not included in J or K equations.


texts: CMOS IC Layout Recommendation for beginners

texts:
I really want to receive advice for books, materials, or advice to start CMOS layout for beginners.
Currently i have no idea. I really want to understand what happens if i place a certain thing in the layout.

Thanks very much!


texts:
I have designed a few PCBs, all of which have worked fine. I'm starting to get into some more complex designs, switching power supplies, etc.. I have a few questions related to proper power handling as it relates to current flow and current loops.

For the questions, I am referencing a 2 layer board. Bottom and top layer are GND pours, with very few signal traces on the bottom pour. Using this simple schematic as a reference:

The main supply voltage gets regulated to 5v. Where should the 5v trace connect to the circuit at? I assume at one of the two decoupling caps.
Letting my assuming for number 1 be true, should I take all additional power traces from that point(this schematic doesn't show any other components, but if there was)? Similar to a star ground, but with 5v.
So I know return current wants to flow under the original trace for high frequencies, does that apply for the LED?
When the return current flows from the LED back to the IC GND, which GND pin will it flow to?


texts:
I am prepairing for my final exam, and the hardest topic for me to understand is finding equivalent resistance. So here is an example task. How to simplify this circuit to see where is parallel and where is in series?

UPD: My attempt to simplify this


texts: Changes when \$V_{be}\$ is increased in npn transistor

texts:
For the given circuit, a statement has been given in my book, saying

  It is obvious that if Vbe is increased by a small amount, both hole current from emitter region and the electron current from the base region will increase. As a consequence both Ib and Ic will increase proportionally

I believe there is a mistake and it should be rather,

  electron current from the emitter region

Because BE seems to be forward biased and thus the majority carriers, that is, electrons from Emitter should increase and go into the base and further in collector.

Am I right or wrong?


texts: Adding Push-To-Talk (PTT) / Mute to 3-pin XLR Cable

texts:
Is it possible to add PTT/Mute to a 3-pin standard terminating XLR cable (with +48V phantom power)?
In my case, I have found myself with a Astatic 40-119 microphone base with a PTT switch that "only" provides dry contact between the 4 & 5 pin of the 5-pin XLR cable. Can I use this fact to cut the power to the condenser mic, or is there some better circuity to accomplish the mute? The base works great otherwise. (There is a competing model that mutes the microphone on a standard 3-pin XLR cable that I've included the spec sheet for completeness.)

40-119 MIC BASE Spec Sheet

This unit features a dependable momentary push
switch that provides a dry contact between pins 4 and 5 of the cable terminating
XLR connector. The switch can be configured for either "push-to-open" or "push-to-close" using the slide switch located on the underside of the base. The 40-119
base is used to control an independent device while audio signal from the mic is
always on.

Just to note: the mic does work as described. Maybe the mentioned "independent device" can mute the mic :)

40-116 MIC BASE Spec Sheet (don't have this, for comparison)

The circuit contains a highly reliable switch to operate
a 55dB mute which will effectively kill audio output without causing a potentially
damaging phantom power "thump" when used with electret type microphones.

These questions were helpful to me but the first two are microcontroller focused. The latter 3.5mm also has a power component, I'm researching into it more.

Microphone mute anti-pop circuit works but still picks up a little audio
5v Electret microphone to PC mute switch pop help
3.5mm Push to Talk Switch

Any help would be appreciated.


texts:
Say a free metal rod is placed at a distance λ/2 from a dipole antenna (fig), both being of same length. I understand it will reflect and dampen the signal going to the left. But how will it impact the signal going to the right in comparison to no rod? And how will its length impact that result?

EDIT:
I meant this to be a transmitting antenna, but it would probably work both ways. The reason for the question is it was a theoretical question with a explanation I did not agree with. As in comments I agree there will be a dampening due to reflection, and also a possible narrowing or widening of the radiation pattern (with changed lobe-maxima). If a length longer than the dipole reflects and a shorter directs, then I assume that would mean the ratio of the effect of reflection/direction. As I can only imagine it will always reflect to some degree, and always direct to some degree, either by widening or narrowing the lobe(s)...(?)


texts: Initial input current of voltage inverter

texts:
The figure below is a voltage inverter from the book Reconfigurable Switched-Capacitor Power Converters by Dongsheng Ma and Rajdeep Bondade.

Link: Reconfigurable Switched-Capacitor Power Converters - Google Books

Please refer to the text explanation below. What I don't understand is why the initial value of Iin is greater than 2*Iout.
Could anyone explain more about the yellow highlighted part?


texts: UHF RFID reader ability to recognize tags in less than 1 m reading distance

texts:
If the UHF RFID reader basic reading distance is up to 5 m, if adjusted to be less than 1 m or to be up to 1 m, can it be able to recognize all the tags? Or since it's for mid range reading, the reading distance should not be set to this short reading distance?

What factors that tags in this range effected by, so some can't be read after adjusting the range to be 1 m or less?


texts:
I look into the D-Type Flip Flop, so I checked it and found some logical diagrams, but they were all differents...

I have no idea what this gate do :

-Does it switch Q and /Q depending of the state of the clock and the activation of the other input :

Clock -> made the states switch only if the other input is true.

-Does if switch Q and /Q depending of the sate of the other input and refresh the output when the clock is true :

Input -> change the state depending on the input value, refresh the output when clock is true

So which one must I follow ?

Another diagram ?

here is what I get :

first one change the output depending of the clock state;
the 2 other change their output depending on the input value. Refresh depending of the value of the clock.

Thanks,


texts: Effects of PWM waveform polarity on PWM-driven hardware

texts: What difference does it make for a certain PWM-driven hardware (such as a DC motor) if the PWM signal starts high or low?


texts: How brush shifting affects current distribution in dc machines?

texts:
I understand that how armature reaction causes neutral plane to shift by some angle . If brushes are placed along Geometrical Neutral Axis, then there'd be sparking during commutation as voltage across coil being short-circuited wouldn't be zero. Then I read that brush shifting (technique which is obsolete since 1910 but still finds its way in tricky questions in kind of exams I'm preparing for) changes current distribution. Now, I have two doubts, please refer to following figures, fig. A (left) and fig. B(right):

Referring to fig. a. If I keep brush at original position (i.e. along Geometrical Neutral Axis), then considering the fact that armature reaction causes neutral plane itself to shift, shouldn't there be current flowing through conductors which are along GNA (because now they're not along Magnetic Neutral Axis, since GNA and MNA do not coincide)? Why is there no current marked on those conductors? PS it doesn't seems that it is just printing error because I've refer several books and all had to say something like "current redistributes when brushes are shifted" (and I assumed "not otherwise").
With ref. to fig. B, I don't exactly understand how current redistributes when brushes are shifted. I mean, isn't the current depended on voltage? And if voltage is depended upon flux density only (speed and other things remaining constant), how can changing brush position redistribute current? I thought effect of brush and commutator is just to rectify induced alternating current into direct, how it affects something inside the machine? (I know it does because so many sources said that, but I can't figure out how, please help me, even small hint would be enough). Also the dot and cross marks are shown for current and not for voltage, right?


texts: CLK net warning for stopwatch code on FPGA nexys2 board?

texts:
I'm coding for a stopwatch which displays 10ths of a second on the rightmost two displays and seconds on the left two displays. The synthesis completes properly but after I make the UCF file and try to implement the design the following two warnings occur.

WARNING:CLK Net: check

WARNING:CLK Net: carry

I tried ignoring the warnings and went to generate the programming file but this warning came up and nothing happened on the FPGA kit and all the displays had 8 on them.

WARNING:PhysDesignRules:372 - Gated clock. Clock net check is sourced by a combinatorial pin. This is not good design practice. Use the CE pin to control the loading of data into the flip-flop.

I have no idea what any of these warnings even mean and I tried searching for them online but I found nothing from which I could understand my problem. I figured that there is something wrong with the check and carry variables but I'm having no luck fixing the problem as it seems all fine to me logic wise. And also I'm having a hard time being trying to figure out how to start and pause the stopwatch. Here's my code:

module stopwatch(clk,rst,a,b,c,d,e,f,g,dot,an);

input clk,rst;
output a,b,c,d,e,f,g,dot;
output [3:0] an;

reg [22:0] count_time;
reg [3:0] first,second,third,fourth;
reg check;
reg carry;

//counting 1 second and producing a tick at every 1 second

always @ (posedge clk or posedge rst)
begin
    if(rst)
      begin
      count_time <=0;
      check<=0;
      end
    else
      begin
      count_time<=count_time+1;
        if(&count_time==1)
         check<=1;
        else
         check<=0;
      end
end

//counting on last two SSDs

always @ (posedge check or posedge rst)
begin
    if (rst)
      begin
      third<=0;
      fourth<=0;
      end
    else if(fourth==9)
      begin
        if(third==1)
         begin
         third<=0;
         fourth<=0;
         carry<=1;
         end
        else
         begin
         third<=third+1;
         fourth<=0;
         carry<=0;
         end
      end
    else
      fourth<=fourth+1;
end

//counting one First two SSDs

always @ (posedge carry or posedge rst)
begin
   if (rst)
     begin
     first<=0;
     second<=0;
     end
   else if(second==9)
     begin
       if(first==9)
         begin
         first<=0;
         second<=0;
         end
       else
         begin
         first<=first+1;
         second<=0;
         end
     end
   else
     second<=second+1;
end

//multiplexing of 4 SSDs using the 'an' bits

parameter X = 18; //we will use the top 2 bits (since 4 SSDs) for multiplexing and the lower X-2 bits for frequency control
reg [X-1:0] counter;

always @ (posedge clk or posedge rst) //counter to produce multiplexing
begin
 if(rst)
   counter<=0;
 else
   counter<=counter+1;
end

reg [3:0] an_temp;
reg [6:0] out;

always @ *
begin
case(counter[X-1:X-2])

   2'b00:
    begin
     out = fourth;
     an_temp = 4'b1110;
    end

   2'b01:
    begin
     out = third;
     an_temp = 4'b1101;
    end

   2'b10:
    begin
     out = second; //dont care
     an_temp = 4'b1011;
    end

   2'b11:
    begin
     out = first; //dont care
     an_temp = 4'b0111;
    end

endcase
end

assign an = an_temp;

//sending digits to SSDs for each muliplexing interval

reg [6:0] temp;
always @ *
begin
case(out)
   4'd0 : temp = 7'b0000001;
   4'd1 : temp = 7'b1001111;
    4'd2 : temp = 7'b0010010;
   4'd3 : temp = 7'b0000110;
   4'd4 : temp = 7'b1001100;
   4'd5 : temp = 7'b0100100;
   4'd6 : temp = 7'b0100000;
   4'd7 : temp = 7'b0001111;
   4'd8 : temp = 7'b0000000;
   4'd9 : temp = 7'b0000100;
   default : temp = 7'b1001000; // H
  endcase
end

assign {a,b,c,d,e,f,g} = temp;
assign dot = 1'b1; //dots are off

endmodule


texts:
My question is similar to this one but with some differences.
I have wireless weather station with 3 remote 433MHz sensors so I cannot change the protocol and program the controllers. Also I'm new to radio but have some basic understanding how it all works.

I'm trying to modify the stock product to increase its capabilities, a sort of DIY project for home.

The sensors and station base are mounted on concrete walls of my home, where maximum distance between base and sensor is about 15 meters (and crosses 3 walls). The Base is able to receive signals from all sensors except one that is the most distant.

Link to the weather station on amazon. Transmitters run on 2 AAA batteries, 3V.

What is the easiest way to allow it receive the signal? Attach better antenna to the transmitter? Or completely replace the transmitter module?

I understand that I didn't provide much information about the circuits because I'm not sure if it matters in my case. I can post images of the inside later if needed.

UPDATE

Here is a receiver module of the station Base.

The Sensor box is harder to open because it looks like sealed. I'll try to open it later and now hope the receiver can give some ideas.


texts:
My irrigation system control box just died and I'd like to replace it with a smart controller based on a Spark Core programmable board, so I can monitor temperature, soil moisture, humidity, and other parameters and use them to intelligently turn on the sprinklers.

My main issue is power supply. The existing system ran off an old-style bulky transformer putting out 24V AC. This voltage was used to operate the solenoid valves (one at a time) and was also used to power the old control board, through some kind of rectifier and voltage regulator circuit which I haven't really dissected.

Most interesting, the old board used an array of triacs to switch the 24V AC current through the solenoid valves, one triac per valve. They used a GPIO pin straight off the MCU, amplified through a transistor, to trigger the gate of each triac. I'm not sure, but I think this would only work if there's a specific relationship between the DC circuit's GND and the incoming AC.

As far as I can see, my options are:

Develop a similar setup, reusing the old bulky transformer and triacs, building my own rectifier and voltage regulator to power my MCU board. This is a bit beyond my skill level and the risk of blowing stuff up would be non trivial. I also see it as power inefficient, unless I use a switching regulator, otherwise I would be dissipating the drop from 24V to 5V, which for 500mA would amount to 10W.
Keep the old transformer, but use a pre-made switching regulator board to pull 5V DC out of the 24V AC; then use transistors + relays to feed 24V AC to each solenoid valve as needed. This is well within my skill level and quite safe, but would still keep the bulky transformer around.
Find out the right DC voltage for the solenoid valves and run everything on DC at that voltage. Suppose it's 9V, I would only need to drop that to 5V to power my MCU board. Everything would share GND so I could use a simple transistor to switch the 9V to the valves.

I would go with option 3. but I'm wondering whether there are other reasons why an irrigation system would power its valves from AC. Specifically, I know AC is used in wet circuits to avoid corrosion, including "cat whiskers" building up between electrodes. The valves are a closed circuit, so electric corrosion shouldn't be an issue, even if they operate in a moist environment. Can I safely power them from DC?

What do you recommend?


texts:
I've wrote a verilog code for Multiplier (8bit). I'm not getting the right result. Kindly tell me where i went wrong.
module Multiplier (x,y,z);

input  [7:0]x,y;
output [15:0] z;

assign z=x*y;

endmodule

It got compiled without any errors. But when simulating, it gives me wrong results. It gives wrong results only when the MSB of the numbers is 1 (i.e when negative numbers are considered).
Here is the picture of the simulation.

Kindly help me with how to rectify this problem. Also, I have another question to ask. While writing a code in modelsim, I observed some line numbers marked in red, Can anyone tell what they mean?


texts: Identify and source replacement common-mode noise choke

texts:
I have a circuit where the marked inductor common-mode noise choke in the image below is damaged.
I am having massive trouble sourcing this inductor common-mode noise choke anywhere. No results on AliExpress and Ebay.
I would be really grateful if someone can point me to a replacement inductor common-mode noise choke.
The circuit is from a MH-24 Nikon charger. The inductor code I can make out is 0R20A153 PC.


texts:
I'm a first year electrical engineering student, and I've been learning about transformers in my electrical subject.
I understand that transformer cores are made up of laminated silicon steel, which are stacked, to reduce eddy current losses etc.
But wouldn't this affect the flux going through the core? I would have thought that, at least as far as flux density goes, a full cylinder-type core with a reasonable diameter would be best. Any help on why this is the case?


texts: How to choose bldc motors to use as generators?

texts: First of all, sorry if I mess up certain words or terms, I am not very specialized in this department. I want to draw power out of an engine, producing around 50hp, or about 37kw of power. A normal generator head is too heavy to make sense in my application, and instead I want to use a large BLDC motor with a high thrust output (most likely a large drone motor) and rewire it to use as a generator. According to various sources, most motors have high amounts of efficiency, as generators if wired properly, and as such, I want to know how to choose bldc motors to use in this application? With my limited knowledge, I am currently thinking of going with a motor with an output of the power I want to convert, with a little headroom for efficiency loss, so around a 40kw motor. Basically, is this form of thinking correct, or would I have to choose a more powerful or less powerful motor, for decent efficiency converting this power?


texts:
I'm looking at the ATMega328p data sheet, and an Arduino Pin diagram, trying to determine if the chip can support three UART connections. I see that PD0 and PD1 are "USART" In and Out. So does that mean the other 10 or so Digital pins can be used for "UART" communications?

I have a need to connect three UART devices through the ATMega chip. The ATMega will forward traffic between two of the devices at a time, depending on which mode it's in.


texts: Application based Heat sink design for Power diode

texts:
Instead of having a heatsink directly connected to the diode, I want to have a 2 mm layer of cold rolled steel in between case and heat sink(aluminium){for waterproofing as needed in the application}.

I have taken in account of the Rth(J-C) and Rth(C-H) for the diode and the thermal resistances of the steel plate and the conductive paste.I want to check the feasibility of the design by ensuring the temperature of the junction does not cross 150 degC. By considering the thermal resistance of the steel plate, there is not much difference in the temperature of the junction with or without the steel plate.

Kindly let me know if I should consider the contact resistance between steel plate and heat sink. If yes, how to calculate the value for the same?


texts: What is impeding current when voltage is stepped up in a transformer?

texts:
What is physically impeding electric current when a transformer steps up voltage? Is there some EM field along the conductor impeding electron movement?

FYI, I'm not asking about losses or leakage. (assuming ideal transformer) I'm trying to get an electromagnetic explanation of how increasing turns on the secondary winding exchanges current for voltage.

Thank you.


texts: Why does the subwoofer hum when no source is connected?

texts:
The hum at 60Hz stops as soon as an audio source is connected and came with a 2 pin connector.
I tried to connect any part of the subwoofer with the ground of a socket. The buzzing stops when no device is connected. I can then connect my phone normally with an aux cable and listen to music. When I try to do this with my laptop, a strange beeping sound is emitted.
The problem occurs on all sockets and therefore I suspect that the power supply has a problem. It is important to note that the subwoofer is a few years old. In the pictures you can see the components of the device. Which component could be the source of the problem?


texts:
I'm playing around with these 433Mhz transmitter and receiver modules in combination with and Arduino Uno.

I first soldered a 17cm long helical antenna to both modules. After I while I noticed that a lot of noise is generated while both modules are working. I've identified two reasons for this:

The antennas themselves: If I removed the antennas from the modules, there was considerably less noise.
The Uno was connected to the USB port of the PC (I wanted to see the output in the serial console). The USB port of the computer seemed to also have an impact on the quantity of the noise.

When I removed both antennas and powered the Uno via an external power supply, no noise was present. Since I still wanted to see the output of the receiver I connected the TX and GND pin of the Uno to the PC via an FTDI cable.

My question is: Why was noise present when the Uno was connected to the PC via an A-B USB cable, but was not present when I connected the TX and GND pins of the Uno to the PC via a FTDI cable?


texts: How exactly does nonlinear quantization in compading help in data compression

texts:
I keep reading that we would need 13 bits to store audio sample with linear quantization but with compading we can get the same "quality" with only 8 bits.

How exactly does nonlinear quanitization help in data compression i.e using 8 bits instead of 13? What is meant by quality in this case?


texts: Incoherence between oscilloscope and spectrum analyser

texts:
There seems to be an incoherence between what I see with my oscilloscope, and what I see with my spectrum analyser.

I have a signal of about 1MHz (if I'm not wrong), 5mV, from an antenna, through RG174 coaxial. It is clearly seen in the following picture of my oscilloscope screen.

Then I connect the same cable to my spectrum analyser, and see nothing like this apparently (see next picture).

Is my spectrum analyser damaged, or am I missing some point ?

Additional information:

OSCILLOSCOPE: AC, 50 ohm, 1ns/div, 5mv/div

SPECTRUM: 50 ohm, start frequency 500kHZ, stop frequency 15MHz, ref level 1mV, attenuation 0db, 10 db/div, set in average mode for clarity, but the same problem subsist in non average mode.


texts: Series circuit LED controlled by Arduino schematic question

texts:
I'm currently making a project with multiple series circuits to PWM control multiple LEDs. I have figured out how to make it work with a transistor, however I was curious if this way would work as well. Thanks for your help!

simulate this circuit – Schematic created using CircuitLab


texts: What is the relation between bandwidth and data rate?

texts:
If I have a 20Mhz bandwidth provided by my 2.4ghz router then will my internet speed will be 20M symbols per sec which is equal to 20×4= 80Mbps (considering 16 qam modulator with 4 bits per symbol)
Is it true?


texts: Can I charge a 12V battery with a variable, low-voltage generator?

texts:
Let's imagine I have a generator that outputs a voltage between 0V and 2V, most of the time around 0.45V or 0.85V.

Is it possible to charge a 12V battery with it ? How can I estimate how long it will take, ignoring voltage variation ?

Please note that my level of understanding electronics is quite limited - I know a bit of theory but can't wrap my head around it...

FYI, the generator I would like to use is a hydrogen fuel cell, converting hydrogen+oxygen into electricity, if I'm not mistaken.


texts: Correct Way to Limit Op Amp Output Current

texts:
I'm planning to use an AD817 op amp in the output stage of my function generator (datasheet).
I'm worried about how the part would stand up to a short, so I ran some simulations.  The simulation below sources 70mA through R3 when the output (probe tip) is shorted.  This makes sense and tallies somewhat with the datasheet which gives a max current of 100mA @ 25degC, but less at higher temperatures.  Since the part (according to spice) is dissipating 800mW it's likely to be hot.  Although 800mW is within the max spec for this device (around 1.4W @ 25degC), I'm not comfortable with 800mW of dissipation.  Which brings me to the question.

Is there a best practice way to limit the output current of an op amp under short circuit conditions?

Basic Amplifier:

Here are some options I've tried, with comments:

1) Push-pull Amplifier to Relieve Op Amp Output Stage

Works well to limit op amp output current but could deliver 10V/47 = 200mA through R3 @ 1W.  The transistors would need to dissipate 500mW each.

2) BJT Based Current Limiter

BJT based current limiter based on some sources I came across (see here and here). This is more like what I'm looking for, but I couldn't make it work!.  Am I correct in thinking that the current diverted away by Q3/Q4 ends up at the base of R3?

Other options:

3) Reduce the gain.  Reduced signal amplitude isn't desirable.

4) Limit the power supply current.  Would (needlessly?) effect other parts of the circuit.


texts: Is it legal to design an open source AHB master?

texts: Is it legal for open source cores to be compatible with the AMBA specification?


texts: Would this 5.5V transient voltage suppressor be damaged at 15V?

texts:
I have a circuit which is designed to be powered with a 5VDC source, but has been powered accidentally by a 15VDC source for a couple of seconds.
On the PCB I see a transient voltage suppressor (TVS), whose datasheet can be found here (the exact one I have is SP0504BAHTG - SOT23-5.)
I suspect this component has been exposed to the 15VDC. Unfortunately, the datasheet doesn't mention anything about absolute maximum ratings for Vin (it does mention that it works up to 5VDC in, but that doesn't imply by itself that the thing would be damaged above 5VDC.)
Would you consider it likely that this thing is broken/damaged?


texts:
The goal is to design a circuit that can accurately measure light intensity with little temperature dependency.

Common application uses photodiodes to do so.

Photodiodes can be measured either in Photovoltaic mode or in photoconductive mode.

The caveat, is that photodiodes have strong temperature dependency almost 1% for 10°C, and I need to correct for it.

An idea I had going through some schematics would be to design a differential measurement between two identical photodiodes in photovoltaic mode.

The photodiodes would be on the same PCB and on top of the photodiodes a piece of translucent, diffusive material would be glued and then covered with a dark casing which is open in one side.

The light would come from one side, hit the first photodiode and then hit the second one with a lower intensity as it's being diffused through the material.

An amplification circuitry would compare the difference between the two photodiodes and the overall circuit calibrated with a known light source.

Would this principle work, or is there issue I overlooked?

Perhaps a simpler solution is possible?

There is a schematic out there that works in photoconductive mode and correct for dark current, but there is seems to be other factors that contribute to the temperature dependency, perhaps they are negligible?


texts: What is the appropriate unit for measuring power consumption by a section of code?

texts:
I am wanting to measure the energy consumption of running some intensive blocks of code on Android, but I am very shakey with my electricity knowledge, so I am unsure what measurements I should be looking for.

In the Android settings,they give power consumption in mAh. An academic paper I am looking at gives energy consumption on mW. I want to make some comparisons between my measurements, and the measurements in this paper. Is there any way to go from mAh to mW? Which unit of measurement is most appropriate?

I appreciate any help. I am a bit lost when it comes to electricity.


texts:
I have designed a PCB using a PIC18F6520 and a 32MHz crystal. Using a breadboard with a PIC16F877A, my code works great. But when I load a simple LED blinking program onto my PCB, the LED flickers when I touch around the crystal and does nothing otherwise. The capacitors are 22pF, which gives a load capacitance of 11pF (the crystal specifies 12pF)

The relevant section of my PCB is attached below (please note that I have turned off the ground pour for better visibility, but it is there):

And here's the corresponsing section of schematic:


texts: Unstable input to trigger LED after 10-15 seconds (12 V)

texts:
I have a small excavator that, when fuel levels get low, the warning light flashes irregularly (due to movement of the machine) until it stays on as fuel level gets really low. It's very annoying and loses the effect of a goofy light as it loses importance in my concentration.

I have looked at the sensor and it is a simple On-Off float switch, not a more complex resistive wiper float switch.

What I'd like to do is to have a circuit that only triggers when the input trigger is on for ~10-15 seconds (ideally adjustable to 30-60 seconds or so - I'd have to work this out in the field) and the warning output stays on until input is reset by turning machine off, as one does when refueling (usually!!)

The output signal ideally would be a bright LED (even flashing ~ 1 second interval is OK) with possibly an audible alarm as well.

I have occasionally mucked around with, and have some, 555's since they first came out ;( and can read circuits OK. I am assuming that these can be used satisfactorily, but happy for any ideas.

I'd appreciate some help here. I searched for similar, but the answer was not quite suitable. Thanks

simulate this circuit – Schematic created using CircuitLab


texts: For the circuit shown find the Thevenin’s equivalent circuit between terminals A and B

texts:
Here I began with Vth making mesh equations :

48-6I1-12(I1+I2)=0

12(I1+I2)+42+8I2=0

With which I get I1=4A & I2=-2A

Then I considered the open circuit part AB to use the 2 mesh currents there which is where I do not understand how to proceed.

For Rth also I am getting an error as well.


texts:
I want to make a simple circuit to monitor if there is activity in a USB 'dongle'. Let's put an example, that I want to monitor if a 16GB usb dongle is working well (if it's not hung)

It's seems simple to monitor the D+ and D-, but the question is:
If the PC doesn't access to it, Does the USB protocol send packets to it, in order to 'control' it even if the PC is not reading/written it?
I want to detect if the USB 16GB dongle hangs or if the PC hangs too.
Thanks.


texts:
I want to understand how the GPIO pins of my TIVA uC will behave when the voltage is above Vcc or below GND. I assumed I could just Ctrl+F "injection current" in the datasheet and that would give me "input high injection current" and "input low injection current", like on this question. Unfortunately, that's not the case:

So, apparently, the datasheet specifies different values for the GPIOs and the pins themselves, but I don't understand how they interact. It seems to me that
 \$ I_{INJ+} \$  and \$I_{INJ-}\$ are the data I'm looking for: if the pin is above Vcc+0.3V, it can sink up to 2mA (through the protection diode), and if it is below GND-0.3V, it can source up to 0.5mA (through the ESD clamp circuit).

If that's the case, then... what do the GPIO's \$ I_{INJ-}\$ and \$ I_{MAXINJ-} \$ mean? Shouldn't they have the same signal? Should I consider the GPIO injection current values or the pin injection current values when dimensioning protection resistors?


texts: How can one model a microcontroller's power consumption?

texts:
I was checking out this EE.SE question and thought I might play around with a similar idea on my own. I started to think about how I would model a power supply for a microcontroller with two possible sources (like a UPS for example), let's say a battery and some regulated supply like a USB connection. As soon as I began, I realized I do not know how to appropriately model a microcontroller in this way. It seems intuitive that I could use the following process (hypothetical problem below):

I know from testing that the average current into V+ of the microcontroller is 20 mA
My source voltage is 3.4v
Therefore, my simulated load should be \$3.4v/20mA\$ or \$170 \Omega\$

Does this approach work? If not, what is a better approach?


texts:
This circuit is in steady-state. The open-circuit represents the capacitors in steady state.
Why is there voltage across Vc1? and no voltage across Vc2?


texts: Can I wire the two sides of a L293D Dual H-Bridge together if I only need one H-Bridge?

texts:
Background: I'm using an L293D dual H-Bridge to drive a DC motor, but only one motor, and the package contains two complete H-Bridges. This is all being soldered onto Veroboard (stripboard).

Question: Is it possible to use the two sides of the chip sort of "dual wired" in parallel? Arguably to supply more current (not strictly necessary) but really so I don't have to cut as many strips on the stripboard.

Here's my reasoning...
Apart from Vin and 'enable', the two sides of the chip are mirror images, in other words, it seems to me that I could leave the stripboard intact across the chip for The inputs, outputs and ground pins. I would use output 1 and 4 together for one terminal of my motor, and Output 2 and 3 for the other. I'd then also have Input 1 joined to 4 and Input 2 joined to 3. (The input signals are coming from a Netduino)

I was already planning on having all the GND connected, as they're also used by the chip for heat sinking.

Here's a badly drawn pinout of the chip.

Edit: Datasheet here: http://oomlout.com/L293/IC-L293D-DATA.pdf

2nd Edit: Having read the datasheet in reference to Olin's answer I Can't find any reference to whether they use FETs or not, (in fact the word "transistor" only appears once in reference to a possible load). I have found reference to people stacking or Piggybacking these chips on top of one another (to provide more current). If that's possible then I'm guessing wiring across should work. I will give it a try and report back.


texts: Is my Precise Capacitor Ratio Repeatable?

texts:
I have designed a 1Mohm, 0Hz-100MHz fixed attenuator circuit (15pf/300pf). I am using 1%, C0G capacitors.
There is also a TS5A2053 analog switch connected to the output of the attenuator.  The switch will add 18.5pf of capacitance to ground (typical).  I will layout the PCB to minimize stray capacitance and I will tune the values to that layout.

My question is, when this ckt is produced in volume how much variation in the capacitance ratio should I expect to see from unit to unit? And what are the causes of this variation?

Obviously the capacitors (+/-1%) themselves will yield +/-2%. The resistors are negligible.
C0G should not change much with age?  Would soldering change the value? How much variation should I expect from the analog switch (only "typical" is specified)?

Edit: Sorry, I was vague about the schematic; but to be specific, it is a simple voltage divider - two resistors and two capacitors.

Edit:  I have found several sources which say that the capacitance of a mosfet does NOT vary with temperature. So, the capacitance of my analog switch will not likely vary with temp - I think only the switch's initial capacitance will vary due to process differences (thickness of the diffusion channel?).


texts: How to switch DMM between 10 different batteries?

texts:
I'm trying to figure a way to switch a DPM from battery to battery in a 10 battery series string. At first I thought I'd do it manually using a small SMD 2 pole 10 position rotary switch but the only ones I've found at a reasonable price & size are coded (BCD). Then I thought it would be better to automatically scan. I bet there is a device out in chip land that could do the deed.

I would prefer to not go smart (i.e. PIC) or relays if possible. Something simple, small & cheap. Discrete FET switches would take up a fair amount of physical space which I don't have. Is there a 20 FET ASIC?

What is a circuit I could use to switch between multiple batteries?


texts: Non-inverting op-amp circuit with gain = 1

texts:
I am preparing for an exam and I have a problem with the following exercise (hope my translation is good enough):

  We have an op-amp circuit with gain \$G=+1V/V\$ for AC signals and
  \$G=0V/V\$ for DC. The op-amp has two power supplies. The input
  resistance (for medium-range AC signals) is \$50k\Omega\$. Assume that
  additional capacitors (if needed) are infinitely large.

  The input signal - square wave with duty cycle \$50\%\$, has
  \$V_{pp}=50mV, \ f=1MHz\$ and offset \$ 5V\$.

  Op-amp parameters: \$A_0=10^5V/V, \ f_{UG}=2MHz, \ I_+=I_-=2\mu A, \
 SR=2V/\mu s\$

  Draw a diagram of the circuit, calculate every resistance
  On one graph, draw \$v_{in}(t)\$ and \$v_{out}(t)\$
  Calculate time \$t_x\$ which passes from the moment when output signal reaches \$-20mV\$ to the moment when it reaches \$+20mV\$

First question: is information about input bias currents important?

Secondly, I think that the circuit will look like this:

And here, for medium-range AC signals \$R_{in}=R_3=50k\Omega\$

In this circuit \$G=1+\frac{R_2}{R_1}=1V/V\$, hence \$R_1=+\infty\$

And since \$R_3\$ is a compensating resistor and it sees only \$R_2\$, then we got: \$R_2=R_3=50k\Omega\$

Because the amplitude of the input signal is equal \$50mV\$, then there is a possibility that SR effect can occur. We need to check it. \$A_{in}=A_{out}=50mV\$

I am not sure about English naming, thus:

\$f_{UG} \ - \ \text{Unity Gain, open loop} \\
f_{CL} \ - \ \text{-3dB point, closed loop} \$

And we have:

\$f_{CL}=\frac{f_{UG}}{G}=f_{UG}=2MHz\$

So:

\$A_{out}\cdot2\pi\cdot f_{CL}=50mV\cdot2\pi\cdot2MHz\approx 0.63V/\mu s < SR=2V/\mu s\$

There will be no SR effect.

Rise time:

\$t_r=\frac{0.35}{f_{CL}}=175ns\$

\$10\%\cdot50mV=5mV\$

Hence, \$t_r\$ is the answer for question no. 3.

And the graph, I think it will look like this

Is my solution correct?


texts:
I have an XLR cable that I am trying to wire directly to a microphone that did have a Micro XLR connected to it. I have cut the male micro XLR's from each side and am left with the following wires -

Lead - Red (2), White (3) Naked (1)

Mic - Red (3), Naked (1)

I am struggling to get these mocked up to produce any sound output. It seems that the lead numbers do not match the corresponding mic numbers or am I wrong?

Thanks,
Chris


texts: Is it ok to connect the output of a solar controller to a fused outlet on a fuse panel?

texts:
The fuse panel is breakered to a battery and is used to power other low amp equipment.  The model is the 6 gang blue sea panel with blade type fuses.
Since the fuse panel is just a couple pieces of metal with fuse holders connecting them I didn't think it really mattered but it felt wrong routing the solar power "backwards" through the panel.


texts:
I have a question regarding a control loop system which is subject to disturbance, unfortunately I missed a couple of lectures on the subject and now am scratching my head as to how to do it. The loop is shown below.

\$D(s)=\frac{K}{s+10},\$   \$M_p(s)=\frac{M_o}{s},\$ \$G(s)=\frac{s+3}{s^2+4s+5},\$ \$I(s)=\frac{1}{s}\$
\$K_t\$ isn't used for now so that can be ignored. \$M_p\$ is a step input disturbance.
Anyway, the question in hand is asking for the steady state error assuming the system to be stable, and I am simply struggling with getting the initial T.F. in order to get this.
It is given that I need to determine \$\frac{\theta(s)}{M_p(s)}\$ and furthermore am given that this is:
$$\frac{(s+3)(s+10)}{s(s+10)(s^2+4s+5)+K(s+3)}$$
But I baffled as to how to get to this result, any ideas?
After this I know what to do but I just want to know how to get to this stage in the first place.


texts: Verilog outputting specific bit from register to output; getting constant 1's

texts:
I am trying to create an program that bit bangs a value from an FPGA to an arduino.  In the module I created, every other clock cycle, the FPGAdata output should be set to the next bit of t.  The problem is that FPGAdata equals 1 the entire time.  What is causing this?

module fpgaread(ARDUINOclk, FPGAclk, FPGAdata);
input ARDUINOclk;
output reg FPGAdata;
output reg FPGAclk;

reg [15:0] count=0;
reg [127:0] t =3542638353836;

always @ (posedge ARDUINOclk) begin
        count=count+1;
        if(count%2==0) begin
            FPGAclk = 0;
        end else if (count <= 256) begin
            FPGAdata=t[(count-1)/2];
            FPGAclk = 1;
        end else begin
            count = 0;
        end
end

endmodule

Note t is just a number that I am testing with.  In the future I want to make it be a variable and not just constant.

The purpose of the <256 is that I want to send 128 bits.  In the future I would add more code in the else for a reset, but this does not effect the question because the output is 1's before it even gets to the end.

I am using quartus II v13 with a Cyclone II

EDIT:
Here is a schematic of what quartus sees from the program.  FPGAdata is just set to 1.


texts: What security risks does the Test Access Port (TAP) introduce?

texts:
Trying to get my head around the JTAG world I looked at how the Test Access Port (TAP) works and although I get why we need it, the diagram seemed to me (as a software developer) introducing some kind of backdoor to the architecture.

In the software world such mechanisms can be used in testing some parts of the software, however they get removed (hopefully) before the software is ready for release.

So the questions are:

Doesn't TAP introduce security risks to the hardware?
Are there standers to mitigate such risks if they exist?