texts: If positive feedback makes output exponentially increase and cause instability in an opamp then why doesn't negative feedback make output extremely small and cause the system to collapse?


texts:
I have followed the tutorial from Makezine about an Infrared heart-beat sensor, and I have essentially used the same components listed on the video (that is, the same resistors and the same IR Emitter and Detector).

So, with a simple source-code just reading the analog output and printing it to the Serial Monitor, I see that the sensor is working fine by just analyzing how the amplitude changes as I move the emitter around the sensor.

The problem begins when I try to put my finger on the sensor (I've tried many different component angles, even 180°), and in my serial monitor, the amplitude is almost constant, that is, it doesn't even make sense comparing to my real heart beat rate. It looks something like (10ms delay):

  34,34,34,34,34,34,34,35,34,34,35,34,34,34,34,34,34,34,34,34,34,35,34,34...

Now, I want to know if there is a way to amplify the sensibility on this sensor, if possible without using any op-amps, or if I'd have to change the IR components to something stronger, like the ones that look like a usual color LED.

Or even if the ambient light is interfering (which I don't think so, because I cover pretty much the entire IR pair with my fingers), or if the unamplified current has too much resistance (which I also think it doesn't influence in this specific problem, but I may be wrong).

Other than that, any solution is appreciated.


texts: op amp biasing... why are voltage sources reversed biased +/-?

texts:
I'm still trying to understand the theory of audio signal processing, namely guitar amplifiers.  The main thing that got me started down this path was a broken amp that I have.  I have since figured out the problem and I know how to fix it but I've also been looking at the schematics for it as an example circuit to help me learn the answers to other questions.  I will attach, as long as it is ok for educational purpose, two cutouts from schematics that go with the amp (or close to it) and ask a question.  I have many questions but I'm focusing on just one:  What is the purpose of the two voltage sources (in both schematics, which are different sections of the overall amp circuit) that are both connected via diodes that are reverse biased?  I've marked the areas with red.  I think I have a guess, but I don't know if it is right.
I included both of these sections to show the similarity, they are nearly the same circuit.  The main difference is the input source is expected to be different as the first is a guitar in jack and the second is an effect return jack.  Let's focus on the first from here on out.  I will try to explain how I think the circuit works, please correct anything that is wrong.  The signal comes in at JS1.  It seems a little complicated, my guess is it is dealing with the option of "balanced TRS" input, but anyway it goes through a little section I think is a filter and maybe has something to do with impedance matching with the coil looking thing (On the real amp).  I'll ignore the details about this section because it doesn't pertain to my real question.  And then the signal line hits a resistor R50 and a capacitor C28.  I'm not sure what R50 does except maybe just to be part of the voltage divider effect with R49.  The C28 capacitor is probably like a DC filter to ensure clean AC.  Then there is a split to a 1M resistor R49, which I think is the other half of a voltage divider to set the input impedance and get a high voltage/low current signal to move on to the op amp + input.  Then there is a leg to a capacitor C57 which I think is an AC filter to remove unwanted frequencies (not in audio spectrum) IE noise.  Lastly, before going to the op amp's noninverting input, there is a connection with +/- 15V.  These are my question.  Both connections go through a diode that is reverse biased, D1, D2.  This seems at first odd and ostensibly useless, but my guess [WAS WRONG!].  The correct reason is given below by several helpful answerers, it's a voltage clamp to protect the op amp, disallowing any voltage that exceeds +-15 in case it somehow was supplied from the external input source.  Thanks in advance for your help!


texts: Buffering Micro-SD data for power saving useful?

texts: I have a datalogger which has only 4KB of SRAM, and because of that it needs to flush its buffer to MicroSD every second. Would adding external SRAM to create a larger buffer safe any significant power? Because when I look into Sandisk's datasheets it says that their cards go into sleep-mode after 5 ms. So it seems there would be no difference in writing every second vs. writing once in 30 seconds? However everything I've hearded untill now seems to contradict that.


texts: Accurate RMS voltage measurement of DC with RF ripple

texts:
As the title says, I have a signal which is mostly DC but has some RF ripple on-top of it.

The signal comes from a pickup coil that receives a 13.56Mhz signal (RFID). That signal gets rectified by a high-speed diode bridge rectifier. This is followed by a leaky low-pass filter, e.g. a small capacitor and load resistor in parallel. (Note: I can't change any of this acquisition circuit).

Now I want to get an accurate measurement of the RMS voltage.

Currently I just hook it up to a digital oscilloscope and use the internal measurement functionality. This however gives slightly different readings depending on the time-base and voltage range selection.

Since I want to automate this measurement in my lab I thought about building a little box that does a more precise RMS to DC conversion in analog, so I can use a precision voltmeter to do the measurements. However, all the "true RMS to DC" chips that I've seen so far won't deal with signals of higher frequencies than a megaherz or so.

Any ideas how I could accomplish my goal?


texts: What frequency accuracy specification for cellular phone hand set? How is it achieved?

texts:
What are 'the industry standard' frequency accuracy specification, in ppm or ppb, for cellular phone hand set?

How is it achieved? is TCXO (temperature compensated) enough?  Does OCXO (oven control) needed?

Does handset frequency control works along or it works with base stations to 'exchange calibration data' to enhance accuracy?

How can the needed accuracy achieved in very very low cost phone? (phone only, small screen, no camera, no add on)


texts: Unable to toggle an LED with STM32 Blue Pill

texts:
I'm a beginner, and I'm using an STM32 Blue Pill board for the first time. I completed a basic tutorial on how to activate the PC13 pin (on-board LED), but now that I'm trying to get an external LED to blink on a breadboard, I'm having issues.
I'm using the STM32CubeIDE, and allowed the IDE to autogenerate the configuration code that I need to use pin PA0 as GPIO output:
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOC_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_0, GPIO_PIN_RESET);

  /*Configure GPIO pin : PC13 */
  GPIO_InitStruct.Pin = GPIO_PIN_13;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

  /*Configure GPIO pin : PA0 */
  GPIO_InitStruct.Pin = GPIO_PIN_0;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

}

Within my loop, I'm simply running
while (1)
  {
      HAL_GPIO_WritePin(GPIOC, GPIO_PIN_0, 1);
      HAL_Delay(500);
      HAL_GPIO_WritePin(GPIOC, GPIO_PIN_0, 0);
      HAL_Delay(500);
  }

Despite this simple code, I can't get the LED to blink. Here's a picture of my circuit:

To summarize, I have the 3.3v and ground pins connected to the breadboard power rails at the bottom (with a red power LED). I have a jumper cable connecting the A0 pin to row 25, and a 330Ω resistor in series with a 5mm LED with a forward voltage of 3.0V and a forward current of 20mA. I then connect the cathode of the LED to the negative power rail on the breadboard (attached to board ground).
I've tried swapping jumper cables, output pins, LEDs, resistance, but nothing has worked. I connected the pin jumper cable to the positive power rail, and the LED lit up (as expected), so I don't think there's something wrong with my circuit. I've also re-programmed the MCU to make sure my program was uploading correctly. Perhaps I'm misunderstanding the relationship between the pin and ground? Any help would be appreciated.


texts: How would you dampen this little quadcopter?

texts:
Well,

I made a little quad from scratch. From scratch as in from PCB design.

After assembling, testing, some coding, it turns out my accelerometers get WAY TOO MUCH vibrations and I can't detect orientation using Kalman filter... Bump!

Has anyone encountered this kind of problem before? How would you solve it?

Image of Quad:

Image of tester I used to visualize orientation:

Any helps much appreciated will be :) I already ordered Moongel but not counting it'll filter out much vibration in my case.


texts: How Signal Integrity check in Altium Designer compares to HyperLynx?

texts:
I've finally discovered how to simulate high-speed signals propagation on PCB using Altium Designer, and it looks easy to use & convinient.

I wonder,

how close to reality results from Altium signal Integrity check (provided that PCB layers are set up correctly, and proper models are used for drivers & receivers), and
what are main benefits of using (more well known/powerful) tools like HyperLynx?


texts: Complete discharging of Initially charged capacitor through Inductor

texts:
I have been trying to simulate a parallel resonant circuit in Pspice . The idea of the circuit is to discharge C18 (Cin) completely (This cap is initially charged to 1.3 V) through the inductor and charge C19 completely. In order to speed up the process, I have used two equal bypass capacitors (C20 charged to 1.3V) so that it does not take infinite times to discharge and charge the input and output caps respectively. I have used voltage controlled switches with a duty cycle of 0.5 to illustrate charging and discharging.
The operation is similar to a synchronous inverting buck-boost converter wherein:

In the first pulse "DT"(PW), S2, the C20 discharges, discharging C18, and the energy gets stored in L8.
During "(1-D)T", the energy stored in L8 gets transferred to C21 which charges C19.
This process ideally continues until the charge in C18 is completely replenished and transferred to C19.
This strategy is basically used to solve the infamous two capacitor paradox.

The values of L and C have been calculated for an inverting buck-boost converter design using design equations. The driving frequency = resonant frequency.

Now my question is:

Looking at the graphs, Energy transferred to C19 is 0.25 of Initial Energy at C18.
Likewise, Charge at C19 is half as that of C18.
Why?

In this case, there's absolutely no use of having the inductor L8, assuming everything is ideal (resistances have been added to prevent floating nodes in pspice), and this should only happen when two capacitors are connected in parallel with a switch.

Does the frequency have to be rightly adjusted to charge C19 to 1.3V (initial voltage of C18)? (I have used resonant frequency, but have also tried to tune them, but no use!)
This is an ideal case. How would I achieve complete charge transfer?

Please help!

Cheers,
S


texts:
How much can a power brick safely vary from what the device it's used with expects?

As an example, let's say I have a device that needs an AC=>DC power brick. The device expects 19V/1.58A, but the brick is missing. Now let's say I find a brick where the connector fits the device and is also 19V, but outputs 3.42A. How safe is this likely to be for the device? Will the device only draw the power it needs, or am I likely to blow a capacitor somewhere?

If that latter, this example the brick provides more than twice the current requested. How much closer would have I have to get to be reasonable? How much can voltage vary vs amps? Given different devices likely have more tolerances than others, is there a good rule of thumb to look for to know how much you cheat on matching power brick to device?

While the example does match a real situation, I'm also interested in the general case.


texts: Hack fibre optic transceiver for wireless data link

texts:
I'm brainstorming ways to implement a high speed wireless laser data link without the exorbitant cost.

Would it be possible to take a standard SFP transceiver module and use that across free space rather than through a fibre?
In other words, to point two transceivers at each other from a distance without any fiber optic cable between them. (It might be necessary to have the modules believe there are cables plugged in)

There would certainly be severe attenuation and noise issues to deal with.
However, since some fiber optic modules have to transmit across 40km links @ 10Gb/s, the existing circuitry might have enough power and sensitivity to handle this.

There is also the issue of beam focus and divergence, although this could be cheaply mitigated by using a telescope.

Would this work for 10Gb/s with a 1 kilometer range?

Does anyone have any modules they could try across a room to begin with?


texts: What is the typical on-resistance of a TFT switch (in an LC display)?

texts:
When using normal MOSFETs as switches, I am used to Ron=1...100, maybe <1k and Roff a few MOhm.
Now I found in a book "When VG=20V, the TFT can be replaced by an equivalent resistor with Ron=5MOhm".
First I thought this must be a typo. 5MOhm I usually round up to infinity.
Can it really be that the on-resistance of a typical TFT on an LC panel is 5-6 orders of magnitude higher than a typical MOS switch we would put on a chip?


texts: Why does the SATA power connector have so many pins?

texts: With only 4 cables, two of which are ground, it seems like it has way too many pins. Why is this so?


texts: Power Analysis for Non-sinusoidal excitations

texts:
For a series RLC circuit excited by a non-sinusoidal voltage expressed as any Fourier sum, we calculate the absorbed power using the formula:
ΣVI \$\cos \theta\$ where \$\theta\$ represents the phase difference between voltage and current for some harmonic.
i.e. Ptotal = V1I1 \$\cos \theta\$1 + V2I2 \$\cos \theta\$2

Basically we are adding the powers obtained by considering each harmonic as a separate source to get the Ptotal for the actual source.(superposition theorem) My question is, we know that power calculations can NOT be done using Superposition Theorem as the expression for power is not LINEAR but we're still getting the right answer anyway! Can someone help me get my head around this?


texts: What applications use ISO/IEC 14443 Type B?

texts: I bought a MFRC RC522 rfid module for my Arduino Leonardo, after I purchased it I notice it only supports ISO/IEC 14443 Type A, and not Type B. I was curious what applications uses Type B anyways? I checked wikipedia, but I am still uncertain about it.


texts: Generating thermal noise from a resistor

texts:
I'd like to create a random number generator based on thermal noise from a resistor, using an opamp to amplify the noise and an inverter to convert the resulting spikes into a digital signal.

Here's my current design:

When I remove R5 and feed Multisim's thermal noise source (set to 10M ohm / 27C / 1MHz bandwidth) I get perfect results. The output of U2 is noisy, the input of U1A ranges from roughly +12V to -12V, and the output of U1A gives me a random-ish digital output. I plan to feed this to a PIC and do bias correction on there.

The problem is that Multisim's resistors are ideal, or at least ideal enough to not produce any noise. As such, I can't test this. Will it work as I expect, or am I missing something?

Update #1:
I've split the opamp into three stages and introduced a second 10M resistor to make the input midscale. I now get a much higher bandwidth output and my gain is about 10,000.

Update #2:
Ok, I think we're getting there. Some resistor values have been tweaked, and a midpoint has been added.


texts: Understanding difference between Interrupt Address and interrupt vector address

texts:
In my undergrads, I was taught 8051 and in interrupts my professor had said that on interrupt SP points to the address that is hardcoded and Program goes to excute those instructions. But in between two address space is only where I can write interrupt handling code and I wrote more than than byte available it will overwrite the next interrupt instructions.

Now when I look at Atmega or LPC2148 Datasheet it has interrupt vector address and I am assuming that it points to a address where instructions for interrupt handling instructions are written( not exactly on those addresses). Is my assumptions correct?

P.S Due to being on low bandwidth net, I am not able to provide links to Datasheet. Would do that when I get back.


texts:
I want to write a spice model of a coupled inductor.
I’m wondering how to find N1:N2 in the figure below.
I have the same windings but different inductances in my two coils.
Is N1:N2 equal to 1:1 or \$\sqrt{L1}\$:\$\sqrt{L2}\$?

I also found the SPICE syntax of a coupled choke.
For example,
L1 1 2 1u
L2 3 4 5u
K1 L1 L2 0.6

Can this example get the same result to the model below?


texts: How to calculate the maximal temperature of a transistor

texts:
let's assume I have this transistor (IRFR640):
https://www.infineon.com/dgdl/Infineon-IRFR6215-DS-v01_02-EN.pdf?fileId=5546d462533600a40153563595592114

$$R_{DS(ON)} =0,295 \Omega $$
$$V_{max} = -150V$$
$$I_{max} =-13A $$
$$I_{load)} =260mA $$
$$T_{a} =50°C \Omega $$
$$R_{\theta ja} =50°C/W$$
We apply on the drain 100V (\$V_d = 100V\$)

What is the good calculation?

1) $$T_{PMOS} =T_a + R_{\theta ja}*R_{DS(ON)}*I_{load}^2 $$
So
$$T_{PMOS} =50 + 110*0,295*(260*10^{-3})^2 = 52,2°C $$

2)$$T_{PMOS} =T_a + R_{\theta ja}*V_{d}*I_{load} = 894°C $$

What is the good answer? And why?
I use same power dissipation
Tthanks


texts: Why can't the orthogonal PN codes help in the near-far effect?

texts:
The CDMA near far problem arises because handsets may be anywhere within the particular cell boundaries. Some handsets will be close to the base station, whereas others will be much further away. In a free space scenario signals decay according a an inverse square law...signals within a cell will have a huge variation in signal strengths. For the receiver to be able to decode all the signals in the channel, they should ideally all be at the same signal strength

I got the above information on a website while trying to understand the near-far problem. I understood the basic concept that the mobile devices near the base station will have a higher amplitude when the signal reaches the base station as compared to the ones far away. But, can't the orthogonal PN sequences used in CDMA be able to handle this. As I recall, the sequences when ex-ored with each other will produce a string of all zeros.
Note that this question has already been answered here. There It has been mentioned that, the mobile phones dont have orthogonal codes. What if they did ? would that solve the near-far problem ? If not, can I know why ?
Basically, In short, If 2 mobile phone signals reach the base station at different levels of power but have Orthogonal codes, wouldnt that solve the near-far problem ?


texts: TFT display wiring on Sparkfun Pro Micro

texts:
Please help me configure the wiring for this TFT display.
I’ve tried using the Waveshare TFT display with both the Sparkfun Pro Micro and the Raspberry Pico but had very little success.  Only the backlight of the display lights up. The 1.3inch TFT display works with the Pico using the connections above. I used a 2 inch display with the Arduino Uno. The screen works fine on the Uno.
I used Python code from Erik's blogpost for the drivers which worked on the 1.3 inch display using the Pico, and code from Adafruit to run the 2inch display on the Raspberry Pi. I attempted using Adafruit's code using the Sparkfun Pro Micro but only had backlights.
Below is the wiring connections list I started making while testing the screens. Some connections might be wrong as I am still figuring things out.


texts: Can the firmware on STM32F4 be updated through USB without toggling Boot0?

texts:
I've designed a device using a STM32F439 and would like to have a PC application where the user can update the firmware of the device.

My firmware developer has told me the we would need to give the user access to the Boot0 pin.

By default Boot0&1 are pulled low but can the MCU be reset into Bootloader mode through software without having to touch any jumpers etc?


texts:
Using this tutorial, I am using ngspice (on Cygwin) to run the following file:

My first circuit
v 1 0 dc 10
r 1 0 5
.end

However, after running it using ngspice < first.cir, I receive the following output:

Circuit: My first circuit

Note: No ".plot", ".print", or ".fourier" lines; no simulations run

How do I print the basic diagnostics of the circuit?


texts: Has fsk over wired communication channels ever been done?

texts:
I have done multiple searches to figure out if fsk encoding of binary data has ever been used in a "wired" communication scheme but have come up with very little.

It seems, at least to me, that utilizing multiple, thin frequency bands to encode essentially parallel pieces of information, cabled internet links could dramatically increase their bandwidth.

Does anyone know if research related to this has been done?


texts:
Searching for images of SPI wiring between Master and Slaves, I found that some of them connect MOSI/SDI of master to MOSI/SDI of slaves and so MISO/SDO of master with MISO/SDO of slaves, meanwhile others connect them as MOSI/SDI to MISO/SDO and MISO/SDO to MOSI/SDI.
There's someone that can me explain when there is the difference?

P.s. I'm working with PICs and I'm trying to drive a LED IC controller, but I'm mostly looking for a generic answer.


texts: Do I really need to put stm32 microcontroller into bootloader mode to program it?

texts:
I have started learning stm32 microcontroller for a while using a very small development board "stm32f103c8t6" (or blue pill). when I started, I learnt from some tutorials that I have to switch a jumper in order to program it.

(The photo is a screenshot taken from a random tutorial, but every tutorial I have watched also said that)

The jumper - as far as I know - only changes the boot mode of the processor to load from the system memory(the bootloader) which only takes effect if I restart the board to starting booting from there.
I don't know how is that supposed to be a "programming mode" as I'm using an external st-link programmer that uses SWD.

So my question here , Is there really such a thing called "programming mode" ?
and if so, How exactly does it work ?
Also it's worth mentioning that I've just tried to program it and the program worked as it's supposed to (I hope I haven't screwed anything up :d ).


texts: How to power a 1.5V motor with a 3V source?

texts:
I just started getting into electronics so I'm still a major noob. Any help would be much appreciated!

I have an Arduino UNO and have made a few basic circuits with LEDs and a small speaker using examples online. I recently learned a few of the electronic circuit equations like Ohm's law and am ready to start designing my own simple circuits.

I have a 1.5V-3V motor I'd like to try running with my Arduino. The issue is that the Arduino only has 3.3V or 5V power sources. I tried to use Ohm's law to figure out what kind of resistor to use, but I can't figure out what the resistance of my motor is. Am I wrong in thinking that a motor is the same as an LED? I assumed since both were diodes they would function the same way.

I'm attempting to make a simple source-resistor-motor-ground circuit, along the same lines as the simple resistor-LED circuits. I've seen people online say that PWM would work, but I wanted to try without it.


texts: USB On-The-Go - What receptacle types does it support?

texts:
Is it possible to use a USB mini B as opposed to the USB mini AB for USB OTG?

Can I use either USB mini or USB micro and does it need to be type AB or can I just use type B?


texts: Simple amplitude modulation of a square wave oscillator

texts:
I'm in the process of creating a classwide project for an introduction to op-amp and transistors. My goal is to create a 49 keys synth that every students can contribute a small part, run test plan and follow standard layout procedure.

I want to implement a simple attack release envelope right after the oscillator output to give more depth of sound and create a variety of  circuits.

From a mathematical perspective, it is easy to understand. You multiply the normalized enveloppe (0-100%) to the actual oscillator signal.

For now, it was easy to get a RC circuits generating the AR signal required. However, I'm currently stuck in the combination of the AR and the oscillator.

Bellow is my high level bloc diagram of one key

I came across different solutions and they mostly played around voltage controlled amplifiers and voltage controlled resistors. The few circuits that I came accross were too complicated for the students (given that the circuit will be repeated 49 times and that even for do once it was rather complex) or simply created the AR waveform, but didn't show how to combine it with the input signal.

I therefore seek help in finding a quick and dirty solution to merge an AR enveloppe with my oscillator. It might be really rough, really imperfect, but keep in mind that it is a mean to get students interested and to tackle a large scale project and learn various techniques along the way.

Edit: rough schematic base on Jonk comment

simulate this circuit – Schematic created using CircuitLab

I didn't calculate any of the values yet. The idea: detect the envelope of the square wave and compare it to 1v if the square wave is present the comparator will trigger...otherwise the line will read 0v (the key button will not let the oscillating signal through). I feed this to a RC network that is different depending on charge or discharge. Finally I get to my VCA.

The problem is: the VCA can't go bellow Av=1 (non inverting configuration in the application note) and I would probably need a range of Av = 0 to 1. I could scale it down afterward (example Av is 1 to 100) and then I put it into a 1/100 divider so that the range become 0.01 to 1. If you have further ideas, don't hesitate to comment bellow.


texts: What are the s-parameters of a rg58 coaxial cable?

texts: Can a the s-parameters of a rg58 coaxial transmission line be calculated. If yes, what are they?


texts:
I have an exercise (and merely an exercise) from my engineering Circuits class.  Either way, the example they wrote up for a supernode makes perfect sense, but the solution to the exercise does not.

I thought that since the answer is expressed as a matrix equation perhaps I simply needed to simplify in some way, but when I used wolfram-alpha to do this simplification, the numerical solutions were wildly incorrect, meaning there must be a problem with my actual systems of equations.  The circuit goes as thus:

simulate this circuit – Schematic created using CircuitLab

The book offers this solution as a matrix equation:
$$ \left( \begin{array}{cc}
\frac{3}{5} & -\frac{1}{2} & \frac{11}{20} & -\frac{1}{2} \\
-\frac{1}{2} & -\frac{3}{2} & \frac{3}{2} & 1\\
1 & 0 & -1 & 0 \\
0 & 1 & 0 & -1
\end{array} \right) \left( \begin{array}{cc}
v_1 \\
v_2\\
v_3\\
v_4
\end{array} \right) = \left( \begin{array}{cc}
0 \\
0\\
10\\
40
\end{array} \right)$$
Which I can't begin to reconcile with my systems of equations, which go:
$$\frac{1}{10}v_1 + \frac{1}{20}v_2 +\frac{1}{2}(v_3-v_2)+\frac{1}{2}(v_1-v_4)=0$$ $$-2(v_2-v_3)+\frac{1}{4}v_4+\frac{1}{2}(v_4-v_1)+\frac{1}{2}(v_2-v_3)=0$$
And of course
$$v_1-v_3=10$$
$$v_2-v_4=40$$
According to WolframAlpha, my Systems of Equations have cleaner (but incorrect) answers, meaning I won't actually bother to try to rewrite them as the book has them.

For starters, I don't understand how the numerator on these fractions ends up as anything but one....

If anyone can be kind enough to point me in the right direction, thanks a bunch!


texts:
Is there such thing as potentiometers that have a low resistance when centered and increasing resistances if you turn either left or right?

Edit: When i say centered, i mean that the pot is at zero resistance normally, when rotated clockwise, it will increase resistance. When rotated counter clockwise from the zero resistance position, it will also increase in resistance. Kind of like two pots put together in opposite directions.

Edit2: Well, specifically, I'm looking to modify a motor controller to give a nice smooth forward and reverse with a roll of the handle (think motorcycle throttle, except if you twist the other way, it reverses smoothly). I know the motor controller accepts a switch as forward/reverse and a pot as velocity control. Anyone ever encountered something like this?


texts: What are the two lines for on top of this tower?

texts: I have seen other towers with the same lines.


texts: cable spec: differential characteristic impedance

texts:
I am hunting around for a cable with twisted-shielded pair conductors with the correct differential characteristic impedance for RS-485 (120 ohm)

Most of the cable spec sheets for cables with twisted shielded pair just say "Characteristic Impedance = ... " (here is an example: http://www.alphawire.com/Home/Products/Cable/Alpha-Essentials/Communication-and-Control-Cable/6365?device=pdf)

Is this referring to the differential impedance of the two conductors or the impedance of a single conductor?


texts: Cursor search commands in probe window on PSpice

texts:
I'm using PSpice, and when I am in the probe window, and I want to mark a specific point in the probe window, I'm using
Trace->Cursor->Search Command
and the I'm typing sf le (10)
This command searching for the closest Y value to the cursor that equal to 10.
So my question is where can I find all the search commands that possible?
I searched in google, and the following tutorials

http://www.seas.upenn.edu/~jan/spice/PSpice_UserguideOrCAD.pdf
http://www.it.uom.gr/project/digital/pspcbscs.pdf

and more..  but couldn't find list of all the commands that are possible.

Does anyone seen this kind of tutorial or cheat sheet??

Regards
Matt


texts:
In MIPS, an I type instruction has the following format.

bits [31, 26] are for opcode
bits [25, 21] are for source register
bits [20, 16] are for transfer register
bits [15, 0] are for immediates

If the number of registers used is halved, then I will have two extra bits to use for the immediates. And if I'm assuming 2's complement form, then, I have 18 bits. So is my minimum value for the immediate \$-131072\$ and max value \$131071\$?


texts: Current source resistor values in differential amplifier

texts:
In this circuit How measure input impedance this differential amplifier in LTspice? the OP has used a 4ma current source in a differential amplifier.  I'm taking it apart to learn how it works.  I see that the diodes will give a pretty reliable 1.4v drop, and the transistor will give a 0.7v drop, which allows us to use a single 180 resistor to set the desired current to approx. 4ma.  This makes sense to me and checks out in a simulation.  Below is that portion of the circuit.  Of course, the collector in my schematic would connect to the emitter resistors in the diff. amp.

What I'm wondering about is the choice of a 3.3k resistor at the base.  It seems to me - as a novice - a waste of energy, as it sees a rather large current of 4ma.  Since the 3.3k resistor will always drop around 13.6v, couldn't its value be increased significantly to reduce how much current it has to handle?  As far as I can tell, the base only requires a small fraction of this 4ma, say around 40uA, sending 99% of that current through the diodes.
So my question is, how should one size this resistor biasing the base in a current mirror?  Is there a minimum required current to get the diodes to drop 0.7v?  Is there some compelling reason to set it at a particular value?


texts: Simulating a Constant Temperature Anemometer

texts:
I am trying to simulate the results I see when using a constant temperature anemometer circuit to sense air flow. An excellent discussion can be found: arduino thermal anemometer.

Here is my simulated circuit: https://www.circuitlab.com/circuit/ttr9y3/simple_cta/

The basic principle of the FS5 sensor (as I understand) is that there are 2 resistors, 1 to heat (RH = 45 Ohms) and 1 to temperature sense (RS = 1200 Ohms). The circuit is designed so that a constant temperature differential is maintained, i.e. when air flows through cooling the sensing resistor, it's resistance decreases, the bridge becomes unbalanced, the op amp activates the transistor, which then allows current to be drawn into the heating resistor in an attempt to re-balance the bridge. Therefore, the bridge voltage is proportional to the air flow.

I am getting the right results in practice with Vout=5V-10V depending on flow, and at rest I read:

Vout = 5V
AM2 = 40mA
RS = 1500 Ohms
RH = 65 Ohms

However, when I try to simulate this, I am getting Vout=9.2V and AM2=82mA! The DC Sweep should show that as RS decreases, Vout increases, yet this is also not the case.

This has been bugging me for a while now, please help me understand why this circuit works in reality, but not in theory! What am I doing wrong??


texts:
I just bought an Arduino Uno (brand new, just opened it now), and the compiler keeps saying "avrdude: usbdev_open(): did not find any USB device "usb"". Does anyone know why?

I'm running Windows 8 x64


texts:
This is probably a basic question for most people on here but I'm new to electronics and tend to learn by example, so figured this was a good one to ask!

I've got a board called a Nano Pi Neo Plus 2 that is very similar to a Raspberry Pi, just with a smaller form factor and cheaper - think of it as a Chinese knockoff ;)

I've also got an Arduino Nano.

I want to send boolean values from the Nano Pi to the Arduino Nano, and after researching different communication protocols I decided to use simple GPIO and turn them on and off to represent boolean true/false.

All good so far - I found some rough examples on the Internet and connected everything up. Unfortunately I've already blown up a couple of Arduino Nanos in the process!

This is where my electronics knowledge is very limited. I'm not sure if I need resistors on the GPIO pins (I presume I do to stop it blowing up) but I don't know if they should be pull up, pull down and what values (no idea how to calculate them).

I'm powering both boards using a single 5V power supply. I've measured the voltage on Nano Pi GPIO pins and the voltage drop was ~3.3v.

Could someone walk me through what's wrong with the circuit and the steps you'd take to work out the resistor configuration and values?

This is the breadboard layout I'm currently using. I couldn't find a Nano Pi part in Fritzing so I used a Raspberry Pi to show how it connects together.

Here's the Fritzing breadboard layout if that helps


texts: Why use MAX232 when using USB-to-Serial cable

texts:
I was wondering the need to use MAX232 type ICs when using a USB to RS232 converters.
A prolific based converter gives the following output, when transmitting 'a'

It seems to me that a simple NOT gate will make it suitable to be worked with a micro controller.

Note: I think my cable uses a PL-2303HXD USB to Serial Bridge Controller Chip.


texts: How many units of electricity will be consumed if we run a 1 HP Motor for 1 hour (with 75% or 50% load)?

texts:
I am very new in this field and trying to understand the basics of electrical engineering. I read this answer that says:

If the motor is fully loaded, it will provide output power of 1 HP = (1 X 0.746) kW = 0.746kW.

Electrical Input Power = (Output Power/Efficiency). Assuming 90% efficiency, Input Power = 0.746/0.9 = 0.83kW.

So, the consumed units of electricity = Power in kW X numbers of hours of operation = 0.83 units (assuming the motor is running for an hour).

Now, I want to calculate the units of electricity consumption on the basis of load. For example, how many units of electricity will be consumed if we run a 1 HP Motor for 1 hour (with 75% or 50% load; or may be with no load at all)? Can anybody help me how to calculate that value (approximate theoretical value or practical insight will also be helpful)? Thanks in advance.


texts: Why is flux-linkage a fundamental circuit variable?

texts:
In his paper Memristor - The Missing Circuit Element, Chua theoritizes the memristor based on observations relating to what he calls

  the four fundamental circuit variables, namely, the current i, the
  voltage v, the charge q, and the flux-linkage phi.

Why is the flux-linkage one of the few "fundamental" circuit variables?


texts: How to find polarity of photo interrupter

texts:
I have scavenged some photo interrupters from multiple printers but I am trying to figure out the polarity and the voltage. I've tried searching up photo interrupter polarity but couldn't find anything. On one of side of a sensor, it is labelled: A and K and on the other side it says E and C. It also says on the sensor H306-41. All the other sensors are unlabelled. Is there an easy way to find the polarity and voltage with a meter?

Edit: Images:
Picture of labelled sensor:

Picture of unlabelled sensor:


texts: Trying to understand MOSFET Turn on Procedure

texts:
I am trying to understand the mosfet turn on procedure. This is from the following application note by TI. https://www.ti.com/lit/ml/slua618a/slua618a.pdf?ts=1613979703351&ref_url=https%253A%252F%252Fwww.google.si%252F
I can't seem to get my head around certain aspects of the description.
In stage 2, the VDS stays constant. The rationale for this in the application note is as follows:

This can be understood looking at the schematic in Figure 3. Until all
the current is transferred into the MOSFET and the diode is turned-off
completely to be able to block reverse voltage across its pn junction,
the drain voltage must stay at the output voltage level.

What is this battery voltage source? Does the diode basically turn off once all the current (from IDC and battery flow through the FET?) and that's when the VDS starts to drop?
The second aspect is around the drain current now staying constant in stage 3. The description for this is:

All the gate current available from the driver is diverted to
discharge the CGD capacitor to facilitate the rapid voltage change
across the drain-to-source terminals. The drain current of the device
stays constant since it is now limited by the external circuitry, that
is, the DC current source

The CGD capacitor is discharging current due to the rapid dv/dt on the drain terminal. This current would it not flow through the drain terminal? Would that not raise the drain current? Why is it limited to the external circuitry now?
I know from the mofet transfer curve, this behaviour happens once the mosefet reaches the saturation region, the current is roughly constant for a given gate voltage but why does that happen whilst the Vds is falling?
I think i might be confusing my concepts, so any alternative explanation to what has been provided in the TI note might just help this click. So thank you for the patience to read through this.


texts: I don't know how transformers work but the primary coil has a closed circuit. If there is 0 load on the transformer it would short circuit


texts: Is it possible to encode a mpeg2-ts video with a FPGA linux core?

texts:
I need to take an unencrypted HDMI input, buffer that to memory, overlay it if possible, than encode it as mpeg2-ts and output it to an external device. I could do that with a raspberrypi and an external hdmi to csi chip, or I could do that with a FPGA.

However, licensing the mpeg2-ts encoder core could be expensive. Is it true to suppose that one can simply place a linux core on the FPGA with enough video processing capabilities to encode a 1080 or 720p (downsampling should be done on the fpga)?

Thank you.


texts: PIC32 vs dsPIC vs ARM vs AVR, does the architecture matter when we are programming in C-language anyways?

texts:
We are currently using 32-bit PIC32 Microcontroller. It is working fine for our needs, but we are also exploring other microcontollers that can suite us better + we have other projects for which we are selecting MCU. For that purpose we have selected ARM based SAM DA microcontoller which is same 32-bit but is ARM based (more popular than PIC32 - industry wise).

Now for PIC32 we use MPLAB but for ARM cortex-M0, we will be using Atmel Studio. We will be using C-language in both the platforms. The thing that is of my concern is, we will be using two 32 bit microcontoller (from same company) but having different architectures. This will require us learn two different devices and will increase our "learning curve" + delivery time. But on the other hand, I also think since we will be using C-Language in both cases, the learning curve for ARM shouldn't be that heard and it is worth exploring that processor as well.

My main question is, how big of difference the architecture makes when we are programming in C-Language since it provides an abstraction of the internals of the micrcontroller. And what are the main differences in MPLAP and Atmel Studio, considering C-language programing.


texts: Using a high frequency LPDDR3 RAM with a lower RAM frequency supported Processor

texts:
I'm designing a board with Allwinner A64 processor and i'm confused in choosing the proper RAM. the SDRAM controller characteristics of the processor is listed as follows:

Compatible with JEDEC standard DDR2 /DDR3 /DDR3L/LPDDR2/LPDDR3 SDRAM
Support clock frequency up to 667MHz(DDR3-1333)
Support 2 chip selects
Up to 3GB address space
32-bits bus width
16 address signal lines and 3 bank signal lines
Support Memory Dynamic Frequency Scale(MDFS)

I need to choose a 1GB LPDDR3 SDRAM. the question is that is it possible to use a DDR3-1866 RAM(for example Samsung_K4E8E324EB-AGCF)? In fact I don't expect the processor to interact with the ram with 1866 data-rate. i just want to know if the processor works with a higher data-rate ram but it just use the processor's last data-rate ability(DDR3-1333 in this case).

if it's not possible, any other suggestion would be appreciated.
in banana pi BPI-M64 4 separate 512MB Micron RAMs with 8-bit BUS are used to create a 2GB RAM. but the model of Ram is not specified and i can't find it anywhere.

Thanks.


texts: What is the difference between these two components?

texts:
What is the difference between the two products below?

PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C

USB LiIon/LiPoly charger - v1.2

I want to charge a battery that I am using with a Raspberry Pi project.


texts: Is there a minimum voltage needed to charge a capacitor? How about for an ultracapacitor? I'm thinking there is not, but I seem to remember someone saying that ultracapacitors were better for use with small solar cells (toy size) because they would be able to charge at a very low voltage as opposed to regular capacitors which had a higher voltage minimum. But, in my research I can find nothing to confirm that.


texts: How is clearance affected by altitude (air pressure)?

texts:
Let's say you have a high-voltage circuit (or any voltage really) and you want to provide appropriate clearance distance for the PCB, connector pins, etc.

(Above image from link)

There are standards for choosing the correct distances. Some of them are behind pay walls, but we can all guess that increasing distance increases the voltage needed to conduct.

However, what happens when altitude comes into play? One might assume that as air density decreases (getting closer to a vacuum), there would be a decrease in air conductance, because there are less air particles, and thus less media for charge carriers to travel in.

BUT, I have heard from peers that the opposite is generally accepted: As air density decreases, the conductivity increases. So as a circuit climbs in altitude, the clearance should be increased for safety.

Does anyone know of documentation that clearly dictates the relationship between air pressure and clearance?

To go deeper: By what factor does clearance increase with increased altitude?


texts:
In the top-right of this panel, you can see two red and two white connectors. Can anyone help me identify what kind of Molex they are?

Edit: Here is what the cable end of the connector looks like, ignore the extra piece of wire shorting some of the connections:


texts: How to design a square wave inverter circuit without an op amp

texts:
I am using an NE555 timer circuit to generate a 0 to 12 volt 10kHz square wave.
I would like to invert that square wave (so inverted signal is 0 when original is 12V and 12V when the original is 0 V.)
I used an NPN transistor that creates a distorted inverted wave.
Is there a simple way to make a clean inverter circuit for this AC signal?
Here are pictures of the circuit and output:


texts:
I am new to pic coding. I am trying to turn motor according to change of accelerometer in x direction. I am using Pic18f452 and adxl345. But I couldnt figure it out how to communicate with adxl345 with using i2c.

Here is my pic code:

int outputs[6];
int x,y,zz;
int px,py,pzz;
int diffx,diffy,diffz;

void motor(int v) {

 PWM1_INIT(2000);
 PWM1_Start();
 if(v>0){
 PORTC.F0=1;          //c0 and c1 is for rotation direction
 PORTC.F1=0;
 }else{
 PORTC.F0=0;
 PORTC.F1=1;
 }

 PWM1_Set_Duty(120);

}

void stopmotor(){
 PWM1_Stop();
}

int i;
 void Read_Data() {

  I2C1_Start();              // issue I2C start signal

  for (i=0;i<6;i++){
  I2C1_Wr(0x32+i);       //read 0x32 to 0x37
  outputs[i] = I2C1_Rd(0);
  I2C1_Stop();
}
}

getDegrees(){
x=(signed) outputs[1]<<8|outputs[0];
y=(signed) outputs[3]<<8|outputs[2];
zz=(signed) outputs[5]<<8|outputs[4];

}

void main() {

 // PORTC.F6 = 0;
//  TRISC.F6 = 0;                 // Configure PORTB as output

PORTB.F0=0;
TRISB.F0=0;
TRISC.F0=0;
TRISC.F1=0;
TRISC.F2=0;

  I2C1_Init(100000);         // initialize I2C communication
  I2C1_Start();              // issue I2C start signal
  I2C1_Wr(0xD2);             // send byte via I2C  (device address + W)
  I2C1_Wr(8);              // for initializing acceloremeter
  I2C1_Stop();               // issue I2C stop signal

  while(1){
  if(x!=0|y!=0|zz!=0){
   px=x;
   py=y;
   pzz=zz;
  }

  Read_Data();
  getDegrees();

if(px!=0|py!=0|pzz!=0){
   diffx=x-px;
   diffy=y-py;
   diffz=zz-pzz;

  }

  if(diffx>0){
      motor(x);

  } else{

  stopmotor();
  }

  delay_ms(500);
  }

}

I know it is not a perfect code but i just want to know weather i am communicating with acceloremeter in a true way or not. While I dont have led screen, I cant see output of data. So I dont have step by step debug options.

How should I modify the code to get output of 0x32-0x37 bits of accelerometer with using i2c?


texts:
Is there a method for automatically sampling and converting an analogue signal into a series of bits?

I have an AM capture of a ceiling fan remote as a wave form, and so far I've been manually writing out the length of the high and low signals.

Is there an application, or other method (particularly for Arduino) that can do this for me more accurately?

Moreover, what prevents me from broadcasting my capture verbatim? I have a CC1101 chip – can it handle such an output (analogue audio)?


texts:
I've made the following 4 bit binary multiplier using a breadboard and in multisim. I have an adder connected to the multiplier, but I'm not getting correct results on my breadboard (I have LED's wired at the output to indicate the answer).
I understand the multisim simulation isn't going to alternate given the inputs are constant (it was more a proof of concept testing before building the multiplier on my breadboard)
Logically does this multiplier circuit make sense, or have I made a mistake somewhere? I was hoping someone on here might spot an error with my design.


texts:
I want to understand a little how a BLE module works. I have the following module ilt254s(the small version) but until now I was unable to communicate with it. Here is the datasheet. I want to be able to communicate with it using a MCU over UART. I have the following questions:

Can I pair this with a laptop running windows 10? I have powered this up and I was expected to be discovered by the laptop but without success. Also, IOS and android phones and tablets were unable to discover it.
When powered up the RX pin P02 is 0V and TX P03 is 0V as well. So I suppose this BLE is not using the UART. Do I need to program the chip(CC2540) in order to set UART active on P0? If yes how can I program it?
How should I do in order to have it discovered and have it communicate with another MCU?

Thank you!


texts: memory space to implement 128-bit AES algorithm on 8 bit microcontroller

texts:
How to calculate(RAM and ROM) memory space needed to implement 128-bit AES algorithm on 8 bit microcontroller?

give some examples please...


texts: I need to replace this button in this circuit board with a relay

texts:
I have a circuit board with a button in it (the clear white button pictured below is the one I'm targeting). I need to somehow remove the button from the circuit and put a relay in it's place. I'm assuming that the easiest way to do so would be to simply connect the ends of the relay to the correct leads of the button, and if I'm not mistaken, the button would simply be shorted out.

Could someone help me in choosing which leads on the relay should be connected to which leads on the button?

Here are the pictures:

If you need any more pictures or info, let me know

edit: I don't have a schematic but here's the bottom of the board with the 4 leads of the button circled:


texts: Is there a mathematical representation that represents the output voltage of a buck or boost converter in discontinuous mode?

texts:
Recently I have learned that in buck or boost converters, the output voltage depends only on the duty cycle and input voltage in continuous conduction mode or when current is continuous. However, in discontinuous mode another parameter is added which is the load. Is there a formula that represents the output voltage of a buck or boost converter in discontinuous mode? I just want to see if there is a mathematical representation of how that loading affects the output voltage.
Reference of the formulas I have.
By the way I could not get my MathJax to work. I've tried literally copying the inline notations from the tutorial and it doesn't work. Hope someone could edit it for me, thanks.
Output Voltage in Continuous Mode
\$ V_o = MV_{in} \$
\$ V_o \$ - Output Voltage
\$ M \$ - Voltage Conversion Ratio
\$ V_{in} \$ - Input Voltage
Voltage Conversion Ratio for Buck Converter
\$ M = DV \$
\$ M \$ - Voltage Conversion Ratio
\$ D \$ - Duty Cycle
Voltage Conversion Ratio for Boost Converter
\$ M = \frac{1}{1 - D} \$
\$ M \$ - Voltage Conversion Ratio
\$ D \$ - Duty Cycle


texts: Switching device for ultra-low power sub-circuit

texts:
I'm looking for a switching device to be used for powering a sub-circuit in a battery powered low / ultra-low power circuit.

It can be a MOSFET, or something similar but it need to have some special properties.

The sleep mode power consumption of the circuit, without the above sub-circuit + switching device, will be in the range of 25-50nA @3.3V.

The ON current for the sub-circuit is expected to be ~25-50μA, with occasional spikes of at most 10-20mA.

Because the above currents are very small, I think we need a low power switching device with very small leakage currents. This way the sub-circuit should not gets accidentally powered and the power consumption in sleep mode is kept at minimum.

As far as now, I looked at following options:

MOSFET-s:

Vishay, Si1499DH - MOSFET, source-drain leakage current 1μA/10μA, gate leakage current 100nA
Texas Instruments, CSD23280F3 - MOSFET, source-drain leakage current 50nA, gate leakage current 25nA

load switches

Texas Instruments, PS22860 - load switch, leakage current 10 + 2 nA
Vishay, SiP32431/2 - load switch, leakage current 0.001nA, with 100nA max @3.3V (note: found this after posting the question, and looks to be good enough)

some JFET-s, but I'm not sure if they could be used / are suitable for such an application

Now, may there may be a lot of devices / solutions I'm not aware of. What do you think are the most suitable devices or solutions for such a problem?


texts: How is this circuit providing solution of the differential equation d^2 v/dt^2 = -9v?

texts:
Book pages at https://books.google.co.in/books?id=d-7owi6uNtMC

What I see is that they have taken d^2 v/dt^2  as an input at point A, integrated it to get dv/dt, integrated it again to get v=2sin3t V, and then inverted the output to get -9v gain. But this makes the feedback input as (-9)(2sin3t) and not double derivative to keep an undamped sine wave as output. The previous assumed double derivative as input is not what is given as feedback to have a sustained sine wave ?

source and problem in : Engineering circuit analysis by Hayt


texts:
what does the breakdown voltage of an APD tell me? I know certain methods how to determine it but, what happens after reaching that point?
More specific: Is the gain afterwards constant or still rising?


texts: Does SSR with DC Motor still nead back EMF protection

texts: I plan to use a solid state relay to control a couple of small 12 VDC motors. One is 12V, 12Watt (1A) and the other is 12V 11amp peak. The SSR can handle 15A DC. Some of my inputs (different part of the device) also use the same 12VDC power supply.  I am using a SSR and the output already has a diode. Should I still include back EMF protection?  Should I use a diode? Zener diode? Varistor? I am concerned about back EMF but also a possible drop in voltage that might cause the inputs to false read. Here is the SSR diagram.


texts: The use of semirelative sensitivity for \$I_C\$ on \$V_{BE}\$?

texts:
When evaluating the quality of a bias network, we use the semirelative sensitivity to evaluate the sensitivity of \$I_C\$ to change with respect to \$V_{BE}\$, with the semirelative sensitivity being equal to:
\begin{align}
\frac{\partial I_C}{\partial V_{BE}}\times\frac{1}{I_C}
\end{align}
My question is: why is it so? What are the benefits of using this value instead of the fully relative value of
\begin{align}
\frac{\partial I_C}{\partial V_{BE}}\times\frac{V_{BE}}{I_C}?
\end{align}


texts: Exponential Stability of State Observers

texts:
Reference to Wilson Rugh's book: It says the goal is to generate
\$ \hat{x}(t)\$ such that:

\$\displaystyle\lim_{t\to\infty}\left( x(t)-\hat{x}(t) \right) \to 0 \tag{1}\$

Then in the standard error equation:

\$\frac{de(t)}{dt} = (A(t)-L(t)C(t))e(t),\$

it says uniform exponential stability (UES) of:

\$A(t)-L(t)C(t)\$

is a stronger than necessary condition for satisfying \$(1)\$.

Is that because UES of A-LC implies:

\$x(t) \to \hat{x}(t) \to 0\$

eventually, whereas we only need \$x(t) \to \hat{x}(t)\$, regardless of \$x(t) \to 0\$ or not?


texts: What's an efficient way to get below the standard 1.25V on buck converters?

texts:
So, I purchased a buck converter which was advertised to be able to range down to 0.8V but, as you can probably guess, it only goes down to 1.25V which I understand is the reference voltage for the chip it uses and quite common.

I'd like to know if there's an efficient and easy way that I can step down the output range further so that I can get down to that 0.8V or even 0V, without modifying the module too much.

I'll be using 24VDC as the input and the actual chip used in the converter, the XL4016, has a range of 1.25V to 36V.

The solution in EEVblog #221 is to replicate and replace the entire chip. That's just too much for me as I'm fairly new to electronics. Another solution might be to find another buck converter that has an even lower reference voltage but then it may not match up with my current requirements.


texts: why ADLs are used for chip design but not for board design?

texts:
I understand why ADLs are used for chip design. But I couldn't see any reason why ADLs are not good for board design.

This question was asked in my exam last week?

Can anyone explain?

Edit: ADL stands for Architecture Description Language


texts: TRIAC controlling a light self-triggering for very short periods

texts:
I've been designing a smart home system for a while and one of its main features is remotely controlling all the lighting.

I'm using a pretty simple design where the main components are an ESP8266 (talking to a home server), an opto-triac MOC3052 and triac BT136. In essence, the switching part is similar to this circuit (borrowed from elsewhere):

I did not include the snubber in the circuit (because I'm not connecting any reactive load) and now I'm wondering whether I should have.

Everything works splendidly, except that especially in one room, the TRIAC seems to shortly self-trigger when some other lights on the same floor are turned on or off, which causes an irritating blink of the light.

My guess is that this is due to long wires between my circuit and the actual light, so enough power gets induced when other lights are toggled nearby, which is a sufficient spike in voltage for the TRIAC to trigger.

Is my guess correct and is this something the snubber will resolve?


texts: Why does voltage stay the same regardless of resistor connect to the source

texts:
I'm learning about clipping circuits, and I have hit a road block with my understanding of one particular problem. The circuit in question is a serial limiter. My issue is why does the output voltage equal exactly 10V when the diode is reverse biased, that is, why doesn't the resistor affect the voltage on the output (I know that when no current flows through the resistor there is no voltage drop on it, but why does it stay the same)? Also, why doesn't the DC voltage source affect the amplitude of the sine wave on the output when the diode is forward biased. Bellow are Multisim screenshots of the circuits and their instruments. The question that bothers me is illustrated with another circuit where the voltage is the same. I used it to try to understand why the resistor changes nothing, but haven't quite got it. The last screenshot is my try emphasized in hope you understand the problem at hand. Thanks in forward :)

simulate this circuit – Schematic created using CircuitLab


texts: Is star grounding sources necessary for this data acquisition system?

texts:
Several single ended output and PSU powered transducers are tens of meters apart from each other outputting 0 to 10V DC like voltages.

Some are temperature transducers some are force transducers ect. Their outputs all go to a single DAQ board which essentially multiplexes these channels and logs the data.

The DAQ board is also single ended and non referenced earth grounded and named as NRSE in the below illustration. The transducer signals are conveyed through BNC coaxial cables. Tr represents transducers below:

I’m planning to star-ground all power supply negative terminals and sensor shields at a single point and earth ground them. So none of the sources will be floating wrt earth. Since the DAQ is NRSE its analog ground will be floating with respect to earth.

I only found this document related topic http://www.ni.com/white-paper/3344/en/.

And mine is the one below encircled in red:

In my case, as I have explained with my first illustration many inputs actually nine inputs from transducers apart from each other will be coupled to the DAQ in NRSE configuration.

Do I really need to star-ground the DC negative terminals and transducer shields at a single point?  SG is the signal Ret is the return wires going to the AISENSE. (For a particular case I got a better result earthing the DC terminal instead of return wire;  it was CM interference due to SMPS transformer), thats why I earth ground the transducer’s from their power supply negative terminal in my illustration.

Edit:

Basically what Im asking is the star connected node(red question mark) need to be earth grounded as well?:

Edit:

AI SENSE is like diff ended with common returns.

AI GND and AI SENSE should not be connected thats what I heard from manufacturer for AI SENSE used scheme. Figure 1 SE scheme must not be used it causes parasitically coupled ground loops.

Now the transducers are powered by power supplies and power supply ground and transducer ground is not isolated.

In Figure 2 if I use AI SENSE and if I also route PSU ground to AIGND or to the nearest earth I get very good results. So it seems to me if I use AI SENSE scheme and a third wire from the red point(the PSU ground) to the nearest earth(yellow) or to AIGND(green) things are fine.

But since I have many of these I was asking should I use the green or yellow route in Figure 2.? Also there are 10 inputs in that case where should these yellow or green wires be star grounded?

But I can assure you SE scheme and tying AI GND to AI SENSE cannot be done. So please the answer be none of that two. AI GND is always earthed through PC motherboard. AI SENSE should not be wired to AI GND. Pls provide a simple drawing in the answer makes things easier to follow.


texts:
I need to send some I2C data through RJ45 cable between Arduinos. One ATMEGA2560 as master and 1-4 328P's as slaves. I've seen some different configurations and I think for my application the solution hinted in this answer using P82B715 will be enough for what I need, as 5 m cable for each connection will be enough.

However I was reading about differential signal pairs which could be implemented for this application using P82B96 and some differential line drivers/receivers, like Pololu guys have done on their "I2C Long-Distance Differential Extender". This could theoretically be the best way of getting really long I2C lines, as I understand.

Now comes the question. If I wanted to send those differential signals would it be better to use separate IC's for each port or can they be just connected all together like this?

As I've read I'd need to have shielded cables for carrying GND this way and there are some pull-ups missing, but you can get the idea.

My reasoning is that by being all connected the noise introduced by the cables would still be able to be canceled-out using the differential method but I'm no EE so I can't be sure about this.


texts: VHDL: I can port map std_logic_vector to a signed or unsigned port, why?

texts:
VHDL is type-safe, thus how is it that I am able to use a std_logic_vector signal and port map it to a entity port that is of type signed?

Shouldn't it require some sort of "qualification" or "casting"?


texts: Johnson counter using structural modelling in verilog

texts:
I'm trying to build a 4 bit johnson counter using JK flip flops and structural modelling. For the FF's themselves I'm using behavioral code and then instantiating them inside the counter module which is using structural style.
module jkff(input j, input k, input clk, input rs, output reg q, output reg qn);
    always@(posedge clk) begin
        if (rs) begin
            q=0;
            qn=1;
        end
        else begin
            q=(j&k)?~q:(j&~k)?1:(~j&k)?0:q;
            qn=~q;
        end
    end
endmodule

module johnson(input clk, input rs);
    wire q1, q2, q3, q4;
    wire qn1, qn2, qn3, qn4;
    jkff jkff1(qn4, q4, clk, rs, q1, qn1);
    jkff jkff2(q1, qn1, clk, rs, q2, qn2);
    jkff jkff3(q2, qn2, clk, rs, q3, qn3);
    jkff jkff4(q3, qn3, clk, rs, q4, qn4);
endmodule

module tb_johnson();
    reg clk;
    reg rs;
    johnson johnson1(clk, rs);
    initial begin
        #0 clk=0;
        #2 rs=1;
        #60 rs=0;
        #500 $finish;
    end
    always
        #5 clk=~clk;
    initial begin
        $dumpfile("johnson.vcd");
        $dumpvars;
    end
endmodule

The problem is in the output. I'm expecting each FF to go 1111000011110000 and so on, and for all ff's to be staggered by one clock pulse to the previous one. What I'm getting is .
I can't find the issue, but I'm thinking it has to do either with reset logic or with my testbench itself? I have tried the same circuit with D FF's instead of JK and am facing the same problem.
EDIT: As pointed out by Shashank V M, using nonblocking assignments fixed the problem. There was another problem that the "falling" states (0111, 0011, 0001, 0000) were taking two clock cycles instead of one. This was because when I switched to nonblocking assignments, the line "qn<=~q" was using the "old" value of q, taking up an extra clock cycle before switching to the newly evaluated value. So the code can be completely corrected by swapping out two lines in the jkff module
q=(j&k)?~q:(j&~k)?1:(~j&k)?0:q;
qn=~q;

for
q<=(j&k)?~q:(j&~k)?1:(~j&k)?0:q;
qn<=(j&k)?q:(j&~k)?0:(~j&k)?1:~q;


texts: 48V 300W DC motor e-bike charging or running directly using solar panels. Is it possible?

texts:
I have an e-Bike with the system voltage of 48V 300W DC motor. The bike is equipped with AC charger 48V 2A adaptor.
The bike has a lithium battery pack with 48V 11Ah capacity.

So my question is, is it possible to run the ebike directly using solar panel?

Lets say my plan is to use these methods:

Method A:

2 X 12V 50W panels placed on a carrier at the back of the bike, then store the power through PWM controller and a 12V50Ah lead acid battery and then using 500W 24v DC-AC inverter to charge the bike using the adaptor.

Method B:

Directly power the hub (the tire) using solar panel where 2 units of 12V solar panels connected with DC-DC converter to make the output to 48V without having a battery in between.

Which method is more plausible to be done and most efficient?
What are the recommended DC-DC converter that is best to step up the voltage?


texts:
I have a question regarding an integrated PCB Antenna that I would like to try out, however, if it fails I want to be able to use another SMA antenna. The PCB Antenna is an inverted F-antenna meaning that it will be "shorted" with one of its ends connected to GND, as seen in the attached picture.

I have added two 0 ohm resistors that I was planning to desolder depending on which antenna I am going to use. Now my question is if the PCB antenna only is connected to the GND (far left) and disconnected everywhere else (i.e. R6 is removed and only R4 remains), could this affect the performance of my SMA antenna?


texts:
Why is D1 considered cutoff and D2 considered conducting ?
Note : I am working with constant voltage model where the diode voltage is 0.7v and I need to figure out I and V. Please explain why D1 is considered cut off and D2 conducting, this is what chegg solutions say.
-Thanks for your time.


texts: Battery Charging Using Battery University Information:

texts:
How would I use this information from Battery University to properly charge a car starter/ing battery--with the following specs:  Vnom=12, CCA=640, CA=800, RC=110 minutes, AH=?

I plan to use a regulated bench power supply for charging. The way I see it, I should setup the max charging A & V controls, ensure the electrolyte levels are correct, connect the battery to the power supply & after the battery has reached full charge (i.e. when the charge current has dropped to 3 to 5% of the AH rating of the battery), I would then change the max charging V to the float V (maintenance charge V) or disconnect the battery, rest it (0h-24h), test it, & put it into service if it is good.  Is that correct or did I miss something in my understanding?

What I don't know for certain is:
1.  The AH rating of the battery (i.e. how this is calculated properly)
2.  The max A for CC charging
3.  The max V for top (saturation) charging
4.  What exactly does 3% to 5% of the AH rating mean?  Does this mean when the charge rate in amps drops to 3% to 5% of the battery AH rating (e.g. charger A = batt AH * .03 or 05)?
5.  What exactly is the correct float V?


texts: Why does touching one 3.5 jack contact (in headphones) together with audio device socket's outter ring make noise?

texts: When a 3.5mm jack of headphones contacts with sound device's socket, headphones produce slight noise. Why does this happen when only one wire is connected? I thought there are supposed to be at least two contacts to make a speaker produce sound.


texts:
1st attempt
I have a problem. I built the FM demodulator circuit, but i am not sure if this signal is demodulated. This was my first attempt which following an answer, resulted in a 2nd attempt further down.

This is my input - fm modulated signal and output :

EDIT - 2nd attempt following advice in an answer:

This is my input - fm modulated signal and output :

Thanks for the help in advance!


texts: What are the draw back of having multiple smps stages in series?

texts:
Application

output - 100V 10mA

Input - single cell lipo 3.7V 5000mAh

overall efficiency > 85% required.

I tested Texas instruments power bench.
Texas instruments power bench cannot generate circuit for 2.8V-4.2V input to 100V 10mA output
my idea is to use two SMPS in series
stage 1, 2.8V-4.2V input to 9V 2A output @ 92% efficiency
stage 2, 9V input  to 100V 10mA output @ 87% efficiency
what can go wrong here or worst case scenario when stage 1 output is connected to stage 2 input?


texts: How to measure the total power in a 3 phase electrical system with one current transformer?


texts: BMS and Charger For LiFePO4 prismatic module

texts:
I just purchased a lithium battery module for an electric tractor project. I'm looking for advice on how to set up my BMS and charger.

Here are the details of the module from the seller: "Prismatic Cells are 3.2v and 22.5ah each. At 22.5ah each they are very stable cells and can be used without a cooling system. Modules are made of 40 cells. In this configuration the total output of each module is roughly 13v with 225ah (made by 4 groups of 10 cells)."

So 10 cells in parallel in a series of 4 groups need some sort of BMS. I'm thinking of options:

Simple: use a 4s bms to monitor the 4 parallel groups and hope the 10 cells in parallel are balanced.
Less Simple: connect two 20s bms to every cell in the whole system.
Other options of different bms configurations such as four 10s.

I'd really like someone who knows their way around these batteries to tell me that option 1 is adequate, but want good advice, not just what I want to hear. Thanks!

Bonus to anyone who sends links to good bms and charger options.


texts:
I want to understand the concept of open-drain ports like port P0 of the 8051 microcontroller. Why do we need to connect pull up resistors to the port P0?

I have basic knowledge of MOSFETs and other electronic devices.


texts: There is a staggering number of variants of the STM32 family of MCUs.  I have been led to believe that a list of the available STM32 microcontroller parts and their various features is available somewhere in spreadsheet form.  Is this true and if so where can it be found?


texts:
If we send a square waveform through an antenna,  will we get square electromagnetic waves with electric and magnetic fields looking like squares?
Also, since there is an abrupt/almost jump in amplitude, will we get very high frequency sine waves like predicted by the Fourier transform?


texts:
I've this TO-247 MOSFET
http://www.datasheet.es/PDF/203551/2SK3271-01-pdf.html
how much current will support this case? I've to control a 12V 80A DC Motor


texts: Unstable output in VT pin of HT12D decoder

texts:
Hi everyone,

I have been recently working on a RF operated water pump project. For this purpose i bought a RF RX and TX module which has HT12E and HT12D chips as encoder and decoder.

The D8 (Dout) pin of decoder is latched output and power on state is active low so whenever the circuit is powered off and then turned ON again it automatically gives output in D8 pin and in turn drives the water pump. I don't want that to happen.

In order to eliminate this i thought to use VT pin which is momentary and indicates whenever valid data is received from TX. So i built this simple set up using the logic gates i have. Even though the auto ON of water pump is eliminated, now the output to ULN2803 IC is not stable and the water pump keep on switching ON/OFF and when ON the motor speed is considerably low.

From searching in internet i found that it is due to the instability of VT pin and also when I checked the logic level in VT pin, it keepsRF on changing.

Can you guys help me with any suggestion or improvement ideas to improve stability of VT pin? or is there any other way of implementing the solution i desire?

Thanks in advance


texts: Noise control in op-amp circuit design by using low spec op amps

texts:
I have a rather strange problem. I have a breadboard circuit on a double sided PCB with plenty of ground plane and a good well decoupled power supply. I am amplifying a small medium frequency signal (mV, hundreds of kHz) and bandpass filtering the region of interest.

Initially, I thought to use the AD829 - very low noise, plenty of bandwidth. The problem appears to be the it is too good! I was getting lots of noise especially at high frequencies leaking through. So, changed the AD829s with the cheap TL051 (10x worse noise spec, 30x lower bandwidth). Problem solved - noise gone!

Now obviously the problem has disappeared because the TL051 cannot handle much in the way of high frequency, which is fine. What worries me is two things. First, how legitimate is it to use low spec components to "hide" a problem like this. And second, do manufacturers ever "upgrade" the spec of their amplifiers? One day, will I put in a TL051 that has been improved and discover the product now longer works?

This is the bandpass section which really looks bad with AD829s


texts: How to find out what level of battery voltage corresponds to 50% discharge?

texts:
In my off-grid solar system I am using 12V lead-carbon batteries capable of surviving 4000 cycles when discharged up to 50%. Capacity is 200Amp-Hours (100 Hour discharge) per battery.

There is no BMS or coulomb counting. I simply configure charging voltage (absorption 14.1V, float 13.6V) and cut-off voltage to limit discharging. The latter is the question: how do I find out the voltage at 50% discharge?

Here are some specs which I reckon should be useful to answer the question but I am not sure how to read them:

(one battery apparently consists of 6 cells in serial).


texts: Difference between always @ block and @ statement in Verilog

texts:
I have not across the statement @(posedge clk) before. I would like to know how this statement is different from the always @(posedge clk) block which I am familiar with.
If I use a sensitivity list in a task for a Finite State Machine synthesis without always block; How is this different from a task with always block and sensitivity list?
As I understand both @ and always @ have the same functionality as both of them are always sensitive to the changes in the sensitivity list. Are there any differences with respect to simulation or synthesis?


texts: How does the commutator work right here?

texts:
I understand that we use the commutator as a rectifier using two segments that alternatively touch the negative and positive brush. That is when we only have one coil. What happens when we have more than one?

In the above diagram we have 4 coils and 4 commutator bars. What are the bars? Shouldn't we have 2 segments for each coil ? That means 8 bars. Maybe the bars and the segments are not the same thing. If they are not , what are the bars here? Because the coil has two sides and it has to get to both brushes. The textbook I'm studying also says that the voltage in the first picture below is eb+ec and in the second picture 7+18+20+18+7=70 volts.

Now here is another part I don't understand. In the simple example of one coil each brush is always in touch with one coil. So I figured, if we have 2 coils we have four segments and we take advantage only of the coil which has the highest voltage each moment. However, that is not true. Here we add every coil's voltage. How can we take advantage of all the coils if only two segments touch the brushes each time?
And how come the voltage in the first picture is eb+ec? Which coils touch the brushes?
(I imagine that two coils could be touching a brush at the same time but only one contributes)
I'm very confused and I can't find an answer.
I also have this image for the actual physical construction of the  first image .


texts: Replacing D cell batteries with power adaptor

texts:
I have a device with 4 series 1.5V D cells batteries (About 8000maHour).

The batteries last 40 hours, making the average draw around 200mA. The problem however is that the duty is about 2% at 1/3Hz, so it seems to deliver bursts of about 10A, and I don't really want to put in a 10A 60W supply for something that is only about 1.2W average. And unless my math has failed me, the bursts are 1000J so I would need about a 55F capacitor, which is out of the question.

Any one know of any other tricks I could use?


texts: Buzzer vs piezo sound for generating sound

texts: Correct me if i'm wrong. Buzzers can only produce 1 tone but are quite loud. While piezos can generate a wide variety but are most suited to ics. Is there anything i missed?


texts: How do you make an antenna with length much greater than the wavelength work?

texts: I've read that antennas work best when their length equals 1/2λ, so how does one make an antenna that is 3/2λ, 2λ, 3λ, etc. work? How do I calculate how much energy I am losing compared to the 1/2λ length antenna?


texts: I have a PID loop running at 100Hz and is working reasonably well, for now. However, if I double the speed to 200Hz it no longer works, which isn't much of a surprise. The question is, what changes should be made to the PID values to get it to work at 200Hz? Is it a linear change in values? Can it be calculated? What is the relationship between stability and loop speed?


texts:
I would like to control the speed of my PSC induction motor.

I found a similar topic here:
varying run capacitor for speed control of single phase motor

However I would like to modify the speed while the motor is running.

Something based on Temic's U2008B perhaps?

Any suggestions?

Thanks,

Juan


texts: Input and Output Impedance of a SAW Filter

texts:
I am reading the datasheet of a SAW Filter B39162B4348P810. The datasheet doesn't say much about impedance of Input and Output port. However, on page 5, it considers Terminating source and load impedance for the specifications.
It says:

Temperature range for specification: T = –40 ˚C to +105 ˚C
Terminating source impedance: ZS = 50 Ω
Terminating load impedance: ZL = 50 Ω || 8.2 nH

Shall I consider to add an inductor of 8.2nH value in parallel at the output port?


texts:
I've been looking into doing some PIC Programming, but unlike some of the other microcontrollers available the sheer number of different chips available has caused me some confusion. It also appears that some of the chips suggested on some sites as good choices for people starting out with PIC programming may have been superseded (or I may just be getting even more confused).

So my question boils down to three parts:

What would be a good PIC chip to start out with?
I'm quite happy doing either assembler or some other language, so what IDEs/languages would you suggest for Linux?
What would you recommend in terms of getting the code onto the chip, over a USB connection from a Linux laptop (PicKit 2? was one possibility) and what circuit/board configuration will I need to do this?

Edit: After a long discussion with Kortuk (see comments below) on the merits of various bits of kit, I've decided to start with the PicKit2 Starter Kit. This comes with a PIC16F690 chip installed.


texts: How must I read this MOSFET specification?

texts:
I'm looking at this datasheet, which has this graph on page 3:

The FET has an \$R_{DS(on)}\$ of \$14 m\Omega\$; how can \$V_{DS}\$ be > 10 V at 100 A? Shouldn't that be 1.4 V? And if it was 10 V, wouldn't the FET evaporate at 100 A = 1000 W?


texts:
I'm trying to measure dry cell charge level. I'm using 6V/4Ah/20Hr dry cell battery.

In my system there are atmega32a and 6 seven segment display; how can I measure the charge level of this battery?


texts: Assistance with schematic notation "R@2V" for pH monitor

texts:
I've been building a circuit I found online for a pH monitor, while most of the circuit seems straight forward I get caught on the "R@2V" notation, a guess would be maybe resistance at 2 volts? I'm not completely sure and if so not certain how I would go about calculating it.

If anyone could help me out on how I would go about calculating that resistors value would highly appreciate it!


texts: Electric car "J1772" charger - "pilot" signal sequencing with passive circuitry

texts:
J1772

Some background: Many electric cars are designed to use a "J1772" charging point. The main signal in the J1772 specification is called the pilot.

Long story short, the car is expected to place a resistor and diode in series across the pilot and ground. A resistor value of 2.74k indicates that the car is present, and a value of 882 ohms indicates that the car wishes to have power.

The spec requires that you make a stopover in state B (2.74k) before engaging state C (882). It does not say how long that stopover must be.

There is a second signal in the specification called "Proximity." It is a signal from the J1772 handle to the car. It is wired to the release button on the handle. When the user is pushing on that button, it is a 450 ohm resistance to ground and when the button is released, it is a 150 ohm resistance.

My Device

I am making a device that has a J1772 inlet and derives its power from the charger to which it is connected. Prior to it placing the 882 ohm resistor value in place, it has no power of its own (unlike most electric cars).

The natural thing to do would be to make a circuit such that when that resistance is 150 ohms, the extra 1.3 kOhm resistor between the pilot and ground is in place. When the resistance is, oh, greater than 300 ohms, that resistor is not in place.

The challenge is... how can one do that with merely passive components?

In short, I want to detect whether a particular pin has a resistance of less than 300 ohms to ground, and if it does, I want to change the resistance between another pin and ground from 2.74k to 882 ohms (or put another way, add another 1.3 kohms in parallel). And I would strongly prefer to do this without a power source.

The left half of the diagram below is the proximity circuit that's part of the J1772 charging handle. It cannot be changed. The right hand side is my circuit. The question, again, is when the proximity resistance is less than 300 ohms, I want to close the "mystery" switch.

simulate this circuit – Schematic created using CircuitLab

If I were going to make something active, this is what it would be:

simulate this circuit

This may be laughable overkill. I'm not sure. But it doesn't solve the power problem. It requires either a set of AA batteries (3 would last around 100 days if my calculations are correct), or a "START" button across the transistor to "bootstrap" the system. Both of those solutions, in my view, are lame.


texts: LED Circuit turns on or off after pulse of varying intensity

texts:
I'm trying to make a circuit that turns a LED on or off by using a pulse voltage. The LED should turn on with a pulse of intensity A and off with a pulse of B, where A and B < 5V. Most of the time, this voltage will be null. Two additional constant DC voltage sources can be used.

I've thought about using OpAmps to determine whether the pulse is high or low enough, but the LED should only change states after the pulse, and it should stay in this new state until a new pulse happens.

What basic components (resistors, capacitors, inductors, OpAmps, diodes, MOSFETs) could be used to maintain the LED on after a pulse and have it off only after another pulse of different intensity?


texts: Identifying Schematic Symbol (mysterious diode looking thing to replace)

texts:
I am trying to replace a component on my Krohn-hite 1000A function generator that burnt up.

The component is connected directly to the high-impedance output. I have found a schematic for Krohn-Hite 1600, which I believe is close. (I believe) my burnt up component is the schematic symbol circled in Red.

Is this some kind of diode? I have never seen this symbol before, and cannot find anything like it online. Looking to replace this burnt component.

full schematic: http://www.waynekirkwood.com/images/jpg/Krohn-Hite_1600_Sheet_1.JPG

Thank you for these replies. I see that the component I highlighted is a switch now.

Attached is a picture of the burnt component.

Anyone know what component this might be on the schematic? I understand more photos might be necessary to answer this question.


texts: SD Card re initialization using fatfs on stm32f103RB

texts:
I am using a SD Card Module that has no pin for checking existence of SD Card, So i should do the check using fatfs libs. The micro-controller is STM32F103RB and i'am using SPI protocol to communicate with SD Card. Up to now i can detect a removal state with this code:

bool check_SdCard()
{
    FATFS check_fatfs;

    if(f_mount(&check_fatfs,"",1)==FR_OK)
    {
        f_mount(NULL,"",1);
        return true;
    }
    else return false;
}

The problem is that i can't check insertion of SD Card (or i cant re init the SD Card properly) to Read/Write to it after removing it from a previous initialization.

the above code returns true if the SD Card is inserted to the module from first startup of the device but always returns false if SD Card removed/reinserted after startup. so f_mount could not reinitialize SD Card after reinsertion. I've also tried disk_initialize(0) with no success. Does anyone know how to solve the problem of re initialization of SD Card using fatfs?


texts: Signals shorted when connected to the input of an unpowered IC

texts:
I use one SPI bus from CPU to two FPGAs with different (i.e. individual) CS signals.

The CPU and first FPGA are powered up, and the second FPGA is unpowered.

When I send SPI signals to both FPGAs, the second (unpowered) FPGA shorts the shared SPI signals and first (powered) FPGA can't recognize the low amplitude signals.

Why this can happen and how to fix it?


texts:
R1 became RS

R2 bacame R

1)Is this a correct shortcircuit protection?

2)What is the max current that can flow before the transistor enters in saturation?


texts: LDO output and input capacitor clarification

texts:
I would like to understand how to size the input and output capacitor of an LDO.

What I think to know:

About the input capacitor:

The input capacitor is used for filtering high frequency input components.

Nevertheless in a perfect LDO, the drop voltage across the P-channel mosfet is adjusted so as to maintain the output voltage constant whatever the input signal as long as the input voltage is higher than the voltage drop across the P-channel mosfet plus the output voltage. So if the output voltage is constant, it means that the LDO filters all the AC components of the input signal. So why do we need to add an input capacitor? I think that the bandwidth of the LDO is not sufficiently large to filter all the AC component, especially the high AC components, so an input capacitor is added to filter what the LDO could not filter. Where I can find this information into the datasheet?

About the output capacitor:

Suppose the load constant at the output of the LDO. The output voltage of an LDO is constant. So the output current is constant. Suppose the LDO is taking no current from the source. So the current taken from the source is equal to the output current and is CONSTANT over the time. So why do we need an output capacitor?

The reasons:
During load transient, the output voltage will vary during a time depending on the bandwidth of the LDO. So an output capacitor can be used for helping the regulation. The other reason is for stability concerns.

Nevertheless, I have already seen 100 uF output capacitor on an LDO and a load around 500 mA under an output voltage equal to 5V. What I do not understand is that the output capacitance seems to be a function of the load, something that I do not understand. Does the stability problem imply to increase the output capacitor at this value and is function of the load? I could fairly understand that the overshoot or undershoot during load transient is dependant on the load, but what transient load need to have a 100 µF capacitor?

Here is the LDO.


texts: Differential equation to state space representation

texts:
Suppose I have a dynamic system in the form:
$$
a \, \dot{x}_1 + b \, \dot{x}_2 + c \,x_1 + d \, x_2 + e = u_1 \\
f \, \dot{x}_1 + g \, \dot{x}_2 + h \,x_1 + i \,x_2 + j = u_2
$$
How would I transform this system into a state space representation?
I would usually isolate for \$\dot{x}_1\$ or \$\dot{x}_2\$, but in this case, they are both a function of each other, and this is a MIMO system. Would one way be to rewrite these equations in matrix form and isolate for  the \$[\dot{x}_1; \, \dot{x}_2]\$ vector (assuming matrix \$[a \; b; f  \; g]\$ is not singular of course)?


texts:
I'm trying to learn the basics of Eagle SPICE simulation with a simple capacitor charging circuit. My netlist is as follows:
* SpiceNetList
*
* Exported from untitled.sch at 21/07/2019 1:17 PM
*
* EAGLE Version 9.4.0 Copyright (c) 1988-2019 Autodesk, Inc.
*
.TEMP=25.0

* --------- .OPTIONS ---------
.OPTIONS ABSTOL=1e-12 GMIN=1e-12 PIVREL=1e-3 ITL1=100 ITL2=50 PIVTOL=1e-13 RELTOL=1e-3 VNTOL=1e-6 CHGTOL=1e-15 ITL4=10 METHOD=TRAP SRCSTEPS=0 TRTOL=7 NODE

* --------- .PARAMS ---------

* --------- devices ---------
C_C1 N_3 0 1000uF
R_R1 N_2 N_1 10M
V_VCUR_1 N_2 N_3
V_V1 N_1 0 DC 10 AC 0

* --------- simulation ---------

.control
set filetype=ascii
TRAN 2e-7 0.0001 0 1e-5
write untitled.sch.sim V(N_1) V(N_2) I(V_VCUR_1) I(V_V1)
.endc

.END

I want to run a transient analysis that shows the current through the capacitor decreasing as the voltage increases. Instead I get this:

What am I doing wrong?


texts: Is there any difference between the terminals of the rheostat

texts:
This is probably a dumb question but I just wanted to be sure for my practical exams.

Is there any difference between the upper or the lower terminal of the rheostat? Are you supposed to connect the positive terminal of the battery to any specific terminal of the rheostat or is it all the same? Thanks in advance.


texts: What is the component on the schematic indicated by the symbol of a diagonal rectangle with a line through it?

texts:
I can't for the life of me, figure out what these diagonal rectangles are...

Help?


texts: Xbee Shield - Turning jumper settings into ON/OFF (XBEE/USB) manual switch

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I have the following Xbee Shield where I need to constantly switch jumpers in order to allow Xbee communication and/or USB communication.

The following is set for Xbee communication:

"Xbee Communication"

The following is set for USB communication:

"USB Communication"

The following is without jumpers (which also acts as USB communication as well):

"Without (also USB)"

As my Arduino and Xbee Shield are going to sit inside an enclosure with screws and my USB port being quickly available to plug a USB cord into I'd like to attach an ON/OFF switch that acts as XBEE/USB rather than have to unscrew it and manually shift the jumpers into the correct places. I'm not quire sure how to wire up a switch to do this.

Looking from a birds eye view. If the pins are as follows:

(1) (2) (3)
(4) (5) (6)

Considering that without any jumpers attached, it acts as USB communication. Am I then safe to assume that hooking up a switch like the following is going to be easy?

Any help is greatly appreciated.


texts:
I would like to create a solenoid like this one:

It should be powered by 5V and of course I want it to take as little current as possible. I know it will probably still take a current of around 0.75, 0.8, or 1A, but the lower the better. At the same time it must be strong. Say it has to lift up an object of 40 grams (0.088 lbs) against gravity.

As far as I know there are two things that make it stronger:

Higher current.
More windings.

Since I want to limit the current, I have to give it more copper windings.
I'm not familiar with solenoids and electric fields.
Therefore I have some questions:

How to determine (approximately) how many copper windings I need for a predetermined current (formula/example) to make it the strong as I would like (lifting 40 grams)?
What can I do to make it hot as slowly as possible?
They say it will be stronger if you cover it with a metal housing to keep the magnetic field inside. Can the housing be of any metal (like aluminium, stainless steel, or tin metal), Should it be of some specific metal, or doesn't it matter that much and is it already beneficial to have a metal housing at all?
Any other tips for building this thing yourself?


texts:
Could I use a PWM output as a digital output? For example to act like an on-off signal by varying the duty cycle between 0 and 100%.
Does it involve any difference in power consumption?


texts:
I'm looking at prototyping a PCB that needs to make many connections over a curved surface. To develop this, I'm looking at using thin/flexible PCBs. For a 2-layer design, I'm comparing a thin (0.2mm-thick) FR4 PCB to a standard Polyimide flex PCB. The 0.2mm FR4 seems like it would be a suitable, less expensive option ($104) versus a typical Polyimide flex circuit ($189). Can I just use really thin FR4 instead of polyimide flex to save a few bucks?
In an effort towards full disclosure, here's what I think matters about the design:

The PCB bend is a relatively large radius, say greater than 100mm / 4in.
The routing isn't particularly demanding in terms of space/trace
The PCB will contain SMT parts populated before bending
The PCB is soldered to panel-mount, through-hole components
Once the PCB is soldered, no further bend/flex of the PCB is intended
Once the PCB is bent in place and solder


texts: Which synthesis tools support VHDL libraries?

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On various places across the net, I read that (some) synthesis tools do not respect VHDL libraries. These tools just throw all entities and packages into a single namespace, so that you cannot have mylib.someEntity and yourLib.someEntity in the same project. I know that Altera Quartus used to have that problem last time I checked (but that was a while ago). I'm afraid that some of the info on usenet archives might be outdated, so I'm looking for up-to-date info.

I also believe most simulators support libraries today.

My question: Which synthesis tools do support VHDL libraries and which don't? If there are any simulators that do not support libraries, I'd also like to hear that.

Can you please also mention the version numbers of the tools, for future reference?


texts: Transmission Line with Short Circuit and Inductor as Loads

texts:
let's consider this situation in which the two ports of a transmission line are connected to a short circuit and to an inductor:

The transmission line is supposed to be lossless. My book makes a mathematical analysis in order to find the resonance frequency (precisely, resonance frequencies) of this network, which may start to oscillate.

But my question is: how can it start to oscillate on its own (since it is a passive device)? I have understood that there are no losses, but I think it is necessarily a form of excitement or accumulated energy in the circuit (for example, to make an LC circuit oscillate, the capacity must be pre-charged at the time of closing the switch).

Oscillation means voltage + current and so energy. And it cannot create energy from 0.


texts: Why do DDR RAMs have both xDQ and xDM signals?

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DDR2 RAMs have these control signals
RAS, CAS - address strobes
UDQ, LDQ - byte strobes
WE - write enable
UDM, LDM - write mask
Why do we need UDM and LDM?  Can't you write a byte by asserting WE and only one DQ?
Here's a link to a typical data sheet.  It tells me what the write mask does, but not why I need it.
https://www.alliancememory.com/wp-content/uploads/pdf/ddr2/AS4C32M16D2A-25BAN_rev1.5.pdf


texts: How do I use a 680 Volt (DC) solar panel with an off the shelf system?

texts:
I've inherited 4 custom built solar panels.  These are not consumer grade panels but industrial sized.  They produce 680 volts DC at 3.8 amps.  The voltage selection was probably selected to minimize the amperage and minimize current loss from transmission.  That said, I would like to put these panels to work.  I want them to produce as much 240, single phase power as possible.  The intended use is to be off grid.  The largest off the shelf charge controller I can find is the Xantrex 80 (amp)-600 (volt) XW.  The voltage from the panels exceed this and I'm not finding a buck converter that will bring the voltage down to 550 or less.  I am not an electrical engineer so please be explicit. I did install a grid tied system so I'm not totally clueless.  :-)

What are my options?


texts: What type of fire extinguisher do I need for lithium polymer batteries?

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I plan on using reasonably cheap powerbanks (like the Aukey Mini 3600mAh) with my own circuits, and - ideally - I'd like to have an appropriate fire extinguisher on hand in case I mess up.

I know that there's protection circuitry inside these things, but if there is a compact, cheap fire extinguisher that I can also use on LiPo batteries if the need arises, I'd like to get one.

This document claims that I do not need a class D fire extinguisher for Li-ion batteries, and that water or ABC will do (but also that you will need one for Lithium batteries - the non-rechargeable kind), but I'm not sure if that applies to lithium polymer as well. This Product Safety Datasheet for Energizer lithium polymer batteries doesn't inspire a lot of confidence.

Again, ideally this thing would be very small, easily available, and not too expensive.