texts: Difference between IRS and phased array/reflectarray

texts:
just wondering out of curiosity the difference between intelligent reflecting surface (IRS) and more traditional antenna arrays such as phased array and reflectarray?
From the surface it looks a whole lot similar but perhaps from different angles (IRS - more system/optimization focused and antenna arrays are more studied as an independent component), but was wondering if I was missing the key concepts/ other differences behind IRS.


texts:
I am new to electronics (using Arduino), begging to venture into creating my own circuits and not following set example. I would appreciate advice on the following.
When deciding upon how to power a circuit how exactly does one go about this? For example, I'm planning on using my Arduino Uno to control six MG996R servos via six potentiometers. For my understanding each:

MG996R servo requires: 5 - 6 V and 1.3 - 2.5 amps (stall to 6 V load working).
Arduino Uno: 5-7 V input and 40 mA per pin output // 5 V input being sufficient as I do not plan on using 5 V output.
Potentiometer: no specific / negligible volt/amp draw

Thus, to power the above I would require a power source of max 6 V (within operating limit of servo and sufficient for Arduino, and a total amp of:

15A (6 x 2.5 amp for all six servos)
240mA (6 x 6 pinouts on Arduino required to control PWM on servos).
Total: 15.24 A

So overall for above I need a power supply: 6V, 15A. Is this correct?
If so, then my next question comes in how to power this from a battery? All the LiPo's (3S) I've used for drone etc thus far are 11.1V and 1500 - 3000 mA // way below the amps needed for above. Also I've always used a power distribution board to provide 5V to the Arduino, which provide only 2 - 3A.
I do have a external variable power supply but I'm reluctant to have 15A running as this seems considerably higher than anything I've used before and I don't trust my working. Also, I can't find a maximum amp limit for the Arduino, but feel that 15A would exceed its working limits.
I'm confused. Either I've got the workings completely wrong or I'm stuck at how to provide sufficient power to six servos using a battery, and not frying my Arduino at the same time.


texts:
I am having trouble understanding how this ring modulator works i.e. how it multiplies the input & carrier to give us appropriate output? Any help or guide will bedeeply appreciated.
 Reference - http://en.wikipedia.org/wiki/Ring_modulation


texts:
I'm doing an Arduino based project using the PWM hooked up to a 0.5W 8Ω speaker in order to make various sounds, I want to implement a digital volume control and I thought about using another PWM output and an Opto-Isolator....would this be possible?

And....if it is possible - could anyone recommend a suitable candidate?

Cheers Chiphackers -
Let me know if this is too vague :)

Update - I've got the speaker connected directly to the PWM output without amplification
       - I'm using a couple of tactile switches to turn the volume up and down

Here's the circuit (In Theory) -

Here's some code too, I've got the PWM set to high speed and I'm using it to ramp the volume of the tones up and down -

/////////////////////////////////////////////////////////////////////////////////////
// Configure PWM on pins 3 and 11 to run at maximum speed, rather than the default //
/////////////////////////////////////////////////////////////////////////////////////

pinMode(3,OUTPUT); // speaker on pin 3

cli(); // disable interrupts while registers are configured

bitSet(TCCR2A, WGM20);
bitSet(TCCR2A, WGM21); // set Timer2 to fast PWM mode (doubles PWM frequency)
bitSet(TCCR2B, CS20);
bitClear(TCCR2B, CS21);
bitClear(TCCR2B, CS22);

sei(); // enable interrupts now that registers have been set

////////// Function for playing tones -

void playTone(long tone, int duration)
{
prevMicros = micros();

  while (micros() - prevMicros < duration)
  {
    analogWrite(3, VOLUME);
    delayMicroseconds(tone);
    analogWrite(3, 0);
    delayMicroseconds(tone);
  }
}


texts: How RFID does not conflict when reading multiple cards?

texts:
I pass on the metro this morning with 2 RFID card on my wallet, one is my metro pass and another my enterprise pass.

How the reader know exactly which read? How it do not conflict between cards?

I already search on the web but only find extensive datasheets with a lot technical information, I'm not expert enough to find this answer.

Thank you.


texts: If we have an H-bridge made of 4 N-MOSFETs, the gate voltage applied to each pair must be different because in an active circuit the sources will have different voltages. How much?


texts: Will Renesas V850ES/Jx3-E support 1 wire protocol (max detect temp/humid sensor)?

texts:
I would like to connect the DATA pin of sensor to Digital I/O pin of a microcontroller. I am confused that in the data sheet of the sensor they have mentioned this:

  MaxDetect 1-wire bus is used for communication between MCU and RHT03. (MaxDetect 1-wire bus is specially designed by MaxDetect Technology Co., Ltd. , it's different from Maxim/Dallas 1-wire bus, so it's incompatible with Dallas 1-wire bus.)


texts: For induction motors, would one expect harmonics to be different between Delta and Y stator windings?

texts: Given two induction motors with the only difference being that one is wound delta, the other Y, would I expect to see a different behavior if the source is a three phase voltage with harmonics?


texts: Why do we use 2 transistors for each path of a MUX in CMOS?

texts:
Below is the schematic of a CMOS level 2to1 multiplexer. As you can see that if we want to choose A0, we set S input as Logic-0.

My question is that what happens if we remove one transistor from each path. PMOS from C0 path, and NMOS from C1 path. Doesn't the circuit work without them as well?

The schematic is taken from Yamin Li's Computer Principles and Design in Verilog HDL book.


texts: Photoelectric smoke alarms leds harmful?

texts: Hi I needed some serious information for the safety of mine and my family’s, I just moved into a new house and I’m removing the smoke detectors because they are really yellow and look old. I was wondering I wanted to put photoelectric smoke alarms because they are better for fires but they haven’t been around for long and I wanna know is the infrared led dangerous in there and can it affect my eyes or my kids because I want my kids to grow up safe and I just don’t want to not be educated on what I buy. Someone please help


texts: Help with two input specs of a DC-DC converter

texts:
Regarding this DC-DC converter datasheet the input specs are given as:

Mine is 12V to 5V DC and called MV 1205S. So my input voltage is regulated 12V DC.
I have couple of issues with this part:

I want to obtain a reverse voltage protection for this converter input by using a 1N4148 because that is the only diode I have. I also have 1N5408 but it has 1.2V voltage drop.
But do I really need that? Because the input specs mentions about reverse voltage protection as 0.3A max. What does that mean?

Can I use 3.3uF at the input safely? It says 1uF or 3.3uF but there is an asterisk(*) so I'm not sure if it would have any complications.


texts: Problems sizing series input resistor for this optocoupler

texts:
Under the electrical characteristics, the optocoupler 4N26 typical "forward voltage" is given as 1.2V. But for sizing the input resistor Im have hesitations.

In my application as a control signal I will use an Arduino 5V digital output for the opto input. The optocpupler will then switch this SSR which requires 16mA to operate independent of input voltage. Here is the basic diagram:

In a net tutorial I found this information: "The CTR depends on the LED input current (IF) and the CTR decreases from a maximum point when the input current is both increased and decreased. If you look at the below diagram, the top of the curve is around the 6mA point. This is where the chip is most efficient."

In my case I have the black package and below is for the CTR vs Forward current:

Here my questions:

1-) So in my case by looking at the plot above I choose the forward current IF as 4mA and from datasheet the forward voltage is typical 1.2V. So I calculate:

R = (5 - 1.2) / 0.004 = 950 Ohm.

So I conclude 1k.

But in many examples I see much smaller resistor value.

Am I doing something wrong here?

2-)

In some examples they place the resistor in return path. Does that have any significance? Her an example:

edit:


texts: Choosing opamp with sufficient output current for Voltage Reference with high impedance load

texts:
I am designing a differential sensor that will be placed on the skin to detect biopotentials. Two inputs are fed into an instrumentation amplifier that has a reference set at 1.5 volts (VREF15 in the schematic). That 1.5 voltage reference is also tied to the skin through a "ground" electrode. The 1.5v reference is used as "ground" in order to capture the full signal wave as the sensor is powered by a single battery.

Using the LTC2055 as a buffer, I've found that I'm not getting enough output current to drive my reference. Is the high impedance of the skin the problem (skin is "SigC" in the schematic)? What do I need to do to calculate the necessary output current needed for the opamp?

The short circuit output current of the opamp I'm using is 140 micro amps.


texts:
I just got this SIM908 dev board, and I'm trying to get it working. However, it keeps telling me "SIM not inserted":

AT+CPIN?
+CME ERROR: SIM not inserted

which of course causes other operations to fail:

AT+COPS=?
+COPS: (1,"AT&T","AT&T","310410"),,(0,1,4),(0,1,2)
OK
AT+COPS=1,1,"AT&T"
+CME ERROR: operation not allowed

I was trying to use the SIM card from my smartphone (StraightTalk on AT&T), and I also tried an unprovisioned AT&T SIM just to see if it was detected.

Could the problem be that the SIM card has the wrong application on it? Should USIM be backwards compatible with a 2G module?

Also, I don't know if this is related, but I noticed that just after power-up, SIM_VDD oscillates briefly at about 2MHz. I think that might be a normal part of the voltage detection process, but I'm not sure.

What should I need to get this working?


texts: Cheapest way to translate 5V SPI signal to 3V SPI?

texts:
I have a MCU that operates at 5V, and a display that recommends a 3V logic level. They are connected via SPI that can operate up to 1.5Mhz. What is the best way and the cheapest way (not necessarily the same), to convert the 5V to 3V? The SPI connection is one way (SCK, MOSI, CS only; no need for the LCD to communicate to the MCU, so the translation is from 5V to 3V only).

Thanks,
Mike


texts: Looking for batteries to power a project I'm working on

texts:
Sorry if this is really basic, but I don't really know much about power consumption and voltage. I'm building a sensor system with a small computer with a 19V, 65W power supply, as well as a cloud sensor with a 15V DC - 1A power supply. A few other things will be added on such as a low power consumption anemometer, but those should be run directly from the computer.

If I'm looking for rechargeable batteries to power this, what should I be looking at? I'm not sure if I should be looking at one large battery or a bunch of smaller batteries together. Are there any other things I should look out for?


texts: EFM8BB1 - C2 Debugging Interface correctly connected?

texts:
I am currently working on a small circuit which features a EFM8BB1 8-bit microcontroller from Silicon Labs. Even though they have well-documented data sheets, I still want to make sure that I do everything right.

The EFM8BB1 uses the C2 debug interface to be programmed via the USB Debug Interface from Silicon Labs (documentation).

This is my debug port schematic:

In the datasheet of the debug adapter, they state that only 3 pins are needed (C2D = P2.0, C2CK = RSTb and GND). Because the 8-bit USB Debug Adapter also features a 5V pin, I utilized it as a power supply for the controller so I don't have to use a battery all the time to program it.

Did I do the wiring correctly? Any help is very much appreciated!


texts: Using arduino as a voltmeter, current drain with a voltage splitter?

texts:
I'm trying to read the voltage of a 3S 11.1v LiPo battery with an arduino, so it can monitor the battery level and report when the voltage is getting low. The easiest way I've seen to do this is with a voltage divider. I've seen tons of "don't use voltage dividers" posts over the years, all for various reasons. My concern is the wasted power lost to heat that the voltage divider might draw.

If I have a low current drawing circuit hooked up, with a voltage divider to cut the voltage down to the range the arduino can read via the voltage reference pin, how much current will be used/wasted by that divider circuit? Is there a way to estimate that, without actually building the circuit and testing it? This is going in a device that is to run long term, and I'd hate to shave a large percentage of time off the runtime just to monitor the voltage.

Is there a better/more efficient way to read the voltage of a 11.1v lipo on a 5v arduino without using a voltage divider?


texts: Sensor to measure distance of moving object

texts:
I am wondering the best type of sensor I can use to measure the distance between a  moving object and a fixed object, i.e. the sensor. For application, think of a moving car going around a corner with a barrier in place. Ideally, the measurement would be somewhat accurate down to at least a centimeter.

I have looked into both small lidar and ultrasonic sensors, leaning towards the lidar given the environment would be loud, but am looking for other types of sensors if something more practical is available.

Any suggestions are much appreciated.


texts: Best way to cut mounting squares out of plastic project boxes?

texts:
My electronic kit-building to date has included pre-drilled kit boxes for mounting.

My latest purchase, however, has a plastic project box, and no pre-made cutouts.

I need a rectangular hole for a small LCD screen - and I don't want to mess it up!

How best to cut the hole?  Tools to use?


texts:
I have an omnipolar (2ssm) hall effect sensor which outputs 400mV when triggered by a magnetic field. Basically what I want to know is, is there a way to increase this output voltage to be able to power an LED?

The aim is to have an array of these setup to detect flux leakage over an area and have the LED's light up in the area the flux is detected.

Thanks for your help.


texts: Simplest "battery low" indicator for a 3.7 volt lithium ion battery

texts:
I just need a single LED to light up when the voltage drops below a threshold like say 3.3 volt ( sharpness is not that important ). I know basic electronics like transistors,logic gates etc. On searching a bit, I think a comparator is what I need (all about which I know is that it gives a logic signal based on which input voltage is higher).
Can I use just the comparator for the 3.4 volt LED and achieve what I need, from the link given below ?
http://www.instructables.com/id/Li-Ion-battery-level-indicator/


texts: Confusion about induced EMF and voltage in Ideal Transformer

texts:
When an IDEAL transformer primary is connected to an AC source, an EMF will be induced in the primary given by

$$E = N \dfrac{d(flux)}{dt}$$

And it must be given sign by Lenz's law. So it should be negative as for opposing the cause. So \$E= - V\$. But in some book it is given as \$E= V\$, so as to counter and exactly balance the cause.

But both are contradictory. I am getting very confused.

Can anyone please help?

Thanking you in advance.

I have added the articles from both the books.


texts: Controlling multiple stepper motors using a single driver

texts:
I want to control ~50 stepper motors using a single driver, and use only one Arduino pin to control each motor.

Currently I'm using a single A4988 driver and a couple of 12v 1amp stepper motors to prototype a part of a machine as a proof of concept, but I need to use many larger motors and better drivers in near future.

As I don't need motors to work simultaneously, I want to use a single driver to control them all.

I tried to validate my idea using 4 different relays and it seems that motors work perfectly as my needs (I tested and switched between them in a 24 hours long test). But as transistors are much cheaper and smaller in size, I want to use them if possible.

I have programming background and never designed a circuit before, but bellow is a schematics that I designed to control two stepper motors with a single driver, I don't know what kind of transistors or resistors should I use, or is this schematics possible at all? (As I mentioned, I already used a "4 relay module" instead of transistors and it worked well).

here is the schematics:

Any help to fix the schematics problems and choosing transistors and resistors would be appreciated.

Thanks.

p.s. As everyone in the comment section is suggesting to use multiple drivers I want to clear it again: Using multiple drivers is not an option, because I need to control larger motors and I need more expensive driver, which I can't afford many of them in a prototype. Any suggestion to use a single driver to control many motors, preferably using a single pin per motor is considerable. Thanks.


texts: What's the logic inside the formula for the calculation of the maximal envelope modulation amplitude of two temporal interfering electric fields?

texts:
Since my question is a bit elaborate, I will first write some details. Thank you all!
I refer to the study conducted by Nir Grossman et al. (2017) about the use of the temporal interfering stimulation to excite neural cells in a specific region of the brain. However, my question is concerning only for the electrical part.
In the image above is represented a scheme of the addressed problem, in which two pairs of electrodes are applied on a spherical target (plane XY) (figure A). Figure B shows the time domain of the electric fields taken in two spatial point (see i and ii on figure A), in particular you can observe the generated envelope from the interaction between E1 and E2.
Considering the case of two interfering fields  and , where  is the position vector of interest, this study provides the following formula to calculate the module of the envelope modulation amplitude :

where  is the direction of interest (details on page 20 in the link above). This formula is easy, and I have no problem to understand it. But, immediately after this formula, as you can see, is provided the formula for the calculation of the maximal envelope modulation amplitude.
By referring to this last equation, I can understand the formula related to the first condition. In fact, looking for example figure B - case ii, I can observe that the envelope modulation amplitude is approximating at the amplitude of E2. On the other hand, is difficult to understand why otherwise it has to be applied the indicated formula. What's the logic about this formula?
Furthermore, I have another question. Why the maximal envelope modulation amplitude is computed with this formula? I mean, the first equation is sufficient to know the maximal, isn't it?
Image:

Reference to Grossman et al. (2017):
https://www.cell.com/cell/pdf/S0092-8674(17)30584-6.pdf


texts: Efficiency of Halogen lamp Transformer when used with LED lamps

texts:
First off: I live in a part of the world where our grid runs at 230V, 50Hz. In case that matters.

I bought this house with numerous 12V 50W Halogen downlights, each with their own step-down transformer. The transformers are, as far as I can determine, good old heavy iron core transformers that supplies 12VAC on their output.

In order to save costs, I very soon started switching the house to LED lamps. These are sold as 5W drop-in replacements that you simply plug into the same MR16 connector of the old lamp, and they appear to work fine on the 12VAC they are supplied with.

I expected the actual consumption on the AC side to be slightly higher than 5W, because transformers are after all not 100% efficient, but what I am seeing now is a little horrifying. It would appear that I use around 15W per lamp, measured on the 220VAC side, rather than the expected 5W.

A quick current measurement on the 12V side shows that I am running 0.3 amps at 12.5VAC, which seems a bit odd but if I compensate for peak vs RMS it gets me exactly 5Watts peak (clever LED sales people, it is sold as a 5W...).

So my question now, is it possible that the efficiency of the transformer, which is of course designed to drive 5 amps rather than 0.3, could really cause such terribly efficiency?

I read on some internet forums that some transformers really do consume 5 to 10 watts of power on their own. Is this what I'm seeing?

What should I use instead?


texts: USB internal control to on/off a pc fan molex circuit

texts:
I am new to electronic circuits so I might not have the correct nomenclature for some items.

Description:

I have 3 high power 12V PC fans (NON PWM) connected to a hub that draw power from MOLEX connector. They can't be controlled by any means except with a on / off IR remote coming with the hub (No hard switches).
They draw some high current. They can't be powered over 5V USB directly.
Issue:

I need advice for simple circuit idea (without Arduino) to connect a USB from Motherboard to control the on/off of these fans (while drawing full power from Molex).

i.e. when the motherboard is powered off, the fans are turned off and when i switch pc on again they turn on automatically (without having to remove the molex connection / using remote every-time i try to switch them off).


texts:
I have had the same digital watch model for many years. Although they inevitably break again and again, I continue to buy the same model (A Casio 53W). I now have quite a collection of them sitting on a shelf for no real reason, but today when I was cleaning up I decided to take one apart.

Inside, I found that the keypad was actually quite interesting. Here's a picture.

I was curious how it actually worked. I couldn't find any connectors; only multiple stacked layers of plastic with a conductive material leading from each button.

How is the signal from the button interpreted by the components inside?


texts: Diode capacitor circuit, what is the output across the diode?

texts:
I'm practicing on some diode problems and I've been stuck on the following one for a while. Let's say that the input voltage(ac source) is:

$$V_{in}=-10\cos{wt}$$

I want to find the voltage across the ideal diode.

First of all, since there is no resistance in the circuit we assume that the capacitor can be charged instantaneously or very fast since there is internal resistance in the components.

At t=0 since the input voltage is negative, current flows counter-clockwise (the diode acts as a short circuit) and the capacitor is charged in no time. So the output voltage at this point is 0 since the diode is on.

Here is an observation:
Clockwise current flow will never be allowed by the diode. Therefore,the capacitor will never be able to discharge.

Moving on with this mind, at t=0+ the input voltage starts decreasing. Since the capacitor cannot discharge, applying KVL gives a voltage across the diode equal to Vin-Vc. However, capacitor has been charged to -10 so:

$$V_{out}=Vin+10$$

This can only be positive, so the diode will be reverse biased and the equation is valid for the rest of time. However, thinking of the result or how the circuit works in practice, I've come across some contradictions:

Since the diode is connected to ground, the potential changes only on the top right node. If the potential there changes, doesn't the voltage across the capacitor change as well?

If the top left node is stuck at -10 volts, how does the input voltage change since it is also connected to the ground?

One explanation would be that the potential of the two top nodes changes so that the voltage across the capacitor remains constant.Is this the case?


texts:
I read in a datasheet that the Input sensitivity of the AD4002 (RFin) is -10dBm to 0dBm.

I know how to convert this to a voltage drop over a resistor, say 50ohm.

But I got myself confused over the exact definition of input sensitivity.

Is it the power that should flow into the pin of the chip?

Or is it the power delivered to a 50ohm termination resistor on the input?


texts: Is There an Alternative to Resistor based Voltage Divider for an DC Audio Signal with Less Noise?

texts:
I have a LMC555 which generates a audio signal between 440-880 Hz. The signal is DC between 0-3V after the chip. To use it as input for an amplifier. The amplifier, a LM386N-1, starts clipping the signal quite early, somewhere around 20mV. Currently I use this solution:

simulate this circuit – Schematic created using CircuitLab

I lack the really deep theoretical understanding. As I know, each resistor in series will increase the noise of the signal. Higher resistance will cause more Johnson–Nyquist noise.

Here I have a 1MΩ resistor in front of the amp input, so I wonder...

...is there an alternative solution to this which causes less noise?


texts: How can I find a specific frequency after doing FFT?

texts:
I have some samples from an SDR that I run through FFT and I want to detect the presence of a specific signal, exactly 148.369MHz.

The maximum sample rate of the device is 2Mhz, this is just something else that I don't understand, how can I detect 100Mhz+ signal if the maximum sample rate is 2Mhz ?

Anyway, if I understand correctly, the maximum frequency in FFT is 1Mhz, via nyquist, my question is, how can I find the bin that corresponds to the 148Mhz signal ? I can see a spike that corresponds to the signal but I want to be able to index into the bins and find it.

Thanks

Edit: This is a plot of the signal using GNU Radio's FFT block, I'm trying to achieve the same results with my code


texts: Correct Part for Connect an Two-Pin LED or Switch

texts:
Quite simply what I'd like to know is, what is the technical information for the male connector that corresponds to the following plug:

The male connectors (headers?) are commonly found on computer devices such as motherboards, and are used for connecting LEDs or switches, usually on a computer's case. However, the device I'm working doesn't include these connections, so I'd like to provide them myself by adding a suitable pair of male pins to the end of the correct wires, rather than having to wire in an LED or switch directly, I'm just not sure exactly what I'm looking for, is there a common male connector I can just add to a pair of wires?

Apologies for my lack of more specific terminology, usually when I work with computers I have all the parts I need or can just order some up :)


texts: Inductor core saturation: DC vs peak current value!

texts:
I am trying to figure out something. I am currently working in SMPS design and as I get deeper different questions arise.
Magnetics is not one of my strengths and this is why I find pretty difficult to answer the following question: what is the current value that will make coil's core to saturate?
All datasheets that I saw give us Isat as a DC bias current that drops L by 10,20,30%. But this is DC bias ... does it mean that my inductor can withstand larger peak current values than Isat? If so, how do I calculate it?
All app. notes that I read use WC value of IL+deltaIL and compare it with Isat (which is a D.C. bias), so it is confusing.


texts: Sawtooth generator not working - transistor won't discharge my capacitor

texts:
I have been trying to build a sawtooth generator using a current source which linearly charges my capacitor and a comparator which was supposed to discharge my capacitor; instead it doesn't. Here is the schematic (first picture) of my attempt which doesn't work.

I decided to break the connection between the operational amplifier output and the transistor base to check the signals OSC_CH2 and OSC_CH3 with my osciloscope (second picture). I figured out that the operational amplifier is working just fine (third picture). The problem must lie in the transistor or the circuit behind the operational amplifier. But how do I fix my problem?


texts: How to solder under already soldered parts?

texts:
I soldered several pin rows on my pcb, and thought that both sides of the pcb are already connected. Therefore I only soldered the pin rows on the bottom of the pcb. Unfortunately they weren't connected, so that I have to solder the pin rows on the upper side of the pcb, too. But with my soldering tip I am not able to get below the pin rows. Is there a way to connect them without having to unsolder them?
Pictures:


texts: What is the name of this current called in this regulator datasheet?

texts:
Which parameter in this data sheet is the default current flowing from the input to the ground regardless of the load current?

In my case an 12V input will be regulated to 5V by the TL780-05. So to estimate the total power dissipation I will use the following formula:

Preg = (I_n × 12) + (I_load × (12-5))

My problem is I don't know how they name I_n in the regulator datasheets, so I got stuck. Where in the datasheet I can find I_n? And is that always named same way?


texts: voltage difference between two batteries connected in parllel

texts:
I have a device that needs a constant power supply and can only use batteries as an energy source. Using multiple batteries, I can swap a drained one for a fully charged one. Since I have to have a constant power supply, I want to install a smaller (lower mah) battery that will supply power during the swap. After I put in the larger (higher mah) fully charged battery, both batteries will contribute power in parallel.

All batteries are Lithium ion 3.7V (only different mah) . The problem arises when I swap batteries. If the difference in voltage between two batteries connected in parallel is greater than 0.2V a huge rush in current is transferred until the batteries equalize. This could be a problem...

The larger battery will need to recharge the smaller one. Would putting in a resistor between the small and large battery do the trick? Or do I need a more complex protection circuit?
Thanks in advanced!


texts: How to test for Bioelecetrical impedance in an body fat analysier

texts:
I have an interesting project for school. I want to test these body fat machines for consistency between different brands. Ultimately to see if a cheaper brand is as good as an expensive one.
http://www.drgrab.com.au/products/handheld-body-fat-analyzer?utm_medium=cpc&utm_source=googlepla&variant=1089145592&gclid=CjwKEAjw96aqBRDNhM6MtJfE-wYSJADiMfgg3iLGVTTN6ccbhbLI3NiCKU8lRDG5K_zzmfkFIP6XshoCU9Lw_wcB
http://www.amazon.com/Omron-Monitor-model-HBF-306C-Black/dp/B000FYZMYK

These machines look to use Bioelecetrical impedance (http://en.wikipedia.org/wiki/Bioelectrical_impedance_analysis). Is there some way that I can simulate a person holding the handles? e.g. with a resistor between wires connected to handles.

I want to compare different machines between different companies to see if they give the same results but to do that I think I need a standard testing rig. I could hold the handles myself on different devices but it seems to change during the day. e.g. the morning is lower and the afternoon higher.

Any thoughts?


texts:
I've become fairly familiar with the clearance and creepage requirements of UL/IEC/etc 60950, 60730 and derived/related standards. I've just realised, though, that they only refer to distances through air (clearance) or along a surface(creepage). In fact, solid insulation is specifically used as a barrier to increase the distances. Does this mean, then, that the PCB itself is considered solid insulation, and completely removed from the clearance rules? Can I safely have 240VAC on one side of the PCB and user accessible low-voltage circuits on the other, provided there aren't any vias in the vicinity?

Extending the question, what role does the thickness, dielectric strength, etc play? If a thing is considered "solid insulation" is the only requirement that it passes the hipot testing, and if so, at what voltages?


texts: Why must this DIY lab bench power supply be powered by an AC supply?

texts:
Technical Specifications:

Input Voltage: 24 V alternating (max)
Input Current: 3 A (max)
Output Voltage: 0 - 30 V, could be regulated continuously
Output Limit Current: 2 mA - 3 A, could be regulated continuously
Output Voltage Ripple: 0.01% (max)

The output of the transformer is single 24 V or dual 12 V (same as 24 V), and the power could be determined according to your need. If a full load output (30 V, 3A) is
needed, the power of the transformer should be greater than 90 W.

The circuit must be connected to 24 V alternating current power, and direct current is forbidden. Why is this so?


texts: How to drive a E1144CS021 (EPD display)?

texts:
I was searching for EPD displays and came across this Pervasive Displays EPD, but after searching in the manufacturer's website, I couldn't find any information on how to actually use it. There are some pre-made kits, but those are intended for evaluation use, and though the schematics are available, there are no design descriptions.

How would one drive such a display? It uses an SPI interface, but what signals should be sent to it? What about all the other pins, how should they be configured?


texts: Parallel driving multiple pairs of LEDs in series from USB supply -- is it a terrible idea?

texts:
Due to a need for a grow light and a surplus of 3mm LEDs & USB chargers on hand, I decided to try to make something serviceable with no additional parts requirements.

Upon measuring the LEDs, I found that the white ones I have have an average Vf of about 2.8. The reds have an average of about 2.0. Arranging them in series and running a couple tests off of my bench power supply just to see how hot they got/what output looked like, they appeared to be somewhat under-driven at 5V, drawing ~15mA. Ramping the supply up to 5.5V drove the test pair at about 50mA with no additional drift in current after several minutes.

Assuming that other pairs perform roughly the same, it seems to me that I could get away with running several pairs in parallel off of one of the many 5V USB charger wall adapters. I'm an utter novice, but from what I can see as long as the voltage regulation isn't utterly abysmal, the combined voltage drop of the LED pairs should self-limit the current they pass. Token research indicates that biggest flaws with many USB wall-warts is that they tend to experience voltage sags when approaching max output current -- which, in this case, would seem to be a positive if anything.

My question is: What am I missing, and why is this a horrible idea that will no doubt burn my apartment down the moment I look away and curse all of my relatives to an early grave? Is constructing a pair of rails and just bridging them with LED pairs until I bump into the maximum current output of the supply a viable solution?


texts:
We have disassembled a transformer from a microvawe oven by cutting the core, put a secondary winding suitable for our purposes (so transformer outputs 16VAC rms) and then tig-welded the core back. Now the core is heating up while the transformer sits with no load on the secondary. By heating up i mean that core gets too hot to touch in about an hour. The primary and secondary do not heat by themselves, i.e. they are cooler than the core.

What might be causing this? Are there any voodoo to fix it?


texts: Are there "Euro strip" terminal blocks with "rising cage" connections?

texts:
I'm continually modifying the connections all over (and under) my centrally controlled house. Terminals with bare screws are hard on the tiny wires, and "wire protectors" don't open back up nicely when I want to change something. So I used pairs of PC-mount "rising cage" terminal strips, and soldered the PC pins of each pair together. And 30 years later the solder joints are occasionally failing...

I'd love to find something like a "Euro strip", with ten or twenty (or linkable sections of) paired connectors - but with rising cage terminals. But I can't even find useful search terms. Different sites use "rows", "poles", or "sections" to mean either the width or length of the strip. And often when there is a width of two or three, it means independent terminals stacked at increasing heights, instead of commonly joined terminals.

The closest I've found are the DIN rail mount sections, like
Connectwell CTS2.5UN
But they are rather huge compared to what I made, and won't fit in some of the tiny spaces available. Has anyone seen something the size of a Euro strip but with paired rising cage connections?


texts:
What is this thing called? how does it work?
I've tried googling so much, even pasted the image in the google search box haha

Its used here on the MSP430:


texts: How to choose the series pass transistor?

texts:
I plan on using the LT3080 to regulate a variable 1-36V 7A DC power supply. This regulator by itself will not provide more than an amp or so, so I will have to use an external series pass transistor per the recommendation in their datasheet:

Now, I am sure this will work fine, however the recommended BJT is expensive, something like $7 a piece. Given I am planning to make a few of these regulator boards, I would like to keep the cost down by choosing a comparable part. This is where I need help.

On Mouser I see plenty of PNP BJTs that support 100v emitter-collector, and 10s of amps for 60 cents, but I don’t know if that will work. So what parameters should I be looking for in the datasheet that would be suitable in this application? It would be great if you can also explain why this part was chosen in the first place and why it is more expensive than other seemingly similar BJTs.


texts:
I'm learning Electronics by my own. And I'm in stuck while reading a book after failed to understand the following paragraph in Chapter 1, Electric Circuits 10th by Nilsson :

  On the other hand, the propagation frequency of radio signals is on the
  order of 10^9 Hz.Thus the wavelength is 0.3 m. Using the rule of 1/10th, the
  relevant dimensions of a communication system that sends or receives radio
  signals must be less than 3 cm to qualify as a lumped-parameter system.
  Whenever any of the pertinent physical dimensions of a system under study
  approaches the wavelength of its signals, we must use electromagnetic field
  theory to analyze that system. Throughout this book we study circuits
  derived from lumped-parameter systems

It's about the definition about lumped-parameter circuit.

I have difficulty in understanding the sentence :

  Whenever any of the pertinent physical dimensions of a system under study
  approaches the wavelength of its signals, we must use electromagnetic field
  theory to analyze that system.

What does "physical dimensions approaches the wavelength" mean exactly?

What are the properties of physical dimensions?

And how do they approaches the wavelength?

It was just about the size and the length.

But.. I don't know why EM theory should be applied when the size approaches the wavelength. I might need to find that answer from EM theory.


texts:
I'm planning to use an Avalanche Photodiode (APD) to perform sequential light sensing - something around 100 readings under a minute. From my calculations this implies a frequency of around 1.67~2Hz. My APD has a capacitance of 320 pF and a dark current around 0.15 uA. The particular light signals I'm trying to measure would output ~0.8 uA (these are all estimates based on the device's datasheet)

When designing a op-amp transimpedance amplifier, what kind of bandwith would I be looking for? The datasheet suggests using an op-amp able to work at 1GHz due to the fast photodiode response (in the nanosecond range - a  photon detection pulse has FWHM of 0.3 ns). However as my application doesn't require sugh high frequencies,could I use slower op-amps or I would lose some signal?

Obviously the gain must be taken into account, but even if I place a 47 KOhm resistor on the feedback loop, I'still get ~10 Hz bandwidth and would not require such high-frequency op-amp. Am I missing something relevant?

EDIT: The APD is the Hamamatsu S12572-100P model, biased with 65V.


texts:
I need to design an amplifier having a Vin=150mVp, 1khz; Vcc=3V that can run an 8ohms, 0.25 watts speaker, with a gain for about 7 without noticeable distortion.

Below is my designed voltage divider biased common-emitter amplifier with Vin=150mVp, 1khz; Vcc=3V.

But here is my concern: I need to have a gain of about 7, or having Vout for about 750mV

The first schematic I design having no load resistor of 8 ohms, when I simulated I measured a Vout of about 762mV, as you can see below:

But when I inserted a Load Resistance of 8ohms (assuming this is the speaker), I only got Vout of about 46mV which is very low, as you can see below:

****My question is what can I do to increase the Vout for about 750mv having the Load Resistance of 8ohms, at the same time without having noticeable distortion?**

Any help will be appreciated. Thank You.


texts: How to bond/connect wires to neodymium magnets?

texts:
After reading this, I learned it is not advisable to solder a wire to neodymium magnets.

After more reading I found this post describing the use of conductive epoxy to bond electrical wires to neodymium magnets, a very messy process which takes several hours of waiting.

I want to ask this community if they have or suggest better methods to bond/connect a wire to a neodymium magnet to act as a conductive connection?


texts: How does SDRAM refresh interact with ECC

texts:
I'm trying to understand how SDRAM hardware works if it also has ECC capability.

If a memory system has ECC capability it will be able to correct a single bit error in a block of memory and detect, but not correct, a multi-bit error. The way I understand it is that when the block of memory is read, the Error Correcting Code for that block is also read, and if there is a single bit flipped from what was originally written, it is automatically corrected by the memory controller.

Now SDRAM, by its nature, must refresh the data it holds or it will be corrupted over time. So it needs to read its memory cells and then rewrite the data back on a regular basis. From what I've read, this refresh read is slightly different from a regular memory read since it doesn't actually have to send data over the bus to the CPU so the refresh happens a whole bank at a time and just reads and writes the data back into the same cells without touching the bus.

My question is, does the ECC process come into play during the regular SDRAM refresh reads, or is that process bypassed in order to make the refreshes as fast as possible so that they won't tie up the memory system and inhibit regular memory accesses? If I have ECC SDRAM, do the single bit errors get automatically corrected on every refresh cycle or does the memory controller wait until an official memory access to detect and correct single bit errors?

Perhaps the answer might depend on the particular memory controller. I'm reading through the datasheet for an Intel 855GM/855GME Graphics and Memory Controller Hub to see if that particular controller does what I'm describing, but I haven't found an answer yet.


texts:
I have a blackfin 533 and I connect it with external flash memory.

I have a software driver that erases a block, fills data, write to flash memory.

I'm using the following chip ST M29W800D.

How would I test and verify the flash that's working ?

Should I earse it, fill it with data and read it ?
but how would I erase it, and I'm running the software that is checking the correctness of the flash eeprom ?


texts:
I'm currently designing a PCB with double side components and I'm limited to 6 layers max. The project has couple of MCUs at 84 MHz. There are USART, I2C, SPI, some analogue lines and high-power lines in the design but not any high-speed lines. There are also some very short RF lines for antennas.
The problem is due to the high density and limited size of the PCB I can't use this stackup: S-G-S-S-P-S
At some parts of the PCB specially around the high pin count MCUs there's need for signal lines to go through the ground or power plane.
Also all the power electronics and switching components are on the back side.
This is the stackup properties provided by the PCB manufacturer:

So my main concern is if routing some signal lines through the power/ground plane will cause me problems or not?


texts: H Bridge not working with two DC motors on paralell -- Arduino

texts:
I've done a simple H Bridge with 5V relays and 2N2222A transistors using Arduino Nano, just like this one:

A 6V 4A battery supplies the Arduino (on Vin). Relays are supplied with 5V of the Arduino, but the Normally Open Contacts are connected to 6V.

When I connect just one DC motor, the H Bridge works fine. But If I want to connect two motors in parallel to the Common Pins, the relay I'm activating sounds, but the motors don't move, then, after some seconds, the Arduino restarts itself (because the Bluetooth module that I'm using disconnects itself and the LED of the Arduino blinks like when you reset it).

Also, if I connect the second motor in parallel while the first one is moving, it works fine, but then, if I try to invert direction, it happens what I said before: Arduino restarts itself.


texts:
I'm using an Altera Cyclone V DE1-SoC for an image processing project and to be able to do the "processing" on the FPGA, I thought I probably needed to store the image data on the FPGA first. So I went ahead and converted a sample image I want to use to a .mif file and used the Memory Compiler megafunction (RAM:1-PORT option). I chose the .mif file I created and made sure the number of words and bit widths match. Everything seems to have worked fine so far but... how do I actually use this data now? The .mif file contains the tone values of a 240x320 grayscale image and I need to go through these values one by one to apply Sobel edge detection. I did this using MATLAB without any built-in functions so I think I'll be able to write the necessary code in Verilog as well, just need to access the data. I'm pretty new to FPGA stuff so I'm sorry if this has a very simple answer.

(Also, if there are any methods that are more straightforward than initializing memory, please suggest them. I may be overcomplicating things unnecessarily but am not sure.)

Any help is appreciated! Thanks in advance.


texts:
Conductive Emission Help needed :
Have a DC to DC converter 28 VDC to 12 V DC  2A , that is loaded by a PWM load , the supply wires contain unwanted  Differential and common mode  conductive Emission signals , any suggestion how to reduce the outages ? especially at the low frequency about 1KHz , any feedback welcome .


texts: Enable Timer interrupt after generating N pulse

texts:
I need to enable a general timer interrupt after generating each pulse in PWM mode. I wrote this program. I will be grateful if you kindly let me know how to enable timer interrupt. This my SPL schematic code:
 void PWMControl(unsigned int Freq){
TIM_TimeBaseInitTypeDef     TimeStructureure;
TIM_OCInitTypeDef       TIMOCStructureure;

        TimeStructure.TIM_Prescaler=Prescale;
        TimeStructure.TIM_CounterMode=TIM_CounterMode_Up;
        TimeStructure.TIM_Period=Period;
        TimeStructure.TIM_ClockDivision=TIM_CKD_DIV1;
        TimeStructure.TIM_RepetitionCounter=0;
        TIM_TimeBaseInit(TIM4, &TimeStructure);
        TIM_Cmd(TIM4, ENABLE);

        TIMOCStructure.TIM_OCMode=TIM_OCMode_PWM2;
        TIMOCStructure.TIM_OutputState=TIM_OutputState_Enable;
        TIMOCStructure.TIM_OCPolarity=TIM_OCPolarity_Low;
        TIMOCStructure.TIM_Pulse=Pulse;
        TIM_OC1Init(TIM4, &TIMOCStructure);
        //TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Enable);
        TIM_ITConfig(TIM4,TIM_IT_Update,ENABLE);

}

According to this post  I need to generate N pulse without/ the least CPU workload. (Max Frequency=1MHz)


texts:
When charging a battery using a solar panel, or even another battery, how is the current flowing through the battery determined?

Will the internal resistance of the battery draw a certain amount when drained and decrease/increase as it charges? Or is the current simply determined by the builder using a resistor or other loads with the internal resistance being small enough to negate?


texts:
I have stm32f030f4p6 Microcontroller and using iar Compiler ,
library cmsis ,
After confige Uart1
the RXNE , FE and CMF bits return 1 whereas not recieve or send was done
if I dont set RXNE bit to 0 thats Stuck on interrupt routine
And that recieve nothing
here is my Uart Config:

  USART1->BRR = 0x1388;
  USART1->CR1 = USART_CR1_UE | USART_CR1_TE | USART_CR1_RE;

and GPIO config
and Nvic:

  NVIC_InitTypeDef NVIC_InitStructure;
  USART1->CR1 |= USART_CR1_RXNEIE;
  NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);

and the register after this 2 line

  USART1->BRR = 0x1388;
  USART1->CR1 = USART_CR1_UE | USART_CR1_TE | USART_CR1_RE;

rx tx connected to sim800 module and its answer to AT Properly

thank you


texts:
I want to trigger a laser externally and I want to trigger it when a rotating small wind turbine blade passes a specific angle. I have a digital signal which tells me when the blade passes that angle. The blade rotates at 13 Hz, but I want to trigger the laser at 1 Hz.

So I need a tick counter that can count the picks in the digital signal and ignore 12 of them, but passes the 13th one. I am looking for a stand alone sensor that can do it for me. That would be great if I can adjust those frequencies too. Any suggestions would be appreciated.


texts: What is the polygon pour and power plane for in a PCB?

texts: I am newly in PCB design.  Can any one explain me what polygon pours and power planes are used for in Altium PCB, or give me a link that explains it?


texts:
Basically I'd like to deploy a sensor temporarily for a period of about a month. The sensor communicates via a wireless protocol and sends a data packet about once every 5 minutes as far as I understand it.
It is normally connected to a device which powers it via the following specifications:

50-60mA and 12-20vdc

Is it practical to do this via a battery?
I was initially thinking that maybe I could use a rechargeable battery pack such as the ones that you can use to recharge your mobile phone via a USB port. A Jackery Bar for example.
I have no real idea of how you match a battery to your purpose so any thoughts gratefully received.
Robin


texts:
Is it possible to design a good bandpass filter with center around 1GHz, using capacitors and inductors?

Or does these components perform too poorly at these frequencies?

I would rater not try to design my filter as a cavity filter (soldering pipes and all).


texts: How to access I2S pins of Lara R211 on the EVK-R2xx board

texts:
I just received the EVK-R2xx board from u blox.
I need to access the i2S pins on the Lara R211 on this board in order to connect it to a beaglebone black so that I can use the audio directly from the Beaglebone
However, on the data sheet, it is stipulated that the I2S pins of the Lara R211 are neither connected to the J300 or J301 pins.
Is there anyway I can access them? Or is there another solution?
Thanks in advance


texts: Illuminate keyboard using Scroll Lock key

texts:
I have a keyboard that I'd like to illuminate when pressing the Scroll Lock key, but I'm not really good when it comes to designing something like that.

I'm planning to use a transistor that will take the current from the Scroll Lock LED, so when activated the transistor will take the higher current from the keyboard input to light one or two LEDs.

I came up with this design but need some help, I don't really know well how to wire the transistor. I measured the Scroll Lock LED voltage on load and it is 2v, I don't know the current since I believe I'd need to unsolder one pin of the LED to measure it (I'm assuming the current is 20mA?).

This is the transistor's datasheet: http://www.futurlec.com/Transistors/C1815.shtml

The resistors on the light LEDs would depend on the LEDs I choose, if possible I'd use white LEDs, if not blue.

I know the transistor leads are actually ECB, I draw them like EBC for the order.

EDIT: Ok I want to add more information, I checked the amperage of a PS/2 keyboard, it was easy because I just had to split a jumper.

The most consuming configuration was with the three LEDs ON and pressing one or more keys continuosly, in that case the amperage was less than 30mA (26.3mA). The voltage is 5.1V.

According to this: http://www.computer-engineering.org/ps2protocol/ PS/2 voltage can go from +4.5V to +5.5V and the max current is 275 mA. Which gives me hopes I can wire the LEDs internally.

I have two white 3.5V 20mA LEDs that work just fine at 3.2V 17mA, so adding them would be around 34mA. That is, less than 30mA from the keyboard plus 34 for the light = less than 64 mA in the worst case (I have to add more components so it will be a bit more at the end), with all the Keyboard LEDs the lights ON and typing.

The circuit would consume less than the max 275mA from the PS/2 protocol.

The other option I'm considering is to make a Joule Thief, and run the lights right from the Scroll Lock LED but I don't know if the frequency of the Joule Thief could interfere with the keyboard or the computer in some way.


texts: making Emergency lighting normal supply and power failure

texts:
How can i make an emergency light that works in normal power supply & also in power failure.
Light will be always in ON condition,In normal condition power from normal power supply,and from power failure power taken from the battery.
please give me necessary advise or circuit diagram...


texts: Charge Controller for Small Lithium Ion (Lithium Titanate, LTO) Cell

texts:
I am interested in using the SLB03070LR35 cell, which is a tiny cell that can handle 20C charge rate. What kind of charge controller can I use to recharge such a small cell? Would an LDO set to 2.8V with a current limiting resistor (120 Ohm, limits to 7mA from 2V dead cell to 2.8V max charge) be acceptable?

https://www.nichicon.co.jp/_assets/pdf/products/slb/en_specification1.pdf


texts: LTSPICE - How to create PWM with rise time

texts:
A simple PWM circuit is simple to create using LTSPICE, such as:

VIN VSIN 0  SIN(0 1 10 0 0)
 VP VTRI 0 PULSE(-1.5 1.5 0 9.998m 1u 1u 10m)
 B1 VOUT 0 V=U(V(Vtri)-V(Vsin))*5

But voltage reflection simulations, i need the PWM rising edge to be more realistic, i.e. with a time delay on the rising edge like this:

I have tried using a PULSE, but its frequency and on-time is fixed.

What I need is something that activates a given pulse, or a behavioral voltage source that can create a pulse if a certain condition is true. The pulse has to be as long as the condition is true - as with conventional PWM.

An example of what I have tried, but which caused a syntax error:

The syntax error is that in the B2-element (to the right), cannot use "V1" as voltage output. It has to be 5 (volts) or something.

How to I solve this? I just started using SPICE two days ago, and I bet there is a few tricks I am not aware of yet


texts: When bitbanging I2C, rather than switching the LOW/HIGH states of the pin, switch between LOW/HiZ by simply altering the DDR/DIR registers.Why is it like this? Why can't we switch LOW/HIGH states of data pin? My controller is communicating with only one slave.


texts: How does an IV curve of a bulk semiconductor look like?

texts: What would an IV curve of a bulk semiconductor (i-type/n-type/p-type) look like if I do a typical voltage sweep?


texts:
I am going to scale PWM 24V generated by PLC to PWM +5V by means of optocoupler TLP521 and MOSFET BSP295 in order to control a micro servo motor (MG90S).
What I have tried till now is the below circuit:

I have two questions please:
1. Will it work as I expect?
2. Are there any better circuits to tackle my problem (Converting PWM 24V to 5V)?

Edit: (based on comments)
1. Required frequency is 50 Hz.
2. Due to current limitation I am not able to use opto transistor directly.
3. The two sides are going to be isolated.


texts:
I'll start by saying that I'm a software guy, I know literally nothing about electronics.

I recently bought a raspberry pi, and while browsing at my local electronics shop, saw this board for $5.

I realize now that I don't know what I would actually use a board like that for.

I would like to know a few things:

Does a board like that require soldering? Is this at all similar to a "breadboard?"
Is it possible to use a board like that to connect with GPIO ports?
If not, what would someone use a board like this for?


texts: What are the 9V battery terminal size specifications?

texts:
I'm trying to find the dimensions of a 9V (PP3?) battery (no specific chemistry). For some reason it's giving me a lot of trouble. I've been able to find most of the information (I checked a bunch of sources and they've all got these same values):

However, I can't figure out the allowable range for the terminal diameters and depths. So my question is, what are the min/max values of these dimensions:

Where:

M = min/max outer diameter of positive male terminal
F = min/max inner diameter of negative female terminal
H = min/max depth of negative female terminal

The min/max height of the positive male terminal I assume is linked to the female depth and also the 0.1mm - 2.1mm minimum range implied (A - D) by the first image above.
Also, there's the lip on the terminals to provide the snap action, so, that too.


texts: Connecting a DIY guitar pedal to a pedalboards power supply

texts: I am new to electronics and I am trying to build a DIY Fuzz Pedal. Before I construct it, I am trying to figure out how to use my pedal board's power supply with it instead of using a 9 volt battery. I am not sure of the parts I would need to get to make this work. Any help would be appreciated!


texts: Why doesn't higher frequency mean higher data rate?

texts: My question is very primitive :) I've read multiple articles today and answers here, on Stack Exchange, but still don't understand one thing. Why doesn't frequency itself affect data rate in mobile networks? 3G/4G networks use QAM modulation, that includes changes to amplitude and phase of signal. Let's say, we have 900 MHz signal with 10 MHz bandwidth and 2600 MHz signal with 10 MHz bandwidth. At the same "snippet" of incoming signal we'll have much more "cycles" to modulate on higher frequency (per same time), don't we? So why doesn't it matter?


texts: Transmission Lines voltage as a function of position and time equation

texts: I am having trouble with part d. How are we supposed to determine v(z,t) if we are not given the length of the wire. I am getting (phase constant) * length = infinity, so then V0+ is zero. Where V0+ is the complex constant given by the boundary constraints of the transmission line.


texts:
My question arises from interest mainly in Outrunner motors which are used on RC planes/drones.

With that being said, I understand that these motors are controlled by an Electronic Speed Controller (ESC), which is used to switch DC power into two of the three different phases of the motor at a specific time by monitoring the back EMF (for sensorless operation) on the third phase. I also understand that to regulate speed, the ESC will use PWM to "modulate" the average voltage to the motor.

If my understanding is correct, then I am utterly confused why I have read, in multiple places, that Brushless DC (BLDC) motors are speed controlled by frequency.

For example:
"BLAC, BLDC (AC stator, DC rotor)
These are basically just Synchronous machines but they have permanent magnets on the rotor. Higher the stator frequency the higher the rotor speed. AC & DC just comes from the type of current control that is used."

Also, I know that Brushless Outrunner motors experience slippage, which means they are definitely not synchronous. Correct?

I am left with the thought that there must be different types of BLDC motors, or different forms of control. May I please have a clarification on this subject or even a correction if I am completely wrong?

EDIT: Changed "Engine Speed Controller" to the correct term: "Electronic Speed Controller"


texts: How to increase the voltage gain in a Class AB Transistor

texts:
I have the following circuit design of a Class AB Amplifier which amplifies the input voltage with a voltage gain of around 42. However, I'm wanting to increase that gain to around 80. Does anyone have any tips or advice on how to do so? I've been trying to change the component values of the resistors to increase the gain however this either doesn't have an effect or distorts the signal.
I've also tried making modifications to the circuit design but have so far had no luck.
Any advice would be appreciated!


texts: 32-bit unsigned binary integer to 8-bit BCD in AVR ASM for ATtiny. How to make it more efficient?

texts:
I wrote a program in AVR ASM for converting 32-bit unsigned binary numbers to 8 digit decimals based on the shift-add-3. (I know that 32-bit is more than 8 digit, but I only need 8.)

The 32-bit input is in R16-R19 (low-high).

The 8 digit output is in R20-R24 (low-high), 2 number / byte, one in the lower nibble, one in the higher nibble.

My problem: It takes ~1500 cycles to compute a 16-bit number and ~2000 cycles to compute a 32-bit.

Can anybody suggest me a faster, more professional method for this? Running a 2000 cycle procedure on a ATtiny at 32,768 Khz is not something I am comfortable with.

Memory usage map:

Definitions:

.def    a0  =   r16
.def    a1  =   r17
.def    a2  =   r18
.def    a3  =   r19

.def    b0  =   r20
.def    b1  =   r21
.def    b2  =   r22
.def    b3  =   r23

.def    i   =   r24
.def    j   =   r25

The code:

BinaryToBCD:
    clr     b0
    clr     b1
    clr     b2
    clr     b3
    ldi     i,  32
    sts     0x0068, i       ;(SRAM s8)

BinaryToBCD_1:
    clc
    rol     a0
    rol     a1
    rol     a2
    rol     a3
    rol     b0
    rol     b1
    rol     b2
    rol     b3

    lds     i, 0x0068       ;(SRAM s8)
    dec     i
    sts     0x0068, i       ;(SRAM s8)
    brne    BinaryToBCD_2
    ret

BinaryToBCD_2:
    cpi     b0,     0
    breq    BinaryToBCD_3
    mov     i,      b0
    rcall   Add3ToNibbles
    mov     b0,     i

BinaryToBCD_3:
    cpi     b1,     0
    breq    BinaryToBCD_4
    mov     i,      b1
    rcall   Add3ToNibbles
    mov     b1,     i

BinaryToBCD_4:
    cpi     b2,     0
    breq    BinaryToBCD_5
    mov     i,      b2
    rcall   Add3ToNibbles
    mov     b2,     i

BinaryToBCD_5:
    cpi     b3,     0
    breq    BinaryToBCD_1
    mov     i,      b3
    rcall   Add3ToNibbles
    mov     b3,     i
    rjmp    BinaryToBCD_1

Add3ToNibbles:
    mov     j,      i
    andi    j,      0b00001111
    cpi     j,      5
    in      j,      SREG
    sbrs    j,      0
    subi    i,      -3

    mov     j,      i
    swap    j
    andi    j,      0b00001111
    cpi     j,      5
    in      j,      SREG
    sbrs    j,      0
    subi    i,      -48
    ret


texts: I'm designing a TEC circuit with a Peltier element, LM35 as the sensor and Arduino uno as the controller. I simulated it with Proteus and to my knowledge it was working, I suppose. But when I tried to replicate the circuit on a bread board with the components, I had problems with PWM. Can you guys please have a look at my circuit and advise for any changes/improvements needed. Thanks.


texts: Current Limiting Resistors for Multi-Branch LED circuit

texts:
I have bought some of the following LEDs (going to try either for brightness/size):

100 Pcs 0603 SMD Superbright LED Yellow Light Emitting Diodes
40 Pcs SMD 1206 LED Lamp Yellow Light Emitting Diodes

I wish to arrange them in three groups of five as shown in the attached block diagram. The idea is there would be three separate strands going off in three directions, each with five LEDs on.

What would be the best arrangement to connect in this way (series or parallel) and also what is a suitable value for the current-limiting resistor for these LEDs, how many and where should they be placed? Also what would be a suitable battery to use - should I go for a PP3 or will a couple of AA's be suitable?

I would appreciate a circuit diagram if someone can help please!

Many thanks


texts:
Some general classifications of amplifiers are wrote down below.

Voltage Amplifier -> Voltage-Controlled-Voltage Source -> Device: OP AMP
Current Amplifier -> Current-Controlled-Current-Source -> Device: FET
Trans-conductance Amplifier -> Voltage-Controlled-Current-Source -> Device: BJT

On no. 2, It states that a device used as a current amplifier is an "ICIS" device, and an example of it is FET whereas on no. 3, a trans-conductance device is a "VCIS" and an example device of it is BJT.

From what I know, FET is a voltage controlled device. So instead, it shouldn't it be swapped with BJT? FET is a VCIS and BJT is a ICIS device.


texts: What are .C1 and .C2 Gerber files in Altium 14?

texts:
I am currently working on a project and I'm about to get the Gerber files checked by FreeDFM.com. My question is, in my Gerber files, there are a couple that have the extension .C1 and .C2. In FreeDFM.com they want me to specify what these are (Inner copper layers, top layers etc.), but I have no idea what they are.

Any help in determining what these are would be very much appreciated!


texts:
I am trying to build one of the example circuits in the LM386 datasheet (any of the first 3) but with a gain of 40 rather than 20, 50 or 200.

I understand that the gain is controlled by the impedance between pins 1 and 8 and that a smaller impedance results in a larger gain. So for a gain of 40, the impedance must obviously be more than the 1.2k and 10uF in series.

So apart from trying different values for the resistor, how can I find the required impedance to get a gain of 40?

Also, why is the capacitor necessary? If it's just a question of impedance then can't the capacitor's reactance be replaced by an equivalent resistor?


texts:
I am trying to recreate the following design:

When I create it in Logisim, this is the error I get:

I understand the incompability is due to the number of data bits. When I adjust the data bits, none of the output will work. How can I fix it?


texts: System Generator: How to make a channel selector?

texts:
I want a system with two inputs,sel and in, and at least two outputs channel A and channel B. Here's some pseudocode of what I'd like to implement:

if sel == 1 {
  channel_A = in;
  float_pin(channel_B); // make high impedance
}

if sel == 0 {
  channel_B = in;
  float_pin(channel_B); // make high impedance
}

How do I do this with Xilinx System Generator?


texts: Finding an Ethernet transformer when I have it's characteristics

texts:
I am using the Novatel OEM729 board for a project, and I need to implement Ethernet in the project.

According to the Novatel OEM7 manual, page 48, the OEM729 does not have Ethernet magnetics, so I have to design my own. According to them, The OEM7 uses the Texas Instruments TKL106 Ethernet
PHY. Follow Texas Instruments’ recommendations for transformer selection.

Unfortunately, the TKL106 datasheet contains only a partial list of transformers (only 2), and both of them obsolete. I went back to the OEM7 manual and found the following table, describing the Ethernet transformer characteristics:

So now that I know how these characteristics, how can I find a suitable transformer? I thought that I could use Mouser's filters, for example, but I couldn't find filters that match the parameters in the table.

Please note I cannot use a RJ45 connector.

Another question:

Looking at the TLK106 datasheet, I found this schematic:

What I don't really understand is the pack of resistors and capacitors on the left. It is said to place them as close to the device, which I assume is the TLK106? But, since that TLK106 is on the Novatel OEM729 board, what can I do? place them as close as possible to the connector (which connects to the Novatel board with a harness) or solder them directly to the wires (on the harness between my board to the Novatel board) so that it would be closer?

Thank you!


texts:
I have a precision resistor 10 ohm and 5ppm/K. Does it mean that on delta 1K it will jump up/down 5 ppm of 1 ohm or 5ppm of resistor value - 10 ohms?

I think that it corresponds to resistor value. But Im not sure 100%.


texts:
I am using a BD-139 NPN transistor for turning on/off a 1.5A dc motor. the collector current of this transistor is also 1.5A but when I use the transistor as a switch in the circuit only 0.6A passes through the dc motor. I am not expert in electronic because my field is mechanics and I'm confused with this problem. Thanks a lot...
here is my circuit:


texts: What exactly constitutes poor mains voltage?

texts: I've been wondering exactly what is meant by a poor quality mains voltage, specifically in places like Africa, where the mains voltage is considered worse than say the UK. Having done some research, one of the issues is the fact that power cuts off entirely, especially in the summer (presumably A/C usage/overheating of supply components?). Having said that, are there other factors to consider? For example, is the voltage supplied noisy with lots of small fluctuations, be it in amplitude or frequency, or is the only issue the fact that the it can cut out entirely?


texts: Panasonic Eneloop BK-3MCC (4th gen) - where I can find maximum discharge current?

texts:
Im looking for some official information source about maximum current for Panasonic Eneloop BK-3MCC rechargeable batteries.

All I found is single page data sheet, there is just 1 table (nothing about maximum discharge current), charge and discharge characteristics.

UPDATE LINK: Datasheet BK-3HCC

/ edited - I fixed my mistake, I meant 6A not 8A /

There is discharge characteristic for 6000mA discharge. So... I can safely draw 6A from that AA cell?


texts: What do these components of an AB amplifier do?

texts:
I'm trying to learn about class AB amplifiers by reverse-engineering a few I see here on SE.  I borrowed this schematic from this question as a starting place.
Ignoring the fact that the circuit lacks emitter degeneration at the output -- which I understand to be a critical flaw -- a few other parts still puzzle me.
All the components in the original were not labelled so I redrew it.

I'm pretty sure I get the basic idea that the input is fed through a differential amplifier Q1 and Q2.  The output stage is a class AB with two diodes preventing crossover distortion.  Some feedback is pulled from the AB back to the differential to help fight distortion, I imagine.
Here's what I'm stuck on:
What is the purpose of R2?  I know that C1 couples the input but what does this resistor to ground accomplish?
Likewise, what do R6 and C3 do?  It seems to be part of the feedback circuit.
Is Q3 working as a constant current source?  What does C2 do to help?


texts: Understanding of microcontroller datasheet

texts: Generally if I start a project with new microcontroller, what shall be the extent of understanding i should have of the microcontroller. Should I be in a position to understand very basic details and each and every feature? Because I find so many details in the data sheet confusing.


texts:
I am analysing some requirements regarding the sampling to be performed on a UART.

There is information provided however I am slightly confused by it and would like some clarification:

"The UART Receiver will sample at least 16 times faster than the fundamental transmission frequency of the UART. E.g for a 2 Mbit/sec bit-rate, the fundamental frequency is 1 MHz, requiring a sampling rate of 16 MHz min. The UART clock will therefore cycle at least eight times within one transmitted bit period."

I understood that 16x Oversampling meant 16 samples per bit (not necessarily all captured depending on the RXR bit validation criteria), not 8.
I understood that a 2 Mbps rate would be a fundamental frequency of 2 MHz, requiring a 32 MHz clock to perform the oversampling (this would therefore require a 1 Mbps rate to O-sample using a 16 MHz clock).

Is the example wrong or am I missing something fundamental here?


texts: What to do with ATmega's XTAL pins when using the internal oscillator?

texts: The XTAL pin on the ATmega16a for example can't be reused as I/Os and I really don't need an external crystal. What do I do? I assume pulling them either high or low is better than leaving them floating and I assume, pulling them low is better than high, but I have no appnote, datasheet or book to support those assumptions. Any pointers?


texts: Altium Designer Libary Ref Field Missing

texts:
I'm trying to create a MySQL database for my Altium company library. I've created a MySQL database with utf16 encoding that contains tables for each category of components. Here is an example table:

CREATE TABLE `Amplifiers - Audio` (`Comment` NVARCHAR(100), `ComponentLink1Description` NVARCHAR(100), `ComponentLink1URL` NVARCHAR(250), `ComponentLink2Description` NVARCHAR(100), `ComponentLink2URL` NVARCHAR(250), `ComponentLink3Description` NVARCHAR(100), `ComponentLink3URL` NVARCHAR(250), `ComponentLink4Description` NVARCHAR(100), `ComponentLink4URL` NVARCHAR(250), `ComponentLink5Description` NVARCHAR(100), `ComponentLink5URL` NVARCHAR(250), `ComponentLink6Description` NVARCHAR(100), `ComponentLink6URL` NVARCHAR(250), `Description` NVARCHAR(200), `Device Package` NVARCHAR(100), `Features` NVARCHAR(127), `Footprint Path` NVARCHAR(100), `Footprint Path 2` NVARCHAR(100), `Footprint Path 3` NVARCHAR(100), `Footprint Ref` NVARCHAR(100), `Footprint Ref 2` NVARCHAR(100), `Footprint Ref 3` NVARCHAR(100), `LastUpdated` DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `Lifecycle Status` NVARCHAR(100), `Manufacturer` NVARCHAR(100), `Part Number` NVARCHAR(100), `Max Output Power x Channels @ Load` NVARCHAR(127), `Minimum Order` INT, `Mounting Type` NVARCHAR(127), `Operating Temperature` NVARCHAR(127), `Output Type` NVARCHAR(127), `Package / Case` NVARCHAR(127), `Packaging` NVARCHAR(100), `PartId` INT NOT NULL, `Part Status` NVARCHAR(127), `Price` NVARCHAR(100), `Series` NVARCHAR(100), `Supplier 1` NVARCHAR(100), `Supplier Part Number 1` NVARCHAR(150), `Supplier 2` NVARCHAR(100), `Supplier Part Number 2` NVARCHAR(150), `Supplier 3` NVARCHAR(100), `Supplier Part Number 3` NVARCHAR(150), `Supplier 4` NVARCHAR(100), `Supplier Part Number 4` NVARCHAR(150), `Supplier 5` NVARCHAR(100), `Supplier Part Number 5` NVARCHAR(150), `Supplier 6` NVARCHAR(100), `Supplier Part Number 6` NVARCHAR(150), `Supplier Device Package` NVARCHAR(127), `Library Path` NVARCHAR(100), `Library Ref` NVARCHAR(100), `Type` NVARCHAR(100), `Value` NVARCHAR(100), `Voltage - Supply` NVARCHAR(127));

I then created a .DbLib file for altium and connected to the database. Altium was able to correctly parse the columns and gave me this view in the Field Mappings:

I have not inserted anything into the database yet so when I click on Table Browser I expect nothing to show up. In reality Altium throws an error when trying to click on Table Browser saying:

This is weird as clearly from the above sql statement we can see this line:

`Library Ref` NVARCHAR(100)

Altium also reflects this in the Field Mappings and detects the Library Ref:

Any ideas on what I'm missing and if there is any documentation online that describes what must be present in the database? I can't find anything.

EXTRA:

Inside the .DBLib file I can see the Altium detected the LibraryRef field:

[FieldMap1052]
Options=FieldName=Voltage Regulators - Linear.Library Ref|TableNameOnly=Voltage Regulators - Linear|FieldNameOnly=Library Ref|FieldType=1|ParameterName=[Library Ref]|VisibleOnAdd=False|AddMode=0|RemoveMode=0|UpdateMode=0


texts: STM32 USB host will not return from reset request

texts:
Note: I have edited this question from its original content since I was able to find a deeper cause/symptom for the problem. I have re-written it to focus on that instead.

I am using a pretty basic configuration for the STM32F405 using the CubeMX configuration system.

Something (a clock, a setting.. something) is not configured correctly, and I can't tell how I could have possibly caused it. Though it could be a problem with the PCB I designed, that seems unlikely as the code runs and debugs and the SysTick interrupt is advancing the timing counter just fine.

I have tracked part of the problem down to this function

/* Reset after a PHY select and set Host mode */
USB_CoreReset(USBx)

Which times out, presumably because the core never comes out of reset (OTG_FS_GRSTCTL:CSRST == 1 always, after being set in that function. USB_CoreReset() tries to read CSRST==0 200,000 times, and if it fails it returns unsuccessfully).

  If you would like to generate this file and look at the output (or
  adapt it to your board), you can take this text and paste it into
  a file called "USB CSRST Problem.ioc". Note: It will probably require
  some tweaking for your board since I have some pins assigned to
  outputs for an LCD display.

I have tracked a discussion down that describes similar symptoms, but I can confirm that my code does set OTG_HS_GUSBCFG:PHYSEL properly (confirmed setting bit 6 before the reset is performed), and generally adheres to the recommended startup procedure as outlined in that thread.

Clocks configuration:


texts: Why is the ouput so low in this LC resonant circuit?

texts:
159.2Hz is the resonant frequency.  Shouldn't the output be at least same as the input at resonance?

EDIT:
I was hoping to see voltage amplification when the circuit was at resonance without using any active components, not even batteries, using only the input signal. Now I see that this is not possible in the shown circuit because of KVL and the diode drop. But I feel this should be possible with some other clever geometric
 rearrangement in the circuit because if we tap a swing slightly at resonant frequency the amplitude will be increased to a arbitrarily large value.

In the shown circuit, the input signal is giving small current pulses to the LC tank at the resonant frequency. Since LC circuit cannot dissipate power, all the energy is used up by the diode?

simulate this circuit – Schematic created using CircuitLab


texts: Voltage divider circuit load resistance?

texts:
For a test on circuits that I just completed, a question asked about a voltage divider circuit (see below.)
However, we were told to assume that the load had no resistance and was parallel with the second resistor.
Wouldn't this mean that all of the current would be diverted through the load, so that no current would run through the second resistor? And wouldn't that mean that there is no output voltage (V_R) since there isn't any resistance after R1?
The question seems to imply that there would be a nonzero voltage VR, however, and it seems nonsensical if it is equal to zero, but shouldn't we be assuming that the load has infinite resistance so that we are investigating an ideal voltage divider?


texts:
I'm trying to build a game console from scratch (as an exercise, not necessarily for practicality).

What I want to do is to have multiple "CPUs", in this case one being the Main CPU and the other one controlling the controller ports. My idea is to use shared RAM, where the "Interface Controller" CPU is polling the controller ports and then writing the results to RAM, where the "Main" CPU can read it.

What I'm trying to figure out is how I would connect the RAM to the system - I doubt I can just connect the address/data pins of both CPUs to the same pin on the RAM chip directly, but I'm not familiar with what arbitration methods exist.

What is commonly done here? Is there some kind of "intermediary" chip that serves as a "switch" to select which CPU is connected to the RAM at any given time? Or maybe some kind of "buffer" that the Interface CPU writes into, and which is then somehow flushed into the RAM? Or is there a simple "Bus" that allows multiple components to access it? (I'm thinking of SPI here, with it's chip select/SS pin)

Assume a system that's using simple CPUs (e.g., Z80, 6502) and SRAM (e.g., Cypress CY62256), so nothing that supports sophisticated protocols out of the box. And if it helps, one CPU would only ever write and one only ever read.


texts: Complex RSSI dBm calculations with shield

texts:
I have a little bit of problem understanding complex attenuation calculations when there is a shield involved between the transmitter and the receiver.

Let's take a simple example:

We have a theoretical isotropic transmitter with 0 dBi gain radiating 30 dBm (1 W) of power in all directions at 1 GHz frequency. Then we have a shield at 5 cm distance. So before the shield we reduce the power to 23.58 dBm, due to free space path loss. Furthermore the shield provides us 50 dB electric shielding, so after the shield we have −26.42 dBm power. And we have another 50 cm distance between the outer shield and the isotropic receiver antenna with 0 dBi gain. That reduces the power to -52.84 dBm. So given that both the receiver and the transmitter works at 100% efficiency, in a theoretical way, that would leave us with -52.84 dBm power at the receiving end. So the total setup would provide us with 82.84 dB attenuation. And therefore our receiver antenna would pickup only 5.2 Nano Watts from the total 1 Watt radiated.

Is my theory/thoughtprocess valid? Can we add up decibel values like this. I am still learning about dealing with decibels in a complex calculation.

Calculations done with:

http://www.changpuak.ch/electronics/calc_10.php

http://www.qsl.net/pa2ohh/jsffield.htm

Edit:

Indeed sorry for typo and errors @Mike, also as @Andy aka pointed out yes its 0 dBi. So I recalculated everything now using the calculator links provided above (for some reason the other website doesnt load). And yes the calculator apparently uses the free-space-path-loss equation, whereas tomnexus has pointed out that I may have to use antenna path loss between antennas.
@Dan Mills pointed out that shielding could be different in the near field, but I specifically referred to the electrical shielding, since the magnetic shielding will be different. So let's just consider 50 dB overall electric attenuation of the shield itself from the incident wave to the transmitted wave, if that is possible.


texts: How to mesure distance between two objects?

texts: I have some idea about make something and make some small production. Idea is to have something that measure distance between two objects. First one called A size doesn't matter, can be connected to pc or something and measure distance to B. B have to be insignificant size. This will operate with maximum distance 5m (10m even better) in xyz with precision of mm. Is there some technology to measure this, and what technology? And A to B is not necessary to be at line of view, and speed of motions is speed of human motions. B can be attached on for example human who is moving some room or open space.


texts: What kind of electronic component is this?

texts:
I am trying to repair the flash of a P900 camera, since it gives a burning smell after being used.
After disassembling the flash unit, I came across this part for which I need some professional eyes in order to identify what kind of component that is.


texts:
I have a car cigarette extension cord with a USB out on it as well. The USB out though will not charge my phone, which is a bit annoying. I had a look at the circuit inside in the device and it looked something like this:

I'm guessing the reason the phone won't charge is the 78L05 chip is only rated for 100mA. Therefore I was thinking of changing it to a 7805 chip, which is rated for 1A. Would this idea stand up to my reasoning?   Or am I likely to damage any equipment I connect if I go down this root?

Also, if I go about this, will I also need to do something with the capacitor and the resistor on the board?

Edit:

Thanks for all the answers.
I didn't think of the heating problems I might have in my scenario above.
Its looking like the best solution for the device is the one Nick Alexeev gave below if I'm going to stick with the device I have.

I have also changed the diagram above as the resistor is actually 360 ohm.

Also, I am including a image of the device itself below as requested to show exactly what I was talking about.


texts: asymmetric signal split at SMA Tee (wires of different lengths)

texts:
I set up a circuit, as shown in the schematic below, to see firsthand how the signal paths of different lengths could lead to a phase difference.

I am using an SMA Tee and there is no reason to suspect that it's designed to split power unevenly.

What I noticed is that when cable 1 and cable 2 are the same length, no matter what the frequency of the signal is, the power split was perfectly even and there is no phase difference, which is perfectly reasonable.

What caught me off guard is how the power from the two output ports of the SMA Tee becomes uneven at some frequency value (on the order of MHz) if the cable lengths are different. At much lower frequency values, the power split appeared more or less even.  The cables are of the same material and company. The only difference is the lengths of the cables.

I now understand that because my oscilloscope does not have a high enough resolution to properly display microwave signal (GHz) it's going to be hard for me to see any noticeable phase lag from the cable length difference.  But, in the range of MHz, I would like to know what could explain the uneven power split at the SMA Tee.


texts: Please help me identify GND on this main board

texts:
My iNew V3 Plus, a MT6592 Chinaphone, stopped working recently, probably due to a bad flash. I can't get the device into preloader mode anymore.

To resolve this, I try to do the Hardware Preloader Mod, as shown in this video. Basically, you have to connect a test point with GND on the main board to make the device enter META Mode, from which you can flash the preloader again.

I think I've correctly found the test points (encircled in red), but I'm having trouble finding GND. I've attached the scan, can you point me where GND is?


texts:
I'm making a simple communication between an ARM mcu and a GSM module.

The problem I'm facing is how to deal with simultaneously writing and reading to and from the FIFO buffer.

Due to scale of the program I have a big buffer array of 1000 bytes long.

At the moment an interrupt is triggered every time a byte received at UART's data register and the interrupt's routine is filling my 1KB FIFO.

My read routine calculates the available data in FIFO and copies some of the data in a second buffer for further processing.

The interrupt routine stops to put more data when no more space is left in FIFO buffer, to prevent overwriting on reading pointer in the cases my main program didn't have the time to process the data.

Now I'm trying to find the best solution to prevent overwriting on reading pointer while interrupt routine never stops to put data. Is there any solution for this or overwriting is inevitable?


texts:
I want to use this element to create a square wave(I know it's possible to make it using VPULSE):

But I don't know how VON and VOFF work. Can anyone help?


texts: AXI4 address calculation for INCR bursts

texts:
I'm going through the AXI4 specification at https://static.docs.arm.com/ihi0022/d/IHI0022D_amba_axi_protocol_spec.pdf. On page A3-47, a number of equations for calculating addresses are given:

  These equations determine addresses of transfers within a burst:

  Start_Address =AxADDR
  Number_Bytes = 2 ^ AxSIZE
  Burst_Length =AxLEN+1
  Aligned_Address = (INT(Start_Address / Number_Bytes) ) x Number_Bytes.

  This equation determines the address of the first transfer in a burst:

  Address_1 = Start_Address.

  For an INCR burst, and for a WRAP burst for which the address has not wrapped, this equation determines the address of any transfer after the first transfer in a burst:

  Address_N = Aligned_Address + (N – 1) × Number_Bytes

However, unless I missed something, the spec does not put restrictions on the Start_Address to be aligned to the size of each transfer for INCR bursts, while it does state it explicitly for WARP bursts. Thus, the Address_N formula would seem to be incorrect for a Start_Address that is not aligned to Number_Bytes in an INCR burst with Burst_Length > 1.

Did I miss something? Is the spec incorrect?


texts: Proper storage of ferric cloride PCB etchant

texts:
I etch about half a dozen printed circuit boards each year at home, using an aqueous ferric chloride AKA iron(III) chloride etchant solution. As I want to minimize the costs and hassle of buying new and disposing of old etchant, I would like to know what steps can I take for maximizing the amount of boards I can etch with a given amount of etchant. I have no background in chemistry, so any suggestions are appreciated.

I prepare a certain amount of etchant solution at a time, use it until it fails to dissolve copper effectively, and finally transfer it to a waste tank awaiting disposal. Does the batch size affect the amount of circuit boards I can etch with a given amount of ferric chloride?
Is etchant sensitive to light or fluctuating temperatures while in storage?
Is etchant oxygenation beneficial or detrimental? Many vendors of the chemical and several PCB fabrication tutorials clearly state that FeCl3 etchant stores indefinitely if kept in an airtight container. On the other hand commercial PCB etching devices purposefully stir the etchant by blowing air bubbles trough it, oxygenating the solution in the process, seemingly without adverse effects.


texts: 3 T Finfet Leakage reduction circuit techniques (VLSI)

texts: What are the circuit techniques to reduce leakage in a 3T Finfet (front and back gate shorted) circuit? Vth in a 3T Finfet is almost always constant, so there is almost no stack effect and hence sleep transistor techniques won't work in this case.


texts: I've become an electrical conductor for my headphones... but how?

texts:
So I have a pair of Bose noise-cancellation headphones that I plug into my keyboard every night to charge them (via my keyboard's USB port). My keyboard happens to be a metallic Apple keyboard. You will see why this may be important to note later.

Over time, I noticed a certain dull, electrical buzzing sound in my right earbud which occurred when I turned the noise-cancellation on. This buzzing sound was not constantly there. It would randomly appear for arbitrary periods of time and then vanish. It wasn't loud either, but it was loud enough to be noticeable and annoying.

For the longest time, I had no clue why this would happen. Sometimes the earbud would be perfectly silent (as it's supposed to be)... and then a buzzing noise would come out of nowhere. This was incredibly annoying and my only remedy was to listen to loud electronic music which blended in with the buzz and made it relatively unnoticeable. Of course, listening to almost any other kind of music proved annoying since my earbud would randomly, intermittently buzz at me.

Finally, one day, I noticed that when I touched my Android phone, the buzzing sound would increase in volume. I thought at first that this was due to my bodily position somehow stretching the wire, but with further testing I confirmed that my Android phone was the culprit. I slowly discovered that touching different objects, even when the headphones were not plugged into the speakers, would result in volume changes of this buzz.

One thing I noticed was that touching the headphone jack, whilst touching the Android phone that increased volume, would silence the buzz. With further testing, I noticed that touching my metallic keyboard would also silence the buzz, even whilst touching the Android phone or under any other circumstance in which there was a buzz.

I finally realized that my body is somehow conducting electricity when touching objects such as my Apple keyboard, headphone jack, or Android phone and that these are all related to the annoying buzz and nullification thereof. I found this bizarre and fascinating.

Ever since this discovery, I've found that I can silence this annoying buzz by pressing any of my fingertips on my metallic keyboard. This is also annoying, since it can make typing awkward to continually have one finger pressing against the metallic part. Nonetheless, I have no idea why this works at all; I suspect it might have something to do with my usage of the keyboard to charge the headphones via its USB port every night, but I have no substantiation of this hypothesis.

So my question is twofold:

How does this bizarre phenomenon work wherein my body is apparently conducting electricity from objects which somehow control some anomalous buzz in my headphones?
And how can I make this buzzing sound stop without keeping my body in contact with those objects? Obviously, I can't hold the headphone jack and listen to anything at the same time, and this habit of touching the metallic part of my keyboard is not great for typing nor my wrists which already suffer from CTS.

Any insight is appreciated.


texts: Does higher power wiring go higher in a control cabinet?

texts:
In looking for a image to answer an Industrial electronics layout and design question, I noticed that:  within the cabinets, the higher power wiring seems to be at the top of the cabinet.  Simply, the thicker wires are at the top.  You can see it in this, this and this example.

Have I just randomly picked three examples that show this by chance, or is there a best practice for putting higher power components at the top of control panels?


texts: LM3414hv Dim input pulled high when leaved open

texts:
I am new in this forum . I had an issue with my newly designed PCB where I use LM3414hv as a constant current driver for led strings. Everything works perfectly except for one thing. When I turn of the main power of my card all leds strings flash briefly. I think its because of the internal pull up of the lm3414hv that activates the driver when  pin is HIGH or left open "high impedance". My DC voltage source always shuts down a few seconds after my 5 volt microcontroller when I unplug the main power.
The question is How can I force by default this DIM pin at GND when the dim pin is left open 'high impedance state'? Or any other idea to avoid that annoying flashing? Here is the datasheet of LM3414HV and the internal diagram of lm3414
Thanks in advance
http://www.ti.com/lit/ds/symlink/lm3414.pdf


texts: Possible causes of loss of electrical contact between PCB traces and male USB Type A connector pins soldered to PCB?

texts:
I have a problem that I've been embarrassingly working on for months and unable to completely solve.  I'm a hobbyist and I have a simple PCB with a male USB Type A connector soldered to it: some of my boards work ok and some only see the power LED light up when I jiggle the connector around (boards are from the same batch).  At this point, I am nearly positive it's a mechanical and not a circuit problem, but I cannot figure out what I am doing wrong and am seeking suggestions.  I've tried different female ends (i.e., different cables, USB hubs, etc).  I've tried different kinds of male Type A connectors soldered to the board (surface mount, through-hole, etc), with the through-hole connectors being the least problematic, but still some of my through-hole-type-A boards exhibit the problem (some don't).

Could it be rosin solder flux residue on the Type A contacts that result from me trying to clean off rosin solder flux on the PCB using a rubbing alcohol bath?  The boards look clean but I'm wondering if just enough residue is being left on the USB contacts within the connector to be causing me problems.  It seems far fetched, but other than this, I can't think of what else it could be -- I'm about out of ideas.

EDIT: When the problem exhibits itself, I see 0V when I put a voltmeter between the 5V and GND pins on the Type A connector.


texts: Complex power delivered by voltage source (with current source)

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Given the following problem:

I'd like to know how exactly one is to find the complex power delivered by the voltage source and the current source, separately, as is shown in the solutions on the right.

I've correctly obtained all the values for the complex power delivered to the resistor, inductor and capacitor. When I attempted to find the power delivered by the voltage source, i ignored the current source, and brought togheter the three impedances to make one, as in:

Z = jwL + R + 1/(jwC)

Then I found the current:

IZ = Voltagesource / Z

And then I found the complex power:

Svoltagesource = 1/2 * Voltagesource * (IZ*)

Which resulted in:

Svoltagesource = 0.295+0.531i

I'd appreciate input on what I might be doing wrong.


texts: Is grounding 12v 100W solar panel to a lightning rod necessary?

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My plan is to put a solar panel on my greenhouse to run a 150 W 12 V heater for 20 minutes max and turned on depending the low temperature is detected by a sensor, automation controller and a grow light for winter. My solar will have a Renology 20 A MPPT hooked to a 12 V 50 Ah lead battery. I am concerned about possible damage in case of a lightning strike near the system.
Just wondering if this low power will require grounding to a lightning rod to direct the high current from a  lightning strike to ground. In addition I live in canada were thunder is not very often as I live snow for 5 months, but in summer there are some thunderstorm.


texts: Capacitor with a lower AC rating than the application?

texts:
I have a question about AC capacitor ratings. I've reviewed this post -

What is an AC voltage rating for a capacitor?

...but it only made things a little more confusing. I have a system wherein the applied mains voltage is 277Vrms/60Hz, but the EMI capacitors only have a rating of 250VAC (printed on the component and listed in the datasheet).

The caps are installed from line to ground, not daisy chained, so the full 277rms (391 peak) voltage is applied directly to each terminal of each cap. It's a power factor corrected device, switching at 40kHz, but if I understood the above linked post, that should only make the rating requirement higher, not lower.

Why don't these caps blow up immediately, or shortly after applying (what appears to be) a higher voltage than is specified? Some of these devices have been installed for years without issue.