texts: How choose MPU for image streaming and transmission

texts:
I want to ask how to choose and how much processing power are required to be able to stream video using a wifi module. I'll explain better; I have a camera sensor of 5Mpx, i want to elaborate video from this sensor and stream it through a wifi module.

My question is: how can i correctly choose an MPU and a wifi module to be able to do that?(considering that i can choose lower image quality)

My first intention was to use an integrated module Cortex-M3 120MHz 128KB RAM with wifi, but the productor said me that is hard to transfer image or video due to the throughput limitation of SPI/URAT interface.

What can you advice me?

EDIT:
As I see online I will need a configuration like this:
Sensor->decoder->MPU->wifi

That's right? Someone can advice me a decoder or mpu+decoder able to do that?


texts:
The board was inside an old hydraulic conveyor machine (produced in the 80's or 90's)

EDIT: after asking for a schematic: This board tests limit switches and light some LEDs. All switches inputs have 3.3 kOhm pull ups also these inputs are RC filtered and straight into this chip (at net between cap and resistor).
The LEDs are directly driven by this chip, each with 150 Ohm resistor in series. Other than that everything is weird. The pull-up supply voltage rail is not connected to this chip at any pin. ground is connected to pins 20-26-27-28.
I may do a neat schematic and further tests but I don't know how will that help identifying the chip.


texts:
So I have an NXP-LPC1313DFB48 MCU and I want to create a PCB from scratch so that I could connect my FTDI RS232 cable to it and program the MCU. What parts would I need to do this and what steps would I take to build this PCB?

Product page of the cable: http://www.newark.com/jsp/search/productdetail.jsp?SKU=34M8872
Product page of the MCU: http://www.newark.com/jsp/search/productdetail.jsp?SKU=83T7141


texts:
I have a 28V power source and a 24V power source on my device. The 28V source is permanent (internal battery) and the 24V can be disconnected.
When 24V is connected, the 28V battery needs to be automatically disconnected by some high-side switch. Disconnecting the low side is not possible.

I tried a solution with a FET but failed as 24V is below 28V... How can I design such a switch?


texts:
[edit: clarifying the question] Is it possible to see events on I2C slaves, or a functional equivalent?

I'm brainstorming a new project. I'm using an ESP-12F as a main logic board to control and receive input from various connected modules (e.g. pushbutton, beam sensor, solenoid valve, shutter trigger) Each module (slave) is PIC based, and communicates with the ESP-12 (master) using I2C. Sending commands for valves and triggers over I2C is straightforward. I'm not sure how to utilize I2C for slave-triggered momentary events though.

Should I just keep sending status requests to those modules and look for changes that way? I'm also considering using XOR logic to flip the level of another line, which I can detect via interrupt to trigger the status request.

My device is timing sensitive, I'd like to get a response to a trigger down to maybe 50-100 microseconds.

I'm new to all of this so feel free to correct me on anything fundamental I'm missing.


texts:
Alright so a little vague title but here it goes.

I'm interested in powering some 5v LED strips with an HDMI cable. I have no idea if this is even possible, I'm lacking knowledge in electronics.

My goal is to essentially have some LED lighting turn on when a video game console is turned on and the HDMI signal is fed to the display, and have the power for the LED strip piggyback off the HDMI connection.

Again I have no idea if this is possible, or if it is if it would create a lag in the signal from the HDMI.

Anyone aware of any products like this? or attempted to create this?

The closest I could find was a HDMI female to male with a USB Male lead, but have no idea if that could even provide the power or interrupt the HDMI signal.

Would this be possible to engineer into such a small connector? Is this beyond what the HDMI can provide?

A for sure system I know that can provide what I want is in using an advanced power strip but I was looking for something not so bulky.


texts: What is this small unconnected solder blob on this PCB?

texts:
There's a small solder blob in the middle of this one-sided PCB (a switch-mode power supply), surrounded by unmasked board. The blob is 1.5mm in diameter, and the non-masked area is 4mm in diameter. There's nothing on the other side of the board, and there is no hole.

What's the purpose of this blob? My guess is some kind of manufacturing artifact, but I'm not sure exactly.


texts: How to choose a resistor value for Wheatstone bridge such that it is a balanced circuit?

texts:
I have a 3V sine wave input and I want to measure resistor precisely from 1 ohm to 40ohm. I have tried using Arduino to measure the resistor using voltage divider but it became obvious that I will not be able to measure within 0.1ohm accuracy. I am now learning to use four point probe (wheatstone bridge).
How do I choose resistor value such that it becomes a balanced circuit to measure resistance from 1ohm to 40ohm. I hope to learn from you all.


texts: Sawtooth oscillations in bidirectional bus splitter

texts:
I am trying to listen in on a SPI-like protocol which is transferred on one busline in both directions (no slave-select). To discriminate which data is sent by which side, I need a bus splitter that transmits the data but lets me see which side it was generated on. The bus idles on high on 5V and is pulled low by either side for clocking out bytes at 156kHz.

I found the following design online (fig. 6) and implemented it on a bread board. For R1 I used 10kΩ. The NOR-gates are TI SN74HC02 and the MOSFETs are ON Semiconductor BS170 (I used BJTs before which resulted in too much of a voltage drop). The power source/groudn level is driven by the master device so that all voltage levels match with the other bus lines (which I do not need to split).

Going over it with a multimeter/Arduino testing program, everything seemed to work okay. When I inserted the circuit into my bus line though, the slave would not be identified by the master anymore. For debugging I set up function generator and oscilloscope and tried to simulate the square wave type signal. Curiously enough, when I applied idle high state on IN1, its voltage would be reduced to around 2.5V, the OUT2 would see sharp peaks to low (otherwise idling on high) and the IN2, where the data from IN1 should be transmitted to in an transparent manner, was a saw tooth. The same behaviour appears with the actual apparatus just idling on high, there is no signal going on here, yet there is an oscillation

IN1 is set to 5V, others floating. Ch1 (blue) is OUT1 (where there should be the inverted signal of IN1), Ch2 is IN1 (which should be steady at 5V

In this picture same setup, IN1 to 5V, others floating. Ch1 is OUT2 (which should low as it inverts the free state of IN2) and Ch2 is IN2 (which should be the signal from IN1, thus high.

Why is the device not working as advertised? I thought the description of it made sense. While looking up flip-flops on Wikipedia I noticed that the device basically is two flip-flop designs thrown together, and that flip-flops might generate these oscillations.

I also added various resistors at U1/2 or between the MOSFET and Q1/2 or between the gat of the MOSFET and GND, to no success. I generally don't have much knowledge of electronics and am just hopelessly puzzled. Does anyone recognize the mistake or can point me to another working design for this type of device?


texts: I was hiking in the mountains when I stumbled upon this antenna. I had no connection throughout the mountain until I reached this antenna. I noticed that it said on the metal. "Alarm Actuated Public Safety Equipment". I was curious if anyone knew why this would arbitrarily be on a random mountain.


texts: SMD component identification - possibly BJT

texts:
I found a defective SOT-23 on a broken PCB, but can't identify it. Probably a BJT, but what kind?
The one on the right seems to be the same as the blown one.

I would appreciate your help.


texts: If I am trying to make an led necklace with a few LEDs connected in parallel(each one separated by a little bit of wire) that connects back to a battery pack with 3 AAs, how can I make the necklace water proof, or at least water resistant enough to protect against rain.


texts: What exactly is the function of VDD_IO pin?

texts:
I see in many ICs 2 sets of volatge, VDD and VDD_IO. VDD is the core voltage,VDD_IO is the I/O interface voltage.

What exactly is the function of VDD-IO volatge?

Does it supply power to I/O drivers?
Does it serve only as the reference voltage level for 'High'?

In one datasheet I read VDD_IO pin does not supply power, instead it acts as the VIH reference.
Power meter IC- Page 14


texts:
So this question stems from a previous question.
Here

Where from several tables one can see that the maximum current (Imax) is proportional to \$1/R\$ where \$R\$ is the resistance.  (Or that \$I_{\text{max}}R\$ is a constant.)

Because it will be easier (mathematically) I'd rather work with the wire radius \$r\$  (And I'll have to be a bit careful not to mix up \$R\$ and \$r\$).

Now resistance goes as \$1/r^2\$.  $$R = \frac{\rho l}{\pi r^2}$$  where \$\rho\$ is the resistivity, \$l\$ is the length). So saying that the max current goes as \$1/R\$ is the same as saying it goes as \$r^2\$.

From table \$I_{\text{max}}\$ ~ \$r^2\$.
Here is a re-posting of the wire table.

Now a naive guess for the current capacity, would be that all wires can carry the same power.  \$I_{\text{max}}^2R\$ = constant.  And with a little algebra one finds that \$I_{\text{max}}\$ ~ \$r^1\$.

Now I realized yesterday that bigger wires will also have a bigger area.  And since the loss mechanisms (radiation, convection, or conduction) will all scale with the surface area of the wire, no matter what the mechanism I can add in the area effect.  (This is the outside area of the wire (\$2\pi r l\$) and not it's cross section area)

So then I wrote,
\$I_{\text{max}}^2R\$ ~ Area = \$2\pi l r\$.
(I'll leave out the algebra, but you can search for Preece's law and find it reproduced. as in the first few pages here.)

My result is that \$I_{\text{max}}\$ ~ \$r^{3/2}\$ in contradiction to the tables.

Does anyone have any idea what I'm missing?  Does convection from a wire not scale with the surface area?

Edit:  Adding a graph generated from Spehro's convection link.
I set the length at 100m, Tc at 100 C and varied the diameter (5m to 100um)  (Granted 5m diameter wire is a bit much :^)
It seems to me that this goes the wrong way!  (But I must admit I'm having a bit of trouble getting my head around all the different plots. I'll sit down tonight with a beer and mull it over.) The wire tables that show Imax ~ 1/R imply that the heat loss from the wire must go as \$r^2\$, where simple convection assumes loss ~ r.  The plot shows that for thin wire the loss is even "slower" than r.

Edit2: I updated the graph of power loss to include data from the I-max. wire table.
Data was scaled for 100m and the power was taken to be \$Imax.^2 * R\$  I also only plotted the relevant part of the graph for diameters form 50 um to 20 mm.  The cable Imax is not too bad.  (I've been using the blue data points to pick wire sizes.)


texts: I'm looking for a new soldering iron. What is the best all rounder soldering iron (soldering station) < $200 USD?


texts: Series-wound motor with DC switching power supply

texts:
I have a winch that I would like to supply with a DC switching power supply. The winch has a current of approximately 40A at 24V under the specified load, but the inrush current will be much higher, I think over 100A. What I would like to use as the supply is a 24V, 100A switching power supply, which has a current limiting function and will shut down after 5s of overload. Since the inrush current will settle down to the nominal current in no time, I think the power supply could handle this. Am I right?

Power Supply:
http://cdn-reichelt.de/documents/datenblatt/D400/RSP_2400_XX.pdf


texts: How do I determine the impedance of Z in this circuit?

texts:
I have a circuit shown as follows:

Known values:

V1: 5 VRMS, F = 4kHz.

V2: 0.5 VRMS @ -28.8 degrees.

Impedance Z = r + L + C.

How can Z be determined?

I've attempted to solve this quickly, does this look mathematically sound?


texts: I'd like to repair older computers, such as C64's, Atari's, Apple IIe's etc and their power supplies. I have a multimeter already but I'd like to get an oscilloscope. I've been offered an Owon PDS5022S really cheap, would this be suitable to start with?


texts:
When snubbing a triac, one of the concerns is minimizing turn-on stress as your snubber triac discharges across the newly-shorted terminals of the triac. This paper says that the main concern is keeping \$ \frac{dI}{dt}\$ below the datasheet maximums during turn-on.

How exactly do I work out what \$ \frac{dI}{dt}\$ will be theoretically given a particular RC snubber?

The datasheet for my triac indicates the "turn-on time" of the triac is \$ 2 \mbox{ } \mu s\$. Is the switching speed? Is the calculation \$ \left(\frac{dI}{dt}\right)_{max}=\frac{80\% \cdot 120V √2}{47\Omega \cdot 2µs} = 1.4 \frac{A}{µs} \$  (for a 47 Ohm snubber resistor) too simplistic somehow? It is based on the assumption that the voltage across the triac terminals drops approximately linearly from 90% to 10% of the peak AC voltage in 2µs. 1.4 A/µs is a good margin under my triac's rated \$ \frac{dI}{dt}\$ maximum of 10 A/µs.

I'm doubting my reasoning because the paper I linked to above says that \$47 \mbox{ } \Omega\$ is barely enough to limit \$ \frac{dI}{dt}\$ to \$ 50\frac {A} {\mu s} \$ at turn-on (see figure 6). Am I to understand from figure 6 that the switching time of STM triacs is much less than 2µs (the STM datasheets don't have a "turn-on time" field). If I'm eyeballing figure 6 properly, it looks like the snubber discharge current peaks only ~0.1µs after it begins to rise.


texts:
Generally we see that  single Port electrical networks (LTI system) that contains resistors and other passive elements are stable .
So is it safe to assume that
passivity(absorbs power) of electrical network is sufficient condition for its stability
or
There may be cases where network consist of resistors and other passive elements is unstable?


texts:
I am using the Cyclone V DE1-SoC in transferring data between HPS and FPGA, using 2 FIFO. I am facing a problem of very late data arriving time, causing the slack to be very negative.
...
if ((Processing_state == 4'd5) && (FPGA_to_HPS_state == 0))
    begin
        a <= a + memo[i] * memo[i];
        Processing_state <= 4'd4 ;
    end

if (Processing_state == 4)
    begin

        if (|a == 0)
        begin
            k<=a;
            Processing_state <= 4'd0 ;
        end

        else if (|a != 0)
        begin

            if(j == 20479)
            begin
                b <= a >> 12 ;
                Processing_state <= 4'd4; //signal fpga the data is ready to be sent
            end

            else
            begin
                j <= j + 1;
                Processing_state <= 4'd0 ;
            end
        end
    end

    if (Processing_state == 4)
    begin
        Processing_state <= 3;
        data_buffer_valid <= 1'b1 ;
        c <= b;

    end

    if (Processing_state == 3)
    begin
        Processing_state <= 2;
        mean <= c / 5;
    end

    if (Processing_state == 2)
    begin
        Processing_state <= 1;
        meaninput <= mean;
    end

    if (Processing_state == 4'd1)
    begin
        Processing_state <= 4'd0 ;
        data_buffer_valid <= 1'b1 ;
        a <= 0;
        j <= 0;

    end
...

if ((FPGA_to_HPS_state==0) && (!(fpga_to_hps_in_csr_readdata[0])) && data_buffer_valid)
    begin
        fpga_to_hps_in_writedata <= meaninput;
        fpga_to_hps_in_write <= 1'b1 ; //write flag
        FPGA_to_HPS_state <= 4'd1 ;
    end
...

The compile report is telling there is a problem on the line
mean <= c / 5;

But the strange thing is when I change the line
fpga_to_hps_in_writedata <= meaninput;
to
fpga_to_hps_in_writedata <= c;
the problem disappear, the compile report about the timing didn't show the problem anymore.
fpga_to_hps_in_writedata will write the data of to the FIFO to send to HPS
Is this a problem on FIFO that something I need to change in Qsys?
I've read the recommendation but I've only learned about basic Verilog so no idea about the timing constraint.


texts:
A time lapse camera rig I'm, working on needs an appropriate fuse. The camera will be powered by a 12 volt deep cycle marine battery. The instructables that I'm using to build this rig is found here.

The camera I'm using is the same as in the instrutables: 8 V, with an unknown wattage.

I bought a dumby battery that had a 120 V AC to 7.5 V DC converter inline. I swapped the AC to DC converter out for a Drok 12V DC to 7.5V DC/ 3A Max converter rated at 22.5 watts.

In the inscrutables, they call for a 20 A fuse. Without knowing how to do the mathematics, this number feels way to high and would likely not blow before it wreck electronics within the camera. I'm I correct in thinking this?

If someone could show me the calculations for an appropriate fuse size, and/or tell me why this rig would need a fuse in the first place, that would be awesome.


texts: Can someone explain to me what is going on with the wiring in the first and third schematic? On the third schematic, I see lines connected to the gate and the source and some resistors. I honestly don't understand what this is doing.


texts:
I have a few small-ish unmarked power transformers.  I would like to know what their ratings would be if I had the manufacturer's specifications.  So far, I have determined that I can safely connect them to the mains without tripping a breaker.

For the voltage, I can use a DMM.  However, an unloaded transformer produces a different reading than one with a load.  Does the spec for a known transformer refer to the loaded or the unloaded reading?

I have heard about methods for approximating the transformer current capacity by measuring weighing them, but:

the transformers are well under a pound, making a weight less
accurate
one type of transformer I have, for which I have 3 units,
has two secondaries, and I would like to know the current capacity
for each; the overall weight of the transformer will give only an approximate total power

I am about to experiment with an empirical approach in which I place power resistors of known values across the secondary in series with a DMM set for current reading, and then use an IR temperature gauge to watch how much the transformer heats up.  The only problem here is I don't know what a typical maximum temperature would be.

Is this a viable approach?  Any suggestions on making it accurate, such as an appropriate maximum temperature for the transformer under load?

I welcome answers with other techniques.


texts:
I understand that if I want to operate BJT as a switch , the transistor needs to be able to fully turn OFF(cut-off region) and turn ON (saturated).

This is from BJT Note

Cut off region

• The input and Base are grounded ( 0v )

• Base-Emitter voltage VBE < 0.7v

• Base-Emitter junction is reverse biased

• Base-Collector junction is reverse biased

• Transistor is “fully-OFF” ( Cut-off region )

• No Collector current flows ( IC = 0 )

• VOUT = VCE = VCC = ”1″

• Transistor operates as an “open switch”

Saturation region

• The input and Base are connected to VCC

• Base-Emitter voltage VBE > 0.7v

• Base-Emitter junction is forward biased

• Base-Collector junction is forward biased

• Transistor is “fully-ON” ( saturation region )

• Max Collector current flows ( IC = Vcc/RL )

• VCE = 0 ( ideal saturation )

• VOUT = VCE = ”0″

• Transistor operates as a “closed switch”

In the circuit above , I am not really sure how it work? when R5 is 10k ohm , BJT is in the on  state and when R1 is increased to 20k ohm , BJT is in the off state

To fully turn on the BJT , Vbe must be greater than 0.7 but when I apply voltage divider rule , isn't R6/(R6+R5) * 12 v = 1.091V. Isn't this amount more than 0.7V which should turn on the BJT but it doesn't as shown in the multisim simulation.

I am still learning how BJT work so I simulate this in Multisim.


texts: How to determine what the states should be in this state diagram

texts:
I'm trying to make a simple state diagram to understand a concept in class. There is one input and one output \$ \left(X \ \text{and}\ Y\ \text{lets say} \right)\$. The output is \$1\$ if an input is false after exactly two true inputs. For example, \$Y=1\$ if the last three inputs were \$110\$. In all other cases, the output should be \$0\$.

I'm having trouble deriving what the states themselves should be (as in, the bubbles in the diagram). Once I figure that out, I can easily apply the input/output conditions. I tried setting the states to represent the current bit (\$1\$ or \$0\$, so two states), but that didn't work.


texts:
I am trying to figure out what is wrong with a medical laser. My client has a laser which shipped with some default values.
At the moment when we query the values they are totally different from what we expect.
Two parameters are off. Value A should be 3000, it is 0 and Value B should be 0, it is 3000.
We think the problem is with a singular 8-Pin IC-chip present in the housing of a box that controls all the valves in the laser.

Laser type: Excimer laser used for spectacle correction - made by Lambda-Physik Germany.
Lambda Physik says they no longer manufacture the laser and so we're stuck with this and virtually no support.

I need to know whether it will be possible to reprogram this chip.


texts: Can 2 boost converters outputs be put in parallel at the same voltage?

texts:
I have a slight doubt here. Can the outputs of 2 boost converters set to output the "same" voltage (isolated, they would never be exactly the same obviously) be safely tied together, as long as there is a capacitive load? If so, is there a minimum to that load?

Context:

simulate this circuit – Schematic created using CircuitLab

I need at least 4Ah of battery capacity, and I was only able to find single cells charger+boost modules, so I have to put them in parallel. It's for long term logging, the current is very low: 30mA peak, and around 5mA 99% of the time.


texts: Which rechargeable battery type for infrequent and low dosage charging

texts:
The answer here may be that a rechargeable battery is not the correct solution, and that a battery that is just used and replaced is more suitable but the intended application is:

An industrial environment where the battery may be subjected to hotter or colder temperatures (it is especially likely to be warmer when charging)

{EDIT} The temperature may get as high as 80 degrees C.. The more I read the harder this will be to find a battery for, rechargeable or not

Only likely to be charged in bursts of <1 minute (though this could be up to 12V ~1A)
Constantly draining at uW levels, with much less frequent instances of 100mW level draw for a couple of seconds
Aiming to power either 3V3 or 5V circuitry
Likely to be shipped internationally, which makes Lithium batteries more of a pain

Without wanting to give away too much information about the intended application, it will essentially be powering a piece of measurement equipment that records the amount of time a device is 'on'. This 'on' state is where the 12V comes from.
This 'on' state would only last a minute or so usually (though you may get times where these minute periods happen quite frequently, maybe a 50% duty cycle for an hour). On top of that, the equipment could stay in storage for prolonged periods, with no charging at all.
The instances of higher power draw are when measurements are read back from the device, but these may be even less frequent than operation, possibly at monthly intervals for example.
NiMH cells in an AA/AAA form factor (that can be easily replaced) were attractive, but some reading leads me to believe that they wont like being charged above room temperature.
Anyone have any suggestions for something that might be suitable?
Many thanks in advance!


texts:
I am designing a package in eaglecad and I got the pin width incorrect. I don't want to change all 100 pads manually. Is there a way to select a group and change the dimensions on all the pads?

Thanks!


texts: What characteristics of a MOSFET should I be looking at?

texts:
I'm trying to determine a MOSFET for a circuit I'm building which will drive the gate of an N-channel MOSFET at 3.3v with an available current 40mA (**this will be driven using PWM at 4MHz), the MOSFET will be driving a load of 10A at 3.5v. I'm not sure what characteristic I should be looking at to create the most efficient circuit. I know that I'll need a low RDSon but I'm not sure if gate capacitance or anything else comes into play when choosing a MOSFET.

Appreciate any help!


texts:
I have to calculate \$i(t)\$ at règime, by knowing that \$v_s(t)=2\cos(\omega t + \pi/2)\$, \$R=1\Omega\$, and that, at the generator frequency, \$X_c=-1\Omega\$ and \$X_L=1\Omega\$.

simulate this circuit – Schematic created using CircuitLab

I know how to solve this by using the phasor domain. That is: using the current divider formula  (after I substituted the series \$v_s\ -\ R\$) with the Norton equivalent (current generator \$v(s)/R\$ in parallel with \$R\$).

But something just came across in my mind: at règime, doesn't the inductor and the capacitor behave, respectively, as a short circuit and an open circuit?
By reasoning that way $$i(t)=\frac{v(s)}{2R}=\frac{\cos(\omega t + \pi/2)}{R}$$

But how can I proceed? Is it correct to reason that way?


texts: Dimming an LED Strip (9v) with a 555 timer and MOSFET

texts:
I'm doing some VERY amateur prop building for an upcoming night of cosplay and I'm trying to create a throbbing/pulsing crystal for the top of a magic staff. Initially, I was just going to use a simple red LED circuit driven by a 9 volt battery, no muss no fuss. But I discovered that I can power the blue channel on a small strip of 5050 LEDs (3 diodes, normally 12v) with 9 volts beautifully, rather than drop $$ on individual blue LEDs.

Solid on is no issue, but fading on and off would be brilliant. Trouble is most of the fading circuits I've found are strictly for one or two low power LEDs. They all call for a 555 timer, 1k-ish resistor, 100uf-ish capacitor and a general purpose transistor. For my LED strip, the transistor was underpowered, but a N-MOSFET gets the job done. Here's the Schematic:

simulate this circuit – Schematic created using CircuitLab

Breadboarding this will light the LED strip, but I don't get any fading. I do see a very quick, but barely noticeable blink ever 2 seconds or so, which I suppose is better than solidly on, but not the effect I was hoping for. I've tried swapping out differently rated capacitors and resistors, but aside from slightly different timing, I haven't had much luck. My understanding of timers and capacitors is only a few days old, so it wouldn't surprise me to know I completely missed my mark. Also note that I've no intention of using a 'duino' of any kind because I want minimize the components I need to hide on the staff itself.


texts: Clipper circuit: Why some of the portion of the positive input cycle remains un-clipped due to the diode cut-in voltage

texts:
I understand that when the input waveform is positive, the diode does
  not conduct hence the positive half cycle of the input waveform gets
  clipped. Also, when the input waveform is negative, then the diode
  conducts hence the negative waveform appears as the output. However, I
  am unable to understand why some of the portion of the positive half
  cycle remains unclipped. I understand, that it is because of the cut
  in voltage of the diode which is 0.7 volts. However, I am unable to
  understand the mechanism. It would be very helpful if someone could
  make me understand why some of the portion of the positive input cycle
  remains unclipped.


texts: How can I feed the right current to a superbright LED with a 3.7V LiPo battery?

texts:
I'm trying to do something that seemed simple at first but is proving to be complicated (shocker, right?) I want to power a super bright LED (Luxeon K2, Cool White, 350mA. It's discontinued, but the datasheet is still the first hit on Google) using a 3.7V LiPo battery from SparkFun. The instructions I have for the LED tell me to regulate the voltage with an LM317 voltage regulator.

Problem being, the LED has a forward voltage of somewhere between 2.8 and 3.4V, and the LM317 appears to eat up too much voltage to make that possible. I don't want to wire 2 batteries in series because my enclosure is pretty small, and there's no space for another battery.

So I found this charging/step-up breakout board that can bump me up to 5V. I'm extremely new to electronics and this is my first project where exact voltage/current/resistance are an issue. My question is threefold:

If I'm using the breakout board to regulate my voltage, do I even need the LM317? Or can I just use resistors to get the current to where I want it?
How can I know what the current will be when it comes out of the breakout board? The datasheet for the voltage regulator on the board seems to say I can program the output current to anything between 15 and 500mA, but I don't understand how to do it.
Am I right about needing the step-up? Or could I potentially just run this with the battery and the LM317?

I'm doing this project in order to learn, so I would prefer answers that show me how to figure this out for myself as opposed to just doing it for me.


texts: PCB dual LED emitter, TIA and voltage regulator (beginner)

texts:
Does this PCB look good for this operation?

The schematic is attached.

I have a voltage regulator connectected to an LED emitter. Voltage regulator to TIA . TIA then is attached to active high pass filter, then a peak detector which then outputs to another circuit to a comparator. LED will be attached with a wire soldered to JP1 and JP2 and a photodiode with a wire soldered to JP3 and JP4.


texts:
I am currently in the middle of a project and I am quite unsure of what type of battery and battery charger I should be using. To be honest I have never worked with battery or battery charger yet.

In this project, I have a 3.3V and 50 uA power source, which is extremely low. Also, this power source is not regulated at 3.3V, so I need some way to stabilize it. Currently, my whole project does work at 30 uA, but I'd like to be able to store some of the power source into some kind of battery. From what I have seen however, this seems to be very difficult as battery requires high current to be charged effectively.

I have currently found an ultra low power energy harvester and battery charger that does seems to satisfy my criteria, but I am very unsure of what battery to use. https://www.st.com/resource/en/datasheet/spv1050.pdf .

Also, about this energy harvester, is it possible to directly take an unregulated power source and plug it directly into the circuit (bypassing the battery) to power on my project?

So if someone with more experience than me could give me his/her input on what type of battery I should use and if it is possible, I'd be very glad to hear it. I am also taker of goods resources to learn on the subject as it is not very well explained in datasheets.

Thanks in advance.


texts: If Manufacturer spice model and Datasheet give different values which should I use?

texts:
I'm trying to simulate an LED circuit but I am getting a large difference in results from the simulation vs calculations done using the datasheet information.  In this case both the spice model and the datasheet info are direct from the manufacturer.  Given the large difference in results, I'm wondering which information I should base my design off of.

In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v.  I'm wiring 4 of these LEDs in series with a target of 18mA.  Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA.

Should I base the resistance off of the datasheet and ignore the simulation in this case, or should I base things more off of the simulation results?  I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.

I'm attaching the specific simulation and Datasheet in this example here as well. I'm using a SML-P12WTT86R model LED from ROHM Semiconductor.

The datasheet is here.

Here is what I got from the spice simulation using ROHM's spice model.


texts: Say I have a device/instrument that has custom LCD for display with mix of text and graphic/icon on the corners. I want to log the values and feed it to the computer or say automate a response when the characters display a set of numerical values. How do I hack the LCD that way? Is there even a generic approach here? Is it just a matter of tapping into the the contacts for each line or pixel (for low resolution characters)?


texts: What is the glowing paper-thin material inside a flat night light?

texts:
I opened up a night light that sits flat against the wall (only about 1/4" thick).  It is basically a flat square that plugs directly into the receptacle.  Inside, I found a paper-thin material that looks black on one side and a silver on the other.  The silver side lights up a soft glowing green color when it is connected.

What is this material, and where can I get a larger quantity of it?


texts: Derating ampacity of a wire if it is stranded?

texts: Do I need to derate a wire if it is stranded? Or will a #12 wire have the same ampacity whether or not it is stranded?  Is this affected at all by AC versus DC?


texts:
I'm trying to calculate the switching loss of the MOSFET which is used for a DC-DC Boost converter.
Input Voltage : 9V-16V
Output Voltage : 30V
Output Current : 0.3A.
Switching Freq : 455kHz
Based on this [App Note][1] the Switching loss formula is given on page 3, equation 4.

If I calculate the switching loss based on the above formula, it comes to around 14W.
In this Article, the formula for calculating the switching loss is different.

Which one is the correct formula and could you explain the reason for 2 different formulas?
[1]: https://www.ti.com/lit/an/slyt664/slyt664.pdf?ts=1617773788537&ref_url=https%253A%252F%252Fwww.google.com%252F#:~:text=MOSFET%20switching%20losses%20are%20a,as%20shown%20by%20Equation%204.&text=where%20VIN%20%3D%20VDS%20(drain%2D,IG%20is%20the%20gate%20current


texts: Good method to provide small additional voltage while on battery?

texts:
I have a circuit that drives solenoid lock rated @ 9V as shown below. The circuit works when the power is connected to the wall, which gives a constant 9V DC to Solenoid Power V+.

I also have a battery backup circuit implemented that looks like the following. When the wallwart is disconnected, the power from battery kicks in. The problem is I'm using 6 x AA rechargeable batteries, giving about 7.2 voltage. This voltage is insufficient to drive the solenoid lock. What's a good way to provide that additional 1.8V I'm missing here?

Edit: The diodes I'm using are schottky diodes: 1N5818. So the forward voltage lost from the diodes are minimal


texts:
I was looking for a MOSFET that I could use to control 3.7v 4A dc motors with for a quad copter. I'm very new to electrical stuff, but I read that I could use MOSFETs to control motors.
I look online for MOSFETs meeting the specs I listed above, and noticed that the majority of MOSFETs have labels with extremely high currents.
For instance https://www.amazon.com/INTERNATIONAL-RECTIFIER-IRLB3034PBF-MOSFET-220AB/dp/B00HKHW9UU/ref=sr_1_13?ie=UTF8&qid=1485926431&sr=8-13&keywords=mosfet
says 195A on it, and it seems really small.

Can MOSFETs that small really handle currents that high? Wouldn't they just melt?


texts: How much current actually passes along household neutral?

texts:
My home has 3-wire single-phase supplied from the power company (Massachusetts, US). Red and black are separated by 180°. Both are 120 V from neutral (white). And in my electrical panel, neutral (white) and ground (uninsulated) are tied to each other and to a copper clad ground spike out in the yard.

Presumably the bare ground wires within the house never carry current except in the event of a short; but it goes back to neutral in the box.

Any 120 V circuit (a light bulb) is wired with one or the other of the two "hot" legs and the neutral; so presumably the original amperage supplied to the light bulb (minus energy dissipated as heat and light) passes thru the neutral line and then to ground. How much current does one actually see on the neutral line from the light bulb to the panel? How much current does one see from the panel ("behind" the ground spike, if you will) back to the electrical company transformer?

Any 220 V circuit (a clothes drier) is wired with both of the two "hot" legs and the neutral. In this case I would expect all current to see-saw between the two hot legs (minus the load again). Is there any current on neutral? Does the energy dissipated by the load appear as current on the neutral? Does any current appear on the neutral between the panel and the transformer?


texts: How to convert DC +350mv ~ -350mv to 3V ~ 0V

texts:
The operating voltage is +/-3.3V DC, Multiple op amps can be used,
As long as the completion of voltage conversion purposes.

simulate this circuit – Schematic created using CircuitLab

I'm simulating at Multisim, Input + 350mv after the output is very beautiful, about 3.25V. But when the input -350mv after the output can not be zero. There are still about -80mv can not be removed.


texts: How to understand an unusual internal power supply?

texts:
I am working with a baseboard thermostat to replace the low voltage control side with some custom controls. The thermostat is divided into two sides, a high voltage board and a low voltage board. There is a 4 pin connector(with only 3 used) between the two that is labeled to have ground, power and control(triggers the load when high). The chip on the low voltage board is an ATmega169P.

Right now, I can control the load(in my test setup, not an actual baseboard) from an external controller if I power it from an external power source(ie USB) and connect the 3 wires to the controller as well. Without the external power, the controller I'm using(just a Adafruit Trinket for now, not my final plan) does not boot up - it's power light blinks dimly and that's it.

I don't have any great scope or similar for checking things, only a multimeter and probes. When I check the voltage across power-ground I get 6.8V, probing at the original ATmega169 power lines get's me 3.3V(as it should) after a on circuit power regulator. If I run the 6.8V through a LV7805 I get a solid 5V there. All this makes sense, but once I put a load on the power coming from that circuit, it fails to keep the voltage up.

Connected to the Trinket, and running through the onboard regulator, I only see 3.0V on the other side of the regulator. If I build a quick and dirty voltage divider and measure it's output(setup to divide in half), I get 1.43V.

At this point I'm well past my knowledge level. I did not expect this part of my project to be what messed with me. A couple of theories that I don't know how to test:
Is the output really low amperage? How can I see what the max output on this power source is?
Is the voltage changing heavily? I don't see any fluctuation on the meter.
Is there something odd with the power source coming from the high voltage side due to it only being a two wire thermostat? The design works with the existing board, but I don't know how it deals with the fact that it only connects inline on the hot wire, no connection at all to neutral or ground. I assume it's allowing some current through all the time to get power for the main processor.

As I try to figure this out, I'm looking for pointers to help move it forward, and I've either not found what I want online, or I don't know the proper stuff to search for. Suggestions on what to try are appreciated, I do want to understand what I'm working with better over time.


texts: Why would this design (Si8261BCC-IS) blow the chip?

texts: I created a design for a simple MOSFET driver using the Si8261BCC-IS. The schematic and Gerber files are available here. The schematic is also shown below. When I connect the input control signal of 3.3V at J1, the chip blows up. There is a proper flash of flame and then blue smoke. The supply voltage on the MOSFET side is 24V. Why would this be happening?


texts: Can't find non-invasive dc milliamp sensor

texts:
Why is it impossible to find a non-invasive DC current transformer in the milliamp range that is split core (can open and close around wire)?
I would like to sense when a wire is carrying current or not. This wire when active will have 300 mA DC.
Using this meter: https://www.digikey.ca/en/products/detail/b-k-precision/316/1682098
I am able to easily sense this current non invasively.
Has anyone ever seen something exactly like this meter, but instead is powered by 5V dc and outputs an analog voltage proportional to the current being sensed?
I have searched digikey and some other electronics sites only to find a few solutions that either only sense current from 1A and higher, or need a 24V input.
EDIT:
I think I found one. Has to be ordered from China, and my source needs to be boosted from 5v to 12v, but I think it will work. Seems like the only supplier on earth who sells something like this!
https://www.chenyang-gmbh.com/en/split-core-dc-current-sensor-cyct04-xnsl.html


texts: Solar panel powered regulated output voltage collapses after short run-time

texts:
I have a PWM DC motor controller for a water pump.

Input voltage 24 V large solar panel (the ones you get on houses).

The PWM has a L7812 so outputs 12 V max.

Pump 12 V, 0.9 A.

Everything starts fine, but after a short while the voltage and amps drop to nothing.

I have tested it on a 12 V, 3 mA PC fan with a regulated power supply, and the same thing happens.

Any ideas why this is happening?


texts: What is this kind of audio cable called?

texts: I broke my headphone cable. It is exactly like the one in the image but I don't know how to search for this kind of audio cable (I only find cables with at least one receiving end). Does anyone know the name?


texts: How to model voltage controlled switch in LTSpice?

texts:
Having trouble making a Buck converter using two complimentary switches in LTSpice. I've got everything laid out exactly as perscribed, but when I run I get the following error:

"Can't find definition of model "SW""

I've put the model for each one right there, so I've got no clue why it wouldn't know what to do with the switches. If anyone has any ideas on how to correct that please let me know, thanks.


texts:
In the YIQ space (I am referring to this wikipedia's article) colors with phases near 0 are close to red.

In the TMS9918 datasheet's table, however, in the expression of colors as A' and phase, blue colors have phase 354. (notice that the two greens have a reasonable phase).

I wondered whether Wikipedia's colors are off with the YIQ space, but they seem to be correct.

In fact let us take the following RGB to YIQ matrix (I found it in this article):

$$
\left[ {\begin{array}{c} Y\\ I\\ Q\\ \end{array} } \right] =
\left[ {\begin{array}{ccc}
  0.299 & 0.587 & 0.114 \\
  0.596 & -0.275 & -0.321 \\
  0.212 & -0.523 & 0.311 \\
\end{array} } \right]
\left[ {\begin{array}{c} R\\ G\\ B\\ \end{array} } \right]
$$

Its inverse is:

$$
\left[ {\begin{array}{c} R\\ G\\ B\\ \end{array} } \right] =
\left[ {\begin{array}{ccc}
  1.0000 & 0.9557 & 0.6199 \\
  1.0000 & -0.2716 & -0.6469 \\
  1.0000 & -1.1082 & 1.7051 \\
\end{array} } \right]
\left[ {\begin{array}{c} Y\\ I\\ Q\\ \end{array} } \right]
$$

and by plugging in the colors for Y

$$I=A'cos(phase)$$
$$Q=A'sin(phase)$$

that correspond to the datasheet's table dark blue we get the RGB color:

$$\left[ {\begin{array}{ccc} 0.6657 & 0.3393 & 0.0159 \end{array} } \right]$$

or, in 0-255 range:

$$\left[ {\begin{array}{ccc} 170 & 87 & 4 \end{array} } \right]$$

which is a brownish red, and not blue:

(Color rendered with the RGB Color Wheel).


texts: Can I use CAN and USB at the same time with STM32F042K6U

texts:
I would like to use the STM32F042K6U but I would like to use USB and CAN.

But when I look up the pinouts in the datasheet it doesn't look like I can map either USB or CAN to different pins.

The device I am using is the 28 pin UFQFP.

Is there a way round this?


texts:
DESCRIPTION:
It will play .wav and .mp3 files from a Micro SD Card. The memory card can be written through USB (its an in-board unit). It will have a LCD screen to show the contents and functions like next, pause, previous, volume control and so on. Obviously, these functions can be remotely operated too.
I am familiar with PIC MCUs but being a beginner I have difficulties in deciding which MCU is enough for the job.
Should I go for a PIC32 or dsPIC? I'd appreciate all suggestions regarding this project.


texts: switch OpAmp down to minimize power consumption

texts:
I'm currently designing a board which senses some stuff. The board is powered using a 6V lithium battery. According to my sensor+OpAmp logic I need to split the voltage into +/-3V.
The circuitry to split that voltage consume 0.6mA and the remaining OpAmp+sensor consumes 1.2mA.

I wish to minimize that by powering this circuitry only when I want to make my measurement, and then switch the all things off, until the next measurement.

I though about using a P-mos directly between the battery positiv pin and the voltage splitter input. According to my simulation, that could work, but I'm wondering if you guys have some inputs or advices to help me ;)

OpAmp with shutdown mode?!
...?
...?


texts: I don't understand why do I need to put a resistor between the gate and the source of a N-type transistor in this circuit

texts:
I have a diagram that represents a circuit whose purpose is enabling/disabling two leds basing on a logic programmed in a micro-controller.

In the circuit below, as far as I understand, there are two n-type transistors, and they have a resistor connecting their gates with their sources, respectively.

My questions is: Why are the marked resistors necessary? (red circle)


texts: Would a better heat sink be tall or wide?

texts:
If we have a heatsink and want to improve it's efficiency would it be better to increase its width or height?

What should be the strategy on installing a fan as well?

If we increase height and install fan at top, distance between device and fan increases. The same happens if we increase width and install fan on side.

Should we increase width if we want to install fan on top, and increase height to install on side? Does it even actually make a difference?


texts: DIY NFC boosting antenna for a mobile device

texts:
I am very new to this. I'm a dentist trying to improve client flow in a busy office.

I would like to develop a cheap proof of concept for an NFC enabled client tracking system using a hacked mobile phone. My idea is to develop a system where I place passive NFC tags on the door frames of my office. As a client walks into the room, the cell phone reads the NFC tag and sends a message via Wi-Fi to a computer which collects the data.

Since NFC only works at short distances, I would like to make an external antenna that would extend the range of the cell phone (Samsung Galaxy 4) and allow it to read tags at a distance of about 30-60 cm. The size/shape of the antenna is not a concern at this point, but practically speaking the largest dipole antenna I would consider is 200 cm. (I'm not completely sure what a dipole antenna is but I read this and it sounded important :)

I know RFID is better at these distances but it's also more expensive and I'd like to keep the cost to the absolute minimum. The same goes for the mobile device. This may be possible with more specialized equipment but the cost and ubiquity of mobile phones make it the preferred reader (also makes programming the tags easier).

My questions are:

Is this feasible?
How would the antennas be designed? Shape - planar circular vs cylindrical vs dipole; Size - 22.11 meters long
What is the best way to connect to the native NFC antenna pins?


texts: Driving DC motor rated at 24VDC@2A Max with 50VDC@10A 40% duty cycle possible?

texts:
Upcoming project I need to speed control DC motor rated at 24VDC@2A Max.

Lab has 12VDC@2A and 50VDC@10A PSU only.

I thinking why not try run DC motor rated at 24VDC@2A Max with 50VDC@10A PSU if I keep 40% or less duty cycle?

PWM frequency is be 20kHz or more.

Is this good idea without burning or damaging that motor?

If this possible, what maximum voltage I can use (after adjust duty cycle properly).

For example, will it be good to try run this same motor off 100V at 20% or less duty cycle?

UPDATE:

Would be positive temperature coefficient thermistor (PTC) be fast to save motor from damaging if PWM circuit or HBridge fail (so motor exposed directly to full PSU voltage and current).

Is polyfuse and PTC same thing or polyfuse faster than PTC (asking as polyfuse uses in computers and saves ports like USB from overcurrent very fast)


texts: Algorithm for getting currents and voltages from resistances in circuit as graph

texts:
For my CS project I have to write simple circuit simulator, where I get list of edges of circuit as (a,R,b), where a and b are nodes at the end of the edge and R is it's resistance (it has a resistor R), and one pair (a,b) where the electromotive force E is put. I am also forbidden from using nodal analysis method.

I've tried reading "Computer methods for circuit analysis and design" by Vlach and Singhal, and also I've tried using loop analysis. The problem with loop analysis is that getting list of all loops for any graph (they can be arbitrarily huge, e. g. 1, 2, 4 thousand edges) is algorithmically very hard.

I also have to avoid getting overdetermined system of linear equations, so if I understand correctly I have to use both Kirchhoff's laws. Using them just as-is would generate too many equations though.

So to sum up: Ss there an algorithm that can produce equation system (not under- or overdetermined) for calculating currents and/or voltages in circuit without knowing it's shape beforehand, only resistances on it's edges and single EMF source?


texts: Difference between UA741 op am and LF356N

texts:
I was thinking of using LF356N as an alternative to the general purpose op-amp UA741. Can someone outline the major differences between the two op-amps?

Thanks!


texts: Calculate the junction temperature of a MOSFET during pulse

texts:
Hi all I have a question regarding using a MOSFET for a constant current source. I have found this question with some answers but it wasn't clear to me yet.

I want to create a constant current LED driver with a MOSFET shunt and opamp configuration. I have designed the schematic below with a 1 ohm sense resistor and a BUK6D43-60E MOSFET. The forward voltage of the LED's will be between 34.5 and 45 volt and the current will be 1 ampere. So the voltage over the MOSFET will be around 12.5 volt maximum.
The LED's will be pulsed with a frequency of <100 Hz and a pulse duration with a maximum of 300 microseconds, this will be a dutycycle of 3%. From the datasheet below I got a Zja of around 4-6 K/W. I know Tjunction = Tambient + Rj-a * P, now Tambient has a maximum of 60C and Rj-a = Zja = 4-6 K/W. Now what do I have to use for P? Is this (Vcc-Vleds-Vshunt) * If or is this (Vcc-Vleds-Vshunt) * If * dutycycle? Because this would be the difference between 135C and 62.25C.


texts: How to setup Drill Dot Open in single layer PCB using Altium Designer?

texts:
I designed single layer PCB in Altium Designer. Now I want to setup Drill Dot open in Soldering layer (bottom layer) to generate Gerber file for the manufacturing purpose. Can anyone help how to do this?
Here are the pictures (blue is my file, red is example for drill dot open).


texts: Explanation why dc-dc converter is a time-variant system

texts:
How do you explain that dc-dc converter is a time-variant system?

I see that there is an explanation as follows:

  dc-dc converter is a time-variant system because its topology changes
  with time.

Do you agree with this? Is there another explanation?


texts: Connecting a 12V DC power adapter to Arduino

texts:
I'm working on a school project and I am a total beginner on this arduino stuff. So, I bought this led strip at IKEA and used this tutorial to connect it and controll it with my Arduino. The thing is that I want to power up the led strip using another power source, so I bought 8x 1,5V AA batteries to power it up.

The idea is to upload the code to the Arduino and unplug the computer and use the Arduino to control my led strip. I was thinking of just using the power adapter which comes with the led strip from IKEA, it's an 12V DC power. It says on the arduino that 7-15V is okay for input voltage.

So is this okay? will I fry my arduino board? Note that I followed all the instructions on this tutorial above and it works perfectly, I just want to use it without my computer.


texts: Adding a waveform on top of an LED driver signal

texts:
My Background:
I have a basic understanding of electronics from undergraduate physics courses and a few high-level digital electronics courses, but basically zero knowledge of anything analog/actually building circuits. The term "coupling capacitor" was new for me not too long ago, if that helps give some perspective.
I recently saw this video and I thought it was super cool. I want to create my own version of it and instead of using an MP3 player, I'd like to use a waveform generator (specifically the AD9833) so that I can better control the light/sound emitted from several LEDs (an array 16 RGB LEDS to be exact) with an Arduino Nano. I'm assuming I can't just connect the output of the waveform generator in parallel with an LED driver (see below schematic) like the guy does with the MP3 player and battery... but I'm not really sure what I'd use instead to accomplish this.

simulate this circuit – Schematic created using CircuitLab
I'm making my question a bit more specific. I was imagining doing something like in the below schematic.
Would a summing amplifier work for this purpose? From the TI schematic, the driver tries to maintain a set current rather than a set voltage (if I've understood it correctly). Would I be safe connecting the circuit up like so?

simulate this circuit
I reread the TI schematic and it seems like the LED Driver is open-drain (please correct me if I'm mistaken). Also, I found out that Op-Amps sort of separate the inputs from the outputs (very little current flows) if there's no connection between the terminals, so it would seem the LED driver would be problematic in the above schematic where it is. My next idea is to add the signal to a 5V supply that would be the main power for the LEDs. What do you guys think?

simulate this circuit
In response to @Tony Stewart Sunnyskyguy EE75's comment about specs:
I'm hoping to use RGB LEDs similar to these. For simplicity, I'd like to design something for only the red component. It has an average forward voltage of 1.9 to a max of 2.5V. The signal I'd like to superimpose on the 5V supply would ideally be within human hearing range (20Hz-20kHz), but I can live with a smaller range if I have to. The amplitude would be limited by the waveform generator (AD9833) which on the spec sheet says 0.038V to .65V. I'm not really sure how to give a spec on noise (is it just an SNR?). I built a circuit similar to the one in the video using an lm386, a solar panel and an LED. I strobed the LED with a couple note frequencies (440Hz for an A, etc) and in a dark room it sounded pretty clear. I'm not sure I fully understand what I read here, but it seems like  op-amp noise frequencies only appear at high frequencies (MHz range), where a person's ear won't really be able to hear it. My target SNR would be something around 30dB, I'm not overly concerned with a little distortion as the goal is to create an instrument.


texts: What happens to batteries connected together with a resistor?

texts:
I have 2 batteries, one is 5V, the other is 1V. I connect the batteries positive to positive and negative to negative. Further more I add a resistor in between the positive and negative leads.

simulate this circuit – Schematic created using CircuitLab

Then what happens?

One thing would be current rushing from the 5V battery into the 1V one possibly destroying it but that's just a poor setup for the thing I'm interested in, what happens to the resistor? Does it get 5V? or 1V? Or both? Logic would suggest the resistor would get 4V but I tried it in a circuit simulator and it failed to analyze the situation and I can't make Google understand what I'm asking.


texts: What could have caused my high-side MOSFET gate driver to break?

texts: I designed a small breakout board for the LTC7004 gate driver to test some high-power MOSFETs. While initially powering the circuit using a 12V AC adapter, everything worked fine and the gate drive pins (TGUP/TGDN) would output 24V when the switch was on. I then moved the setup to run off of a 12V car battery and attached a 1/2 ohm dummy load in parallel with R2. At this point the LTC7004 stopped working and will no longer work even using the bench power supply. What might I have done wrong? There is no visible damaged to the chip or PCB and nothing got hot.


texts: How does one calculate the spectral irradiance from an array of IR LEDs?

texts:
I would appreciate any help.
The question may seem similar to the question asked at this link: Help me calculate spectral irradiance of an LED from a LED spec sheet , but the answer was never given or posted.
So here is my questions:
I am building a device that illuminates the human eye from a distance of approximately 120mm, with an array of 40 IR LEDs for around 7 seconds. The purpose of this is beyond the scope of the question.
In order to have theoretical evidence that the IR LED's will not cause any hazardous harm to the eye, the total Infrared Radiation exposure should satisfy the limits of the IEC62471 standard.
I have posted an image/snippet from the standard of the equation that I need to use below:

My problem is that I do not know how to calculate the spectral irradiance of the IR LED from its datasheet.
Here is the datasheet: https://4donline.ihs.com/images/VipMasterIC/IC/OSOS/OSOS-S-A0002483803/OSOS-S-A0002483803-1.pdf?hkey=52A5661711E402568146F3353EA87419

The parameters of my setup are the following (Some values retrieved from the datasheet):
IR LED wavelength: 950 nm
IR Centroid wavelength: 940 nm
Number of LEDs: 40
Shape of array: A square of 30 x 30 mm that is positioned in between both eyes (at a distance of 120 mm)
Typical Radiant Intensity per LED: 11 mW/sr
Spectral bandwidth at 50% (∆λ): 42 nm  (I am unsure if this is what is needed in the equation)
Distance from eye: approximately 120 mm
Duration of Illumination 7 seconds
Half angle: 60°
Total radiant flux: 35 mW

The units for spectral irradiance is W⋅m^-2⋅nm^-1. Therefore, if I am correct, I can get the W/m² by saying:

11 mW/sr*40(Num of IR LEDS) = 440 mW/sr
W/sr/m² = 0.44/sr/(0.12²) = 30.55 W/m² = 30.55 W.m^-2

However, that's where I get stuck.
Therefore,  I would like to know the following:

Am I on the right path?
If so, how do I convert W/m² to W/m²/nm (W.m^-2.nm^-1) ?

Thank you for the help


texts:
I'm doing a project where it requires to control 10,000 I/O.

5000 output - For 5000 LED, where only 1 LED will be light up at one time

5000 input - For 5000 sensor, where it'll sense the presence of an object.

Basically , i'm doing a storage system (something similar to pigeon hole) whereby, small box will be placed in this pigeon hole. Currently i have about 5000 boxes placed over 20 racks. Each rack has 250 hole (10 coloumns x 25 rows).

Each of this holes will have one LED and one sensor. therefore, i need 5000 LED & 5000 sensors.

all sensors and LED will be connected to a system. When i need to place the box in the pigeon hole, i'll scan the barcode of the box and register it in the system. The system will then look for empty slot in any racks and light up the LED. I'll placed the box in the pigeon hole and the LED turn off.

If i need to retrieve any box, i would then enter the box number and the LED of the exact location would light up.

Not really sure how to start. Would like to know what kind of hardware that have such quantity of I/O ports.


texts:
According to Ohm's law V=IR. This means that if the current is zero there is no voltage. Does this mean also that an unplugged battery has zero voltage? Then why does it say otherwise in the package.

In other words:

What does it mean that a battery is 1.5 Volts if, after all, it depends on the resistance?
What does a voltmeter measure if the voltage depends on resistance.

I'm sorry if this looks like a silly question. I'm not from electrical background.


texts: What is the behavior of circuit with multiple Q points?

texts:
On Q-Point of a circuit

The top answer says that if you use DC current source, then the Q point is the "solution" of the circuit.

I interpret this as, if you use a DC current source of I amps, then the Q point will tell you what voltage will appear across the nonlinear device (e.g. diode)

But on this page, it says we can have multiple Q points, some are stable, some are unstable.

Can someone confirm my understanding of Q point and elaborate on the meaning of having multiple Q points?

Is quantum tunnel diode the only device having multiple Q points?


texts: How do I decide whether to use Kirchhoff's Voltage Law or Kirchhoff's Current Law?

texts: When I solve questions, I usually get confused between when to use the Kirchhoff's Voltage Law (KVL) and when Kirchhoff's Current Law (KCL). Please help.


texts: What is the optimal way of clearing solder from surface-mount PCB pads for rework?

texts: Say I have an assembled PCB with a QFP package on it. This device gets damaged and I need to replace it. Getting the device off is straightforward, but now all the pads have solder blobs on them. Is there a standard way of cleaning these pads off, so the replacement device will sit flat on the pads again?


texts: Is wireless power transfer by induction at 60Hz possible, or does the frequency need to be changed?

texts:
I want to build a wireless power transmitter that works over a very short distance. Can I use my line voltage(120V at 60Hz) through the primary coil to induce voltage into a secondary coil about 1/4" away.

Am I foolish to think this is possible, or does it have to be at a high frequency?


texts: Does the separation of the differential pair shielding of a SATA cable matter?

texts:
Basically I want to replace a consumer grade SATA cable with something a bit more tolerant to high temps and other environmental stresses.

The general cross section of a SATA cable looks like this:

And the cable I want to use looks like this:

My Question is

Does the gap in the SATA cable provide a noticeable difference in speed/reliability compared to a cable that has its differential pair shielding in contact with each other?


texts:
When transformer secondary is short circuited, what would be the value of current flowing through short circuited side? Shouldn't it be infinity ideally? If yes, is it only due to large cross-section & highly conductive copper wires that wires don't get melted?

For e.g. suppose I have 1 kVA, single phase, 250/125 V transformer. Now if I short circuit 125V side and set full load primary current i.e. 1000/250 = 4 A in primary then what would be value of secondary current?


texts: Suggestions for the placement of decoupling and filtering components

texts:
The following diagram depicts a circuit intended for activation via reed switches. Q1 is normally conducting through the voltage divider R1 and R2. With Q1 conducting, Q2 is biased off (non-conducting) via R3 and R4. The SCR remains non-conducting. When the magnetic reed switch opens, Q1 no longer conducts, after which C1 discharges into the base of Q2 via R3, which causes Q2 to conduct. The SCR receives current through C1,R5 and R6 and it activates the relay. I'd like to know whether this circuit benefits from filtering components, considering the reed switches (window contacts) are connected via long wires to the circuit and might need components to remove RF and other sources that might induce noise into the circuit.

I was thinking of adding a reverse diode (or TVS) before the first voltage divider. Also, adding 100nF cap at base of Q1. Please share your suggestions.


texts: What happens to my LED when I supply too much current?

texts: I read somewhere that LEDs could self limit current up to a certain point and had a few lying around in my box so I decided to test this statement. Its true for roughly the voltage drop across the LED. But the question comes is what happened when I applied 20V to the LED? It made a loud popping sound. What happened to the internals of the LED?


texts: Meanwell Led driver: internal 3-in-1 dimming circuit

texts:
In Meanwell led drivers like the ones from the XLM, HLG or LCM families, how does the internal circuitry for the 3-in-1 dimming feature (0-10V, 10V PWM, 0-100kOhm) look like?
I use a LCM-25 in my specific case.
There already is a question on that topic here, but the circuit the OP provides there appears to belong to 2-in-1 dimming (0-10V, 10V PWM):

From my understanding, dimming this circuit with a variable resistance between DIM+ and DIM- would in deed work, but there is this sentence in the datasheet: "dimming source current from powersupply: 100µA (typ.)".

This sounds like they use a constant current source to measure resistance and I measured 100µA flowing through any resistance in the range 0-100kOhm, accordingly. In the above circuit, the current would depend on the connected resistance and so it does not seem to be the circuit Meanwell uses for 3-in-1 dimming.
The reason why I'd like to understand how the circuit works:
I'm going to control the dimming input with an external device. For my tests I use a bench power supply but finally it will be a DAC with amplifier.
As I don't have a negative power supply for the opamps of the final circuit I would like to add some extra offset to the driver's off-voltage (normally, the driver is on when the dimming voltage is above 0.2V, but I'd like it to switch on at a higher voltage). I expected to achieve this by simply adding a diode between DIM- and the external device's ground. For my surprise, now the driver does not  switch off at all. Whatever Vext the external device provides in the below circuit, I measure Vdim = 27V at the driver's dim input. Instead I expected Vdim to be 0V for Vext<0.6V.
In my test, "external device" is a

simulate this circuit – Schematic created using CircuitLab
Do you have an idea how the internal circuit look like and how I could apply the desired offset?
As an additional info: the DIM input has an input resistance of 300kOhm.


texts: How to read the following datasheet of a sensor?

texts:
I wanted to write about static and dynamic characteristics of the Honeywell pressure 19mm transducer. I found my sensors datasheet but could not find the following characteristics mentioned in the datasheet directly.Could you help me know if any of the below are mentioned in the datasheet.

Characteristics : Accuracy, Precision, Sensitivity, Linearity, Resolution, Reproducibility, Repeatability, Threshold, Tolerance, Range, Stability, Drift, Hysteresis, Speed of Response, Measuring Lag, Fidelity, Dynamic Error, Noise.

I found some like Time Response, Range, Repeatibility because they were directly written.

Data Sheet Link : https://sensing.honeywell.com/honeywell-sensing-19mm-series-isolated-pressure-sensors-product-sheet-009132-3-en.pdf


texts: I have 20 pushbutton inputs where any number of inputs can be pressed simultaneously. I have to read the output of the buttons and transmit it. I am planning to use a binary to decimal encoder for reading all the 20 inputs at a time and convert them to decimal for serial output to the wireless device for transmission. Is this a better approach than having a microcontroller? Also can matrix of 5 X 4 switches be a better choice for reducing the number of input pins? My objective is to make the design as smaller as compact as possible.


texts: Resistor for connecting two 9-volt batteries to 12 V thermostat

texts:
I have two 9 V batteries connected in series to make an 18 V supply. I would like reduce it to 12 V for powering a thermostat.
So which resistor should I use?


texts: I2C Master and Multiple slave configuration: How to cut off capacitance of unused I2C devices

texts:
For my application, I plan to use around 5xI2C devices that are wired to one Master device over a cable length of around 1-2m for each (so 10m in total), I can use a low pullup resistor of around 1-2kOhm to battle the parasitic capacitance.
Is there a chance that I do a sort of multiplexing and cut off the capacitances of the unused slave devices? I just want to read out one device at a time.
This I2C Multiplexer PCA9543A seems an option for my needs, please see the datasheet:

Capacitive  Load  Sharing  -  Adding  more  I2C  and  SMBus  devices
on  the  bus  may  exceed  the  400  pF  limitation.  The
multiplexers  and  switches  can  isolate  devices  that  are  not
currently  needed  to  reduce  the  overall  system  loading  and
maintain  the  total  system  load  below  400  pF.  When  active,
the  channels  act  as  a  wire  and  the  cumulative  capacitive
loading of the upstream channel and all active downstream channels
must be considered.

References:

I2C capacitance problem discussed on stackexchange
8 Channel I2C Multiplexer
Adafruit 8Channel Multiplexer


texts: Input Impedance of Noninverting Amplifier

texts:
I simulated a simple noninverting amplifier using an operational amplifier in LTspice and i was wondering about the input impedance.

The input impedance of a noninverting amplifier should be the input impedance of the OPA itself plus the resistor to ground. The OPA I'm using (LT1014) should have an input resistance of 4 GOhm in common mode or 300 MOhm in differential mode according to it's datasheet.

But at a DC input of 0.1V LTspice shows a current of about 12nA through V3 which would suggest a resistance of just 8.3 MOhm (0.1V / 12*10^-9A).

Am I doing something wrong or what causes this huge discrepancy?


texts:
I'm currently developing a solar powered data logger that sits outside in direct sunlight for a good chunk of its life. Preliminary testing has shown that the inside of the enclosure can get up to 70°C on a hot day in the Australian Sun.

My first prototype iteration used a single 5000mAh 3.7v prismatic lithium polymer cell. This met the power requirements perfectly but on moderately hot days the 50°C over-temperature cutoff would kick in and the cell would stop charging from the solar panel and the board would fail to stay on when removed from the sun. I also have concerns about the lifespan of these cells under heat-stress and using potentially flammable li-poly cells in hot conditions.

The device requires 2-3000mAh of capacity with a board Vcc of 3v, the average current draw is <100mA. I'd prefer not to vent the enclosure as the device is used in pretty dusty conditions and I'd like to keep it as a sealed unit. By better insulating the enclosure, I may be able to bring the inside down to around 60°C if that makes things easier. The battery needs to be less than 12mm thick.

For my next iteration I'm considering different chemistries to address this issue. So far the only cells rated for such temperatures I've found are the SAFT high-temperature lithium ion cells (http://www.saftbatteries.com/force_download/VL32600_125.pdf) that are rated up to 125°C, but they don't come as a flat cell and they're not readily available in small quantities.

I've also read mixed literature about what temperatures LiFePO4 cells can be used at.

What options have those of you who've needed batteries in high ambient temperatures found?

If anyone could point me in the direction of some other chemistries or specific cells that might meet my requirements I would be very appreciative.

Thanks!


texts: What is the maximum acceptable baud rate error for RS-232 serial communication?

texts: What is the maximum clock difference between a transmitter and receiver for error-free asynchronous serial communication?


texts: How are pin mapping done in LCD driver / microcontroller

texts:
I'm getting a custom LCD made, and it is a non COG version (to save on tooling costs), which means I'll need to use an external LCD controller. My LCD has 128 segments, so 32+4COM pins would suffice. I'm thinking of using HT1621 LCD controller (to save on costs again). I'll be using some ST microcontroller, and want to interface with LCD using SPI.

Now, I have the mapping of "FP + COM Pin #" to Segment#. Now I need to know how is programming done to run the LCD using SPI interfacing with the microcontroller (I've never done this before).
Here's my thought of how these things are done, and I fear its not right, which is why I need some advice:
In microcontroller, an object contains info of all the things which I want to be shown :

Battery value (1/2/3)
5 Icon values (on right of battery at top)

boolean value for either visible or not

Values for each of the 5 numeric groups

When I want to display the value, for which there should be a function to "display" the LCD, which would use the mapping of the "FP + COM Pin #" with segment. Each segment now gets some hex address. So one by one, the microcontroller would need to "send command" to LCD driver to turn on those segments.
I'd want to know if above is in line with how its done. A real world sample code / links would help understand this better.


texts: I have a potentially stupid question, but I have no idea how to handle the problem. I want to use 9V battery with a diode that requires 5V. So I need a resistor. How do I find the resistance if (as far as I managed to find out) it is improper to speak about the current in therms of batteries. So  have two unknowns in Ohms law: required resistance and current. All I have is potential.


texts:
I'm using copper tracks laid out on an FR4 board as a heater device. It's a serpentine design with the copper 0.3mm wide and 0.2mm spacing. I have three sets of tracks which I intend to heat up at different temperatures, one of which at 95°C.

At about 85°C, the board near the tracks starts deforming(see image), with smoke emanating out, from the tracks.

My question is, does increasing the width of the tracks help in increasing the thermal stability? Also, does the spacing play a major role in it as well?

Does using a thicker board help with dealing with the thermal stress? If not, how can I add in the heatsink capability for it?

FWIW, I'm using a TIP122 transistor with a PWM input to heat it up. The current consumption is about 1.5 ~ 2 A.


texts: Altium Designer, change decimal separator

texts: I'm wondering if it is possible to change the decimal separator in Altium Designer from a "." to a ","? I have looked for it and Googled it but I can't find anything.


texts: Need help understanding why noise temperatures are added, but real temperatures aren't

texts:
Wikipedia says:

In a wireless communications receiver, the equivalent input noise temperature \$T_{eq}\$ would equal the sum of two noise temperatures:
$$T_{eq} \ = \ T_{ant} \ + \ T_{sys}$$

I understand that these values of \$T\$ are related to temperatures, but they are not themselves actual temperatures that one measures with a thermometer.
If I put a 273K ice cube in my 357K coffee (no pun intended) I'd get cooler coffee, not 630K coffee. The same applies if they are two streams of fluid mixing rather than static objects.
In another setting; at given frequency, the noise power of an external radio source, like a blackbody source, would scale as the fourth power of temperature, not linearly.
I need help understanding why noise temperatures are simply added, even though in the real world the last thing we'd think of doing is adding two temperatures together.


texts: Are dual MOSFET devices isolated from each other? If so, to what degree?

texts:
I am using an OnSemi NTGD3148N dual MOSFET in a project. I cannot find a specification anywhere in the datasheet stating the isolation between the devices; and this holds true for most dual MOSFETs for example Si4946EY (which I used in a different project.)

Obviously I can't put 100kV on one drain pin and 0V on another without something blowing up. (Ignoring for the moment that it can't take 100kV D-S; the source in this example is left floating.)

This is important for me, as I am switching two independent loads which cannot be allowed to short together. E.g. one might be 12V and another 5V.


texts: Mistake in published paper about magnetic levitation?

texts:
As I was reading through this paper: Nonlinear Model & Controller Design for Magnetic Levitation System, I stumbled cross section 3.3 which I could not follow.

Summarizing section 3.3 Non Linear Model.

The magnetic levitation system can be described in terms of the following equations.

Equation (2) indicates that L(x) is a nonlinear function
of the ball position x. Therefore we need to approximate the inductance for the MLS. The authors chose the following approximation:

They then proceeded to substitute into equation 2.

Should it be 2*C or simply C in Eq.5?

How did they end up with equation 5, from equation 2? I am having trouble understanding the origins of the negative sign (which I am sure that there is an explanation to) in the second equation of the image above, but also where the 2 in front of C has gone.

Is there a mistake here, or am I missing something? Can someone help me with the math and show how this was worked out?


texts:
So I thought the ripple voltage was approximated by the formula

Vr,pp = Vp / fRC

for a half-wave rectifier, and Vp/2fRC for a full-wave.

Yet simulation shows about 55% of this value.

So is the formula wrong? Just very inaccurate? Or under what conditions is it otherwise more accurate?


texts:
I'm tracing a circuit. What is this part?

This is back of it.


texts: What would be the polarization loss factor, if transmitting antenna is circularly polarized and receiving antenna is linearly polarized, but they are aligned in such a way that maximum radiation pattern of both overlaps each other


texts:
I'm trying to work out why a 0.7pF capacitor was chosen.  The circuit operates at 12GHz.

At 12GHz, the capacitor has an impedance of about \$18\Omega\$.  Also at 12GHz, TL3 is \$0.259\lambda\$ (which is roughly a quarter of a wavelength.  I worked out the characterstic impedance of TL3 to be \$74\Omega\$.

I thought that C1 was meant to be a DC blocking capacitor and prevent the 12GHz signal from going into the DC supply; however, I don't understand why an \$18\Omega\$ capacitor was chosen, as a quarter wavelength piece at \$74\Omega\$ does not transform \$50\Omega\$ to \$18\Omega\$...

Could someone point me in the right direction?

Thanks.


texts: Why do differential signals need an inverse wave?

texts:
At the moment, I'm working on converting a single ended audio signal to a differential one (source is a CS42L55, need a differential input for a CSR8670. The latter's datasheet is indecisive about how to approach this issue). I have a few options, and I'm wondering about the validity of each.

Tie the negative differential input to analog ground
Use an op-amp to create an inverse signal
Use a transformer (I've only just read about this, not sure how it works yet)

This got me thinking - why does a differential signal need an inverse input, if the noise on both cables is the same?
For example (all waves start from 0v):
                   /\
Positive input:   /  \

Negative input (neutral) : ----

If the same waves had noise, like this for example:
                 __
Positive input: /  \
                          _  _
Negative input (neutral):  \/

Therefore, pos - neg = pos without noise right? (the sum being the function of the converter?)
Is there a benefit to using an inverse wave instead of ground (op-amp > just tying to gnd?)
I guess I am missing something here, and I'd like to know what.


texts:
I'm trying to use a non-inverting operational amplifier to amplify a voltage by a gain of 2 (using 2 10 ohm resistors). I'm using a 12 volt battery (made by combining 8 1.5v batteries) to power the op amp, and I'm using the 3.3v pin on a Raspberry Pi to connect to the non-inverting input of the op amp.

Here is the circuit on PartSim: https://www.partsim.com/simulator/#99446

The output of the op amp is reading 0 volts when I connect the multimeter to the output of the op amp and the ground terminal used on the Raspberry Pi.

To be specific, the op amp I'm using is the UTC3580. (Datasheet)

Why is the op amp outputting 0 volts when it should be outputting around 6.6 volts?


texts: How to get current to the load with a buffer Op Amp

texts: I am reading about voltage buffer Op Amp configurations and it seems like there is no current through the circuit, specifically the load. So why would you want to get a specific voltage to the load if there is no current? I guess I am just confused by the reasoning why you would use a buffer op amp setup.


texts: Measuring just half the sine wave of a current measuring transformer?

texts:
I'd like to measure current of electrical devices using one of those split-core transformers you clip around an AC wire, which has a built in shunt resistor and hence outputs a voltage.
I'd like to to this with minimal components.

All the tutorials online add a DC bias to shift the wave up a bit, and then run it through a ADC.

Could I get away without adding the relatively complex DC bias?
If I just measure the amplitude of the positive side of the sine wave and multiply it by two (and cut off the negative side in case the ADC doesn't like negative voltage, I guess), shouldn't I get the exact same measurement?

Or would it make a difference to simply rectify the incoming sine wave and measure that wave's amplitude?

What is the benefit of the DC bias?


texts: Switching between transmit and receive in a transceiver

texts:
My current project involves building a proximity sensor that uses RF and is low-cost (so no microcontrollers). I've come across two circuits that look quite promising, a transmitter and a receiver.

I want to combine these two circuits so when two transmitter/receiver pairs come into range, it will activate a circuit on both transceivers. I need a method of quickly switching between the transmitter and receiver circuit so that an individual transceiver doesn't pick up its own signals.


texts: Adding to the output of a DC/DC Boost Converter using the same power supply as the input?

texts:
I've got a project that requires a variable output between 24-48V. This needs to be continuous-current, not PWM.

Items that I have handy from my 'box of bits', and ready to work with are: an 0.6-36V Variable Boost Converter, and a 12V Regulated Switching Power Supply. Obviously, I'd prefer to use these rather than purchase a specialised supply if possible.

There are two things that I know at this point, therefore:

I can use the 12V supply as the input to the Boost Converter, but the output voltage won't be high enough.
If I had a 12V battery, I could add this in series with the Boost Converter output, to get a variable output from 12.6-48V.

The diagram below shows 'Point 2'. There is a 12V source in to the Boost Converter, and an additional 12V source in series with the output, leaving me with a variable 12.6-48V. This is great, except for the fact that I only have one 12V source.

Which then brings me to my question, can I use the 12V supply in place of the battery, in series with the output from the Boost Converter? There are now effectively connecting wires going from the output of the boost converter back to the input, which makes me nervous!

The image below shows the same circuit, but with the wires linked back to the original 12V source, rather than to a second one.

I have built the closest circuit I could in Falstad to hopefully illustrate what I'm thinking. They don't have a Boost Converter component, though!

Could this work as a solution?
Is there a way to effectively split the 12V source into two separate supplies so I can enact the first diagram?
Failing the above, do you have a hardware recommendation for a source that's directly variable through the appropriate range?


texts: Measuring >40VAC from 230VAC Phase against air

texts:
Austrian 230VAC.
I took a DMM and made a voltage measurement between phase and a 5 meter long curled 1.5mm² copper cable with isulation and got a voltage from 40VAC to 100VAC varieing how i curl the cable. The cable is not connected to anything on the other side.

What I am measuring here?

Is this a reflexion on the line? If thats the case, is it too fast for the FI circuit breaker to detect the flowing current? Ireflexion - Il = 0?


texts: Re-annotation from pcb now means my components are linked with different designators

texts:
After placing my components I re-annotated from the PCB to get positional annotation. This worked fine. But I've just noticed that components on my PCB and schematic (whilst linked, i.e I can click on the component on PCB and it will highlight it on schematic) do not have the same designators! R39 on schematic is linked to R40 on the pcb!
I tried doing an update schematic from PCB but it isn't picking up any changes?
How do i fix this??


texts:
A friend gave me a transformer from an APC UPS that supposedly was capable of \$1300 VA\$ (I have my doubts, but it is very large and I am not going to be using nearly so much power, so OK). He doesn't have any other info about it, so I thought I'd experiment.  I have a good idea of how these devices work, so it was easy to identify "mains" side vs "secondary" side (of course they would be backwards when using the batteries).  The mains side has three wires: white, yellow, and black.

I figured that the this was to accommodate a \$120/240 V\$ switch, but on testing them, I get \$16.4V\$ from the white/black (expected), but then \$18.4V\$ from the white/yellow, which was not expected. If my conjecture had been correct, I would have expected to see half that voltage from the white/yellow mains inputs (I would have been putting \$120V\$ into a tap wanting \$240V\$ to return \$16.4V\$).

So what gives?  Does anyone have experience with these transformers that could point me to an explanation?

simulate this circuit – Schematic created using CircuitLab


texts: How to solve this problem in the simplest way via LTspice?

texts:
My netlist file is:
5.24(a)

.param Va=1 Vb=0 Vc=0

Va a 0 {Va}
Vb b 0 {Vb}
Vc c 0 {Vc}

Ra a 2 {Ra}
Rb b 2 15k
Rc c 2 {Rc}

R1 1 0 20k
Rf 1 3 100k
RL 3 0 4.7k

X1 1 2 3 OPAMP

    .SUBCKT OPAMP 10 20 30
    Rin 10 20 1E15
    E1 30 0 20 10 1E10
    .ENDS

.step param Ra 1k 35k 1k param Rc 1k 35k 1k
.save V(3)
.op
.end

I have solved it by doing 3-simulations setting:

\$V_a=1 \quad V_b=0 \quad V_c=0 \quad \text{yields} \qquad  V_o = 1 \\\$
\$V_a=0 \quad V_b=1 \quad V_c=0 \quad \text{yields} \qquad  V_o = 2 \\\$
\$V_a=0 \quad V_b=0 \quad V_c=1 \quad \text{yields} \qquad  V_o = 3 \\\$

and then search for the output using cursor.
The results are  \$\: R_c=10k \quad \text{and} \quad R_a=30k \$.


texts: Default behavior of a USB device in the presence of 5v

texts:
This is a follow on from this question

Given a home made USB charger that simply provides 5 volts across the GND and VCC pins of a USB port, what should the default behavior be of any mobile device (mobile phone, tablet, iphone etc) plugged into that device. ('data +' and 'data -' left unconnected)

Will it...

completely ignore the device (i.e. not charge at all)
attempt to trickle charge very slowly at low current
attempt to charge at a current of no more than 500ma
attempt to charge at a current exceeding 500ma

I have read this but am no wiser.


texts: charging speed from USB QC3.0 to USB-C PD

texts:
I am trying to find this information online for a while but I cannot find any precise info, thus Q on this community seems appropriate.
I would like to know if a device having USB PD charging port (capable to charge with 60W) will be able to use USB QC3.0 charging speed capabilities well?
Maybe it is manufacture specific matter and I should not expect to be any rule here? Then I just need to write to manufacturer and ask it is in cas of that specific device.
Thank you


texts: What exactly is happening when a graphing calculator LCD malfunctions when batteries are weak or overloaded?

texts:
I'm a beginner in electrical engineering, and I have limited knowledge of how electronics work internally.  I'm trying to understand some odd LCD behavior when the batteries are weak or subjected to a heavy load.

I'm running a TI-Nspire with Clickpad graphing calculator in diagnostic mode.  When I run the USB OTG test and connect a USB device that accepts power over USB using the mini-A-to-mini-B cable (supplied with the calculator), the batteries are subjected to a heavy drain.  Because the batteries are not monitored in this mode, if the batteries become weak, the handheld malfunctions.  Specifically, the calculator no longer responds to keystrokes and most notably, the LCD goes haywire, displaying a fast-moving pattern of horizontal and vertical lines.  I've read a voltage of as low as 3.24 volts from the 4 AAA batteries on my DMM while a USB device is connected.  No hardware damage actually occurs, only the AAA batteries get drained.  The handheld seems to eventually regain its sanity and reboot normally.  The LCD appears to be that of the STN type.

The question I'm trying to ask is how this fast-moving pattern of lines is generated on the display and why this occurs instead of normal operation.  In other words, why does the LCD do this with insufficient power and an active heavy load?

Edit: The display is a grayscale 320x240 dot-matrix LCD.  When it starts to act up, slight disruptions appear first: horizontal lines appear on top of the normal content and the content may shift slightly or shrink vertically by up to 12% as more and more lines flash on the screen.  Eventually, the content is lost and the screen is dominated by randomly flashing horizontal lines.  At this point, the background is simply a series of squiggly vertical lines, which can be hard to see behind all of the horizontal lines. Vertical lines occasionally flash on the screen momentarily in place of horizontal lines.

If the load is removed (by disconnecting the USB cable), one of three things can happen:

If the batteries are OK, the calculator will function normally and accept input.
If the screen was starting to flash horizontal lines, but the normal content was still present beneath these lines, the horizontal lines disappear and normal content will be restored but the calculator is frozen and does not accept input.  The display will malfunction again when the cable is reconnected and the batteries are placed under load again.
If the normal content was lost, the horizontal lines will disappear, but all that is left is either squiggly vertical lines or a blank screen.  The calculator is actually powered on, even if the screen is totally blank.  If the cable is reconnected, either the horizontal lines reappear, or the calculator shuts down altogether, momentarily flashing a single horizontal line on the screen.


texts: Why do LEDs require a constant current source and not a constant voltage source as power supplies?

texts: Most electronic devices use constant voltage source as power supplies. Why do LEDs require constant current source?


texts: Power Mosfet - Unreliable High Speed Switching Behavior

texts:
Im having a peculiar problem with my circuit, your help is very appreciated :)
My Set-Up
I am using an FQP30N06L N-Channel MOSFET to pulse an array of LEDs at 38 kHz. A micro-controller (Arduino Uno R3) is used to send 38 kHz pulses at a 27% duty-cycle to the gate of the MOSFET (I am using a 100 Ohm resistor from the micro-controller to the gate of the MOSFET and a 470 k-Ohm resistor from the gate of the MOSFET to GND). With each pulse the MOSFET connects the circuit from the LEDs to ground thus allowing the current to make a complete proper path.
To power the LEDs I am using an LM317 voltage regulator set-up as a constant current supply with an out-put of 100 mA per string of 7 LEDs (300 mA total for 3 strings of 7 LEDs/string) Later on I plan to upgrade my circuit to have a total of 3 strings of 7 LEDs per string (a total of 21 LEDs). At a 27% duty-cycle the current through one string of 7 LEDs should be approximately 27 mA.
Here is my schematic....

simulate this circuit – Schematic created using CircuitLab
The Problem
The current flowing through the LEDs is not steady. It starts fine then exponentially drops and levels-off. For example I connected my multimeter between one string of 7 LEDs and the MOSFET. The multimeter starts reading around 27 mA and exponentially decreases to 17 mA where it seems to stable off.
Sometimes when I place my hand the circuit (without touching the circuit) the current significantly changes from a few milli-Amps to 10, 20, 30 mA change. When I remove my hand it returns to normal.
Diagnosis
I think the problem lies with the MOSFET. I checked the output of the LM317 and that remains stable at 100 mA. Do you happen to know why the circuit is performing this way and how to remedy it?
This is how I connected the multimeter to verify the LM317's output....

simulate this circuit
Thanks!
Pictures
Picture 1
The small green module is the power supply. The TO-220 next to the Arduino with the two terminals and the diode is not used in the circuit. It is disconnected.

Picture 2
The TO-220 on the upper left of the board is the N-Channel MOSFET FQP30N06L used to pulse the LEDs at 38 kHz. The TO-220 on the upper right of the board is the LM317 voltage regulator.
The white wire connected from the Arduino is connected to the gate of the MOSFET. It is pulsed at 38 kHz.
You may also notice the CAT5e cable (ethernet cable) on the upper right. I will be using it to connect a second string of 7 LEDs. As of right now the wires of the ethernet cable are only soldered on but not connected to any circuit.

Picture 3
The larger square of aluminum foil covers the infrared LEDs. The foil is completely covered with clear tape. I use it to prevent the infrared receiver from receiving unwanted signals from with-in the the circuit housing.
The smaller square of aluminum foil covers the rear of the infrared receiver and is also completely covered with clear tape.
The three wires (red, black, blue) are for the infrared receiver. They are completely disconnected from the circuit during testing.

Picture 4
On the left is the infrared receiver. On the right is the string of 7 infrared LEDs

Resources
LED datasheet: http://www.mouser.com/ds/2/311/SFH%204545,%20Lead%20%28Pb%29%20Free%20Product%20-%20RoHS%20Compliant-318958.pdf
Voltage Regulator datasheet: http://www.mouser.com/ds/2/149/LM317-64104.pdf
MOSFET datasheet: http://www.mouser.com/ds/2/149/FQP30N06L-244344.pdf
BJT Transistor datasheet: http://www.mouser.com/ds/2/149/2N3904-82270.pdf


texts:
Hello! I've built a small adjustable PSU with a buck converter (XL4015 module) and a cheap 10A digital voltmeter and ammeter. It worked fine for a few minutes but after that the voltmeter started fluctuating between the real voltage and something like half of that, most of the time showing the wrong value.

I've wired it following a schematic on the internet, but powered the voltmeter from the input of the buck converter (where as in the schematic the red -meter power- and yellow -Vsense- wire where connected) because the output will go as low as 1.5V, not being able to power the meter. I've tested the meter separately and confirmed that the problem is related to it. I do have a spare one, but I don't want to do the same thing with it. Is the wiring correct? Is there any chance I could fix the meter?

(edit:) Sorry for the lack of details, it was my first post.
Links:

10A Voltmeter Ammeter
Buck Converter

The shunt is connected to the thick black and red wires. And I've let the thin black disconnected because It's common with the thick one.


texts: Arduino +squidbee GSM shield + ethernet shield

texts:
I am triying to make a webserver of the ethernet shield to send SMS messages via the squidbee GSM shield
Apparently i can't connect both the GSM shield and Ethernet Shield to the Arduino...
Is this possible? Is there any sort of pin incompatilibity i have to reroute ?
edit:
GSM shield: link
ArduinoEthernetShield: link


texts: Current carrying cable/busbar cooling ways in an aircraft

texts: For an aircraft has an altitude 35000 feet, what'd it have to cool its cables/copper busbars up? High altitude means lower air density and it means lower oxygen, convection doesn't make sense and if I put aside a fan system, what else the ways would be to cool them up?


texts: Eagle: LD1117 from Sparkfun library has wrong pinout?

texts:
I did insert in schematic the LD1117 V3.3, from Sparkun library. I need to convert 5V to 3v3.

Device selected is V_REG_LD1117VXX, package 78XXL.

I want use it for LM1117v33 (or LD1117V33). This is the datasheet:

https://www.sparkfun.com/datasheets/Components/LD1117V33.pdf

When I did switch to board, seems to me that PINOUT is inverted (from Left to Right I red IN/GND , GND/3.3V and OUT/5V) and also the names on it are wrong.

I attach an imagine (small and larger). Where am I wrong? Thank you very much.


texts: Gate drive transformer for lower frequency (25 kHz)

texts:
I am doing this half bridge to generate High voltage from 300VDC.(Around >10000Volts for a corona discharge tube to produce ozone)

I have gone through many application notes for making one GDT for my purpose. I am planning to do this in 25 kHz. But most deign pages are dealing this somewhere above 50 kHz.
So primarily I am looking for design formulas for inductance in this frequency. At above 50 kHz, the suggested inductance is 2 mH. So obviously I have to use more. That means more turns and more leakage. Torroid or E core? So what would be the ideal method to proceed?
Thanks for reading.
NB. My purpose is to make a High voltage corona discharge Tube for ozone generation. example picture here. Any suggestions which can help me is greatly appreciated.


texts: The connector on the left is a standard BNC, but could someone please tell me what the connector on the right is?