texts:
I am trying to send data from Arduino mega (message "ping") to  Arduino nano, then send back (message pong) to the mega board, I am not receiving "pong" back to the mega board, why is that? I have used uart tx complete interrupt to switch rs485 DE and RE pins as shown here in both Arduino boards
mega code
//Atmega2560
#define SerialTxControl 52 // DE RE
#define RS485Transmit HIGH
#define RS485Receive LOW
char buffer [100];
byte state = 0;
void setup (void) {
    UCSR1B |= (1<<TXCIE1);     // TX Complete Interrupt Enable serial 1
    Serial.begin (9600); // set the serial port to 9600baud speed

    Serial1.begin (9600); // set the serial port to 9600baud speed
    pinMode (SerialTxControl, OUTPUT);
    digitalWrite (SerialTxControl, RS485Transmit); // put the device into transmitter mode
}

ISR (USART_TX_vect)
{
   digitalWrite(SerialTxControl, RS485Receive);
}
void loop (void) {

//transmit rs485
digitalWrite (SerialTxControl, RS485Transmit);
Serial1.print ("ping"); // send text rs485

//receive rs485
int i = 0;
if (Serial1.available ()) {// if any data came to the port
    delay (5); // wait a bit for the entire data packet to be accepted by the port
    while (Serial1.available ()) {
        buffer [i ++] = Serial1.read (); // read data and write it to the buffer
    }
}
if (i> 0) {// if there is something in the buffer
    buffer [i ++] = '\ 0'; // convert the buffer contents to a string by adding a null character
        if (strcmp (buffer, "pong")) {// if the accepted string is equal to the ping text
        digitalWrite (13, state); // blink LED
        state =! state;
        Serial.println("pong"); // print serial monitor
        }
}
}

nano code
//Nano
#define SerialTxControl 3 // DE RE
#define RS485Transmit HIGH
#define RS485Receive LOW

char buffer [100];
byte state = 0;

void setup (void) {
    UCSR0B |= (1<<TXCIE0);     // TX Complete Interrupt Enable serial 0
    Serial.begin (9600);
    pinMode (13, OUTPUT);
    pinMode (SerialTxControl, OUTPUT);
    digitalWrite (SerialTxControl, RS485Receive); // put the device into receiver mode
}

ISR (USART_TX_vect)
{
    digitalWrite(SerialTxControl, RS485Receive);
}

void loop (void) {

//receive rs485
int i = 0;
if (Serial.available ()) {// if any data came to the port
    delay (5); // wait a bit for the entire data packet to be accepted by the port
    while (Serial.available ()) {
        buffer [i ++] = Serial.read (); // read data and write it to the buffer
    }
}
if (i> 0) {// if there is something in the buffer
    buffer [i ++] = '\ 0'; // convert the buffer contents to a string by adding a null character
    if (strcmp (buffer, "ping")) {// if the accepted string is equal to the ping text
        digitalWrite (13, state); // blink LED
        state =! state;
        digitalWrite (SerialTxControl, RS485Transmit);
        Serial.print ("pong");    //transmit rs485

    }
}
}


texts:
I have plant,
$$P(s) = \frac{1-s/5}{(s^2 + s/4 +1/4)}$$
I am taking a mixed sensitivity approach for that I have chosen \$V\$,\$W_1\$ and \$W_2\$ as follows:
For bandwidth, \$\omega\$ =1 so I chose M as,
\$M = s^2+ s.\sqrt(2)+1\$
\$D = 1/s^2\$
So, \$V = \frac{s^2+ s.\sqrt(2)+1}{1/s^2}\$
and the remaining values, \$W_1=1\$  and \$W_2=0.1\$
My code is as follows:
s=tf('s');
P = (1-(s/5))/(s^2+s/4+1/4);
M=s^2+sqrt(2)*s+1;
G=[M/s^2 P;
0 0.1 ;
-M/s^2 -P];
G=minreal(ss(G));
nu=1; % u has nu=1 entries
ny=1; % y has ny=1 entries
C=hinfsyn(G,ny,nu); % default rel. tolerance 0.01
K=tf(C) % so

L=P*K;
T=L/(1+L);
% bandwidth(T)  % 0.9963
S=1-T;
figure(1)
bode(T,K*S,P*S,S);
legend('T','KS','PS','S');
grid
figure(2)
step(T,K*S,P*S)
legend('T','KS','PS');
grid

I am not getting and controller \$K\$ for this code. I would really appreciate if you give some suggestion about choosing \$M, W_1, W_2\$ or anything that might help me get a controller \$K\$


texts: Sourcing Transformer with Specific Turns Ratio

texts:
I am looking at a building an electronics project that calls for a transformer with a specific turns ratio '1:4:50', and am trying to source a component. I am working on the project from this tutorial: https://circuitdigest.com/electronic-circuits/diy-stun-gun-circuit
When I search power transformers on Mouser or Digi-Key there is no option in the parametric search for turns ratio. The only category that does have a turns ratio option is 'Current Sense Transformers', but after reading up on these devices (used for metering AC current draw) they seem incorrect for my application. The purpose of this project is to use the transformer in "flyback mode", building up a large DC charge from a small AC signal at the input. I am assuming for this application I need a power transformer.
This part has been weirdly impossible to source, which seems strange as the application isn't that esoteric. Can anyone give advice on how I would go about searching for correct component?


texts:
I am working with matlab in college and I need to generate sine wave whcih represents signal going through a wire.

But its not clear to me what t equals to and how can I multiply \$y\$ by \$t\$

this is the formula

$$y(t) = 1.2\sin(35.000\pi t+2.15\text{ rads})$$

This is my Matlab code

time = 1:1.0:10;
radstodegrees = 2.15*180/pi
y = 1.2*sin(35.000*pi*time*radstodegrees);
y = y*time
plot(y)

It gives me error when I want to multiply y*time

Anyone know where to go from here?


texts: I hate reading datasheets or user manuals on the screen, and printing such documents tends to waste a lot of paper/ink. Has anyone tried to use an eBook Reader for this purpose? Are they good enough to display the sometimes complex diagrams found on datasheets?


texts: How can I remove this (With picture...wire clip?)?

texts:
I'm not very familiar with a lot of electronics but I was told that this is a wire clip (white 'clip' holding the black and brown wire). I want to test the black and brown wires and removing the clip seems to be the only way of doing it. I'm nervous about just pulling out the two wires... is there an appropriate way of doing it? And I'm very sorry if this is not called a wire clip.

Thanks for your help


texts: How to read CPU temperature into Arduino

texts: I'm not sure about this and if it is possible. I need to read CPU temperature (normal computer) into an Arduino. This could be possinble (at least I think) by connect some kind of sensor that can be placed between heatsink and cpu, where the thermal paste is placed. Or, second option is to read values from the system somehow, or from the motherboard. I hope I'm not talking about stupid things. I need some advices about this.


texts:
I am feeding square wave (0-5V) at 1kHz through a AD713JNZ op amp which I have wired up as a unity gain buffer, but I'm getting 5V DC on the output:

What am I doing wrong?


texts:
I have breadboarded a simple circuit using a 2N6395 thyristor to drive a resistive load. In simulation all works well, and even the physical implementation works sometimes.

simulate this circuit – Schematic created using CircuitLab

The emitter of the transistor should be approximately 800mV and the SCR gate should be approximately 700mV by design with an emitter current of 10mA. The transistor is thus in saturation and all is well. A SPICE simulation reveals all this to be as expected.

After physically building this circuit I found that nothing happened when triggered despite the expected voltages/currents being present with a nominal 10mA current draw. After tinkering with the circuit a bit I found that if I applied a larger pulse voltage to the gate of the SCR it would trigger and latch.

So, what I found seemed to require a component redesign, right? Actually, after the circuit initially conducts in the manner described above it will trigger thereafter by the transistor when an appropriate pulse is applied to the base. In summary:

Circuit is 'cold', active-low base pulse has no effect
Provide higher voltage/high current pulse to thyristor gate (load/thyristor heat up)
Remove power from circuit, reapply power - circuit is off (no load conduction) as expected
Apply active-low base pulse, thyristor triggers as expected

Trigger and resetting the circuit will continue to work as expected from this point forth until I allow the circuitry to cool down before trying again.

I thought it may have something to do with the given gate current not allowing sufficient charge to be stored quickly enough at the thyristor gate, so I tried leaving the circuit on for a sufficient amount of time for the charge to build; this had no effect.

Looking at the gate current/pulse duration curve given in the datasheet, 10mA should be sufficient. This is especially true considering the pulse is done physically and not controlled by logic.


texts:
I am trying to replace a fried lamp in my very old amplifier (a Dual CV 1280 Integrated). As I essentially only use the mode that is indicated by the fried lamp, I thought I could just switch it with a working one. However I have no idea how to get it out. Can anyone enlighten me? I don't even know how they are called, hence no idea what to google. It only says Osram 24/1.2.

Photos from front and back (the grey thingies):


texts: 64-bit Data Output On DHT21(AM2301) Sensor

texts:
I am trying to read the sensor data from the DHT21(AM2301) temperature and humidity sensor. According to the spec, the process of reading data is below:

MCU sends start signal - Sensor sends acknowledge signal - Sensor sends 40-bit data.

I am observing the data line through a scope. Start signals are okay, but sensor sends 64-bit data. Is there any possibility that causes the sensor to send 64-bit data instead of 40-bit data? If I do the calculations according to the first 40-bit, I get parity error. Here is the example output data:

0xFE - 0x80 - 0xFE - 0xDA - 0x59 - 0xFF - 0xFF - 0xFF

I also attached the scope view.


texts: Shunt capacitor as discontinuity in transmission line

texts:
As in the following circuit

simulate this circuit – Schematic created using CircuitLab

suppose that an infinite transmission line (with characteristic impedance \$ Z_0 \$) ends upon a capacitor \$ C \$, then another infinite transmission line (with the same characteristic impedance \$ Z_0 \$) begins.

Suppose that a step signal of amplitude \$ V^+ \$ is going from left to right: it will charge the capacitor. The charge process can be described by the following equation

$$V_C (t) = V^+(1 - \exp{(-t/\tau_C)})$$

where \$ \tau_C = CZ_0 / 2 \$. So there is a delay before \$ V_C(t) \$ can reach the value \$ V^+ \$: this expression is exactly the same as an RC circuit.

These are all the informations I have. My considerations are the following:

The key fact in the charge of a capacitor in a normal RC circuit is the equation

$$V_g - V_C (t) = R I(t)$$

But here it can't be written, because there's not a resistance! The only constraint imposed by the transmission line is that

$$\frac{V^+}{I^+} = Z_0$$

The right line can be represented by an impedance \$ Z_0 \$ in parallel with \$ C \$ (considering that it generates no reflections): this could be the load of the left line. But I don't know how to represent the left line with the incoming \$ V^+ \$.

So, how is \$ V_C (t) = V^+(1 - \exp{(-t/\tau_c)}) \$ obtained? And why is \$ \tau_c = CZ_0 / 2 \$ and not \$ \tau_c = CZ_0 \$?

The circuit should be

simulate this circuit

but I don't know why and if a transmission line (the left one) can be represented by a Thèvenin equivalent circuit.


texts: Class AB power amp DC bias at the emitter

texts:
I tried using KVL to prove that indeed the DC bias at the emitter of both Q1 and Q2 is Vcc/2.
The following assumptions I made are:
R1=R2
D1,D2 and the Base-Emitter diodes of both Q1 and Q2 are exactly match.

As you can see in my solution I end up with a contradiction. What am I missing?

Thank y'all!


texts: Converting 110v at 8.5 amps to 208 three phase amperage

texts: I have some equipment that uses 8.5 amps and 1050 watts on a 110v. Any idea what the amperage would be on 208 three phase?


texts: LTspice a voltage source as a function of time

texts:
I saw the ability to control R by time in someone's drawing, tried it, and it worked fine. Then, I thought that I could use that "time" keyword also to control the voltage of a DC source. However it didn't work. It gives an error:

  Error on line 2 : vcc n001 0 time*2
       Unknown parameter "time*2"
  Vcc: Missing value, assumed 0V @ DC
  .OP point found by inspection.

So, is there an easy way, as easy as it is with the resistor value, to do what I want?


texts:
I want to use a STM32F072 for a new product and saw table 35@page 65 in the datasheet.

This table lists the current consumption of several peripherals of the MCU.

I'm asking why relative simple modules, like USARTs or timers have such an high current consumption, compared to USB? Can anyone explain this for me?


texts:
I'm designing a telemetry station for air quality measurement. Right now, I'm trying to estimate the power consumptions of different hardware configurations, but I'm struggling with the GSM/GPRS module. Any idea on how to estimate it? I will be sending small amounts of data (~300 bytes) periodically (every second), but I can send bigger packets of data with less frequency if that lower the power consumption, not sure.

Any idea?


texts:
I have seen this multiple times in schematics with LEDs. Why is the symbol for the cathode a 'K'? Is there any specific reason for this?

Example A, example B


texts: Why is three-phase offset by 120 degrees?

texts: For three phase electricity the wave is offset by 120 degrees(2\$\pi/3\$ Rad). Why aren't the phases closer together? Is it because it will affect the frequency of the phases? How was this 120 degrees chosen?


texts: How is a connector with only edge contacts as in MagSafe practically possible?

texts:
I'm rather puzzled with MagSafe connector - the close-up photos of the part which is on the device show that there're no holes, only round curved plates and the contact pins on the opposite connector part are just placed against those plates.

In usual connectors there's usually a rather long thin pin that is inserted into a variation of rather long thin hole and this provides huge contact area and also the act of insertion cleans the surfaces and this addresses possible dirt on contacts.

Looks like there's no "insertion" in MagSafe - the connector parts are just placed against each other (and held together by magnets) and the pins are just placed against those curvy plates and I suspect the area through which current actually flows is rather small.

I wonder how would such connector address dirt on contacts and also pass rather high power (up to 85 watts) without overheating, burning and sparking?


texts: Minimum feedback resistor Rf for given opamp ex: opa2134

texts:
i have a problem that needs solving;
What is the minimum feedback resistor for modern opamps like opa2134 ?
can it be 100 ohm?
Im asking because in lt1028 datasheet its says it cant be <100ohm because it causes distortions ,very heavy by the way.
How can this value be found for any given opamp?
Does it depend on output current ?
The configuration of the setup is DAC I/V with multiple feedback low pass filter with High Voltage output -6VRMS
the stage procceding it is a Voltage follower buffer


texts: Single-stage amplifier biased by a simple current mirror device

texts:
the goal is to  the Derive an expression for the voltage gain for the circuit below.
the course notes I have is pretty vague, and I have no idea how they came up with the answer. is there anyone who can explain to how to derive the voltage gain expression.
Thanks


texts: Isn't it overkill to use a regulated power supply for a nixie tube?

texts:
I've seen any number of nixie tube designs on the web that use regulated 170V supplies for the nixie tube anode.

Wouldn't it be possible to use unregulated, half-wave rectified 170V peak power for this? Yes, the illumination wouldn't be continuous, it would in fact flicker at 60Hz, but this is fast enough that it shouldn't matter to the human eye. The brightness would vary with line voltage, but since that doesn't usually vary more than a couple of percent, this effect also should go unnoticed to the casual observer.

The up-side of this would be that you could dispense with the relatively costly regulated supply, and use a simple 1:1 isolation transformer and a single rectifier diode to get the anode supply, since sqrt(2) * 120 gives very close to 170.

In fact, if you used SCR's to pull the cathodes to ground, you could do away with the rectifier, because when the AC reverses direction, the SCR will cut off just like a diode. A single current limiting resistor should suffice if placed on the anode side of the tube.

Would it work? If not, why not?


texts:
I was looking at this component, which has strange interface pins.
I have never seen anything like it.  I wonder how am I supposed to connect to them. What connectors can I use and what's special about them? Is it good for RF stuff for example? What are they called? I could research more if I knew what these pins are called.

Edit: Answered in the comments: They are turret pins where you wrap a wire and solder to.


texts: How to calculate series resistor to provide a certain voltage to a pin?

texts:
I (theoretical physicist, all the basic theory, no further electrical engineering background) am just diving into Arduino and I have a very basic question:

I am playing with a Zilog ePIR motion detector (https://www.sparkfun.com/products/9587) in hardware mode. I would like to use a fixed resistor to supply a voltage of, say 0.2V to Pin 3 (DLY), to set a delay for the motion detection switch-off (the whole thing runs on 3.3V).
From Kirchhoff's voltage law I would think that I need the internal resistance of the module to calculate a ratio with the series resistor. I am getting R = R_Module*(3.3V-0.2V)/0.2V.
However: I don't know any internal resistance, nor can I measure any between GND and DLY.
How do I calculate the needed resistor? Am I thinking totally wrong?

I am using the circuit from http://macherzin.net/article17-Arduino-Sensoren-Infrarot-ePIR
Bonus question: How did the author know that he needs an 80 Ohm resistor if he connects the module to 5V?


texts: Reducing voltage for increased current through wire

texts: I am wondering, if I reduce the voltage going through a specific sized wire, can I therefore increase the current? I am creating a series-parallel battery bank and it will output 7.4 volts at 75 amp however all cable rated for 75+ amp is far too thick for the product. 10awg is the biggest I can really go. Someone please give me your knowledge!


texts: What would be the Transfer Function of this Block Diagram?

texts:
I have a block diagram that I am trying to get the transfer function for but can't seem to figure it out, I am sure that I am making it more difficult than it needs to be but still can't get it. The diagram is below and any help would be great!

Edit
So far I have got myself to this point but I am unsure if it is correct:
$$\frac{\theta }{M_p}=\frac{G(s)(I(s)-K_t)}{1+D(s)G(s)(I(s)+K_t)}$$
I feel I should try solving the inner loop and then the outer but I can't work out how to put the inner loop in one function. Any ideas?

EDIT INNER LOOP SIMPLIFICATION


texts: What is function of this complicated circuit?

texts:
Here is my task:

a) Explain principle of working of circuit below. Draw waveforms of voltage
at points A, B, C, D and Q, as well as capacitors voltage waveforms.

b) What is minimum time constant of charging of C3 (ie value of resistance R6) so that voltage waveform of point Q are rectangular pulses

It is known: R1, R2, R3 (R2=R3), R4, R5, R6, C1=C2=C3, 5R1>>R2 and R1>>R3. Threshold voltage equals VDD/2.

Any suggestion?
I did nothing because I have no idea how to start :( I'm beginner in Digital electronics. In analog electronics and in circuit theory, there are well known methods for solving circuits, but what to do here? I'm really stuck :(

EDIT: This is not homework question. I don't have final result. This was on my exam. I didn't solve it on exam and I'm trying to figure out what is solution to this problem. Every suggestion is welcome, I want to pass exam next time :)


texts: How to calculate maximum amount of bulbs I can connect in parallel to match design specification of 1.5 A?

texts:
I'm designing a sensor triggered circuit that involves 220 V passing on a PCB, so I designed the board thickness to withstand a maximum of 1.5 A. The main load on the circuit would be a series of LED bulbs, each bulb draws 4 W (says on package). I'm confused on calculating the maximum bulbs I can attach to the load, I'm guessing its one of those scenarios:

  Max load = 1.5A / current per bulb = 1.5 / (4/220) = 82 bulbs

  Or does the manufacturer calculate power drawn from voltage regulator (5 V) and thus:

    Max Load = 1.5A / Current per Bulb = 1.5 / (4/5) = 1.8 bulb = 1 bulb.


texts:
A rectifier I salvaged from a broken oasta machine uses am odd plastic barrel connector. On the rectifier end, it looks like a banana pin housed in a translucent white plastic barrel. On the cable end, it looks like a tube. The diameters of the terminals are smaller than a standard banana connector.  Both terminals snap together on two ridges.

What is the name of this connector?


texts: Increase working hours for an external speaker

texts:
I have an external speaker which uses one 18650 cell (3.7V). I would like to increase the working hours by adding one more cell of the same type.
I have two questions:

Should I add the second cell in parallel with the other cell?
The speaker has a charging LED which powers off when fully charged. Will this still detect full charge if I increase number of cells?

Thanks for help!


texts: Is there a way to use off sheet connectors in a hierarchical design within Altium?

texts:
I'm running into a situation where I am running out of space on each sheet I have for a design. I can't increase the sheet size because when I print off the design, the contents would be too small.

I have a top level sheet with multiple off sheet connectors. However, one of those sheets (under the top level sheet), I need to add more components and there just isnt enough space without it getting messy. So I'd like to use off sheet connectors to expand horizontally rather than vertically, however, I am running into an error when I compile which says that there are two top level sheets.

Is there a way to use off sheet connectors in a hierarchical design or a way to tell Altium or a setting or option that says I can do both vertical and horizontal connectivity ?


texts:
I encounter this circuit:

I wonder what the purpose of this circuit?

I built an simulation for this circuit,
and from what I can see from the simulation:

its just takes sine wave and convert it the pulses of 4v.

there is a lot of other circuits that does the same, does this circuit does anything different?

where can I see usage of such circuit?

Thanks!


texts:
As a foreword I would like to say that I am asking this question as part of a computer science course assignment, and any responses here might be referenced in my report. I am ideally looking for hints and tips to get me on the right track rather than straight up solutions.

What I am trying to get my head around is a 2 bit magnitude comparator circuit that takes in 2 sets of inputs. For example set A would contain a0 and a1, and set B would contain b0 and b1.
The only output I am interested in is A > B which means the sum of all inputs in set A is bigger than set B so a0 = 1 , a1 = 1, b0 = 1, b1 = 0 would overall output a 0 and so on.

I understand how a 1 bit comparator works :

this is the most basic circuit I came up with that takes in 2 inputs and gives out an output if A > B.

However, I have been stuck for several hours trying to increase the number of inputs. My initial plan was to somehow reuse the 1 bit comparator and reuse it 3 times but every time I end up with something that ends up with an overly complicated version of the initial 1 bit circuit where the 3 inputs actually only give out 1 output and so in the end you are going in a circle and comparing 2 numbers rather than 4.

Any advice an tips on this would be very appreciated.


texts: Switching regulator enable pin low, but output isn't fully off. Why?

texts:
I'm working on a battery-powered application using two Texas Instruments switching regulators and a Linear Technology pushbutton power controller:

I have confirmed that when I push the button and turn the regulators on, they work as expected, and I can measure the 3.3V and 5V with a multimeter. They are also successfully powering the load, which is a microcontroller on the 3.3V rail and some LEDs on the 5V rail.

However, I've found that when I turn the power button off, I'm still seeing voltage on the output of the switching regulators. ~3.9V on the 5V rail and ~0.9V on the 3.3V rail. I know there might be some leakage through the components from the batteries to the rails, but this seems pretty high to me. It's high enough that some of the LEDs on the 5V rail are on, even after I hold down the power button to turn off the LT chip and PWR_EN drops to 0V.

Is it normal to see this much voltage drop from the battery to the switching regulator outputs, even when the EN pin is being pulled low? I've tried grounding the EN pin directly to make sure the LT chip wasn't stuck in a weird state.

What am I missing here? Why aren't my switching regulators fully shutting off? Isn't driving EN/!SHDN low enough?


texts: Switching Mode Power Supply Fluctuating Output

texts:
I designed a switching mode power supply using LNK-562, I share the circuit schematic below.

Note that NTC, fuse, and the input filter inductor is replaced with shorts in the real circuits.

I am testing the circuit in varying conditions and I noticed that the circuit fails  to keep the output voltage the same for every condition. For example, if I use 100 Ohms as the load, the output is 3V.  For the case of an output load of 220 Ohms, I get 5V (which is the intended voltage). Eventually, the voltage converges to 8V with no load condition. The circuit should be able to handle an output power of 1.5W. So, I understand that the circuit will fail to keep the voltage at 5V in the no load case, however, a small variation of changing the resistor to 220 to 100 should not change the output figures that much. Given the power requirement, I should be able to connect a 20 Ohm resistor.

I tested every node of the circuit. Bias circuit seems to be working fine. The LNK562 operates by keeping the voltage at TP1 constant. Namely, it should be 1.69V for all cases of loads and this is verified by an oscilloscope measurement.

Note that the fluctuations in the output voltage are kept at minimum. For the case of 5V output, the ripple is measured to be 12mV which is a very good figure considering that this is a student project and by no means it is designed for commercial market.

What do you suggest I do? Which nodes I should check and what kind of waveform might be an indication of a problem? How do you define the problem I have?

The circuit is now being tested at 110V RMS. Also, I am a senior EEE student. Also note that the circuit is printed and verified by the professor.


texts: Measuring the input impedance of an oscilloscope

texts:
I am measuring the voltage drop on a 1MΩ resistor with an oscilloscope, and as I understand to get accurate readings I should compensate the internal impedance of my measurement device for such a high value resistor.

It's a Tektronix TDS2024C oscilloscope, from the manual I know that it has a 1MΩ internal impedance and I'm using a 10x attenuation probe, which should have a 9MΩ resistance. According to everything I read that should add to a 10MΩ internal impedance, even though I'm not quite sure why and would like to know it a little more accurately.

So, two questions:

Are there any simple methods to measure the input impedance of an oscilloscope accurately instead of taking the word of the manufacturer?
How does the input impedance add to 10MΩ anyways, if the internal resistance isn't connected in series? Shouldn't it form a voltage divider for 0.91MΩ? Schematic below:


texts: Why do we use 32.768 kHz crystals in most circuits?

texts:
Why do we use 32.768 kHz crystals in most circuits, for example in RTC circuits? What will happen if I use a 35 or 25 kHz crystal?

I assume because the IC internal Xin, Xout pin circuitry should be in CMOS/TTL/NMOS technology. Is it that true?


texts: What are the alternatives of the transistor 2sc9013?

texts: I will use a 2sc9013 transistor to design a Li-Po battery charging circuit. But, this transistor is not available on my design software. What can I use instead of this transistor?


texts: Solving for voltage but getting opposite sign than answer

texts:
So I'm trying to solve a bunch of exercises but I always end up with the opposite sign for the voltage than the correct answer.

The question is to find the voltages of the nodes.

I'm trying to solve it using KCL for each node like this.

\$v_1\$ is the leftmost node above \$R1\$.
\$v_2\$ is the middle node above \$R2\$.
\$v_3\$ is the rightmost node above \$R3\$.

Equation 1: KCL for \$v_1\$
\$\frac{v_1}{5\Omega} + \frac{v_1 - v_2}{4\Omega} - 3.5A = 0 \Rightarrow v_1 = \frac{70}{9} V + \frac{5}{9} v_2\$

Equation 2: KCL for \$v_2\$
\$3.5A + \frac{v_2 - v_1}{4\Omega} + \frac{v_2}{2.5\Omega} + \frac{v_2 - v_3}{5\Omega} = 0 \Rightarrow 3.5A + \frac{17}{20\Omega} v_2 - \frac{1}{4\Omega} v_1 - \frac{1}{5\Omega} v_3 = 0\$

Equation 3: KCL for \$v_3\$
\$2A + \frac{v_3}{10\Omega} + \frac{v_3 - v_2}{5\Omega} = 0 \Rightarrow - \frac{20}{3} V + \frac{2}{3} v_2 = v_3\$

Solving for \$v_2\$ by plugging in equation 1 and 3 into equation 2 like this
\$3.5A + \frac{17}{20\Omega} v_2 - \frac{1}{4\Omega} (\frac{70}{9} V + \frac{5}{9} v_2) - \frac{1}{5\Omega} (- \frac{20}{3} V + \frac{2}{3} v_2) = 0 \Rightarrow v_2 = -5V\$

The answer according to the circuit simulator is \$5V\$. The book confirms that \$5V\$ is the correct answer for \$v_2\$.

What am I doing wrong?


texts: How to connect switches to power transformer?

texts:
I'd like to use two rocker switches, each is single pole and including a light bulb on the inside (230VAC) to control the powering the system.

I'd like to connect both of them to the transformer with single primary winding(230VAC) and double secondary windings (each rated as 26V), but here's the trick: The RED rocker switch is the "head" of the circuit: if the red one is turned off, then nothing should be working (neither +26V neither -26V line). But, if I turn on the RED switch, the +26V line must be turned on, while I have an option to turn on the -26V line with the GREEN switch or not.
Only turning on GREEN switch while RED is turned off should result into both circuits being turned off.

Here's a chart I've written, how should schematics work.

RED | GREEN | +26V | -26V
 0  |   0   |   0  |   0
 1  |   0   |   1  |   0
 0  |   1   |   0  |   0
 1  |   1   |   1  |   1

And here's the schematics.


texts: Resistance measurement using high side current sense amplifier

texts:
I want to measure very small resistances (0.5 to 1 Ohm) using a high side current sense amplifier. The device I have in mind is MAX9611. The typical application circuit from datasheet is like:

My idea is to replace the Rsense with the unknown resistor which should be measured. Then, I would connect the Rsense to a precision 1A current source. Is this idea going to work? I do not know how the current source would work, so I am not sure if it shows me the voltage it is using to force the 1A through that Rsense resistor or not (I will propably use a bench current source) to simply use the R=V/I formula.

One more thing is, I do not know if I would need the LOAD in the current path or not (effectively shorting the current source to ground through my small Rsense unknown resitor).

I have really no idea if this idea is going to work or not. I would appriciate if you can shed some light over this idea!


texts: Resistor ladder with Same resistor value and different resistor value

texts:
Im trying to connect 8 buttons to Arduino Analog input. I found its good to use input shift registers. But with my very basic knowledge I end up with resistor ladder. But Im a bit confused with various sketches when I googled it. Some having same resistor values. Some using different values. In my case I dont need multiple buttons at a time. Only one button at a time.

Im thinking about using this sketch below.

But I really getting confused by the different values resistor sketch in another result. So which is the best suits in my case. Also please suggest a good value for resistor and pull down resistor.

This is another one I found to depend.

But there a confusion why there are two extra resistors. I imagine the 100k is pull-down. But what about the 2k.

In your suggestion which is best or any better sketch anyone can suggest?


texts: Positive voltage with an inverting buck boost

texts:
in the inverting buck boost the output is Vout = -Vin(d/(1-d)) , where d is the duty cycle of the switch.
The output voltage is alsways negative. In my case the input voltage is provided by a battery.
Is it possible to attach a load that requires a positive voltage supply simply by inverting its terminals?
I'm asking this question because I can't understand why on the internet I found inverting and not-inverting buck boost converter.

Thanks


texts: What do i need to communicate my sensors with LoRaWAN, simply?

texts:
I'm new at wifi communications, i need to use Lora at my job project. I searched the internet to learn what the long range rf is. So, if i want to communicate with my sensors(on my mcu kits) over long distance(>10 km for example), are these enough?:

mcu host with sensors
lora modules for each node
lora gateway

I read about base station requirements to use lora,does base station mean lora gateway? i have this figure:
http://www.rfwireless-world.com/images/LoRa-network.jpg
So i connect my mcus to lora modules, then it sends data to gateway at lora rf frenquencies. Is this true?


texts: stm32L0 - can I use LSE clock for 1ms tick and use HSI for systick?

texts:
I am using STM32L051, our task has two requirements for clock management:

Need to be running under 16Mhz or higher frequency (thus we use the MSI/HSI for Systick) for fast task processing.
Need a higher precision clock source (50ppm 32khz LSE is ok; and our board has an external 20ppm 32khz crystal) to limit the clock deviation to about 100ms per 30minutes.

How can I configure the clock system to use both the MSI/HSI (for Systick) and external 32khz crystal (for lower clock deviation)?

I have searched the datasheet and google a lot, however didn't find a solution. I am not familiar with MCU development. Please kindly refer me to the datasheet section (several keyword is ok) or cortex-driver API for further research, thanks!


texts: Powering 3.3v-5V LED strip with 18650 batteries

texts:
I have a fun project I want to do. It's really simple: I want to power a long LED strip using a bunch of 18650 batteries. The batteries I use are 4.2v fully charged and about 3.5v when discharged (I don't want to push them further down than this).

The LEDs are WS2812b and they work from 3.3v to 5v easily. I successfully power 10 of them with a single 3.3v signal from my ESP8266 and they're bright enough.

Now, what would be best?

Wiring 2x 18650 in series, making a maximum of 8.4v and a minimum of 7v, then use a buck converter to make it 5v all the time.
A single 18650 battery at 4.2v maximum and 3.5v minimum.

I will make a bunch of these in parallel, so I have more current to run the strip for a longer time. Option #2 would definitely be a better option for me, as it doesn't take that much work.


texts: Is a multimeter with 1,200,000 counts actually a 6½ digit multimeter?

texts:
The Keysight 34465A Digital Multimeter is specified as a 6½ digit multimeter.

However, the meter is actually a 1,200,000 counts meter, since the meter wraps at 1.2, so if measuring a 1.19 kOhm resister, the reading is 1.190,000 kOhm, and if measuring a 1.21 kOhm resistor, the reading will be 01.210,00 kOhm.

Usually the ½ in specification of a multimeter means that it wraps as 2.0 (see EEVblog #26), for example a 3½ digit multimeter has 2000 counts, and can do reading up to 1999, so if measuring a 1.9 kOhm resister, the reading is 1.900 kOhm, and if measuring a 1.2 kOhm resistor, the reading will be 02.10 kOhm.

Based on this, I would think the Keysight 34465A Digital Multimeter should be specified as less than 6½ digits, for example log10(1200000) = 6.08 digit multimeter.

So, is a multimeter with 1,200,000 counts actually a 6½ digit multimeter?


texts:
I've designed my own board using the MPU6000. I am using it in I2C mode. Using both Adafruit's MPU6050 code and the (common) I2C scanner code with Arduino the device is not recognised. I think it has to do with the CS pin. In the datasheet it says (0=SPI mode) in the pin descriptions but I can't see anything about I2C and the typical operating circuit schematic leaves CS floating.
When using the MPU6000 in I2C mode should CS be ground or VCC?
Attached is my circuit. VCC is 3.3V and verified on the physical board.


texts: I need help sing a 555, op-amp integrator, and comparator to generate a voltage controlled PWM signal

texts:
I have LM358p op-amps Datasheet

I'm trying to base my design off this:

retrieved from here.
My control voltage will vary between 0 and 3.5v. I want the output pulses to vary between 2.5 and 0.5ms and at a frequency of about 50Hz. This is to control a servo using Vcontrol.

My clock signal is from a 555 timer in astable mode. The square wave voltage is 0 to 8.4v.

I understand that this diagram is based on the ideal op-amp, so I'll need a resistor on the non-inverting input equal to the inverting input resistor. I'll also need a high value resistor parallel to the capacitor. The output will probably not reach 0v, but that's ok as long as the triangle is at least 2.5ms wide at its widest point.

I only have a single rail power supply, 0 to +12v to power the op-amp. The clock signal also never goes negative. I don't quite understand how the op-amp integrates. Is the non-inverting input the reference line, above which the integral begins to rise and below the integral falls?

What should my input pulses look like and how do I calculate the R and C values for the op-amp?


texts: Grid voltage swell and sag, what happens to harmonics?

texts: I know that when a load draws too much power the voltage of the grid at the fundamental frequency begins to sag. Though my understanding is that loads can't use the power generated by harmonics, so does that mean the grid voltage will only sag at the fundamental frequency and the amplitude of the harmonics won't?


texts: Simulate and compare the responses of a linear and non linear system

texts:
A metalic object is held up in air under an electromagnet. The vertical displacement of the object can be described by the following differential equation $$ m\frac{d^2H}{dt^2} = mg-k\frac{I^2}{H^2} $$ Where m = Mass of the object, g = Acceleration due to gravity, k = a positive constant, H = Distance between the electromagnet and the metallic object ( output signal ), I = Electromagentic current ( Input signal ).
How do I find the equilibrium points and write the dynamics of the system in state space form?
Also how do linearlize the system and compare the responses of linear and non-linear systems in SIMULINK?


texts: automatic submersible pump actuation project

texts:
I have a project for automatic submersible pump actuation using a microcontroller.
I've done for two voltages like 5 V and 12 V and its corresponding relay. Also, in each board there is a transistor circuit for the motor actuation. It's nothing special. At any given time, the pump is getting actuated either by transistor circuit or by relay circuit, but not both at the same time.
Some points to be noted are:

I'm driving the 5 V circuit using a 5 V, 5 A, DC adapter and the 12 V using a 12 V, 5 A, adapter.
Motor current is around 250 mA. Is this circuit OK for the inrush current of the motor? I'd given the max value of i/p caps - is that OK?
Is a reverse protection diode necessary at the power input side here? I'm powering the board using a DC jack and if I use a diode then there's a diode drop I've got to allow for in ADC calculations.
I'm not using external reference voltage so I haven't connected the VREF.
PCB snapshot is also attached. Let me know if you need any information from my side.
Please check the overall circuit and let me know in case if I've to change something.


texts: High Frequency Ferrites for Transformers

texts: There are many Ferrite material grades Available.The optimum frequencies start around 20KHz and extend well into the MHz range.There are also many core sizes to go from watts to Kw .Planar cores are now readily available .Planar transformers are now more normal where 20 years ago they were exotic.WHY don't they make large cores like say E64 in high frequency ferrite grades like 3F45  or      3F5 for say 2 MHz?  Is there some technical reason maybe to do with metallurgy why they don't OR is it some market thing because most people don't do Kw at MHz ?


texts: High Power LED Circuit Design & Constant Current Source Question/Feedback

texts:
I'm trying to design a dimmable LED circuit board. It's controlled by Arduino with its PWM signals. I'm new to electronics so I have some question regarding my design and knowledge on it. I've attached two diagrams I've made to help with the visualization. Vcc is 24 VDC and the 5V is the PWM pin from the Arduino.

The idea is to control the RGB LEDs (1W per channel) using a TIP122 Darlington transistor. From what I know, there is about a 1.4V drop from the base to the emitter in the TIP122 (Vb-Ve = 1.4V). The voltage at the collector and base should be the same (Vc=Vb).  The base voltage is the voltage out of the voltage divider (R1 & R2). If R1 is equal to R2 (R1=R2), then Vb should be half of 5V or 2.5V (Vb = 2.5V). From that, the emitter voltage is 1.1V (Ve = Vb - 1.4V = 1.1V).

The emitter current is the summation of the base current and collector current. However, the base current is super small compared to the collector so we can assume the emitter current is the same as the collector current (Ie = Ic). By changing the value of resistor (R_Q) after the TIP122, we can control the current flowing through the circuit (Ie = Ve/R_Q = 1.1V/R_Q). This is assuming that current gain is not bigger than 1000.

From beginner LED circuits, I’m suppose to put a resistor (R_L) in series with the LED(s) to limit the current flowing through the LED and prevent the LED from being destroyed.  But if the resistor after the TIP122 will limit the current, do I still need the R_L resistor?

As an example, let’s use the circuit in the second diagram. The usable voltage that can power the LED would be the difference between the supply voltage and the voltage at the TIP122 collector (Vcc-Vc = 24V-2.5V = 21.5V). Let’s assume the 3 LED in series each has a forward voltage of 6V (Vf = 6V) and a forward current of 750mA (If = 750 mA). Thus there is 18V of total forward voltage and 3.5V leftover (21.5V – 3*6V = 3.5V). Now normally, we’d put a 4.67 ohm resistor (R_L = 3.5V/750mA = 4.67 ohm) to keep the current flowing through the LEDs 750 mA. But with the TIP122 and R_Q, is the R_L still necessary? If R_L is NOT needed, is it still true even if the leftover voltage is a lot larger? So say 2 LED is in series instead of 3 thus giving a leftover 9.5V instead.

If anything I said is false, please let me know. I’m just explain my thought process in my design and would appreciate any feedbacks on it. Thanks.


texts: Is the 1N5821 Schottky diode made of silicon? Or is it composed of other materials?


texts: Use of 3 phase transformers which are ∆-Y connected and Y-∆ connected

texts:
Different literatures say different things regarding ∆-Y and Y-∆ 3 phase transformer connection...

Some say that ∆-Y is used for step down and Y-∆ is used for step up while others say just the opposite things...

Depending on this step up and step down ability they are used in transmission and distribution of power... So please can anyone explain me what are ∆-Y and Y-∆ actually used for(which for step up and which for step down) along with a mathematical reason...
Thanks in advanced!!


texts: Would an unconnected coaxial cable act as a wifi antenna?

texts:
I am building an underwater drone and I connect to it via wifi when it is at the surface.  The wifi signal often gets blocked by water waves though.  I don't really want to have another penetration of the pressure housing and wondered what would happen if I took 50cm of RG58 coaxial cable, stripped 5cm of shielding from either end, attached one end to the housing close to the wifi transmitter and had the other end poking up out of the water.  The shielding of the housing cable end would be exposed to the water for grounding.

Would there be any useful wifi transmission/receiving signal at the above water cable end?  The connection runs Remote Desktop so I don't need a particularly large bandwidth, just something to make the wifi connection slightly more reliable.


texts: L293D (Motor Driver sheild. ) Overheating issue

texts: I really do have a doubt. Actually I'm making Vplotter and for that I'm using 333nNm 0.31 A Stepper motor NEMA 17. And I'm giving an external supply of 5V and 1 A to motor driver sheild. Will L293D heat.


texts: How to compensate an op-amp at a particular frequency?

texts:
I am trying to design an op-amp but because it is going to be used at a max frequency of 10kHz, I only need to make sure the phase margin is good enough at this frequency. Most of the methods for designing op-amps that I found compensate the op-amp for the worst case scenario which is when it used as a buffer. However, in my case, it will never be used as a buffer. Is there a method I can follow that shows how to design an op-amp that is compensated at a particular frequency ?

Please see an image of the circuit:
https://imgur.com/a/5IwOVge

The maximum frequency the input signal is 10kHz. The high-pass circuit sets the closed-loop gain at 40dB.


texts: Causes for negative port resistance of passive device (or obtaining |S11|>0 from measurements)

texts:
Suppose you have two reciprocal (passive) devices, A and B, both described with S-parameters \$S_a\$ and \$S_b\$. With a VNA, you measure \$S_a\$ and \$S_{\rm tot}\$ (S-parameters of AB, both devices cascaded).
From circuit theory, we can convert both to its T-parameters, \$T_{\rm tot}\$ and \$T_a\$. Now we know that $$T_{\rm tot}=T_a T_b\,.$$
So we can obtain
$$
T_b = T_a^{-1} T_{\rm tot} ,
$$
and convert this to \$S_b\$.
There is just one problem: For my measurements, \$|S_{b,11}| \gt 1\$ or, in other words, the real part of the input port impedance of B (its resistance!) is less than zero.
This is clearly wrong because the devices are passive. How can this happen? Which sanity checks can be invoked to see where things/intermediate results are wrong (maybe which measurement point is off)? Intuitively, under which condition can this happen?

Additional Info: The measured results at 915MHz are:
$$
S_a = \begin{bmatrix}
  -0.0376-i0.2195 &  0.0949-i0.7257 \\
   0.0949-i0.7257 & -0.2423-i0.1649 \\
\end{bmatrix} .
$$
\$S_a\$ is is a signal path on a PCB which includes (passing) RF switches, a discrete delay line and ac coupling caps. Parameters were measured using the method from https://ieeexplore.ieee.org/document/780284 with an Agilent VNA at -30dBm but large amount of averaging. The magnitues (return loss and insertion loss) make sense to me and are on the order of what I expect from simulations.
\$S_b\$ is actually a one-port (just a termination impedance), hence I only care about \$S_{b,11}\$. When I measure \$S_{\rm tot}\$, I can still treat it as two-port, just with \$S_{12}=S_{22}=0\$ and \$S_{21}\$ arbitrary. My measurements for \$S_{\rm tot}\$ are:
$$
S_{\rm tot} =  \begin{bmatrix}
  -0.2285+i0.2936 & 0 \\
   1 & 0 \\
\end{bmatrix} .
$$
Using this measured data and the approach from above, I obtain:
$$
S_{b,11} = −0.2194−i1.1959 .
$$
Choosing a characteristic impedance \$Z_0=50\Omega\$, this corresponds to a negative input impedance: \$Z_{\rm b,in} = -8.2055-i40.997\Omega\$ (any \$Z_0\$ will result in a negative input impedance!). This is unphysical (it could only be generated by an active element). For comparison, the output impedance of block A is \$Z_{\rm a,out}=29.0993-i10.4982\Omega\$. As such, it is not possible to find an L-match to match the impedance between the two blocks.


texts: Connect speaker output to microphone input

texts:
What exactly is the difference between a microphone signal and a speaker signal?

I want to make a simple cable to connect a PC speaker output to a microphone input. Does anyone have a good idea or circuit for doing this?

Edited

I want to transfer data with audio cable and a way to connect speaker output to microphone input. I found this circuit. Is it a good solution?


texts:
There was an older question about "Power output of ignition coil".
The system would not let me comment on that question.

So, I'll ask here. In regards to a ignition coil (non specific).

OK,you have 60,000W output in 1ms.

Does the wattage reduce by half each time you increase the time(x) by X?

60,000   1ms
30,000   2ms
15,000   3ms
7,500    4ms

What is the formula to convert watts-miliseconds to watts-seconds or watts-hours?

Would you use the equations for a pulse transformer to design a ignition transformer?

I'm trying to understand how an CDI ignition coil is designed. Something that looks like it can handle 120watts at best, handling 60kW in 1ms.

If something is designed to run at 120watts continuously is it just inherent it will handle running at 60kW for 1ms?
What is the formula to figure that out?
What is the nomenclature to research it properly?

Thanks


texts: Can I get Simulink blocks from commlib individualy

texts:
We were simulating communication with DPCM modulator in school. I saved the Simulink scheme and now I would like to simulate some more situations at home, but my commlib doesn't have the modulator we were using. commsrccod2/DPCM Encoder and commsrccod2/DPCM Decoder

I tried to google those, but didn't find anything useful.

Can I download those blocks? Or can I somehow upgrade the Communication library?


texts: Per Unit System: what details am I missing

texts:
Ok, so I had a problem about a three-phase system with the following data

$$V=220kV$$

$$S=150MVA$$

$$\cos \phi=0.85$$

where V is the phase-phase voltage, S is apparent power, and \$\phi \$ is positive (inductive load).

Ok I was asked to find out the phase-neutral voltages, the phase-phase voltages and the currents.

I had no trouble doing it so I just post the outline of my work.

Phase-neutral voltages

$$V_a = \frac{220}{\sqrt{3}} e^{j0}$$
$$V_b = \frac{220}{\sqrt{3}} e^{-j120^o}$$
$$V_c = \frac{220}{\sqrt{3}} e^{j120^o}$$

Phase-phase voltages

$$V_{ab} = V_a-V_b= 220 e^{j30^o}$$
$$V_{bc} = V_b-V_c= 220 e^{-j90^o}$$
$$V_{ca} = V_c-V_a= 220 e^{j150^o}$$

Currents

$$I_{a} = \frac{S}{\sqrt{3}V} e^{-j31.7^o}= 393.6 e^{-j31.7^o}$$
$$I_{b} = 393.6 e^{-j151.7^o}$$
$$I_{c} = 393.6 e^{j88.3^o}$$

And the impedance for each load (a,b and c) is
$$Z= \frac{V_a}{I_a}= 322.7 e^{j31.7^o}$$

Now they say for me to imagine that the system becomes unbalanced with b becoming 1.1Z and c becoming 0.9Z

$$I_n= I_a+ I_b + I_c = \frac{V_a}{Z} + \frac{V_b}{1.1Z} + \frac{V_c}{0.9Z} = 68.5 e^{j61.8^o}$$

Now I was asked to redo this using the pu system with given base values

$$V_{phase-phase-base}=220kV$$

$$S_{base}=100 MVA $$

This lead me to

$$V_{phase-neutral-base}=220/\sqrt{3} kV$$
$$I_{base}= \frac{S_{base}}{\sqrt{3}V_{phase-phase-base}}=262.4A$$
$$Z_{base}= \frac{V_{phase-phase-base}}{\sqrt{3}I_{base}}=484 \Omega$$

For phase-neutral voltages I have to divide my previous value by \$ V_{phase-neutral-base}\$ leading to

$$V_a = 1 e^{j0}$$
$$V_b = 1 e^{-j120^o}$$
$$V_c = 1 e^{j120^o}$$

As for phase-phase voltages, I divide by \$V_{phase-phase-base}\$ leading me to

$$V_{ab} = 1 e^{j30^o}$$
$$V_{bc} = 1 e^{-j90^o}$$
$$V_{ca} = 1 e^{j150^o}$$

  Now my question is: why if I apply the formulas
  $$V_{ab} = V_a-V_b$$
  $$V_{bc} = V_b-V_c$$
  $$V_{ca} = V_c-V_a$$
  using pu values the equations don't verify. Is it because I use different base values for each and this is just a question of proportionality?

However, then I continued my problem and obtained the rest of the values:

$$S=\frac{150}{100}=1.5$$

$$I_{a} = \frac{S}{V} e^{-j31.7^o}= 1,5 e^{-j31.7^o}$$
$$I_{b} = 1.5 e^{-j151.7^o}$$
$$I_{c} = 1.5 e^{j88.3^o}$$

Everything looks fine here, because if I multiply the currents by \$I_{base}\$ I obtain the values I did before.

$$Z= \frac{V_a}{I_a}= \frac{1 e^{j0}}{1,5 e^{-j31.7^o}} = 0.667 e^{j31.7^o}$$

Then again, multiplying by \$Z_{base}\$ we obtain the value before.

Finally,

$$I_n= I_a+ I_b + I_c = \frac{V_a}{Z} + \frac{V_b}{1.1Z} + \frac{V_c}{0.9Z} = \frac{1 e^{j0}}{0.667 e^{j31.7^o}} + \frac{1 e^{-j120^o}}{1.1 \times 0.667 e^{j31.7^o}} + \frac{1 e^{j120^o}}{0.9 \times 0.667 e^{j31.7^o}} =  0.261 e^{j61.8^o}$$

And multiplying by \$I_{base}\$ I obtain the same value as before.

  So in this last calculations using the pu values works pretty well and I obtain values equivalent to the calculations I did before.
  The only calculation that's failing is the one about the voltages phase-phase. Why does this happen? What is the mathematical subtlety I am missing here?

Thanks!


texts: Decreasing and reading output of a sensor (0 - 10 V) using a voltage divider - Output impedance

texts:
I have a pressure sensor giving an output between 0 - 10 V.

I want to read and save the value using an arduino, so I am using a voltage divider (https://learn.sparkfun.com/tutorials/voltage-dividers) to scale it down to 0 - 5 V. Since I want to halve the voltage, I am using the same resistance twice.

I have noticed that the voltage changes according to the value of the chosen resistance pair. I assume this is due to the output impedance of the sensor.

On the sensor there is a label reading "OUT 0...10 V RL>10K". I assume this is the impedance of the output.

Does this mean that one should use a pair of at least 10K Ohm resistance for the voltage divider?

Info on the sensor = https://www.hubacontrol.com/fileadmin/user_upload/domain1/Produkte/Product_catalogue.pdf - Page 109 (Sensor type 692)


texts:
I am using stm32f407 and LM75 with I2C Bus serial communication.
In this code, I am Using a lot of interrupts and etc.Sometimes I2C Can give a error I can accept this but I am uncomfortable with signals.
There is only LM75 IC on the bus line and Rp is 4.7K ohm.

Sometimes I2C Bus give an BERR Error or I2C Status stuck busy or i2c bus line stay zero volt.

How can I fix the signal? Or is it normal?

I have tried 10pf capacitors between ground and scl and  between ground and sda. But signals are same.

There are oscilloscope views below

Photo1: I2CBUS Diagram

Photo2: 1MHZ speed I2CBUS

Photo3: 100KHZ speed I2CBUS

Photo4: 400KHZ speed I2CBUS

Photo5: PROPS

Photo6: I2C ROUTES

Photo7: Ground and Supply noises(Channel 1:MCU Ground, Channel 2:MCU Supply)


texts: STK600 routing & socket for SOIC8 ATtiny85

texts:
I just purchased an STK600 (Atmel programmer for AVR8/32b) and a bunch of ATtiny85 chips in a DIP8 package.

The documentation of Atmel is really outdated on the routing and socket cards to use. From what I understood, I choose pick a ATSTK600-RC02 as routing card, and ATSTK600-SC01 as socket card.

Now for my final project, I would like to use the SOIC8 package of my ATtiny85, but I cannot find the proper routing and socket cards to use.

Atmel mapping of chip to routing/socket card does not mention the SOIC8 packages of the ATtiny85, only DIP8. (not to mention all the dead links... (http://www.atmel.com/webdoc/stk600/stk600.introduction_devicesupport.html)

I guess I could take the somehow generic ATSTK600-SC11 as socket card, but its documentation states "SOIC 14/20/24/32", so I am not even sure I will be able to have a proper pinout for my SOIC8 there.
I have some intuition that tells me the ATSTK600-RC46 could be used as routing card, but again the documentation states it is designed for DIP14.

I am really lost here, the documentation from Atmel is full of dead links, I guess because of the move to the microchip website. And there are really little documentation on internet on these chips and how to program them. I am just beginning the direct chip programming, coming from the Arduino world, so since this is a significant investment, I really would not want to buy useless routing/socket cards.

Any help greatly appreciated!


texts: Determine power rating of induction motor

texts:
I got a 1-phase induction motor (230v/50hz) that was taken from a tile cutting saw that I planned to use in a home made disc sander, the labeling on the machine says it's a 600W motor but the motor itself has no information at all on it.

I am doubting that it's 600W because last night as I was truing up the plywood disc by mounting it and using the motor as an improvised lathe. The motor got incredibly hot from running only 5 minutes or so and I stopped to let it cool down, and to considerif this was going to work at all. I don't think I could put that much stress on a 600W motor (.8HP) by spinning a 24cm diameter piece of 12mm plywood.

It also looks smaller than other 600w motors I've seen, I have a 750w 3-phase motor (400V/50hz) that is much larger and heavier, but I do not know how good an indicator size alone is.

I am wondring if there are some simple ways to determine what kind of power range this motor falls into? Perhaps using a power meter and checking the amp draw while the shaft is spinning without any load? Not sure what kind of draw I should be having for a 600W motor though.


texts: Determine the values of a and n leading to the optimal curve fit

texts:
The current, I in mA, in a circuit is measured for various voltage values V in volts. If the law connecting I and V is I = aV^n, where a and n are constants, draw an appropriate graph and determine the values of a and n leading to the optimal curve fit for the following set of values.

Can anyone explain me how to solve this excercise?

The solution is as follows


texts: Where to connect shield in USB power supply for Arduino?

texts:
I'm making a 5 volt portable regulated power supply (using LM7805 regulator IC) for Arduino UNO. I'm planning to use a USB connector as its output socket, this way I can just plug and power the Arduino via USB. My problem is where do I connect the USB sockets's shield ? As far as I know it should be connected to the ground if it is a host device - can we consider the power supply as a host device?

Note: I've asked this question in arduino.stackexchange and advised to get in here.


texts: Driving MOSFET with 5V PWM for 12V fan speed control

texts:
I came up with this circuit to control a 12V 6A fan's speed, with a 5V PWM from another circuit. I'm not sure if it's going to work (I'm not very experienced nor knowledgeable in electronics) and I have a few questions:

To compensate for Q1's Vce, and turn off Q4 completely and reliably (when Q1 in on and A is low) I added one extra diode in series with Q4's base (total 2). Is this a good idea? Is it necessary, as I thought?
Are D4, D5 and D12 necessary in this circuit? (I put them there as part of the Baker clamp for each transistor, to charge/discharge the base faster when switching.)
Is there anything else that you think is unnecessary/lacking/wrong?


texts: What is this component? (Labelled 338 M828)

texts: There is a 3 pin/connector component connected to the PCB below. It is labeled with "338" and "M828" (the image quality is too low to show this). What purpose does it serve?


texts: How do I calculate power of this combination?

texts: How did they come to the expression for total power calculated when both the current source and the voltage source were active?


texts: Sampling a +/- 12v signal with a 0-3.3v micro pin

texts:
It's been ages since I've had to use my old school notes.

I am trying to get an esp32 to read an analog voltage that ranges from -12 to +12. Obviously, the 3.3v esp32 won't like those voltages so I have to come up with a way to scale down and shift the signal.

What I have so far is:

So here, V2 is the signal input voltage. In the image it is 12v, but in reality it will be either 12 or -12 at any given moment.

OP2 is an inverting, "attenuator" that will step the +/-12v down to +/-1.65v.

OP3 is a differential amplifier that will, essentially, add a 1.65v bias to the +/-1.65v input signal bringing it to 0-3.3v.

Now looking at this, I can't help but feel there is some optimization to be done here. Is it possible to combine the 2 amp stages into 1? I tried doing it mathematically but I end up with a negative resistance...

Can the two stages be combined into 1? Thanks.

Also, I'd like to make sure nothing outside of 0-3.3v ever comes out of OP3. Is it possible to power OP3 with 3.3v and GND in stead of +/-12v? My simulation software (qucs) doesn't seem to allow me to select the supply voltages...


texts:
I need help with what is probably a very simple question that I don't know.

When you put 12v at 10 watts and bring it down to 5v with a regulator would the wattage change?

And just say the regulator had no max on what it could output.


texts: How to 3x or 4x a DC voltage while minimizing board space with no microcontroller?

texts:
I have a 3.7V DC voltage source that I'd like to boost to at least 10 Volts.

I've been using Microchip's TC7660 component as a voltage doubler. But it only comes in SOIC (rather large for SMT). And since it can only double voltages, to get to 10 volts, I would have to use two of them as a voltage quadrupler (plus four diodes, also rather large).

There are actually a lot of components for increasing a DC voltage, especially in the context of microcontrollers and "erasing" RAM memory. But I can't seem to find a way to efficiently boost this voltage. I suppose I'm looking for efficiency both in terms of space on the board and in terms of price. Right now Microchip's solution adds about $2.50 per board including the diodes and capacitors which is really high. When you add in the design considerations due to the large board space it is really a lot more than that for something I think could be done better.

There's also a lot of confusing or seemingly overlapping concepts when I try to research this: Boost converters, charge pumps, etc. Most of the results when I research this are about AC to DC conversion which is really frustrating to research this. I've looked into arranging batteries in series or even non-Lipo batteries, but all other solutions seem to be too big.

Ideally I would have a single SOIC or two smaller components for getting this 3.7 V to 10V. Something else using rudimentary components (e.g. transistors) would also work.

Thanks for any help you can give me.


texts: Replacing BD139 for TIP122 - Cooler speed control circuit

texts:
I'm using a cooler (=fan) to conduct heated air through a hose to a closed chamber using an Arduino UNO PWM . A PID system controls the current across an array of resistors to target the setpoint temperature at the chamber. The purpose of the cooler (12V - 2.9 W) is to generate an air flow.
I started out using this circuit (for the cooler only) using exactly the same components:

At the same time I'm running a user interface using a 20x4 LCD and a rotary encoder, a PID control system to control the temperature in a box. The arduino and the PID system are powered by a 12V 10A switching power supply.
At the beginning the thing worked well, when in the interface you hit 'Start' both the cooler and the PID system started (I do not know the voltage across the fan). After a few assays the cooler started running a bit slower or delaying the start and when measuring the voltage it resulted in approximately 10 V. I do have cables conecting the cooler's + and - to the PCB board but the voltage drop is less than 0.1 V. I supposed that the transistor was damaged or something and replaced it with a TIP122 transistor which can deal with more power and has high gain. After this, I tried running a new assay but the cooler didn't even move, the voltage across it was 7.5 V! I then proceeded to replace the 1k Ohm resistor to a 220 Ohm one hoping that I would get a higher voltage in the base. The cooler started moving buy really slowly. After the last mentioned change, I ran a new assay and measured everything:

Voltage across cooler: 9 V
Arduino's PWM (255): 4.6 V
Voltage drop across 220 Ohm resistor: 3.4 V
Vbe: 1.2 V
Vbc: 1.9 V
Vec: 3.1 V
Power Supply: 12.8 V

After this, I'm out of ideas. It's pretty weird that the circuit used to work and started losing power with time (I'm no genius but it's a pretty simple circuit) .
If you look at the BD139 datasheet it doesn't make much sense that it was damaged due to power overload.
TIP 122 Datasheet
BD139 Datasheet
EDIT:
After the previously mentioned assays the cooler was connected to the 12V power supply and worked perfectly well.


texts: Question about the transfer function found from state space model

texts:
I'll make up a problem to explain what I'm having trouble with. $$\dot x=\begin{bmatrix}0&1\\-5&-6\end{bmatrix}x+\begin{bmatrix}0\\1\end{bmatrix}u=Ax+Bu\\\\y=\begin{bmatrix}0&1\end{bmatrix}x=Cx$$

Now because of the matrix form we can easily get the transfer function $$T(s)=\frac{s}{s^2+6s+5}$$

That's usally how the problems start. At some point I'm given that a value from the matrix changes, say -5 becomes κ-5, altering the transfer function. Basically, I have to draw the root locus as k changes but in order to do that I must know if what I've found is the open loop or the closed loop transfer function. Which one is it?


texts: Suggestions for toggling between 3 voltage levels from 100MHz to 1 GHz, to generate square waves?

texts:
Can anyone suggest what would be some better ways(purchased with minimal work if possible) to generate square waves at 3 tunable voltage levels toggling arbitrarily(EDIT: as in a PRBS/PRBS7/PRBS31, DC balanced, the stream of PRBS can be predefined and hardcoded, does not matter to the experiment) from one voltage to the other at high speed from 500 MHz to 1 GHz?

I have a Xilinx Kintex 7 KC705 eval kit and can purchase add on boards- the one way I was thinking of that is more conceptually straightforward is to just use a DAC board and drive the outputs at the desired voltages.  https://www.abaco.com/products/fmc170-fpga-mezzanine-card are ok for a few hundred MHz, but none of the cards can get a ~10-20% of the cycle rise/fall time at 1GHz.   For 1GHz arbitrary square waves with say 0.2ns rise/fall times, need about 3.5GHz minimum to get anything, then about >10GHz of analog bandwidth to make it appear "more square".  For 500MHz, about ~ 8-10GHz (maybe 5GHz and a less square appearance) analog output bandwidth may be ok, and those cards may be sufficient, but I'd still be on the lookout for something suitable for the 1GHz square wave.

Effectively that is an AWG...Am I thinking about this the wrong way?  I don't need all the fancy features of an AWG, but just able to set 3 voltages (roughly a range of voltages from 0-2.0V, a set of these 3 voltages, for example, 0.1V,  0.35V 1.5V would be fine, however, it's not critical bc I have high-speed amps and bias T's) and toggle between then arbitrarily (ideally driven by data patterns out of the Kintex FPGA). Everything is 50Ohm impedance. At the higher speeds (1 GHz/ 1ns per bit), 0.2ns rise/fall time would be acceptable-- this is experimental so if it ends up worse than 0.3ns then that's what I'll have to live with until I can buy more expensive things.

Thanks for your help!


texts: Op-amp selection for reverse polarity protection on an Arduino voltmeter

texts:
I made an accurate voltmeter using an Arduino Nano as the microcontroller.
What I want now is to add a reverse polarity protection using an op-amp with a gain of 1 without changing the actual accuracy it has.
In the image I show both my actual circuit and the circuit I designed for reverse polarity.

What rail-to-rail op-amp would you suggest for this circuit?


texts: This connector is used in a Remote car's key, somone knows which connector is this?

texts:
This connector is used in a Remote car's key.

Adding information requested: Pitch 1mm
I Added the female connector too

(click for larger images)


texts: How to shift left/right a STD_LOGIC_VECTOR value within a WHEN statement?

texts:
I'm attempting to create a parametrizable ALU which handles N-Bit signed data. However the methods I know of shifting left/right, either won't work because the values are defined as STD_LOGIC_VECTOR:

--Declaration
A, B, X : in  STD_LOGIC_VECTOR(N downto 0);
--Usage
OUTPUT <= (A sra X) WHEN OPERATION = "0000" ELSE

Or because it's within a WHEN statement:

OUTPUT <= (A <= X(N) & X(N downto 1)) WHEN OPERATION = "1001" ELSE
--This causes Type of OUTPUT is incompatible with type of <= error

To reiterate, I need to  shift left/right A by X bits. Could anyone point me in the right direction?

Full code:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use work.DigEng.ALL;

-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity core is
    Generic (
           N : INTEGER);
    Port ( CLK : in  STD_LOGIC;
           A, B, X : in  STD_LOGIC_VECTOR(N downto 0);
              OPERATION : in STD_LOGIC_VECTOR(3 downto 0); --Allows us up to 16 operations
              FLAGS : in STD_LOGIC_VECTOR(7 downto 0);
           ALU_OUTPUT : out  STD_LOGIC_VECTOR(N downto 0));
end core;

architecture Behavioral of core is
    signal TEMP_OUTPUT : STD_LOGIC_VECTOR(N downto 0);
begin
    TEMP_OUTPUT <= (A) WHEN OPERATION = "0000" ELSE
                --Bit-wise Logic
                 (A AND B) WHEN OPERATION = "0001" ELSE
                 (A OR B) WHEN OPERATION = "0010" ELSE
                 (A XOR B) WHEN OPERATION = "0011" ELSE
                 (NOT A) WHEN OPERATION = "0100" ELSE
                --Arithmetic
                 STD_LOGIC_VECTOR(SIGNED(A) + 1) WHEN OPERATION = "0101" ELSE
                 STD_LOGIC_VECTOR(SIGNED(A) - 1) WHEN OPERATION = "0110" ELSE
                 STD_LOGIC_VECTOR(SIGNED(A) + SIGNED(B)) WHEN OPERATION = "0111" ELSE
                 STD_LOGIC_VECTOR(SIGNED(A) - SIGNED(B)) WHEN OPERATION = "1000" ELSE
                --Shift
                 --(A <= X(N) & X(N downto 1)) WHEN OPERATION = "1001" ELSE
                 "1111";

end Behavioral;


texts: What is required to activate the "PS_ON" on the motherboard, to power on a computer? Looking to use a microprocessor/accessories to power on a pc

texts:
As the title says I'm trying to figure out what is needed to activate the power on, on the motherboard's header.

I have read that essentially the switch is a "momentary" switch which I assume just connects for an instant to allow power to boot up.  Would more power cause damage or is it just not necessary?  Will holding the button down not matter either?

So essentially I am looking to connect some accessories to a microprocessor, and wanted to know if I used something like a touch sensor, or a button on the Arduino, if I could power on my computer?

I found this image and it lead me here, but it talks a bout a lot of things that I'm not sure of like "TTL" it mentions "TTL LOW" which I believe LOW means off? and HIGH is on?

So essentially I'm just curious about the PS_ON since I cannot find much information about it, and I'm interested in how the computer turns on, and how I could do it myself in all sorts of interesting ways that are different from the traditional "pressing a button" to turn on :).

Thank you all for any help/advice.  I'm new to electronics, but I know how to write software, so I'm excited to combine the two together!

EDIT:  JUST TO BE CLEAR

I am looking to just emulate a button press, i.e., instead of pressing a button, I can click a switch, or something.  I want the mb/computer to do what it normally does, but I just want to turn on my computer with things other than the power on button.  It seems the easier method is to do exactly what the button does, send the info through the green PS_ON or whatever wire to the motherboard header, and then the mb do it's thing.


texts: PIR motion detector or Emitter receiver pair or?

texts:
I have a simple 3 ft by 3 ft goal. I want to electronically detect when a ball passes into the goal but not when it goes wide.

I had initially thought i could use a simple PIR motion detector pointing downward  on the cross bar but I am concerned that
1) it might detect balls that go wide? (how do i restrict the arc)
2) it might be too slow for a fast moving ball
3) it might miss balls in top corner etc

Option two is a series of emitter reciver ir pairs on each side of the goal post. Enough to make sure that a ball can't get through. See attached sketch of the options.

I have zero experience with this. I am thinking the emitter pairs is best option but I am unsure? Maybe there is another alternative? The overriding concern is that the solution must require minimal power to run (and cost!).

edit as directed by site to explain why not duplicate -- to reiterate my comment below:
yes they are similar questions. I think my question was more specific. I asked specifically for option a) or option b) or something else. Steve G kindly informed me why the PIR was not suitable -- as it uses temperature -- as opposed to use solution this because i think so. For this reason I think this question is worthy as a standalone and I will update the answer to reflect why PIR was not suitable.


texts: Why did the light that I tried to turn on flicker green?

texts: I was just turning on a light in my house (just a normal ceiling light, I think it is the round bulb kind, not the spiral bulb) and it flashed green and went out. It will not turn on anymore. This happened before with a chandelier light and there is one light that is burnt out on it, but I think that light was burnt out before it flashed green. Anyone know what happened? Sorry if this is a noob question, I'm not very educated on electronics.


texts: Supercapacitor Bank Wont Charge w RPi Load

texts:
I am attempting to build a simple, mini USB UPS for my Rasberry Pi 3 to survive sudden, short-term voltage drops. I have built the working circuit below on a breadboard.

When the 5V supply is removed and the voltage level (from supercaps) drops to 4.3V (between Multi+ and Multi-), the circuit does not recover when the 5V supply returns.

At 4.4V and above, the circuit recovers and the supercaps recharge back to ~5.35V. If the circuit is stuck at 4.3V or below, and I remove the USB power to the RPi, the circuit recovers and the s-caps recharge to ~5.35V.

What am I missing or doing wrong, and/or how can I fix? Why wont the system bounce back to ~5V after the voltage level drops to 4.3V or below? Thank you in advance!

Update: schematic updated based on answer 13 JUN 17

simulate this circuit – Schematic created using CircuitLab


texts:
I need to plug a micro controller in device which seems to run a PSU with a common VCC and two "grounds"

A common 0V a -3.3V and a -5V. I want to add a 3.3V powered microcontroler (The easy part) and drive a 5V relay using the microcontroller.

I tried to drive the relay using a mosfet but since the relay is 5V powered and as far as I understand there will be a 1.7V Vgs between the -5V and the -3.3V (GND ref for the microcontroller) and this will be enough to switch on the mosfet.

So I thought about this: http://www.circuits.io/circuits/2632

Will this work ?


texts: If I want to constrain a signal to +- 5 V, what arrangement and rating of zener will I need?

texts:
I have set up a circuit with two zener diodes head-to-head with a resistor upstream, to limit a circuit signal voltage to +- 5V. On measurement, the 0.7 V of one zener appears to be summing with the 5.0 V of the other, creating a bound of +- 5.7 V. I'm not sure if this is the expected behaviour, but leads me to think 4.3 V zeners head to tail might give the +- 5V bounding I'm looking for.
Then with the resistor, I had started with 100 Ohm, but it looks like a Zener's 'stiffness' isn't that high, so might need a much higher value resistor to catch swings of a few volts each way.
Have I understood the situation correctly?


texts: Which is most used Barrel Connector ID? 2.1m or 2.5mm?

texts:
I'm working on an project which  will be given to some friends and will be open-source too.
I need to choose the power supply connector (5V or 12V @ 3A) and I'm thinking to barrel connectors. I found there're 2 version of them, the 2.1mm and 2.5mm for the internal pin.

I read also the 2.5mm male will fit the 2.1 female but connection is not stable, so it is not a reliable solution to choose the smaller one to accept both.

So, which is the most used? The goal is to have the maximum compatibility with existing PSU around the house.


texts:
I'm struggling to see how the output of this circuit is $$V_{0} = {I_{s} R_{s} R_{L}/{5k}} $$

My work thus far:

I understand the voltage into the base of the BJT is $$I_{s}R_{s}$$
I understand the voltage into the collector is Vin

Now what I am struggling to see is where the 5k term and the R_l term come from.

I see that the IsRs is the voltage across the the two leads of the opamp, this detects the current. Where the 5k and how Rl interacts I don't understand.

My guess would be the 5k is a result of voltage division.

Can someone guide me to understanding this circuit?


texts: Can anyone identify this type of connector?

texts:
My Sony CMT-X5CD (CD/DAB hifi soundbar thing) uses a very non-standard antenna connector, as shown in the photos. Can anyone identify it? It's used for the aerial(but unfortunately, the aerial supplied is absolutely terrible..) 2pence coin for scale (26mm dia) about the same size as a $1 American coin).

Thanks!


texts:
I am new to the concepts of using adders to add numbers but I tried using the definitions which I understood as given two binary digits A, B the full adder takes three inputs A, B, C where C acts as a control bit or a carry bit, gives the SUM= (A XOR B), C=A.B, where . is the AND operator. NOw to find the sum of numbers let's say 2 and 6, first, I write the binary representation of both i.e 010 and 110, since they are 3-bit numbers I use 3 full adders
and proceed as follows

a0  b0  c0    S0     C

0   0    0     0     0

1   1    0      0     1

0   1    1      0      0

So my ouput string becomes '000' but it should have been '1000' i.e 8, what am i missing can somebody explain.


texts: What is the use of series resistor in VBAT line of CAN transceiver?

texts:
In the application diagram CAN Transceiver TJA1043  (Page – 19), there is a series resistor in the VBAT line.
What is the use of this resistor? How to select the value for this resistor?


texts: Why would anyone use an inductor on a mux?

texts:
I read a schematic where it has a Z80 CPU tied to a 78LS138.  The CPU's WR line is tied to pin 1 (A) of the 138.  Also, the schematic shows a 42uH inductor tied to pin 1 of the 138 as well.

What is the purpose of this?  As of my understanding, inductors are primarily used to filter AC current no?

And if the Z80 <-> 74LS138 is DC only (I am assuming) then wouldn't the inductor really just act as a small piece of wire and if anything, a super small resistor?

Could it be because the entire circuit (this is for a Colecovision, BTW) is expected to have AC noise?  I see several examples of using inductors on various pins in the circuit.

Thanks.


texts: How negative resistance feature of Tunnel Diode is used in oscillators?

texts: How is the negative resistance feature of Tunnel Diodes used in oscillators with the help of this circuit diagram.


texts:
I'm trying to drive a MCU input with a RS-485 driver chip, specifically the SP3485 on the SparkFun RS-485 transceiver breakout.

When I connect the MCU pin directly to the 3.3V power rail, the pin reads 3.3V and an ammeter shows 6.8 uA of current going into the pin.

I assert the RS-485 signal and measure the voltage at the SP3485 receiver output (RO) pin with the pin floating (disconnected from the MCU). I see 3.3V.

When I connect the RO pin to the MCU the MCU pin is only driven to 1V and the ammeter shows 3.7 uA of current going into the pin.

What is going on? Surely the RO output pin isn't current-limited to 3.7 uA?


texts: I have this bench psu. (datasheet, manual). It has worked wonderfully so far, but my one problem is that the current adjustment knobs are only 1 turn, while the voltage knobs are 10 turn. I want to replace them with 10 turns, but I before I start soldering things on my brand new power supply, I want to make sure I am going about this correctly. How would I do this mod? The pots in it right now are 10k 1 turns.


texts: How do I connect a NPN transistor so it operates in the saturation region?

texts: I am learning about NPN transistors and I could not find how to connect the transistor so it operates in the saturation region.The circuit that I have made works in the Active region,because when I run the simulation the current on the emitter is higher than the current on the base.


texts: Hybrid two port network modelling, as described by the texts, is a topic which enables one to reduce a complicated network into a simple two port network. I guess this is something which must have originated from mathematicians. I would be really grateful if someone provides me a link , introducing this topic, and endowed with mathematical rigor. I hope the demand of my question is going to be clarified in the following lines. In a two port network,   the input affects the output by a Norton current source and the output affects the  input by a Thevenin voltage source. Is it so that in any case the input can only affect the output  by current source and the output can only affect by a voltage source , why not the other way round, the input affecting by voltage and the output affecting by current ? In case of a transistor it is clear and it holds good, but can we develop a formal and general proof for it?  Definitely, I need a mathematically proven way to construct a model for a network. It will be even more appreciable if anyone can illustrate the benevolence of this network model in case of even more intricate networks.


texts: Use of global variables in Embedded Systems

texts:
I started writing firmware for my product and I'm a rookie here. I went through many articles about not using global variables or functions. Is there any limit for using global variables in an 8 bit system or is it a complete 'No-No'. How should I use global variables in my system or should I completely avoid them?

I would like to take valuable advice from you guys on this topic to make my firmware more compact.


texts: How does a DC generator vary power output to suit load

texts:
I am working on an project where I intend to install a bicycle DC generator to power a set of LED strip lights. The specific product I will be using is the Pedal-A-Watt permanent magnet generator which is capable of output around 400 W of power. For the sake of my question let's assume that I will have 100 W of lighting load with additional an 50 W lighting load being switch on by a relay if a certain condition is met.

My setup will be as follows: DC Generator -> 12 VDC Voltage Regulator -> 12 VDC /120VAC Inverter -> LED Driver/Power Supply -> LED Strip Lights.

My concern is that the the motor can output significantly more current than the lights will require. I realize the load dictates the current being drawn from the generator, but if someone is pedaling hard and determined to max out the generator, will they be able to overcome to counter torque cause by the magnetic fields inside the motor and fry the lights, inverter, and/or power supply? If no, why not?

I should add that my field of expertise is not electronics and thus I would like to use off the shelf products as much as possible.

Thank you in advance.


texts: What are the effects of running a PIC μC slightly above its rated working voltage?

texts: I experiment with the PIC24 series of μCs fairly often and have noticed that I can run them successfully from a 3.7v LiPo battery pack without a regulator. The batteries charge to around 4.2v fully charged and down to a little below 3.7v drained. This is only slightly above the suggested 3.3v. I just wondered if there are any side-effects of this? Does it affect the internal oscillators or some other internal processes? Or is the effect negligible?


texts:
Two MOSFET-s \$M_1,M_2\$ are in saturation. Canal lengths: \$L_1=2L_2\$, Drain currents: \$I_{d1}=I_{d2}\$, \$V_{ds1}=V_{ds2}\$ and \$\Delta L\$ is same for both of these MOSFET-s.

So, I don't know what exit resistance is. Is it \$r_{ds} = v_{ds}/i_d\$ ?


texts: 12V 10A linear LED supply keeps failing; need a better design

texts:
I homebrewed a flashing LED landing light for my high performance experimental aircraft.  The details are here

Because I was afraid of electrical noise (which could impact communications or navigation equipment), I went with a linear regulator.  That's been a mistake.  Either the linear regulator or the MOSFET I used keep blowing (even with very large heat sinks attached).  I've got to do better.

What I'm after is a system that can handle between 7 and 10 amps, either flashing (normal) or constant (for night landing operations).

I've concluded that a buck regulator is probably the only way to handle the demands.

I'd sure appreciate any input!  Thanks!


texts:
I am looking for a simple way to encode some data over a dc power line. (Probably using a very low cost IC) In my design, I have a port that provides 5V, 200mA for connecting some device, but now I like to extend the capability of my port to send and receive some data over that port. The idea I have is to encode data over 5V line. The distance the signal needs to travel is in the order of 10-15cm. Never more than this.

I have no data rate requirement but If I could achieve a 1-2Mbps it would be fantastic. If this is not possible, I am OK with a lower transmission rate. This would be a closed loop system, i.e. I control both ends. Therefore, I don't need to worry about standards etc.


texts:
When DC voltage is applied across an inductor, would the current through it be ramp? According to voltage current relationship in an inductor, the current should be ramp if voltage across inductor is constant.

Is this practically possible only when there is no resistance connected in series with inductor?

Why would the current through inductor be ramp in this circuit of dc-dc buck converter?

Edit

The large value of capacitance reduces the change in output voltage and so the voltage across inductor remains constant. This would mean that load current and hence output voltage is not really constant. Why is this acceptable?

What would be the nature of voltage across the capacitor(output voltage?


texts: How, if at all, can a memristor be emulated with active components?

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I find existing explanations of memristors are either overly vague, or an unapproachable mass of academic, mathematical analysis. I want to gain an intuitive understanding of what a memristor is, what it does, and what its applications might be in terms accessible to the ordinary engineer.

If an inductor can be emulated with a capacitor and active components, then I bet it's also possible a sufficiently clever circuit could emulate a memristor, at least within a limited region of operation. Though this circuit may not have the same properties that make memristors potentially useful, it could still be a useful demonstration and platform for experimentation.

Is there something I can build on a breadboard that looks, within some reasonable operating operating parameters, like a memristor? If not, what about something that can be simulated with ideal components? Bonus points for summarizing the theory of operation, and succinctly and intuitively describing what a memristor is without resorting to abstract mathematics or models far removed from even idealized real components.


texts: How would I find the total resistance of the following circuit?

texts: I tried finding the total resistance but my answer isn't correct. The answer is supposed to be 6.66 kΩ.


texts: Eagle PCB Aggregate multiple parts into one Symbol

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I wonder whether I can aggreate multiple physical parts (say 10 capacitors of same value and footprint) into a single symbol to reduce the clutter on the schematic. I know that the other way around - one physical part (say capacitor array) can procude multiple individual symbols but feel that the other way around would be just as useful.

Any thoughts?


texts: Avoiding collisions with SMD components in Altium

texts: I am trying to make a circular PCB board with 50 parallel lines of 4 LEDs in series and I am getting collisions errors on some parts on my board. This is my first altium project so I am not sure how to fix it. I have seen people saying you have to create a 3D model but I am not sure how to do that.


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I would like to transmit 1 byte through an AC line from an arduino to another which is power by the AC line. This is something like what I want to do:

simulate this circuit – Schematic created using CircuitLab

So, let me explain what I have thought. The first arduino detects the zero crossing using the opto-isolator and after that for half a sine wave triggers the triac 8 times to form a byte inside the half wave. The second arduino, which is powered by the AC line also reads this wave and when it detects the encoded wave does something with that information. So there are some questions:

Can that be done?
Will there be problems?
Are there any other ways to pass small info through the AC line without using off the shelf products?
Can that be done for more bytes?

The specific example will be used to control a light bulb and an led strip both attached to the second arduino using a rotary encoder attached to the first.


texts: Why is the input reflection signal very weak?

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I built a PCB filter in Class "Band-pass" with center frequency of 2.4 GHz. The board has two SMA's (input 1 & output 2).

S(1,2) looks like this:

The frequency is good, However, the attenuation is bad. My problem is that my Reflection signal S(1,1) looks like:

(I thought I would see a valley going down at the 2.4 GHz frequency)

(Note: I am using a transmission line design)

The PCB Circuit:

Specifications:
Filter Type:    Chebychev bandpass
Ripple:  0.5 dB
Ctr. Freq.: 2.437 GHz
Att.:       50 dB @ 2.459 GHz
Tgt. BW:    20 MHz

Substrate:  Rogers RO4350B
εr :    3.48 +/- 0.005
Tsx:    1.524 mm
TCu:    35 μm

Board + Layout:


texts: How to use SPWM with reference voltage waveforms

texts: I'm doing a simulation for an IM drive in MATLAB/Simulink and Plecs(Blockset). My model is a closed loop system and I generate the reference voltage to be applied across the motor. Now I need to generate these voltages by switching the inverter with PWM scheme but simply scaling the ref. voltage and comparing it to a triangular waveform is not working for me. Any ideas on how I can generate the switching pulses?


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I did some research on different inexpensive RFID readers and I ended up building my project around this one

https://www.parallax.com/product/28340

I also bought these tags:

https://www.parallax.com/product/28161

The problem is that whenever I get close with the tags, sometimes it doesn't read them at all, other times it takes 1-10 seconds to read it.

I use this code to test it on my ubuntu (I tested it on a raspberry pi as well, same issue):
http://theatticlight.net/posts/Using-a-Parallax-RFID-reader-on-the-Raspberry-PI/

I am not sure if this is a problem with my reader or something else I am doing wrong.

Would a 13MHz reader/tag have faster reading speeds? Is this problem related to the specific antenna of the module?


texts:
Hi I am trying to build simple photo gate to measure speed of incoming ball.
I decided I will use one photo gate with high frequency.

Because ball is much smaller then the box, which is comming in, I need to use more gates as on attached image.

Do I understand correctly that in this case I have to use some laser which sends centred light instead of IR LED diode which sends light in 120 degrees? I think that in case of IR LED the ball might not cover even one photo reciever.
Which element is better (faster) photo diode or photo transistor ?

Ball diameter is 3cm, max speed I need to read is oround 40 m/s


texts: Correcting DC offset in op-amp based controlled current source

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In an attempt to develop an automated potentiometer measuring device I have implemented the following op-amp based voltage controlled current source, controlled by the output of a DAC. The voltage across two terminals of the potentiometer is then measured using a differential ADC (not pictured) from which one of the resistances is found.

simulate this circuit – Schematic created using CircuitLab

I'm having a problem with this circuit in that the DC offset introduced in the op-amp is causing problems when the potentiometer resistance is low. The measured voltage goes negative instead of positive, or remaining at 0V.

To correct this I am thinking of using a chopper-stabilized op amp to minimise the DC offset. This would also need to be rail-to-rail as the supply it is driven from is a single supply +15V. Do these exist?

My question is: would this suitably reduce the DC offset? Or is there a compensation technique I could use in this circuit to reduce the offset?


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I have simulated the following circuit using partsim.com:

I don't understand why R1 and R2 function as a simple voltage divider. I would expect R1 and R4 to to provide parallel resistance (keeping in mind the ~0.7 voltage drop of Vbe). Can someone explain what I'm missing?

Further, seeing R4 as (1 + beta) R4 from the R1, R2 node does not seem to explain the behavior when the R4 resistance is lowered since R1 and R2 don't act like a voltage divider then:


texts: Circuit that makes capacitors behave like inductor and vice versa

texts: They can be used in ICs. I vaguely remember reading about it few months ago, but I cannot remember its name right now. Can anyone help?


texts: Implement IR protocol using only one timer

texts:
I want to implement the transceiving part of an IR protocol for my Samsung remote on an nRF54822, using an ARM Cortex M0 core. The protocol is very much like the NEC Protocol, and is using a carrier frequency of 38kHz with bursts of the carrier frequency in different time periods to indicate logical '1's and '0's.

  Example: 38kHz ON for 540µs, signal OFF for 1.7ms, signal ON for
  540µs.

If I use two timers this should be fairly trivial. One timer to keep the 38kHz carrier frequency active at all times, and the other to keep track of when to set the output of timer one at the IR LED.
But what if I am using only one timer? I am able to trigger timer clear (count from zero) and timer stop at value Compare. I can also trigger toggle, set and clear on GPIO at compare.

Any ideas on how I can achieve this?


texts: 555 Timer: Does the discharge pin show ground when in reset?

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It is not clear to me whether the discharge pin could be used to (for example) discharge a capacitor when a 555 timer is in reset.

I didn't see anything in the datasheets that gives hints about what will happen, aside from internal schematics. Block diagram from a CMOS 555 timer variant:

The Wikipedia article describes the discharge pin as "in phase with the output," whatever that means. If you take that to mean that the discharge pin is shorted to ground whenever the output is LOW, then putting the 555 in reset should ground the discharge pin. These two articles say the same thing.

However, I just tried this in a simulator and discharge was not grounded when reset was applied.


texts: What does Low/High mean on the connections of a chip?

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This is similar to this question, but that seems to apply more towards programming microcontrollers rather than directly setting hardware-controlled chips. I have a PCM5102A, and the datasheet tells me to make selections by setting the pin to "low" or "high".

Here's a sample:

The datasheet doesn't say anything about how to implement this. What should I do if I want to set it to LOW, and what should I do for HIGH? Should I add voltage, connect the pin to ground, leave it...


texts: What are these electronic components from an old radio?

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I disassembled an old radio that I found in my attic and found some electronic components that I can't recognize.

I think that the first component is an inductor. I'm pretty sure about that... But I can't understand why it's made the way it is. There is more than one coil on the same core, so the coils should be coupled... But for what purpose?

As for the second and third component I really have no clue about what they are.
However, I tested the third component  with my tester and I found out that the resistance between the majority of its pins is really low and many of them are short-circuited on the PCB.

Finally, there's a photo (below) of a speaker. I'd like to know why the connection to the speaker is made with a "coil". There are a lot of connections made like that on this circuit.


texts: BJT cut-off currents magnitudes and directions

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I was reading the datasheet for the 2N3904 transistor (NPN BJT) recently and found out that I couldn't wrap my head around the cutoff current values.

For the given conditions, both junctions are reverse biased (\$V_{CE} = 30V, V_{EB} = 3V\$), the datasheet says that the base cutoff current is 50 nA, and the collector cutoff current is also 50 nA.

Consider the collector-base junction. Since it's reverse biased we have a reverse saturation current which goes into the collector and this is equal to 50 nA. Holes from the collector move to the base and then recombine with electrons there, thus generating some portion of the base current which is directed out of the base. So according to KCL, the emitter current must be zero or very close to it. On the other hand the emitter-base junction is also reverse biased so there also must be a reverse saturation current flowing into the emitter, so according to KCL, the base current must be a combination of the emitter and collector currents.

Either the emitter current is extremely low or I'm missing something. So the question is what really happens to carriers inside BJT when we use it in a cutoff mode.