# All Questions

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### PCB Layout Mentor Graphics - basic question about transmission lines and components

I am currently doing a PCB Layout for an amplifier and would like to know if there is any way to add a transmission line to the Layout. As far as I noticed there is no corresponding symbol for such a ...
4 views

### Read MicroSD card with USB reader while it is connected to (powered-off) microcontroller

I have created a small breakout board, where a microSD card is inserted and I can access its signals. Now, when the necessary SD signals are connected to an AVR microcontroller via SPI, they ...
8 views

### How can power in dc motor increase when current decreases?

In many graphs for dc motor torque speed power and other characteristics we can clearly see as the speed of the motor increases the torque decreases because back emf increases and torque depends on ...
9 views

### Looking for an explanation of grounding in relation to computers and DVI-HDMI adapters

I recently found that a DVI-HDMI adapter, purchased to connect the micro-HDMI port on my new Raspberry Pi 400 to the DVI port on my monitor, behaves strangely: it works well when connecting to my ATX ...
16 views

### What is the value of these resistors?

In these two resistor of the center of this figure, i am seeing the colors: brown, white, red, red, black. I am wondering in what is the value of this resistor, ...
5 views

### USB-C PD Source / Sink capable IC

Does anyone know of a combined source / sink IC for USB-C PD? Ideally, one that is rather simple to configure, by holding configuration pins to ground or similar. This is not super necessary though. ...
13 views

### Autocorrelation question

I measured the Autocorrelation of a demodulated AM signal in matlab. This was the graph I got. What does this result mean for my signal?
15 views

### Is there a risk of TO-247 Packages conducting current through the internal heat spreader?

It is common to mount a 2N3055 to the chassis. I want to know if it is safe electrically to do so with an IRFP260N and other TO-247 packages?
12 views

### Analog Design of a Miller OTA: Am I doing it right?

So I am doing a class on Analog Design. I have to design a two-stage Miller OTA. I would like to have some feedback about my design procedure and also some help because I am stuck. My professor doesn'...
39 views

### How does this circuit act as a half wave rectifier?

I'm having trouble to understand how this circuit operates exactly. The op amp is an LM339 from ST (datasheet link). The circuit in question is as follows: The op amp should be a comparator, but the ...
47 views

### Will connecting unused CMOS outputs to VCC damage the chip?

I am using a 74HC154 4x16 decoder in a design I'm working on and I'm not using the last four outputs. During PCB routing it would be very convenient if I could tie these unused outputs to the VCC ...
36 views

### LTSpice: op-amp integrator/differentiator not working for all R and C?

I am trying to test a simple op-amp integrator (from my textbook) in LTSpice with a square-wave input. As can be seen, the output is an (almost) triangular waveform for a resistance of 1 kΩ and a ...
41 views

### How much can the voltage range of Lithium-Ion cells be stretched?

I recently received a cheap (and probably non CE-certified product) that is capable of charging a few 18650 cells. I use it to charge recycled cells before decharging them to measure capacity. However,...
41 views

### BJT High Frequency Effects?

I am studying high frequency common emitter amplifier and I came across a model where parasitic capacitances C_CB, C_BE, C_CE of BJT are included. In my textbook the small signal current gain beta of ...
88 views

### Why doesn't my battery pack run a 12 V lamp very long?

I am new to this forum. While I have been experimenting with electronics for years, I guess I am still a novice. Please help me understand why my battery pack doesn't run a 12 V LED lamp very long. I ...
46 views

### Removing DC offset in MATLAB

My teacher has a demodulated signal and he removed the DC offset with this one line of code in MATLAB: y_dc = y - mean(y) Can someone please explain how this line ...
16 views

### DAC converter: offset error

If I have for example a 5-bit DAC converter with a Vref = 16V and the Vout = 0 when the input is '00000': Can I calculate the offset error of this DAC if the Vout = 375mV and input is '00000000' even ...
68 views

### Why can't WiFi hardware be used to receive radio stations?

Special hardware is needed to receive radio waves in different frequencies i.e a RTL-SDR. My question is why can't the WiFi hardware get also used to pick up radio ...
14 views

### Thevenin equivalent for a two-port network load

Consider the case of two voltage sources supplying current to a load, which is a 'Pi' two-port network (see figure). How do we go about applying Thevenin's equivalent theorem (if at all possible) to ...
38 views

### Inverting amplifier not acting as expected with non-ideal op amp

I'm fairly new to using op amps, so this may be a simple issue. I am building an inverting amplifier for monitoring a negative voltage on an analog rail. Since the ADC I'm using requires a positive ...
49 views

### Need help identifying Diode and Capacitor

I am trying to repair the ballast in a older video projector, and these two components seem to have shorted out. One is a capacitor with the markings 473K, and I think these are the equivalent ...
18 views

### Gate Drive Circuit of an AC Voltage Controller

The circuit shown is used to control the gate drive of an AC Voltage Controller. I am trying to understand the functions of each of the parts and cannot understand the need of the NPN transistors Q1 ...
21 views

### ST7789 display: pins IM0, IM1, IM2, IM3 are not accesible

In a [ST7789 LCD](https://www.adafruit.com/product/3787, how do I set the IM[3:0] pins for select the MPU Interface Mode? The manual just shows the values of IM[3:0] for each interface but doesn't ...
35 views

### How do I calculate accuracy marked as ±(4 ppm rdg + 10Digit)?

Trying to figure out the correct way to calculate accuracy with LSD. I looked at a few sources, but I'm still confused on the topic. The question: A digital voltmeter can display counts up to 1999999 ...
32 views

### Component footprint symbol cross-reference / cheat sheet / appnote?

While shopping for components I've noticed different manufacturers / suppliers will use different names / codes for identical footprints, which can make it a chore to work out what will actually fit - ...
64 views

### Why are my IGBTs failing?

I am testing this H-Bridge circuit for driving a DC motor. The Vdrive signal is a full wave rectified $220 V_{RMS}$, and I am using a PWM signal in the SD net to control the final voltage. The motor ...
83 views

### How do certain oscilloscopes have high isolation between channels?

At first, I couldn't think of any mechanism to get great isolation between the front-end and the sense amps because hundreds of volts of isolation sounds like capacitive isolation. Capacitive coupling ...
71 views

### Why doesn't the current in a BJT transistor depend on the emitter-collector voltage?

In my understanding, in an NPN junction for example, an increase in the emitter-collector voltage should widen the depletion layer in the base-collector junction therefore increasing the electric ...
58 views

### SPI connection to Raspberry Pi

I want to flash and configure a processor using a Raspberry Pi. For this I'm using the SPI pins of the Raspberry Pi. I read that the Raspberry Pi pins can provide no more than 8 mA out of each pin. Do ...
22 views

### Does the standard for M12 A-Coded 4-pin plugs (female) have a dummy center hole to accommodate 5-pin socket (male) connectors?

I have a project that will tap into an existing sensor that uses a 4-pin M12 A-Coded connector. My plan is to use a Y Splitter to allow me to tap a parallel connection to the sensor. The splitter I ...
36 views

### Problem in the current waveform during PV power injection to the electrical network

When I connect my photovoltaic system to the electrical grid through a dSPACE DS1104 testbench, the inverter output current becomes as shown in the attached figure. Before connecting and during the ...
56 views

### How do you get a Vout of 2.29 in the simulation with a differential opamp and a wheatstone bridge?

I made a circuit to read the resistance of a PT-1000 (a platinum RTD [Resistance Temperature Detector] of 1 kΩ at 0°C) and I know I messed something up with the linearity; whatever I try, I can not ...
40 views

### Why am I having communication issues between ESP12F and ATmega328?

I am working on a PCB to enable an ATmega328 to connect to an MQTT network through an ESP12F. I am using a voltage divider in the TX line from the ATmega to reduce it to 3.3v (using nets SR+ and SR- ...
54 views

### How to find the complete transfer function based on phase measurements

I want to find the transfer function with a certain number of poles of an electronic amplifier circuit based on the same number of phase measurements. For example, I have 3 phase measurements: \begin{...
235 views

### How to distinguish a 1N4148 diode from a Zener diode visually

The 1N4148 looks like this and a Zener diode looks the same. What is the most recommended way to distinguish or identify them visually?
60 views

### Why do almost all DALI master circuits calls for using an interrupt pin for RX?

I was searching for the DALI communication part for Dali Master Design and almost all designs use opto isolation circuits (which vary differently in components) and use MCU interrupt pin for DALI ...
105 views

### Resonant LC filters on a spherical capacitor [closed]

In the setup below, the circles are plates of a capacitor, and there are two LC filters mounted on it. Would the current prefer to pass via the filters if they are tuned to resonate at the frequency ...
99 views

### What is common-mode voltage in a differential amplifier?

I am using an LM2904 for my application. One of the input voltages, the voltage at the negative terminal of the op-amp (Vin-), can vary from -400mV to 500 mV. However, the voltage at the positive ...
95 views

### Why is a capacitor connected across the power MOSFET in the DC-DC stage of most SMPSs?

In many of the schematics of the DC-DC stage of SMPSs, there is an external capacitor connected across the MOSFET switch (across drain and source). Why is this capacitor required? MOSFETs have an ...
245 views

### Double Bridge-Rectifier Circuit Question

I am up to building a NE555 controlled PWM circuit that will power a 220v heater. NE555 will use a typical configuration and will drive a 20N60 Mosfet. The mosfet Vgs(th) is 10v, so NE555 needs to be ...
64 views

### Does the antenna design equate to the range?

There are a ton of different antennas out there, here specifically I'm talking about directional antennas. Options include Yagi-Udas, parabolic, LDAP, etc. antennas. All of these have somewhat of a ...
54 views

### How to use current sources correctly

In this simulation the circuit generates a AC signal at "Electrode". Here I am using two SPDT-Switches (Ron = 4 Ω). My first question: Why isn't the signal correctly rectangular? And how ...
50 views

### Reading the analog pin A0 on Wemos D1 Mini

I am doing a personal project with a Wemos D1 mini and one thing that was of interest to me was to detect a servo-motor stall. Very glad to find an useful answer to this question: How do I detect ...
55 views

### Is this circuit the right way to drive a piezo buzzer?

I am trying to drive a piezo buzzer and came up with the following circuit. Am I doing it right?
54 views

### How important really is the impedance of an USB 2.0 signal line?

The USB 2.0 specs requires a differential impedance of 90 Ohms and a common mode impedance of 30 Ohms (with some tolerance). This, by definition, gives a target of an odd mode impedance of 45 Ohms and ...
479 views

### Is it possible that north and south poles of a disc-shaped magnet change position over time?

[See update at the bottom] We build brushless DC motors of about 1 kW power at 48 volts. In order to drive the motor, we need to know the rotor position and, to do that, we fit a disc-shaped magnet on ...
36 views

### How to route NFC traces on a PCB?

I am designing a PCB with connector on the PCB board for the antenna connection. The traces from the NFC RF chip goes to matching network and then to the antenna connector. I want to know how to route ...
40 views

### Why does the below SPICE simulation show an initial current even before the voltage source is applied?

LT-spice simulation is showing a sudden jump in MOSFET current from 0 to 5mA at t=0. What would be the explanation for this? Is it a tool issue? All the capacitor initial voltages (C2, C1 and C4) are ...