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Q&A

General Q&A about the design and function of electronic systems, electric power systems and infrastructure, their theory, and tools specific to those fields. Read these guidelines before posting.

Filters (None)
77%
+5 −0
Unterminated SPI bus needs expansion board to work properly

I'm supporting a piece of legacy hardware that routes the SPI bus through a set of headers to an expansion board. Since the expansion board doesn't actually use the SPI bus, we simply ignored the ...

1 answer  ·  posted 1y ago by TimH‭  ·  last activity 1y ago by Olin Lathrop‭

70%
+5 −1
Minimizing Common Mode Radiation - Separating Grounds

There are various different methods to keep common mode currents off the cables, one of them being discussed on the site here and with Olin's decoupling caps post on StackExchange. Slight digressio...

1 answer  ·  posted 1y ago by 2kind‭  ·  last activity 1y ago by TonyStewart‭

22%
+0 −5
BJT common emitter amplifier equivalent circuit (π hybrid model) [closed]

Im studying the equivalent model of a BJT common emitter amplifier at high frequencies.At university we tought that the BJT at high frequencies looks something like this: However when designing ...

0 answers  ·  posted 1y ago by MissMulan‭  ·  closed 1y ago by Olin Lathrop‭

85%
+10 −0
Rules and guidelines for drawing schematics?

We see schematics of varying quality and conventions. What is good and bad? What are the rules and conventions for drawing good schematics? What matters? What doesn't? This question is about sch...

1 answer  ·  posted 3y ago by Olin Lathrop‭  ·  last activity 1y ago by Olin Lathrop‭

75%
+4 −0
Oscilloscope potentially ESD striked

I have a Rigol DS1104 oscilloscope. Last week I stood up quickly from my table and saw a spike on the scope. Right now all the channels have a DC offset when probe is connected to ground or unconne...

2 answers  ·  posted 2y ago by ScopeMan‭  ·  last activity 1y ago by Lundin‭

71%
+3 −0
Energy harvesting from non-invasive current sense transformer

I have a non-invasive current sense transformer (SCT-013-030) which according to its datasheet it is voltage output type. I want to harvest energy and supply a wireless sensor that consumes 5-6 uA...

1 answer  ·  posted 1y ago by DeadMouse‭  ·  last activity 1y ago by Andy aka‭

33%
+0 −2
Effect of adding stages to a filter

Suppose we have a RC low pass filter of 1st order. If we add multiple stages every time we add a RC stage identical to our original does the slope of the curve in the bode plot db/Hz becomes wild...

2 answers  ·  posted 2y ago by MissMulan‭  ·  last activity 1y ago by a concerned citizen‭

57%
+2 −1
pH Electrode Buffer - Offset when solution grounded

Problem pH electrode buffer offset appears when solution is grounded. Detail I have a pH electrode in some conductive solution (~1000uS). The output (measurement electrode) is buffered by an el...

2 answers  ·  posted 1y ago by rherma‭  ·  last activity 1y ago by TonyStewart‭

70%
+5 −1
How do PLCs normally measure 4-20mA current loops?

I'm looking for input from anyone with insight in the PLC world. How do PLCs usually measure 4-20mA current loops? I would assume it's one of these two alternatives: Through an external "shunt"...

3 answers  ·  posted 2y ago by Lundin‭  ·  last activity 1y ago by KalleMP‭

75%
+4 −0
Can confusing the plugs for earphones and microphones do any damage?

The plugs for microphones and for earphones are the same, however their functionality obviously is quite different. Now because of the same plugs it is easy to insert one of them in the wrong socke...

2 answers  ·  posted 1y ago by celtschk‭  ·  last activity 1y ago by TonyStewart‭

28%
+0 −3
Design high -pass filter with 2 points of the bode plot

Im designing a high-pass filter which has a gain of -8dB at half of the roll-off frequency and I am stuck ,I dont know how to continue the design. In the bode plot of that filter we have 2 points:...

3 answers  ·  posted 2y ago by MissMulan‭  ·  last activity 1y ago by LvW‭

77%
+5 −0
Is there a way to reliably measure antenna return loss outside a lab?

Assume I'm a complete beginner at RF. Is there a way to measure return loss of an antenna, in such a manner that I can reliably reproduce the measurement later on? What I'm talking about is produ...

2 answers  ·  posted 3y ago by Lundin‭  ·  last activity 1y ago by TonyStewart‭

60%
+1 −0
Results of analysis of Hartley oscillator dont make sense

I want to find the conditions of oscillation of the following Hartley oscillator.I have attached a load (ZL) to my Hartley oscillator I have written KCL for nodes A,B: For node A: $$\frac{V_{A...

3 answers  ·  posted 2y ago by MissMulan‭  ·  last activity 1y ago by TonyStewart‭

75%
+4 −0
What are the key programming skills for an embedded systems engineer?

I am looking to improve my knowledge of embedded systems programming, specifically regarding microcontrollers and embedded Linux systems. A lot of the information that can be found regarding C/C++...

1 answer  ·  posted 1y ago by Mu3‭  ·  last activity 1y ago by Olin Lathrop‭

71%
+3 −0
Pick & place file generated by Altium does not match the actual component rotations/positions

I am generating files for manufacturing my design in Altium 22 and ordering through Eurocircuits. What I noticed during the ordering process is that the rotation of many components (and sometimes ...

1 answer  ·  posted 1y ago by Mu3‭  ·  last activity 1y ago by DSI‭

33%
+0 −2
Op Amp Hartley oscillator

Im designing a Hartley oscillator this time with a opamp providing the open-loop gain.I have tried drawing the small-signal analysis of my circuit to use KVL and KCL to find the conditions of opera...

1 answer  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by Olin Lathrop‭

33%
+0 −2
Small signal analysis of BJT in saturation region

The small signal analysis of a BJT when the BJT is in amplification mode: is easy.However what happens when the BJT is in saturation mode? Can we replace the dependent current source with a r...

1 answer  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by MissMulan‭

77%
+5 −0
Siglent1104 oscilloscope channels lagging

First I noticed that clock begins before chipselect gets pulled low on SPI. After eliminating potential sources I started to suspect the scope. I connected all 4 channels to function generator at d...

3 answers  ·  posted 2y ago by Elleanor Lopez‭  ·  last activity 2y ago by Elleanor Lopez‭

50%
+0 −0
Finding voltage gain of Hartley oscillator

I am trying to find the AC analysis of a BJT Hartley oscillator but I cannot continue. How do I find the voltage gain? When no feedback is there, we just find the output resistance and the current...

1 answer  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by MissMulan‭

33%
+0 −2
How to design a low-pass filter when certain conditions must be met

I am designing a low-pass filter with cut-off frequency = 100Hz and after the cutoff frequency from -3dB to -10dB the average decrease in db/Hz = -0.1 db/Hz.I know how to design a low-pass filter ...

2 answers  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by MissMulan‭

60%
+1 −0
Cutoff frequency of single phase transmission line

Signals with frequency above the cutoff frequency of a transmission line cannot be transmitted through the transmission line. But how can I calculate the cutoff frequency of a single phase transm...

0 answers  ·  posted 2y ago by MissMulan‭  ·  reopened 2y ago by Olin Lathrop‭

33%
+0 −2
Re model of transistor is the same in 2 different configuration

I was studying the Re model of a transistor: But the Re model for 2 different configurations (common emitter and common base )turns out to be the same! I don't know why I am really confused.How...

2 answers  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by LvW‭

66%
+4 −1
PCB ground planes with isolated voltage

I have designed a PCB that I need to work in which a microcontroller drives a 24 V brushed motor. The input power to the board is 24 V, this is then lowered to 5 V by a step down converter, and thi...

3 answers  ·  posted 2y ago by Alinik‭  ·  last activity 2y ago by KalleMP‭

77%
+5 −0
Unexpected impedance spike when paralleling capacitors

I was watching a video from EEVBLOG about bypass capacitors, and he presented a theory that randomly connecting different values of capacitors in parallel can create unexpected impedance spikes: ...

3 answers  ·  posted 2y ago by Elleanor Lopez‭  ·  last activity 2y ago by Andy aka‭

50%
+3 −3
What reactance actually is?

I saw that equation of reactance is written like this $$I=\frac{V}{|R+X_L j|}$$ $$I=\frac{V}{|R-X_c j|}$$ When there's capacitor and inductor in a single circuit then it is written like : $$I=\...

4 answers  ·  posted 2y ago by deleted user  ·  last activity 2y ago by Andy aka‭

80%
+6 −0
DAC controlled high side current source.

I'm designing a high side current source that can be controlled with a Digital-to-analog and can source up to 100mA with voltage supply up to 36V. By high side I mean one side of load will be alwa...

1 answer  ·  posted 2y ago by DeadMouse‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+4 −1
How to choose the right value for input voltage ripple of an SMPS?

Which important system design parameters need to be locked in order to estimate the maximum allowable level of the input voltage ripple of an SMPS? I have encountered ballpark figures of <1%, &...

1 answer  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by Olin Lathrop‭

77%
+5 −0
Press fit PCB receptacle for plated holes (Marked for non-plated holes)

I saw that this PCB socket: Is marked as pressfit for non-plated holes. However, can it be used with plated holes as well, or will it damage the plating inside?

1 answer  ·  posted 2y ago by Wilkins Ticklebum‭  ·  last activity 2y ago by Olin Lathrop‭

PCB
50%
+2 −2
Inductance vs frequency

Suppose we have a sine signal applied to a inductive load. Is the inductance of the load changed if the frequency of the signal is changed?

3 answers  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by coquelicot‭

83%
+8 −0
How long does it take for energy to propagate in a circuit?

The premise In a recent video by the pop-sci channel Veritasium, the concept of the flow of electricity and energy transmission in a circuit was discussed. In that video a thought experiment is pr...

5 answers  ·  posted 2y ago by Mu3‭  ·  last activity 2y ago by coquelicot‭

77%
+5 −0
Why are there more N type than P type MOSFETs?

I was looking at different transistors, especially MOSFETS and I saw that N type MOSFETs seem to be way more popular to be used in circuit design. Is there a reason for that, or am I mistaken?

2 answers  ·  posted 2y ago by crusadEEr‭  ·  last activity 2y ago by Olin Lathrop‭

33%
+0 −2
What happened to my headphones? [closed]

I recently started working at a construction office in another country. I usually listen to music when working, and I saw a headphone jack in the wall, so I thought it is radio or something, I plug...

0 answers  ·  posted 2y ago by Headphone Jackson‭  ·  closed 2y ago by Olin Lathrop‭

57%
+2 −1
Choosing Y value in photoresistor graph

I have designed a graph of the current in a photoresistor related to the brightness of light which hits the photoresistor. Our professor told us that it is more correct to draw the Current/Brigh...

1 answer  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by Olin Lathrop‭

80%
+6 −0
Standardized schematic/layout file formats for PCB CAD tools?

As we know there exists numerous different kinds of PCB CAD software. The big ones seem to be Eagle, KiCAD, Altium, OrCAD, Solidworks, DesignSpark and probably a few more. When it comes to mechani...

1 answer  ·  posted 2y ago by Lundin‭  ·  last activity 2y ago by Olin Lathrop‭

80%
+6 −0
Location of AGC in a superheterodyne RX chain

RF novice here. If using a superheterodyne receiver for the purpose of FM/FSK modulated signals, I'm wondering if the location of an optional automatic gain control (AGC) circuit is always placed o...

0 answers  ·  posted 2y ago by Lundin‭

80%
+6 −0
How do I design a flyback converter? What are the basics I should know?

I need to design a simple flyback converter like this: - I want to control duty cycle from another circuit such as an MCU but, I'm unsure how to proceed. My requirements are: - Input voltage 125 ...

2 answers  ·  posted 4y ago by Andy aka‭  ·  last activity 2y ago by Andy aka‭

77%
+5 −0
Why do large RAM chips not have a serial interface?

I have a PIC32MZ2048ECG064, a 64-pin 32-bit microcontroller with 512kB RAM. This is not enough for my purposes, I need to extend it by at least 32MB, preferably 64 or 128. I believe this means I ca...

0 answers  ·  posted 2y ago by Keelan‭

22%
+0 −5
Why won't this Globe Electric Dimmable LED securely fit my IKEA November Lamp? [closed]

On the LEFT is what I just bought today — Globe Electric 4W (40W Equivalent) Daylight (5000K) Dimmable LED Light Bulb, G9 Bi-Pin Base, 400 Lumens, 15,000 H. Here's Globe Electric's Dimmer Compatibi...

0 answers  ·  posted 2y ago by TextKit‭  ·  closed 2y ago by Olin Lathrop‭

77%
+5 −0
PCB Copper Layer Spacing & Voltage Rating

One standard used for spacing conductors based on voltage is the IPC-2221. This standard differentiates spacing requirements for inner and outer conductors. Does the IPC minimum separation betwee...

1 answer  ·  posted 2y ago by DavidE‭  ·  edited 2y ago by Lundin‭

77%
+5 −0
Design considerations for a differential pair

Differential pairs, such as for ethernet or a CAN bus, can be designed to be loosely coupled or tightly coupled. For a loosely coupled differential pair, the odd-mode and even-mode impedances are ...

1 answer  ·  posted 2y ago by DavidE‭  ·  last activity 2y ago by Olin Lathrop‭

75%
+4 −0
Via on pad: acceptable or not?

I am designing a PCB with somewhat limited space. To save space, I am placing some vias on component pads. However, I am not sure if this is a good practice in PCB design. As far as I understand, t...

1 answer  ·  posted 2y ago by Mu3‭  ·  last activity 2y ago by Olin Lathrop‭

28%
+0 −3
Phase shift between phase and line quantities [closed]

In a 3 phase Star source-Star load circuit the phase voltage has different phase than line voltage and in a 3 phase Delta source-Delta load circuit the phase current has different phase than the li...

0 answers  ·  posted 2y ago by MissMulan‭  ·  closed 2y ago by Olin Lathrop‭

42%
+1 −2
Splitting of message inside the layers [closed]

Assume a app generates a message (stack on computer).Each layer of the sending entity will put then control information in the data depending on the protocol and transmit the data to the next lowe...

0 answers  ·  posted 2y ago by MissMulan‭  ·  closed 2y ago by Nick Alexeev‭

86%
+11 −0
208VAC triple-phase to single-phase conversion

The question: Is there a way to convert from triple-phase 208VAC to single-phase 208VAC? Background: Hi everyone, I am stuck on a project I'm working on. I'd like to convert 208VAC (three phase,...

2 answers  ·  posted 2y ago by cosined‭  ·  last activity 2y ago by Andy aka‭

75%
+4 −0
ESD USB Shield Connection & Filtering

I have a handheld ARM Cortex M based device, which has a USB input port. The product is battery powered and there is no metal chassis. We are going through CE testing, and are having ESD issues a...

4 answers  ·  posted 3y ago by leroy105‭  ·  last activity 2y ago by Pete W‭

50%
+0 −0
What is minimum resolution here?

In this datasheet it says that the minimum resolution is 0.1uA for the 10mA range.What is this minimum resolution?Is it the sensitivity of the multimeter for the 10mA range?

1 answer  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by dsr‭

66%
+2 −0
Resistance of digital ampmeter

Can we find the internal resistance of a multimeter ,when we use the multimeter like a ampmeter, from its datasheet? I am trying to find the internal resistance of IDM 505 and I went to the datash...

2 answers  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by Canina‭

66%
+4 −1
What is sacrificed when buying cheaper oscilloscope probes (of same BW/cap/R/gain)

I'm wondering if there are particular aspects of an oscilloscope probe's performance that tend to suffer, or failure points to look out for, if/when buying lower-end makes of oscilloscope probes (l...

1 answer  ·  posted 2y ago by Pete W‭  ·  last activity 2y ago by Olin Lathrop‭

81%
+7 −0
Low-frequency PWM-controlled Mosfet heater circuit

The circuit above is used to control a 240W ceramic heater by means of a PWM signal at 30Hz, generated by a microcontroller, with 5V logic. The input is a standard 280W AC-DC external power adapt...

2 answers  ·  posted 2y ago by francesco‭  ·  last activity 2y ago by Pete W‭

50%
+1 −1
MOSFET not turning completely off

Hello everyone, I have a simple circuit in which I control some LEDs via an MCU and DMG2302UK ( N-channel MOSFET ) The EN pin is connected to an MCU gpio pin that works at 3.3V. The circuit wo...

1 answer  ·  posted 2y ago by AhmedMobarez‭  ·  last activity 2y ago by Olin Lathrop‭