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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.

87%
+12 −0
What is a bootloader, and how would I develop one?

I've heard that a bootloader is code that runs on a microcontroller, and is used to get your application code onto the micro. How does that work? Is there anything special that needs to be done to...

1 answer  ·  posted 2y ago by Olin Lathrop‭  ·  edited 2y ago by Olin Lathrop‭

85%
+10 −0
How to calculate pullup resistor value for pushbutton?

What value pullup resistor should I use for a pushbutton connected to a microcontroller input? I've seen values from 1 kΩ to over 100 kΩ. Some references just say to use 10 kΩ because it's a "goo...

2 answers  ·  posted 2y ago by Olin Lathrop‭  ·  last activity 2y ago by Circuit fantasist‭

84%
+9 −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 1y ago by cosined‭  ·  last activity 12mo ago by Andy aka‭

83%
+8 −0
Why 3V3 instead of 3V?

Usual values used in doing electronics/power supplies are almost always round numbers: 5V 12V 28V 48V 60V I understand that in some cases IC's are built to accept the voltage directly com...

2 answers  ·  posted 2y ago by 2kind‭  ·  last activity 1y ago by Mu3‭

83%
+8 −0
Flyback transformer with Intrinsic Safety

I have no experience designing for Intrinsic Safety (IS), but need to do that now. I have read thru IEC 60079-11, which seems to be the relevant standard for my purposes. The board I need to desi...

4 answers  ·  posted 12mo ago by Olin Lathrop‭  ·  last activity 1mo ago by Hawk2020‭

83%
+8 −0
Why are some PCB design software programs considered to be 'hobbyist' programs?

Recently I have heard this opinion from experienced engineers when discussing PCB design software. The common opinion was that Allegro and Altium are supposedly professional programs whereas Eagle ...

2 answers  ·  posted 10mo ago by Wilkins Ticklebum‭  ·  last activity 10mo ago by Andy aka‭

81%
+7 −0
Why do DC/DC switching controllers seem to favour the buck-boost topology over similar ones like Cuk, SEPIC and Zeta?

I am looking at various DC/DC converter topologies for a power system I am designing. The most suitable topology for me is one that can perform both step-up and step-down functions, so I am looking...

2 answers  ·  posted 1y ago by Mu3‭  ·  last activity 1y ago by Nick Alexeev‭

81%
+7 −0
Technique to reset pulse transformer core quickly

I am analysing a pulse transformer which is required to transfer below communication protocol pulse from primary to the secondary side. The pulse duration is 32 μs and off time available to reset t...

2 answers  ·  posted 3mo ago by kadamrohan16‭  ·  last activity 3mo ago by Andy aka‭

81%
+7 −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 2y ago by Olin Lathrop‭  ·  last activity 29d ago by Olin Lathrop‭

81%
+7 −0
High Speed Design - Which grounding strategy to choose?

Although I have done multiple PCB designs which passed FCC and CE equivalents using the MCU's/Multiple MCU's, I have a doubt about how to approach the high speed design using FPGA SoC - main thing ...

1 answer  ·  posted 2y ago by 2kind‭  ·  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 1y ago by francesco‭  ·  last activity 1y ago by Pete W‭

81%
+7 −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 1y ago by Mu3‭  ·  last activity 10mo ago by coquelicot‭

80%
+6 −0
How to access a hardware register from firmware?

When writing firmware in C for a microcontroller, how can I directly access a memory location such as a hardware peripheral register, given its absolute address? Is there a way to do this safely an...

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

80%
+6 −0
Should I connect signal reference and chassis ground in a battery powered application?

Hello. I have a grounding problem on my acquisition system. I have read many articles, app notes and whatever but still could not find a convincing solution for the topic. The acquisition system is...

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

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 9mo ago by DeadMouse‭  ·  last activity 7mo 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 11mo ago by Lundin‭  ·  last activity 11mo ago by Olin Lathrop‭

77%
+5 −0
Buck-boost converter fed from split input supply

I have recently finished designing a buck-boost converter for a job that uses a split (+/-) input power supply. Load power is taken equally from both positive and negative input supplies and, the ...

1 answer  ·  posted 2mo ago by Andy aka‭  ·  edited 2mo ago by Andy aka‭

77%
+5 −0
Capacitor ESR vs. Impedance

One of the ceramic capacitors that I've found(link to the capacitor) specifies the following characteristics at 10 kHz: The difference in value is quite significant, almost 100 fold. Which grap...

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

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 1y ago by Lundin‭  ·  last activity 4mo ago by TonyStewart‭

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 5mo ago by Elleanor Lopez‭  ·  last activity 5mo ago by Elleanor Lopez‭

77%
+5 −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 2y ago by Andy aka‭  ·  last activity 11mo ago by Andy aka‭

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 6mo ago by Elleanor Lopez‭  ·  last activity 6mo ago by Andy aka‭

77%
+5 −0
What is this fourth connection in NMOS device?

I know that in transistors there is base, collector and emitter, and in FETs there is gate, drain and source, but what is the fourth grounded connection opposite the gate in this NMOS circuit?

1 answer  ·  posted 7mo ago by NMOS lover‭  ·  last activity 7mo ago by Andy aka‭

77%
+5 −0
When do I need to put anti-aliasing filter in front of SAR ADC?

Signal characteristics are: 0 to 3.3V span 0 to 100Hz range( there will be noise superposed on top with unknown characteristics) Output resistance Rout=4700 ohm I want to sample that with a...

2 answers  ·  posted 8mo ago by 2kind‭  ·  last activity 8mo ago by TonyStewart‭

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 10mo ago by Wilkins Ticklebum‭  ·  last activity 10mo ago by Olin Lathrop‭

PCB
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 12mo ago by DavidE‭  ·  last activity 11mo ago by Olin Lathrop‭

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 11mo ago by Keelan‭

77%
+5 −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 11mo ago by Lundin‭

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 2y ago by leroy105‭  ·  last activity 1y ago by Pete W‭

75%
+4 −0
What should be considered when picking a flyback diode?

Which are the parameters I should looking for when picking a flyback diode to be placed across a generic coil, such as a relay? That is: a coil with plain on/off functionality, for example a 24VDC ...

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

75%
+4 −0
MOV vs TVS diode

Simple thing that I realized I should know but do not -- when is an MOV preferable to a TVS diode (with some associated network to really make it work, in both cases)? Is it even something to routi...

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

75%
+4 −0
Can you call an IC pin 'N.C' if it has hidden functionality?

The particular IC I ran into this issue with was DS3231 RTC. The pin configuration shows: However, the datasheet specifies To my knowledge, 'N.C' appears on ICs when it is decided to use a cer...

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

IC
75%
+4 −0
What is this metal panel under power lines?

I was hiking around the Berkshires in western Massachusetts yesterday, and came across this metal panel where some power lines were crossing a ridge: The panel is a few meters wide, and appe...

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

75%
+4 −0
What is the difference between emitter and collector of a transistor?

In all descriptions of how (non-FET) transistors work I've seen, there is an inherent symmetry: There's either an n-doped layer between two p-doped, or a p-doped between two n-doped, and the descri...

2 answers  ·  posted 1y ago by celtschk‭  ·  last activity 1y ago by Olin Lathrop‭

75%
+4 −0
Thermal relief for through-hole on multi-layer PCB

When using through-hole ("THR") connectors on a multi-layer PCB, I frequently notice problems with the ground pins, when these are connected to the ground plane(s) through various "thermal relief" ...

1 answer  ·  posted 1y ago by Lundin‭  ·  edited 1y ago by Nick Alexeev‭

75%
+4 −0
Is ESD overhyped?

I have seen many engineers talk about ESD protection but I had never seen its effects myself. I made many small DIY projects and I have used bare hands to touch ICs and their pins,but nothing got d...

6 answers  ·  posted 2y ago by aditya98‭  ·  last activity 1mo ago by Nick Alexeev‭

75%
+4 −0
CAN "split" pin, bus termination and common mode stabilization

Modern CAN transceivers like MCP2561FD that support CAN FD with high baudrates come with an optional feature called SPLIT, which is to my understanding a reference voltage output pin used to give a...

1 answer  ·  posted 1y ago by Lundin‭  ·  last activity 1y 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 12mo ago by Mu3‭  ·  last activity 12mo ago by Olin Lathrop‭

75%
+4 −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 12mo ago by DavidE‭  ·  edited 11mo ago by Lundin‭

75%
+4 −0
What benefit has a differential amplifier when measuring a sensor signal?

What benefit has a differential amplifier when measuring the signal from a sensor that is remotely located such as in this example: - Why can't I use an arrangement like this: -

1 answer  ·  posted 2y ago by Andy aka‭  ·  last activity 2y ago by Andy aka‭

75%
+4 −0
Chokes, Beads and Inductors in Pi-filters

I have seen pi-filters using chokes, ferrite-beads, and plain inductors as the L-element What are the main differences between them? when use one or other?

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

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 3mo ago by celtschk‭  ·  last activity 3mo ago by TonyStewart‭

75%
+4 −0
What are the most common causes of CAN bus communication errors?

I can't get my CAN bus application (ISO 11898-2, classic "high speed CAN") working and I'm receiving various CAN error frames. These error frames manifest themselves as sequences of 6 bits with my ...

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

75%
+4 −0
Deriving resistor values for a taper pad attenuator

A taper pad is a resistive attenuator that maintains impedances on both ports and provides a specific amount of gain-loss ($A_{12}$): - I have derived formulas for each resistor (that I know to ...

2 answers  ·  posted 2mo ago by Andy aka‭  ·  last activity 2mo ago by a concerned citizen‭

75%
+4 −0
Low-pass filter after the output DAC in CD players

[Disclaimer. This is not for an academic class. I'm self-studying.] I’m reading an introductory book on DSP for audio and computer music [Steiglitz 1996, ISBN 0-8053-1684-1 p. 287]. One of the ...

3 answers  ·  posted 2mo ago by Nick Alexeev‭  ·  last activity 1mo ago by Olin Lathrop‭

75%
+4 −0
How to perform initialization of static storage variables in embedded systems?

Whenever declaring a variable in C outside a function at file scope or when specifying it as static, it gets assigned a life time known as static storage duration. Meaning it will be accessible thr...

1 answer  ·  posted 21d ago by Lundin‭  ·  last activity 21d ago by Lundin‭

75%
+4 −0
PNP Darlington pair as a current limiter

I am trying to analyse what is controlling the load current in the below Darlington configuration. Is it the base current of transistor Q3 which is controlling current through R14 / emitter curr...

1 answer  ·  posted 10mo ago by kadamrohan16‭  ·  last activity 10mo ago by Olin Lathrop‭

75%
+4 −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 10mo ago by crusadEEr‭  ·  last activity 10mo ago by Olin Lathrop‭

75%
+4 −0
What effect will extreme temperatures have on impedance in a wire?

My scenario is this: radio equipment controlling an overhead crane inside a steel mill. Specifically it is used for transporting melting pots. With the current, unfortunate installation, the antenn...

1 answer  ·  posted 6mo ago by Lundin‭  ·  last activity 6mo ago by Olin Lathrop‭

72%
+6 −1
How to protect RF switches from ESD?

Assume that I have some generic antenna connector, followed by a pi-filter/50ohm impedance matching components, then a DC blocking cap (as per the RF switch recommendations) and then a RF switch fo...

4 answers  ·  posted 10mo ago by Lundin‭  ·  last activity 9mo ago by Nick Alexeev‭